[advances in agronomy] volume 128 || environmental chemistry and toxicology of iodine

47Copyright copy 2014 Elsevier Inc

All rights reserved

Advances in Agronomy Volume 128ISSN 0065-2113httpdxdoiorg101016B978-0-12-802139-200002-0

CHAPTER TWO

Environmental Chemistry and Toxicology of IodineEthan M Cox Yuji Araisect1

School of Agricultural Forest and Environmental Sciences Clemson University Clemson SC USAsectDepartment of Natural Resources and Environmental Sciences University of Illinois at UrbanandashChampaign Urbana IL USA1Corresponding author E-mail yaraiillinoisedu

Contents

1 Introduction 482 Indigenous Sources 48

21 The Global Iodine Cycle 4922 Marine Iodine 5023 Iodine in Soils 51

3 Anthropogenic Sources 5231 Radioactive Iodine Sources 5232 Radioiodine Contamination 52

4 Iodine Toxicity 5441 Radioiodine Toxicity 5442 Ecotoxicology 54

5 Impacts on Human Health 5651 Iodine Deficiency 5652 Excessive Iodine 57

6 Environmental Chemistry of Iodine 5861 IodateIodide and the Hard Soft Acid Base Theory 5862 ReductionOxidation Reactions of IodideIodate in Solution and Soils 5863 Metal-IodateIodide Complexation and Solubility Products 6164 Volatilization of Iodine Species 6265 Hypervalent Iodine 63

7 Iodine Sorption in Humic Substances and Soil Minerals 6571 Iodine Interactions with Humic Substances 6572 Iodine Sorption in Clays and Clay Minerals 85

8 Remediation of Iodine Contamination 8881 Volatilization 8882 Immobilization and Precipitation 8983 Phytoremediation 90

9 Conclusion and Future Challenges 90References 91

Ethan M Cox and Yuji Arai48

Abstract

Iodine is a trace halide found in the environment A majority of global iodine budget resides in ocean while lithosphere and pedosphere contain the rest limiting the bio-availability of iodine in terrestrial environment Iodine cycles involve the multivalence state chemical speciation at the airndashwaterndashsediment interfaces The mobility and reactivity of these inorganic and organic iodine species are impacted by changes in physicochemical factors (eg pH and ionic strength) and macro- and micro-biological activities Although iodine aqueous biogeochemistry has been extensively investi-gated in marine systems in the past the partitioning mechanisms of iodine at the geomediandashwater interface remained poorly understood This chapter covers environ-mental soil chemistry of iodine and the impact to human and ecological health

1 INTRODUCTION

Iodine belongs to the group of elements known as halogens It is the least reactive of the halogens because of its large atomic size besides asta-tine but can exist in several different chemical states in low- temperature geochemical environment namely iodide (Iminus) elemental iodine (I2) iodate (IOminus

3 ) and periodate (IO minus4 ) This redox sensitive chemical speciation makes

the iodine cycle in environment extremely complex Among 37 isotopes nonradioactive iodine-127 is the most stable and common isotope Approxi-mately 70 of global iodine is present in marine systems and iodine in litho-sphere and pedosphere is often limited causing iodine deficiency in some parts of world The two most common radioactive isotopes are iodine-129 (t12 16 million years) and iodine-131 (around 13 days) (Downs and Adams 1973 Grogan 2012) that are anthropogenically produced through the fission of uranium and plutonium at nuclear reactors (Michel et al 2005) Many attempted to understand the environmental chemistry of iodine in predict-ing the transport of radioiodine in subsurface environment and in develop-ing the best remediation technologies This chapter provides an overview of iodine environmental chemistry and toxicity as well as an extensive review of iodine sorption reaction in inorganic and organic soil components

2 INDIGENOUS SOURCES

As a trace nutrient iodine is scarce in the environment The concentra-tions of other halogens fluorine chlorine and bromine greatly outnumber iodine concentrations Iodine can be found naturally in minerals known as lautarite (Ca(IO3)2) and dietzeite (7Ca(IO3)28CaCrO4) These minerals occur naturally in the Caliche beds of Chile where they are mined and sold The

Environmental Chemistry and Toxicology of Iodine 49

Caliche beds are the number one source of commercial iodine in the world (Downs and Adams 1973) The various structures of halogen compounds are clear to scientists except for the structure of iodate Chlorate and bromate crystallize with distorted lattices like those found in sodium chloride but iodatersquos structure is different than its halogen relatives Studies have found that there are large intermolecular forces at play in between the oxygen and iodine These interactions give the molecule a trigonally distorted octahedral area around the iodine This configuration can also be seen in lithium iodate ammonium iodate and cerium iodate (Downs and Adams 1973) The isotope of iodine in the environment that is most abundant naturally is iodine-127 but radioactive isotopes also occur naturally in the environment Iodine-129 (129I) is produced naturally in the upper atmosphere when cosmic rays from the solar system hit the element xenon Xenon degrades into this radioactive iodine and beta particles and gamma radiation (Edwards and Rey 1969)

21 The Global Iodine CycleThe iodine cycle on Earth involves many different geological and biologi-cal stages The most common forms of iodine are found in the ocean as iodate iodide and elemental iodine Ocean sediment accounts for 68 of the iodine in the natural environment while sedimentary rock consists of 277 Table 21 provides the relative concentrations and percentages of iodine in the environment Sedimentary rocks and igneous rocks have

Table 21 Distribution of global iodine budget in environment

Unit

Iodine Chlorine

Abundance (ton) Proportion ()


Seawater 700 times 1010 081 266 times 1013 722Oceanic sedi-

ment590 times 1012 682 338 times 1011 092

Mafic oceanic crust

540 times 1010 062 420 times 1011 11

Sedimentary rocks (conti-nent)

240 times 1012 277 440 times 1012 119

Metamorphic and mag-matic rocks

230 times 1011 27 510 times 1012 138

Total 865 times 1012 100 369 times 1013 100

After Downs and Adams (1973)


higher iodine concentrations compared to metamorphic rocks Leaching of iodine from sedimentary rocks is high and researchers hypothesize that iodine can be lost from the interstitial spaces in the sediments (Christiansen and Carlsen 1989)

Iodine species are readily emitted into the atmosphere from the ocean as methyl iodine (CH3I) and mix with precipitation in the atmosphere to fall back onto the soil as iodate and iodide Researchers have also suggested that methyl iodide can be emitted from the soil solution via soil microbes and plant emissions (Amachi et al 2001) Figure 21 shows the complete global iodine cycle (Muramatsu et al 2004)

22 Marine IodineIodine is also accumulated in the ocean by brown algae mostly the Lami-naria genus red algae Rhodophyta and some sponges Brown and red algae have a higher affinity to bioaccumulate iodine but the reason why is not currently understood Red and brown algae can have levels of iodine as high as 7000 mg kgminus1 of body mass compared to terrestrial plants such as mosses deciduous trees and grasses that only have around 35 30 and 60 mg kgminus1 respectively (Fuge and Johnson 1986) Marine animals also have a strong affinity for iodine although this affinity is not as high as the marine plants

The distribution of iodide is varied at the ocean depth because iodide is at the highest concentrations in shallow waters near the continental shelf but iodate concentrations dominate at deeper levels beneath the photic

Emission

CH3Ihv

I2IndashIO3

ndashI2 HIO

Brine

SoilBacteria

CH3ICH3IHIOEmission

Deposition Rainfall

Plants

River

Magma

Hydrothermalwater

(iodine rich)

Cold seep SedimentationAlgae

Oceanic PlateBasalt

SeawaterBacteria

Marine SedimentsIndash

IO3ndash

Figure 21 The global iodine cycle After Muramatsu et al (2004)


zone The iodate concentration is at almost a constant level in these areas of the ocean (Wong 1991) The higher levels of iodide in the shallow waters are attributed to the abundance of organisms near the continental shelf that are able to reduce iodate to iodide for use

Marine algae have been shown to utilize inorganic iodine (Iminus) as an antioxidant The process is complex and Laminaria have been the first organism shown to use an inorganic product as an antioxidant When Laminaria are submerged the algae can use an enzyme called vanadium haloperoxidase to accumulate iodide from the seawater When low tides occur and the algae are exposed to atmospheric oxygen the accumulated iodide is released to scavenge reactive oxygen species (ROS) as well as hydrogen peroxide and ozone The scavenging properties of iodide are involved in a cyclic reaction with hydrogen peroxide and are regener-ated The release of iodide by the Laminaria also releases some elemen-tal iodine (I2) which goes into the coastal atmosphere adding excess iodine to the atmosphere Organoiodide complexes are also formed and this process is thought to increase the concentration of organoiodide complexes (such as methyl iodide) in the marine environment (Kuumlpper et al 2008)

23 Iodine in SoilsThere are many different inputs of iodine into soils around the world resulting in a broad range of soil iodine concentration lt01ndash150 mg kgminus1 The average concentration in lithosphere is 03 mg kgminus1 (Fuge 1988) The most important iodine input into soils is from precipitation Iodine in the atmosphere is dissolved into precipitation and then falls back onto soils Another important source of iodine is from the weathering of primary minerals The bedrock from which the soil is derived has a large impact on how much iodine the soil has Agricultural practices can also add iodine to the soil in coastal areas when algae are used as an amendment to the soil Fertilizers can also have trace amounts of iodine in them as well (Fuge and Johnson 1986)

Iodine concentrations in soils are also affected by the distance that the soil is from the ocean Soils that are closer to the ocean have a higher con-centration of iodine Goldschmidt (1956) found that in European countries such as France Germany Ireland Italy and Poland soils that were closest to the ocean had higher concentrations of iodine than those found further inland (Goldschmidt 1956)


3 ANTHROPOGENIC SOURCES31 Radioactive Iodine Sources

Although iodine is usually considered a trace element the production of nuclear power has been adding anthropogenic radioactive iodine to the atmosphere and terrestrial environment since before World War II (Michel et al 2005) Iodine-131 and iodine-129 is produced anthropogenically through the fission of uranium and plutonium at nuclear reactors most specifically uranium-235 (Michel et al 2005) Radioiodine can also be produced from the fallout of nuclear disasters such as Chernobyl Six Mile Island or Windscale (Raisbeck and Yiou 1999) Radioiodine is produced via neutron-induced fission Neutron-induced fusion involved launching neutrons at the nucleus of uranium-235 to produce lower atomic weight atoms and energy This type of neutron-induced fusion can create around 17 different isotopes of iodine but there are only two that are the most important iodine-129 and iodine-131 (Kaplan et al 2000)

Iodine-129 has an extremely long half-life (approximately 16 million years) so it poses problems to ecosystems in the long term 129I does not produce many deadly decay products (such as beta particles or gamma radiation) but this isotope can be deadly if it gets into the body through ingestion (Hansen et al 2011) Iodine-131 produces beta and alpha particles as it decays but its half-life is only approximately 8 days Iodine-131 is known to cause damages to humans and ecosystems in the short term (Kaplan et al 2012)

32 Radioiodine ContaminationRadioactive iodine has not been given the attention of the scientific com-munity because it is not a widespread contaminant However the radioac-tive iodine only occurs in large amounts in a few places around the world The most important radioiodine contamination sites around the world are La Hague France Sellafield United Kingdom West Valley New York Hanford Washington Savannah River Site South Carolina Fukushima Japan and Karlsruhe Germany (Raisbeck and Yiou 1999 Steinhauser et al 2012) In the United States there are two US Department of Energy (DOE) sites that have the highest amounts of radioiodine con-centration Hanford Washington and the Savannah River Site in Aiken South Carolina These two sites are still dealing with the consequences of burying radioactive waste in several different trenches and basins around the nuclear power plants (Kaplan 2011)


Hanford Washington is one of DOE sites that created plutonium and other radionuclides to be used in nuclear weapons during the Cold War The site operated from 1944 to 1987 As the Cold War raged in America the Hanford site continually built nuclear reactors and generated nuclear waste The nuclear waste was stored in trenches cribs reverse wells and other tanks underground but the waste was not well contained and radio-active materials leaked out into the soil and the Columbia River Currently Hanford has about 190 million curies of radioactivity and 170000 metric tons of chemicals (Gephart 2010)

The Snake River Plain in Idaho has also had difficulties with radio-iodine The creation of nuclear power during the Cold War has caused a significant amount of radioiodine to be released into the Snake River and the river plain (Bartholomay 2009) Over the period from 1993 to 2003 the amount of radioactive iodine in the Snake River Valley decreased to a healthy level In a study in 2011 Bartholomay (2009) found that every well in the study was under the EPArsquos maximum contaminant load (MCL) load for radioactive iodine (1 pCi Lminus1 for I-129)

At the Savannah River Site (SRS) in Aiken South Carolina radioiodine and other radionuclide contaminants are leaking from an acidic plume from nuclear waste produced during the Cold War As in Hanford Washington nuclear waste accumulated here from 1944 to 1988 and has infiltrated into the groundwater The radionuclides at this site were disposed of in an acidic water soluble form to create three basins (Kaplan 2011) Scientists estimate that approximately 7 billion liters of acidic aqueous waste were deposited into these basins (Zhang et al 2011) These basins were closed in 1988 by adding a slurry of limestone and blast furnace slag The basin was then covered with a low permeability cover In 1993 the concentration of radio-active iodine in a well near the groundwater basin was determined to be sim200 pCi Lminus1 In 2010 the concentration of radioactive iodine had con-tinued to increase to anywhere from 400 to 1000 pCi Lminus1 but areas down-stream of the acidic plume had shown lower levels of radioiodine The high organic matter stream beds and oxidizing conditions have distributed the radioiodine throughout the stream system (Otosaka et al 2011)

La Hague France is known as one of the largest nuclear reprocessing plants on Earth La Hague accepts nuclear waste from multiple countries in Europe such as Germany Poland the Netherlands Belgium and Italy and disposes of them France has become under scrutiny because they are releasing radioactive iodine into Skagerrak Basin which is directly south of Scandinavia (Raisbeck and Yiou 1999) In a study by Aldahan et al (2006)


researchers found that sediments in the Skagerrak and Kategatt Basins have extremely high levels of iodine-129 due to the release of reprocessed nuclear fuel from Sellafield and La Hague The liquid releases from these facilities are even more dangerous than gaseous releases from nuclear disas-ters such as Chernobyl (Aldahan et al 2006) The releases from La Hague and Sellafield have also been transported via ocean currents to the Gulf of Mexico In a study by Schink et al (1995) researchers found that the ratio of iodine-129 to iodine-127 was higher in the sediment than what could have been produced by natural processes Researchers studied ocean currents and discovered that radioactive iodine was most likely transported from these two nuclear reprocessing plants in Europe (Schink et al 1995)

4 IODINE TOXICITY41 Radioiodine Toxicity

Since the 1950s the thyroids of animals have been used as biomonitors for the accumulation of radioactive iodine In 2012 Steinhauser et al (2012) observed the effects of the Fukushima nuclear disaster on wildlife in Austria The study found that although iodine-131 has a low half-life (approxi-mately 8 days) the radioactive material lingers longer than the hypothesized 8 days in the thyroid The study also found that herbivores are more sensitive to radioactive iodine due to their ingestion of plants that have accumulated radioactive iodine Due to its beta decay iodine-131 is known to cause the cell mutation and death in cells The deposition of iodine-131 from precipi-tation onto the soil has led to increased uptake by plants which are eaten by herbivores (Steinhauser et al 2012) The accumulation of radioiodine in herbivores and thyroids were also reported after the Chernobyl explosion Cows and other livestock near the nuclear power plant had high concentra-tions of radioactive iodine due to eating plants that contained high levels of iodine The concentration of iodine dissipated quickly due to the small half-life of iodine-131 but thyroid cancer still persists in children who ate meat from these cows or drank the milk (The Chernobyl Forum 2006)

42 EcotoxicologyEcotoxicity of iodine has not been extensively investigated since iodine itself is not a major industrial contaminant except for the emission of radio-iodine A summary of few iodine studies on fauna and flora is discussed below Iodine is used by all mammals in the thyroid gland The thyroid is the mediator of metabolism in the mammalian body The different valence


states of iodine have different toxicological impacts Elemental iodine (I2) dissolved in water is known for its antibacterial properties Elemental iodine is used to disinfect water supplies and clean wounds Iodine I2 is a nonpolar molecule which allows it to diffuse across the cell membrane of bacteria Inside the bacteria cell the iodine molecule readily binds to thiol groups on cysteine proteins perturbing the structure of carbon to carbon double bonds in fatty acid chains (Amachi et al 2005)

In a study by Laverock et al (1995) it was found that low concentrations of iodine in an aquatic environment are extremely toxic to rainbow trout (Oncorhynchus mykiss) The LC50 for rainbow trout ranged from 053 mg Lminus1 for elemental iodine to 220 mg Lminus1 for iodate to 860 for iodide The LC50 was even lower for Daphnia magna with an LC50 of 017 for elemental iodine 053 for iodide and 103 for iodate Although these concentrations are extremely low the researchers also found that the amount of radiation emitted by radioactive iodine would kill short-lived aquatic organisms such as D magna before the concentration of iodine could accumulate enough to be lethal (Laverock et al 1995) Bringmann and Kuumlhn (1980) studied the effect of iodine on Scenedesmus quadricauda (green alga) resulting in an EC05 of 40000 μg Lminus1 Overall the results of these studies suggest that iodine is not toxic to aquatic organisms

Shepperd and Evenden (1995) investigated iodine ecotoxicity in soil biota in a clayey soil an organic matter soil and a sandy soil They found an EC25 of 25 mg kgminus1 for soil microarthropods and a No Observed Effect Concentration (NOEC) of 1000 mg kgminus1 for earthworms Lewis and Powers (1941) examined effects on Azotobacter in suspension culture and noted an NOEC for nitrogen fixation at 50 mg kgminus1

While the toxicological data of radioiodine is limited in aquatic and terrestrial organisms it has been more frequently tested in plant species The impact of iodine species on plant species has been being debated in the literature Iodine species can either have a detrimental or beneficial effect on plants The determining factors seem to be the concentration and the iodine species in soil This hypothesis has not been fully substantiated yet but current studies state that low concentrations of iodine are actually beneficial to the growth of plants up to a certain point (eg 1 mg Lminus1) and medium iodine concentration could result in negative impacts (Lehr et al 1958 Shepherd and Evenden 1995) andor the iodine accumulation (Sekimoto 2009) Akagare disease observed in rice grows in high iodine soils (Ou 1985) Yamada et al (2005) postulated that the mechanism of iodine is associated with redox reactions at the rhizosphere Iodide can be


oxidized to elemental iodine (I2) which can readily pass through the cellular membrane to produce ROS

At concentrations lower than 1 mg kgminus1 the weight of tomato fruit and amount of fruit produced by tomato plants increased (Lehr et al 1958) Contrary to this statement concentrations above 1 mg kgminus1 induced wilt-ing and chlorosis on leaves These plants also showed a quicker flowering time (Lehr et al 1958) In a study on the fertilization of spinach with lower concentrations of iodine sim10 μM Lminus1 researchers found that iodine accumulation in the leaves was equivalent to 3 mg kgminus1 of dry weight (Zhu et al 2003) Some researchers proposed that iodine accumulation is pri-mary incorporated into the cytoplasm into the cytoderm and then into organelles (Weng et al 2013)

5 IMPACTS ON HUMAN HEALTH51 Iodine Deficiency

Iodide is the form of iodine that is taken up by thyroid Iodide is taken up by a sodium-iodide symporter This symporter pumps iodide into the thyroid against the concentration gradient Inside the thyroid iodide is con-verted by thyroid peroxidase into neutral iodine (I) or iodonium (I+) where it is added to the structure of thyroxine (T4) the major thyroid hormone that controls metabolism (Amachi et al 2005) Although it is a trace nutri-ent required by the body deficiencies can be detrimental to human health (de Benoist et al 2004)

Iodine is required by the mammalian thyroid for the production of thy-roxin a hormone that controls metabolism Although most Americans do not have a problem with iodine deficiency iodine deficiency is a worldwide prob-lem as many countries around the world do not readily have access to iodine In the United States iodized salt is the most common way that humans get their daily iodine Iodine is added to salt as iodate since this form is more stable The iodate levels that are added to salt are extremely safe and no known health defects have occurred due to iodized salt Switzerland has made iodate additions to salt mandatory for humans and animals (Burgi et al 2001) Euro-pean as well as many African countries have recently become under scrutiny because of their iodine deficiency Around the world health organizations estimate that 22 billion people are iodine deficient (Vitti et al 2003)

Iodine deficiencies are very common around the world Some health issues related to iodine deficiencies in the fetal period have been known to cause deafmutism spontaneous abortions stillborns and congenital


anomalies (de Benoist et al 2004) In teens and adults without sufficient iodine mental defects hypothyroidism hyperthyroidism retarded physical development and goiter can develop and persist for the rest of their lives Especially in adults iodine deficiency can cause goiter impaired mental capacity hypothyroidism and hyperthyroidism (de Benoist et al 2004)

52 Excessive IodineThe toxicity of iodate also has been associated with an excessive dosage An excessive dose of iodate can induce blindness due to iodatersquos ability to inter-act with the epithelium pigments in the eye but this excessive dose is two orders of magnitude higher than the level found in iodized salt (Burgi et al 2001) Overexposure to radioiodine via inhalationingestion is extremely hazardous to human health In Hanford Washington residents that lived downwind from the nuclear power plant who were exposed to higher levels of iodine-131 and iodine-129 reported higher instances of thyroid cancer stillborns and spontaneous abortions (Gephart 2010) A survey conducted by Grossman and Morton (1996) discovered that 50 of women who lived near the Hanford site had hypothyroidism which led to spontaneous abor-tions Of the 147 women who had hypothyroidism in the survey 84 spon-taneous abortions were reported (Grossman and Morton 1996)

Similar problems of excessive radioiodine have occurred in Europe in areas in the former Soviet Union near the Chernobyl nuclear reac-tor Many children who were 1ndash5 years old when the nuclear reac-tor exploded have higher instances of thyroid cancer than those who were older when the nuclear disaster occurred (Michel et al 2005) The major problem with radioiodine is that the mammalian body only requires trace amounts of it in the thyroid Since the thyroid is the only organ in the body that requires iodine 90 of the iodine accumulates in the thyroid and can cause nodules which can develop into cancer In a study by Dalke et al (2012) researchers found that mice which were exposed to iodine-131 had more thyroid lesions 18 months after expo-sure than the control group which was not exposed to radioactive iodine (Dalke et al 2012)

Iodine-129 has an extremely low MCL of 1 pCi Lminus1 in drinking water which is equivalent to 57 ng Lminus1 or approximately 6 μg Lminus1 To compare uranium-238 has an MCL of 30 pCi Lminus1 This discrepancy in the MCLs shows how dangerous radioiodine is to humans and wildlife This low MCL makes this isotope extremely dangerous if radioiodine enters the public water system (Grogan 2012)


6 ENVIRONMENTAL CHEMISTRY OF IODINE

Iodine ([Kr]4d105s25p5) exists in several oxidation states in low tem-perature geochemical environment The most commonly known iodine species are iodide (minus1) iodate (+5) and elemental iodine (0) Iodine readily interacts with inorganic and organic molecules The two most abundant species are iodide and iodate Organic forms of iodine exist in the natural environment including methyl iodide which is the most abundant iodine species in the atmosphere Organic forms of iodine are also referred to as organoiodine or organoaniline (Fuge and Johnson 1986) Elemental iodine is only slightly soluble in water but iodinersquos solubility is increased when it is placed into solution with iodide which undergoes a redox reaction to form the triiodide (Iminus

3 ) anion (Burgot 2012)

61 IodateIodide and the Hard Soft Acid Base TheoryAccording to Pearsonrsquos Hard Soft Acid Base (HSAB) theory hard acids are those ions that have high density charge and small size while soft acids are those ions that have a low density charge and a large size Soft acids also have outer electrons that are easily excitable In the HSAB Theory hard acids bond with hard bases and soft acids bond with soft bases (Sparks 2003) Iodide (I) is a soft base but iodate is a hard base Iodate commonly pairs with hard acids such as potassium (K+) sodium (Na+) and lithium while iodide (Iminus) commonly pairs with soft acids such as silver (Ag+) copper (Cu+) and gold (Au+) Most of these soft acids are known as toxic met-als in the environment so they do not occur as readily as the hard acids ( Wulfsberg 1991) The softer base nature of iodide can explain why novel ldquogettersrdquo containing mercury and silver thiols adsorb higher levels of iodide

62 ReductionOxidation Reactions of IodideIodate in Solution and SoilsThe oxidation and reduction reactions of iodine in the environment are very complex The EhndashpH diagram (Figure 22) for iodine species shows that at environmentally relevant pH (35ndash10) and reduction potential the major spe-cies of iodine is iodide (Iminus) Iodate dominates at higher pH and higher Eh suggesting that iodide is an easily oxidized species (Baldwin 1986)

Iodide (Iminus) exists mostly in anaerobic environments These envi-ronments promote reduction of elemental iodine and iodate to iodide (Councell et al 1997) The oxidation state of iodide is the lowest


oxidation state that iodine exists in Iodide can be oxidized in a two-step process Iodide is first oxidized to elemental iodine (I2) and then is further oxidized to iodate (IOminus

3 ) Although this process occurs fre-quently in the environment the oxidation process requires a strong oxi-dant (Downs and Adams 1973) When elemental iodine and iodide are both added to solution triiodide (Iminus

3 ) will be formedIn soils iodine can be oxidized in several ways but only a few are likely

The first oxidant is dissolved oxygen (O2) in the soil solution but this oxidant is only present in extremely low concentrations in soil The next oxidant is nitrate (NOminus

3 ) but since it is readily leached out of soil this oxidant is probably not the most likely choice If nitrate oxidizes iodide to iodate then iodate would be less leachable due to its retention on soil colloids The final most likely iodine oxidant in soils is manganese (Mn2+) Manganese has been known to have strong oxidizing properties on other metals in the soil such as arsenic and chromium (Fox et al 2009) A study by Truesdale et al (2001) showed that the manganese oxidation reaction is only possible under acidic conditions The manganese oxidation reaction is not possible at pH greater than 75 The study showed that some of the iodine is adsorbing to the surface

deg

deg

Figure 22 EhndashpH stability diagram for dominant iodine aqueous species at 25 degC based on 10minus8 mol Lminus1 of dissolved iodine After Um et al (2004)


of birnessite (MnO2) (Truesdale et al 2001) Under anaerobic conditions soluble ferrous iron can reduce iodate to iodide (Councell et al 1997) Table 22 summarizes the redox potential of common iodine redox couples

Iodide itself is known as a good reducing agent for other halides includ-ing the iodine species permanganate dichromate ions and hydrogen perox-ide whereas iodate is an oxidizing agent that can oxidize iodide to elemental iodine (I2)

When in an acidic solution together iodide and iodate react in a redox reaction to form elemental iodine and water The kinetics of the iodidendashiodate reaction in aqueous systems is very complex There are many intermediate ions that the reaction must undergo in order to create elemental iodine and water

The overall chemical reaction is

IOminus3 + 5Iminus + 6H+ larrrarr3I2 + 3H2O

Most researchers have found that this reaction is a fifth order reac-tion while others have found that it is a sixth order reaction Dushman (1904) was the first to research the kinetics of the iodidendashiodate reac-tion He found that this reaction followed the rate law 13 times 109(H+)(Iminus)2(IOminus

3 ) + 9 times 108(H+)2(Iminus)(IOminus3 )(I

minus3 ) Other researchers have substanti-

ated this claim (Fox et al 2009 Guichardon et al 2000 Shetaya et al 2012)

The reaction mechanism by which iodate is reduced occurs in the fol-lowing reaction steps (Schmitz 1999)

IOminus3 + H+ larrrarr IO3H (21)

IO3H + Iminus + H+ larrrarr I2O2 + H2O (22)

I2O2 + H2O rarr IO2H + IOH (23)

Table 22 Reductionoxidation reaction couples of common iodine speciesReaction Electrical potential (EO) (Volts)

IOminus3 + 6H+ + 5 eminus rarr 12I2 + 3H2O 118

Iminus rarr 12I2 + 1eminus 05432I2 + eminus larrrarr Iminus

3079

Iminus3 + 2eminus larrrarr 3Iminus 0536

HIO + 2H+ + 2eminus larrrarr I2 + 2H2O 135IOminus + 2H+ + 2eminus larrrarr Iminus + H2O 131

After Burgot (2012)


I2O2 + Iminus rarr IOminus2 + I2 (24)

I2O2 + Bminus rarr I2O2Bminus (25)

I2O2Bminus + Iminus rarr IO2 + I2 + Bminus (26)

Reactions (24)ndash(26) occur rapidly and are irreversible Bminus in reaction (26) refers to the anion from the buffer solution which most likely is the acetate anion (CH3COOminus) The order of reaction at low concentrations and buffered solutions is two while at high concentrations and unbuffered solutions the order of reaction is one The presence of chloride and bro-mide can accelerate the rate of the reaction (Schmitz 1999)

The intermediates which iodine undergoes are purely experimental and many have differing viewpoints on the intermediates of the iodidendashiodate reaction Some intermediate forms may only exist for a matter of seconds and only under specific collision conditions (Morgan 1954) Elemental iodine intermediate is only a weak oxidizing agent and does not perturb the reaction The presence of an iodine cation (IO +

2 ) is also discussed as an intermediate in the iodidendashiodate reaction The basis for this theory is the solubility of iodic acid in liquid hydrogen fluoride Solubility in liquid hydrogen fluoride only occurs when the solute is capable of entering into a cationic form

63 Metal-IodateIodide Complexation and Solubility ProductsIodate and iodide are both known to readily complex with metal ions in solution since iodic acid (HIO3) and hydroiodic (HI) are near or com-pletely dissociated in water at most environmentally relevant pH values (pKa for HIO3 080 for HI ltlt1) Tables 23 and 24 show the equilibrium constants for various alkaline alkali earth metal and transition metal com-plexation with iodide and iodate Tables 25 and 26 summarize the solubil-ity constants of various metal-iodate and metal-iodide solubility products Comparing the formation and solubility constants in these tables it is clear that iodide forms stronger complexes and or solubility products with metals than iodate does The formation of strong aqueous complexes such as silver-iodide (log K for AgIminus

3 (aq) = 131) is notable Another key point in the data set is that the alkaline earth metal-iodideiodate pairs have high solubility whereas soft acidic metals in Pearsonrsquos HSAB theory tend to form solubility products with iodide that have very low solubility


64 Volatilization of Iodine SpeciesElemental iodine (I2) is known for its ability to volatilize from solution Henryrsquos Law Constants are used to describe the dissolution of a gas in solu-tion The chemical reaction that occurs when iodine gas dissolves into solu-tion is I2 (g) larrrarr I2 (aq) The Henryrsquos Law Constant for the partitioning of iodine

gas into solution is KH =[I2 (aq)]

PI2(g)

= 31 M atm minus 1 indicating that iodine would

favor the aqueous phase at 25 degCMethyl iodide (CH3I) is another iodine species that is volatilized via

plants The Henryrsquos Law Constant for methyl iodide is 00054 M atmminus1 which is lower than for elemental iodine but close to the Henryrsquos Law Constant for carbon dioxide in the atmosphere (Sander 1999) A list of the Henryrsquos Law Constants for various iodine species is shown in Table 27

Table 23 Formation constants of metal-iodide species

Metal Complexation reactionlog K at 25 degC and 0 ionic strength

Cesium Cs+(aq) + Iminus(aq) rarr CsIo

(aq) minus003Potassium K+

(aq) + Iminus(aq) rarr KIo

(aq) minus019Silver Ag+

(aq) + Iminus(aq) rarr AgIo

(aq) 658Silver Ag+

(aq) + 2Iminus(aq) rarr AgIminus

2 (aq)117

Silver Ag+(aq) + 3Iminus

(aq) rarr AgIminus3 (aq)

131

Copper Cu+(aq) + 2Iminus

(aq) rarr CuIminus2 (aq)

89



94



97

Zinc Zn2+(aq) + Iminus

(aq) rarr ZnI+(aq) minus204

Cadmium Cd2+(aq) + Iminus

(aq) rarr CdI+(aq) 228

Cadmium Cd2+(aq) + 2Iminus

(aq) rarr CdI02(aq)

392


(aq) rarr CdIminus3 (aq)

50


(aq) rarr CdI2minus4 (aq)

60

Lead Pb2+(aq) + Iminus

(aq) rarr PbI+(aq) 119

Lead Pb2+(aq) + 2Iminus

(aq) rarr PbI02(aq)

32


(aq) rarr PbIminus3 (aq)

39


(aq) rarr PbI2minus4 (aq)

119



65 Hypervalent IodineHypervalent is a term used to describe any ion that has more than an octet of electrons Hypervalent iodine is formed when and iodine spe-cies is oxidized to first remove three electrons and then the iodine species is further oxidized to remove five more electrons The mecha-nism by which iodine complexes with organic molecules and becomes

Table 24 Formation constants of metal-iodate species

Metal ion Complexation reactionlog K at 25 degC and 0 ionic strength

Barium Ba2+(aq) + IOminus

3 (aq) rarr BaIO+3 (aq)

110

Calcium Ca2+(aq) + IOminus

3 (aq) rarr CaIO+3 (aq)

089

Hydrogen H+(aq) + IOminus

3 (aq) rarr HIO3(aq)077

Magnesium Mg2+(aq) + IOminus

3 (aq) rarr MgIO+3 (aq)

072

Potassium K+(aq) + IOminus

3 (aq) rarr KIO3(aq)minus026

Silver Ag+(aq) + IOminus

3 (aq) rarr AgIO3(aq)063

Silver Ag+(aq) + 2IOminus

3 (aq) rarr Ag(IO3)minus2 (aq)

190

Sodium Na+(aq) + IOminus

3 (aq) rarr NaIO3(aq)minus048

Strontium Sr2+(aq) + IOminus

3 (aq) rarr SrIO+3 (aq)

100

Cerium Ce3+(aq) + IOminus

3 (aq) rarr CeIO2+3 (aq)

190

Chromium Cr2+(aq) + IOminus


100


Table 25 Dissociation constants for various metal-iodide solids

Metal Dissociation reactionlog K at 25 degC and 0 ionic strength

Bismuth BiI3(s) rarr Bi3+(aq) + 3Iminus

(aq) minus1811Copper (I) CuI(s) rarr Cu+

(aq) + Iminus(aq) minus1190

Gold (I) AuI(s) rarr Au+(aq) + Iminus

(aq) minus2280Gold (III) AuI3(s) rarr Au3+

(aq) + 3Iminus minus46Lead (II) PbI2(s) rarr Pb2+

(aq) + 2Iminus(aq) minus801

Mercury (I) Hg2I2(s) rarr 2Hg+(aq) + 2Iminus

(aq) minus2872Mercury (II) HgI2(s) rarr Hg2+


Silver AgI(s) rarr Ag+(aq) + Iminus

(aq) minus1607Thallium TlI(s) rarr Tl+(aq) + Iminus

(aq) minus726

After Downs and Adams (1973) Sillen et al (1964)


hypervalent iodine is extremely complex and is still not fully under-stood The binding of hypervalent iodine uses a pure 3p orbital to create a t-shape with other organic moieties or halogen atoms (Moriarty and Prakash 1986)

Table 27 Henryrsquos law constants for various iodine speciesIodine species Henryrsquos law constant (M atmminus1)

Elemental iodine (I2) 31 times 10Hypoiodous acid (HOI) 41 times 105

Hydrogen iodide (HI) 25 times 109

Iodine atom (I) 63 times 10minus3

Iodine chloride (ICl) 11 times 102

Iodine bromide (IBr) 24 times 10

After Sander (1999)

Table 26 Dissociation constants for various metal-iodate solids


Cadmium Cd(IO3)2(s) rarr Cd2+(aq) + 2IOminus

3 (aq)minus764

Calcium Ca(IO3)2(s) rarr Ca2+(aq) + 2IOminus

3 (aq)minus615

Cerium (III) Ce(IO3)3(s) rarr Ce3+(aq) + 3IOminus

3 (aq)minus1086

Cerium (IV) Ce(IO3)4(s) rarr Ce4+(aq) + 4IOminus

3 (aq)minus163

Cobalt (II) Co(IO3)2(s) rarr Co2+(aq) + 2IOminus

3 (aq)minus40

Copper (II) Cu(IO3)2 (s) rarr Cu2+ (aq) + 2IOminus3 (aq)

minus713

Lead (II) Pb(IO3)2(s) rarr Pb2+(aq) + 2IOminus

3 (aq)minus1261

Manganese Mn(IO3)2(s) rarr Mn2+(aq) + 2IOminus

3 (aq)minus636

Mercury (I) Hg2(IO3)2(s) rarr 2Hg+(aq) + 2IOminus

3 (aq)minus1371

Mercury (II) Hg(IO3)2(s) rarr Hg2+(aq) + 2IOminus

3 (aq)minus1789

Nickel (II) Ni(IO3)2(s) rarr Ni2+(aq) + 2IOminus

3 (aq)minus433

Potassium KIO3(s) rarr K+(aq) + IOminus

3 (aq)343

Radium Ra(IO3)2(s) rarr Ra2+(aq) + 2IOminus

3 (aq)minus894

Silver AgIO3(s) rarr Ag+(aq) + IOminus

3 (aq)minus751

Strontium Sr(IO3)2(s) rarr Sr2+(aq) + 2IOminus

3 (aq)minus694

Thallium TlIO3(s) rarr Tl3+(aq) + 3IOminus

3 (aq)minus551

Yttrium Y(IO3)3(s) rarr Y3+(aq) + 3IOminus

3 (aq)minus995

Zinc Zn(IO3)2(s) rarr Zn2+(aq) + 2IOminus

3 (aq)minus541



7 IODINE SORPTION IN HUMIC SUBSTANCES AND SOIL MINERALS

Sorption is one of the important abiotic processes in soils because it can limit the bioavailability of contaminants and nutrients Iodine spe-cies are known to sorb to both organic matter and to mineral surfaces The process by which the different iodine species sorb can be reversible or irreversible which makes it hard to determine the amount of bioavailable iodine This section reviews the general findings of iodine sorption research In addition an extensive summary of past iodine sorption studies (type of adsorbent reaction condition experimental methods and results) are shown in Table 28

71 Iodine Interactions with Humic SubstancesThere is considerable research evidence that iodine retention in soils is largely influenced by the organic matter content (Ashworth and Shaw 2006 Bors and Martens 1992 Schwehr et al 2009 Tikhomirov et al 1980 Whitehead 1973 Yamada et al 1999 2002 Yuita 1992) While the high surface area of humic substance contributes to the reactivity many studies indicated that the importance of chemical functional groups in the iodinendashhumic interaction Fawcett and Kirkwood (1953) found that the reaction of elemental iodine (I2) with polyphenols resulted in iodine-sub-stituted phenolic compounds (Fawcett and Kirkwood 1953) The similar substitution reaction in the aromatic rings of the natural organic matter was suggested by Stenberg and co-workers (Steinberg et al 2008) Warner et al (2000) also reported the complexation of I2 (aq) with several phenolic com-pounds The formation of π-complexes between I2 and aromatic functional groups was also suggested by Allinger et al (Allinger et al 1976) Mercapto groups (ndashSH) in proteins could possibly react with I2 forming ndashSI and ndashSI3 moieties (Jirosek and Pritchard 1971) Furthermore Benes and Whitehead showed the importance of aliphatic- and benzene-carboxylic amino acid and the phenolic functional groups of organic matter (Benes 1985 White-head 1974)

While these studies showed the chemical complexation controlled iodinendashhumic interaction other research showed that the redox reaction controlled reaction The reduction of iodate by thiol ligands has been earlier reported by Hird and Yates (Hird and Yates 1961) Steinberg et al (2008) found that the hydroquinone portions of the natural organic matter were

Ethan M Cox and Yuji Arai

66

Table 28 A summary of iodine sorption studies in geologic materials and humic substancesIodine species (references) Adsorbent(s) Reaction conditions Methods Summary of findings

Iodide (Ashworth et al 2003)

Wick Sandy Loam Series topsoil from Imperial College Ascot United Kingdom OM 4

pH sim4Sodium iodide radiotracer

background

Column experi-ments using 125I as a radiotracer

Iodine sorbed to soils under anoxic and oxic conditions

Iodide iodate and periodate (Couture and Seitz 1983)

Georgia Kaolin (Mn and Fe oxides removed)

Unbuffered solutions of 01 M NaOH and 0001 M NaHCO3 with 20ndash100 μL of radioiodine stock solution

pH sim4 6 and 7

Radiotracer studies

Negligible sorption of iodate or periodate

Approximately 30 sorption of iodate (180645E-09 mg kgminus1)


Hematite Fe2O3 Sodium acetate and acetic acid buffer at pH 287 390 576 and 867


Batch sorption experiments

Iodate strongly sorbed (312878E-08 mg kgminus1) in hematite in an unbuffered and buffered solu-tion pH 27ndash8

Iodide sorbed approximately 30 on hematite (47619E-11 mg kgminus1)

Periodate is more strongly sorbed than iodate with Kd values eight times as high as iodate (sorption ratio 1100 400 170 at pH 29 39 58 and 87 respectively)

Environmental Chem

istry and Toxicology of Iodine67

Iodate (Dai et al 2004)

Twenty different soils from across China includ-ing Aridisols Luvisols Cambisols Ferrisols Anthrosols Vertisols and Isohumisols

Solidndashsolution ratio 100 g Lminus1 reaction time 40 h

[KIO3]total 4 mg Lminus1

Background electrolyte 001 M CaCl2 pH varies from 4 to 9 depending on soil type

Desorption studies spiked with 4 mg Lminus1 of [iodate]total


Multiple regression analysis showed no correlation between iodate sorption and the soil properties (CEC pH aluminum oxide content) except for free iron oxide content

Kd values 1ndash56 g mLminus1The highest degree of hysteresis in

Perudic ferrisols

Iodide (Sazarashi et al 1994)

Allophane (Kanuma Japan) attapulgite (Georgia USA) chalcopyrite (Ontario Canada) cinnabar (Spain) and montmorillonite (Kunimine Industry)

Solidndashsolution ratio 50 g Lminus1 [KIO3]total tracer (1000 Bq) solution with concentration 1 μM

pH 37 63 and 10


Radioiodine tracer studies

999 sim40 and 10 sorption of iodide in cinnabar chalco-pyrite allophane respectively Negligible sorption (0 and 2 respectively) in montmorillonite and attapulgite

Continued


68

Iodide and iodate (Hu et al 2005)

Loamy sand soils from Savannah River Site SC pH 49ndash542 0013ndash23 OC CEC 0064ndash18 cmolc kgminus1 and clay mineralogy hydroxyl interlayered vermiculite goethite and kaolinite

Loamy sand from Han-ford WA pH 846 006 OC CEC 74 cmolc kgminus1 Clay miner-alogy smectite chlorite and mica

Kaolinite (Edgar FL) illite (Rochester NY) ver-miculite (Sanford NC) and montmorillonite (Panther Creek CO)

Background electrolyte 5 times 10minus6 M CaCl2

[Iodide]total and [iodate]total 01ndash001 μM respectively

Solidndashsolution ratio 4 g Lminus1 in batch sorption experi-ments in kaolinite illite vermiculite and mont-morillonite

Column studiesBatch sorption

experimentsIon chromatog-

raphy

Negligible iodide sorption in soils and sediments

Reduction of iodate by Fe(II) bearing illite

No oxidation of iodide to iodate

Iodine species (references) Adsorbent(s) Reaction conditions Methods Summary of findings

Table 28 A summary of iodine sorption studies in geologic materials and humic substancesmdashcontrsquod

Environmental Chem


Iodide (Kaplan et al 2000)

Soil samples from 200 area of the Hanford Site with the textural classes loamy sand silt loam and sand 03 and 2 amophous am iron oxide and CaCO3 respectively

Montmorillonite (clay mineral repository) ver-miculite (Libby MT) and quartz (Unimin Corp)

pH 82 for soils originallySolidndashsolution ratio

100 g Lminus1 ionic strength 001 M CaCl2

pH 36 50 79 and 94 in illite

Natural groundwater ionic strength 000918 mM calculated from MINT-EQA2


Radioactive decay mea-surements

Not strongly sorbed in calcite chlorite goethite montmoril-lonite or vermiculite

Significant sorption (Kd = 2770 mL gminus1) in oxidecarbonate removed illite

Presence of halogen exchangeable iodide

Iodide (Mattigod et al 2003)

Self-assembled monolayers on mesoporous support (SAMMS) mercury thiol SAMMS silver thiol SAMMS argen-tine chalcocite chalco-pyrite and cinnabar

Background electrolyte natural groundwater or simulated glass leachate with 125I

pH 632ndash724 for Hg-thiol SAMMS 346ndash834 for Ag-thiol SAMMS 266ndash833 for argentine 832ndash847 for chalcocite 818ndash827 for chalco-pyrite 797ndash803 for cinnabar

Solidndashsolution ratio of 100 mg getter in 10 mL spike solution 100 mg in 50 mL spike solution 100 mg in 100 mL 50 mg in 250 mL and 25 mg in 250 mL


Sorption capacity 3 times 108 Bq gminus1 to 69 times 105 Bq gminus1 of radioiodine

Silver and the mercury ver-sions had a Kd value as high as 104 mL gminus1

Continued


70

Iodate (Nagata and Fukushi 2010)

Fresh (4 h aged) hydrous ferric oxide surface area sim600 m2 gminus1

Synthetic iron oxyhy-droxide (goethite) BET surface area 51 m2 gminus1

Aluminum oxides (Merck and Company) BET surface area 180 m2 gminus1

pH 4ndash10Ionic strength 0001 001

010 and 1 M NaCl solidndashsolution ratio 01 021 1 and 10 g Lminus1

[IO minus3 ]total 1 μM

Bath sorption experiments

Computerized modeling to predict surface com-plexation

Inner-sphere sorption of iodate in hydrous ferrous oxide and goethite

Outer sphere sorption onto aluminum oxides

Inner-sphere increases with decreasing pH and increasing ionic strength

Iodide (Nagata and Fukushi 2009)



Aluminum oxides (Merck and Co Inc) BET sur-face area 180 m2 gminus1

Ionic strengths 001 005 and 01 M NaCl


X-ray absorp-tion near edge structure spectroscopy (XANES)

Outer sphere complexation of iodide

Iodide sorption increases with decreasing ionic strength and pH

Iodate and iodide (Nishimaki et al 1994)

KUR-Sand from the ground of the Research Reactor Institute Kyoto University

CEC 323 cmolc kgminus1 010 of organic car-bon and pH 54

Sterilized by 60Co gamma irradiation

10minus3 M HCl at pH 35 times 10minus4 M CaCl2 at medial

pH10minus5 M NaOH and 10minus3 M

NaCl at pH 10[Iodine]total 370 kBq Lminus1

Column experiment

Mathematical modeling (one-dimen-sional advec-tive-dispersive transport model)

125I radiotracer

Sorption of iodate was greater than iodide

High sorption of iodate at pH lt3Biphasic iodate sorptionIodate sorption increased with

decreasing pH



Environmental Chem


Iodide and iodate (Szczepaniak and Koscielna 2002)

γ-Aluminum oxide (Merck and Co Inc) BET surface area 97 m2 gminus1

Washed with 10minus2 M NaOH and then eluted with water

Ionic strength 006 M NaClO4

[Iodide]total and [iodate]total 5 times 10minus3 M

pH 15ndash95


Iodide sorbed the least while fluorine iodate and periodate sorbed the most strongly

The formation of outer-sphere surface complexes for iodate and iodide

88 sorption of iodate at pH 145 and decreases with increasing pH

Iodide (Xiangke et al 2001)

Calcareous surface soils (Jiuquan county China)

OM 135 calcium carbonate and CEC 594 cmolc kgminus1

Background electrolyte 01 M CaCl2 at pH 81

Influent an iodide radio-tracer (concentrationactivity) in 1 times 10minus4 M CaCl2

Solidndashvolume ratios were 100 50 or 3333 g Lminus1 soil


Column experiments

125I radiotracer experiments

Sorption of radioiodine in a calcareous soil was related to the organic matter content

Negligible effects of calcareous nature of the soil to iodide sorption

Iodide (Lefevre et al 2003)

Synthetic chalcocite (Cu2S) and roxbyite (Cu175S)

Solidndashsolution ratio 30 g Lminus1

Anoxic conditions under N2 purge

01 M NaClO4 at pH 85ndash9Addition of 250 μg Lminus1 of

KI after 2 8 and 10 days


High Kd value (2440 mL gminus1) in copper sulfide minerals

70 of iodide was immobilized after 24 h Inner-sphere complexation of iodide was suggested

Continued


72

Iodide (Fetter et al 1996)

Na saturated erionite (Sonora Mexico)

Purified bentonite (Mineralos no Metalicos SA)

Synthetic solndashgel hydrotalcites

All solids were calcined at 773 K

01 N of NaI solutions at pH 6

Reaction time 24 h


125I radiotracer studies

Low iodide sorption onto hydrotalcites

Thermal treatment (high temperatures) of the hydrotalcites allowed iodide to more easily replace other anions in the structure of the hydrotalcite

Iodide was not sorbed at all in bentonite or erionite (sorption was zero)

Iodide (Aimoz et al 2011)

Natural pyrite (Huanzala Peru and Navajun Spain)

BET surface area 046ndash094 m2 gminus1

Anoxic conditions in a glove box

pH varied between 33 and 8

Solidndashsolution ratios of 5ndash50 g Lminus1



Very weak sorption of iodide in pyrite (Kd values less than 0002 m3 kgminus1)



Environmental Chem


Iodide and iodate (Fuhrman et al 1998)

Illitic shale (Kimmswick MO) goethite (Biwabik MN) kaolinite (Mesa Alta NM and Twiggs Co GA) clinochlore (CA and Yancey Co NC) calcite (Iceland spar) limonite (Cart-ersville GA) biotite (Ontario Canada) pyrite (Huanzala Peru) magnetite (Ontario Canada) and hematite (Ironton MN)

lt180 μm mineral fraction[iodide]total or [iodate]total

1000 mg Lminus1

Aerobic condition0005 M NaHCO3 buffer at

initial pH of 87pH for kaolinite was 68

limonite 77 pyrite 26 magnetite 885 biotite 93 clinochlore 86 illite 67

XANES spec-troscopy

Radiotracer experiments


Iodate sorption on pyrite via surface mediated reduction of iodate 82 sorption in less than 1 day

Biotite sorbed iodate (20 after 15 days) but did not sorb iodide

Magnetite sorbed iodide but did not sorb iodate

Iodide (Anschutz et al 2000)

Bioturbated samples of fine grained muddy sedi-ment from the Lauren-tian Trough Canada

Contains manganese oxides iron oxides and quartz

Anaerobic conditionsNatural groundwater condi-

tionsDissolved sulfides oxygen

organic matter and man-ganese oxides

Redox experi-ments

Manganese minerals are oxidized by dissolved iodate in solution iodide maximum coincides with the depth where upward diffusing manganese becomes undetectable

Iodine species reacting with dissolved oxygen and then becoming sorbed to iron oxides or incorporated into natural organic matter

Continued


74

Iodide and iodate (Ashworth and Shaw 2006)

Homogenized field moist sandy loam topsoil (Wicks Series) from Berkshire UK

pH of soil 43Deionized water used for

synthetic water tableInitial concentration of

radiotracer iodine solution 20 Bq mLminus1

Column experi-ments

Radiotracer experiment

Radioiodine accumulated at the anoxicoxic border

Varying the height of the water table increased the dissolved concentrations of iodide which does not sorb as strongly as iodate

Sorption of iodine species onto the soil was low (Kd 1 mL gminus1)

Iodide (Bors and Martens 1992)

Loamy sand (podozol) pH 65

Clay silt (chernozem) pH 75

Soils were not treated to remove impurities

10 g of soil with 20 mL of distilled water containing 63 kBq of Iminus which corresponds to 01 ng of Iminus

Increased biomass by adding glucose KNO3 and K2HPO4

Decreased biomass by fumigating soil with alcohol free chloroform

Sterilized soil samples using 60Co irradiation added 6 mL of 370 kBq Iminus dropwise to simulate precipitation

Batch and col-umn experi-ments

Increasing biomass by adding soil amendments increased Kd values for radioiodine (con-trol 276 mL gminus1 amendments 376 mL gminus1)

Decreasing biomass by fumigating soil with alcohol free chlo-roform decreased Kd values (control 276 mL gminus1 fumigated 25 mL gminus1)

Irradiated soils decreased Kd values of radioiodine by 2993 in the podozol and 693 in the chernozem soil



Environmental Chem


Iodide (Fox et al 2009)

Synthetic birnessite created by adding concentrated HCl to 04 M KMnO4

BET surface area 41 m2 gminus1

pH range 450ndash625Solidndashliquid ratio

01ndash10 g Lminus1

[Iodide]total = 01ndash10 mMBackground electrolyte

010 M NaClO4


Iodide is oxidized to iodine (I2) then to iodate through mul-tiple intermediate forms (HIO IO2) by the mineral birnessite The reaction proceeds via a first-order rate law

Iodide oxidation occurs more quickly at lower pH

Iodate (Fox et al 2009)



pH 50Solidndashsolution ratio

1 g Lminus1

[Iodate]total = 5 μMndash5 times 10minus4 M

Background electrolyte 010 M NaClO4

Reaction time 22 h


Iodate sorption was rapid reaching equilibrium in 30 min but low (0024 mM gminus1)

Continued


76

Iodide (Katz et al 1996)

Glacial till (Unity and Township Maine) BET surface area 149 and 336 m2 gminus1

Marine clay (Wiscas-set and Bangor Pre-sumpscot Formation Maine) BET surface area 23665 and 30715 m2 gminus1

Additives bentonite (Wyo-Ben Inc Billings Montana) zeolite (XY Clinoptilolite Teague Mineral Products Adrian Oregon) andisol (Wuksi soil from Medi-cine Lake Highland California) iron oxide (predominantly hema-tite Pea Ridge Iron Ore Co Sullivan Missouri)

0002 M ionic strength from synthetic inorganic leach-ate containing sodium magnesium ammonium manganese calcium mag-nesium chloride sulfate nitrate and bicarbonate

pH 2ndash8[iodide]total = 10minus9 MSolidndashsolution ratio 20 g Lminus1


Natural glacial till soils did not show a high amount of sorption (Kd = 00014 m3 gminus1) at pH 5

Natural marine clay soils did not show a high amount of sorption (Kd = 00016 m3 gminus1) at pH 5

The andisol additive and the bentonite additive showed the highest amount of iodide sorp-tion at pH 5 (Kd = 00687 and 00025 m3 gminus1 respectively)

Andisol and bentonite mixtures with natural glacial till and marine clay increased Kd values compared with all natural glacial till and natural marine clay at pH 5



Environmental Chem


Iodide (MacLean et al 2004)

Bacteria Bacillus subtilis-168 rinsed five times with 01ndash0001 M KNO3

Background electrolyte for sorption studies 001 0005 and 0001 M KNO3

pH 25ndash75Solidndashsolution ratio 1 10

40 100 g bacteria Lminus1

[Iodide]total = 10minus9 M


At high ionic strengths (001 and 0005 M) there was no sorption of iodide onto the bacterial cell walls

35 sorption in 0001 M at pH 25 in 10 g bacteria Lminus1

High ionic strengths displace iodide suggesting that sorption is electro-static (outer-sphere)

Iodide and iodine (Warner et al 2000)

Phenol m-cresol p-cresol guaiacol m-methoxy-phenol resorcinol salicylate p-hydroxyben-zoate (Fisher Scientific)

Soil fulvic acid soil humic acid and Suwanee River fulvic acid (International Humic Substances Society)

Soil humic acid from surface horizon of a Mudwell Soil Series (Inceptisol Mount Shasta California)


pH 50 for 2-Hydroxy-benzoate (salicylate) 55 for 4-hydroxybenzoate 15 for resorcinol 2 for 3-methoxyphenol 35 for all other organic molecules

pH varied from 3 to 450 for kinetic study

[iodine]total = 2625 times 10minus2 M[iodine (I2)] = 125 times 10minus4 M[iodide] = 25 times 10minus3 MSolidndashsolution ratio 50 mL

of phenol molecules in distilled water


The decrease of the occurrence of the triiodide molecule is least rapid at low pH values and becomes more rapid as pH increases from 3 to 45

The reaction rate decreases as the iodide concentration increases from 127 times 10minus3 to 144 times 10minus2 M

Sites for iodination on phenols depend on the resonance struc-ture and the substituents on the ring structure

The fulvic and humic acids reacted much slower than the simple phe-nol molecules The rate of reaction decreased as the iodide concentra-tion increased

The Suwanee River fulvic acid had a faster rate of reaction with iodine (I2) than the soil fulvic acid which can be explained by the fact that stream humic substances contain more methoxyl carbon groups

Continued


78

Iodide (Weera-sooriya and Wickrama-rathna 1999)

Kaolinite (Rattota Sri Lanka)


Background electrolyte 01 M NaNO3 and 0004 M NaNO3

pH 4ndash8Solidndashsolution ratio 10 g Lminus1

(isotherm studies) and 15 g Lminus1 (edge studies)


Sorption of iodide on kaolinite was low (025 at pH = 4 and ionic strength = 400 times 10minus3 M)

Sorption of iodide on kaolinite decreased with increasing pH

Iodide sorption decreased with increasing ionic strength sug-gesting an outer-sphere (electro-static) complexation

Other halogen anions (Fminus in par-ticular) outcompete iodide for sorption on kaolinite

Iodide and iodate (Yamaguchi et al 2010)

Andosol soil sample from surface layer of upland field and forest (Ibaraki Japan)

Acrisol from surface and subsurface layer from upland field (Okinawa Japan)

[Iodide] and [iodate] = 2 μmol gminus1 sprayed on moist soil

Deionized water added to maintain water content

Reaction time 1 and 60 days

One soil sample per group irradiated with gamma rays to kill fungi bacteria and other biota

Background electrolytes included natural ground-water and deionized water



Iodate was present at day 1 but not after 60 days which sug-gests that iodate was changed to another iodine species

In the upland andisol only 50 of iodate was incorporated into the organic matter while 100 of iodide was incorporated

In the forest andosol sample both iodate and iodide achieved 100 incorporation into the organic matter

In both samples of the acrisol 100 of the iodate was incor-porated into the organic matter

Gamma ray irradiation seemed to have no effect on iodine incor-poration into organic matter



Environmental Chem


Iodide (White-head 1973a)

Permanent grassland soil (025 Al2O3 149 Fe2O3 211 organic matter pH = 7) from Hurley Berkshire England ranging in depth from 0 to 40 cm

Temporary grassland soil (015 Al2O3 123 Fe2O3 125 organic matter pH = 698) from Hurley Berkshire England ranging in depth from 0 to 40 cm

Organic matter removed by 30 H2O2

Background electrolyte 001 M CaCl2


[Iodide]total = 315 times 10minus6 M to 630 times 10minus5 M KI (corresponding to 25 and 6 μg I gminus1 soil)

pH 2ndash10Reaction time 40 hChloroform added to sup-

press microbial mass


Sorption of iodide was greatest at pH values 20 to 40 (sim35 mg I kgminus1 soil) for both soils in the depth range 0ndash10 cm and 30ndash40 cm

Sorption declined sharply between pH 5 and 6 but increased again (from 12 to 18 mg I kgminus1 soil) around pH 9 possibly due to sorption onto organic matter

Reduction in sorption with increasing depth

Treatment of soil with H2O2 decreased sorption greatly removing organic matter and forming oxalates with iron and aluminum metals

Continued


80

Iodide (White-head 1973b)

Permanent grassland soil (156 free Fe2O3 024 free Al2O3 370 organic matter pH = 67) from Hurley Berkshire England

Additives grass root com-post (perennial ryegrass OM = 64) hydrated ferric and aluminum oxides (synthetically cre-ated) chalk (upper chalk and oolitic limestone) limestone (upper chalk and oolitic limestone) kaolinite (English China Clays Ltd) montmoril-lonite (Laporte Industries Ltd)



[Iodide]total = 788 times 10minus7 and 315 times 10minus6 M KI

pH 3ndash8Reaction time 40 h


Root compost sorbed high amounts (33 mg kgminus1) of iodide at pH 4 and as high as 35 mg kgminus1 at pH 8 and 9

Added clays such as chalk lime-stone kaolinite and montmoril-lonite did not sorb any iodide in sorption studies

The soil alone only sorbed high amounts (30 mg kgminus1) of iodide at pH 3 and low amounts (7 mg kgminus1) at pH 7

Hydrated ferric and aluminum oxides only sorbed iodide at low pH (3 and 4) (20 mg kgminus1 for ferric oxides and 8 mg kgminus1 for aluminum oxides)



Environmental Chem


Iodide (Raja and Babcock 1961)

Aiken Clay Loam (183 cmolc kgminus1)

Yolo Loam (175 cmolc kgminus1)

Kaolinite (Minerals Unlimited Berkeley California)

Bentonite (Commercial Volclay)

Soil samples were auto-claved digested on a steam bath digested at various pHs digested with H2O2 and treated with alcohol

Background electrolyte 002 N CaCl2 Ca(NO3)2 CaSO4 Ca(OH)2

pH 45 55 65 75 and 85


30ndash40 μc radiotracer iodide



Autoclaving reduces fixation of iodide retention in soil

Peroxide treated soils reduced iodide fixation

Sorption to bentonite or kaolinite was minute to negligible

Iodide reacted mostly with organic matter in the soil

Iodide and iodate (Yoshida et al 1992)

Andosol (Tokai-mura Ibaraki Prefecture Japan) pH = 54 carbon = 44 nitrogen = 030 CEC = 020 cmolc kgminus1

Kanuma (Kanuma-shi Tachigi Prefecture Japan) pH = 62 carbon = 056 nitrogen = lt01 CEC = 016 cmolc kgminus1

Background electrolyte varying concentrations of KI KIO3 and KCl

pH 3ndash9[Iminus]total = 0012ndash175 mg Lminus1

[IO minus3 ]total = 0012ndash

175 mg Lminus1


Iodide was electrostatically bound to the surface via the same mechanism as chloride

Iodate still sorbed strongly (sim65 sorption) at high pH indicating that iodate is specifically sorbing to the surface on the Kanuma soil

Iodide sorbed strongly (sim60) in soils with high organic matter concentrations (andosols)

Continued


82

Iodide and iodate (Couture et al 1979)

Hematite (Fe2O3) Background electrolyte 2 NaClO4 and 0001 M NaHCO3

pH = 69 and 67


Hematite showed an appreciable ability to sorb iodate from solution (sim100 sorption)

Hematite also has a small exchange capacity for iodate adding a reducing agent such as NaHSO3 caused iodine species to desorb

Iodide and iodate (Yamada et al 1999)

SA-3 an andosol nonal-lophanic from virgin land pH 48 CEC 343 cmolc kgminus1 carbon 92 mg kgminus1 total iodine 391 mg kgminus1

KU-7 red yellow soil mountain soil from Kameoka Kyoto pH 53 CEC 106 cmolc kgminus1 carbon 84 mg kgminus1 total iodine 216 mg kgminus1

Background electrolyte 010 M KCl

[Iodine]total = 3 μgSolidndashsolution ratio

01 g Lminus1

Extraction with tetramethyl ammonium hydroxide ascorbic acid and citric acid

Inductively coupled plasma mass spectrometry (ICP-MS)

High levels of iodine recovery in fulvic and humic acids

In SA-3 humic acid recovered 20 mg kgminus1 of iodine and fulvic acid recovered 6 mg kgminus1 of iodine

Recovery rate for small amounts (3 ng) of iodine was over 100 for both types of soil (103 and 106 recovery)

Iodide was incorporated more into the organic matter than was iodate (50 vs 100 respec-tively)



Environmental Chem


Iodine iodide and iodate (Yamaguchi et al 2006)

Clay loam Andosol sample (National Institute of Agro-Environmental Sciences Tsukuba Japan) CEC 244 cmolc kgminus1 carbon 39 g kgminus1 nitro-gen 37 g kgminus1 free Al 2767 g kgminus1 Free Fe 2503 g kgminus1

Clay loam Gleysol (National Institute of Agro-Environmental Sciences Tsukuba Japan) CEC 163 cmolc kgminus1 carbon 24 g kgminus1 nitrogen 19 g kgminus1 Free Al 23 g kgminus1 Free Fe 122 g kgminus1

Background electrolyte 010 M KNO3 or K2SO4 or 005 M KNO3 or K2SO4

pH 48ndash55 for Gleysols and 646ndash8 for andosols

[Iminus]total = 300 μg gminus1 soilSolidndashsolution ratio

115 gram soilSet of soil samples sterilized

by gamma ray irradiation



Redox experi-ments

[Iminus] was higher when the soil was flooded due to the decrease in redox potential Redox potential decreased with increasing depth

After 30 days IOminus3 disappeared

possibly due to the reduction to I2 or Iminus I2 was possibly incorpo-rated into organic matter

Irradiation with gamma rays inhib-ited the reduction of iodate suggesting that microbial reduction is a factor

Iodide did not oxidize to iodate under nonflooded conditions


SA-3 an Andosol nonal-lophanic from virgin land pH 48 CEC 343 cmolc kgminus1 carbon 92 mg kgminus1 total iodine 391 mg kgminus1




01 g Lminus1



Size exclusion chromatogra-phy (SEC)

Inorganic iodine was incorporated into the structure of humic and fulvic acids determined by SEC and ICP-MS

The organoiodine compounds were found to be very thermally stable

Bromine was incorporated into the structure of the organic matter as well

Calculations from data estimate that SA-3 contained sim3 iodine atoms per 105 carbon atoms and KU-7 contained sim8 iodine atoms per 105 carbon atoms

Continued


84

Iodide and iodate (Yuita 1992)

Fukui brown forest soil (Cambisol from Fukui Prefecture Agriculture Experimental Station Fukui City) pH 50 carbon 062 light clay free Fe 894 free Al 144 iodine 15 ppm

Tochigi ando soil (Andosol from Utsunomiya City Japan) pH 51 carbon 114 light clay textural class free Fe 569 free Al 92 iodine 26 ppm

Flooded and nonflooded conditions

pH 42 and 45 (cambisol) 45 and 59 (andisol)

Background electrolyte distilled water

Solidndashsolution ratio 200 g per plot with 100 mL water

Redox experi-ments

Under flooded conditions iodide was the most dominant form of iodine in both soils at 868

Under nonflooded conditions iodate was the most dominant form of iodine in both soils at 858

The redox potential was deter-mined to be the only deter-mining factor for speciation of iodine

The concentration of iodine (I2) and organoiodine were extremely low (close to zero) in both soil types




responsible for reduction of I2 to hypoiodous acid Hypoiodous acid was then incorporated into the structure of the natural organic matter In other study by Steinberg et al (2008) researchers discovered a mechanism by which the phenolic functional groups on natural organic matter reduced iodate to iodide and then to form hypoiodous acid (HIO)

More recently Yamaguchi et al (2010) showed the new evidence of abiotically induced iodine(minus1 and +5) redox reaction upon the reac-tion with organic carbon rich soils (Yamaguchi et al 2010) The X-ray absorption near edge structure (XANES) measurements clearly indicated that sterilized organic rich soils reduced I(+5) to near I(0) and oxidized I(minus1) to near I(0) less than 24 h while microbially mediated iodine redox reaction generally require more than months to complete the redox reac-tion (Councell et al 1997 Farrenkopfa et al 1997 Schwehr et al 2009) Kinetics of abiotically controlled iodine redox reactions with humic sub-stances seem to be more predominant than biotically controlled reaction suggesting an importance of abiotically driven iodine redox reaction in OC rich soils

Predicting the structure of organoiodine compounds is difficult because of the complex nature of organic matter No two organic matter substances are exactly the same and the presence of different functional groups on each carbon atom can indirectly affect the bonding of iodine species to that carbon whether or not the hydroxyl carboxylate or aniline functional group is ortho- or para-from the iodine species can have a huge impact on the binding affinity of iodine for that binding site (Warner et al 2000) Hydroxyl functional groups are para and ortho directing while the car-boxylic acid functional group is known to be meta-directing Schlegel et al (2006) investigated the bonding mechanisms of iodine in iodinated humic substances using X-ray absorption spectroscopy The analysis showed the IndashC interatomic distances to be 201ndash204 Å with a carbon coordination number of about one corresponding to iodine association with aromatic functional groups They indicated that similar complexes might be forming in iodine-reacted humic substances

72 Iodine Sorption in Clays and Clay MineralsIodine reactivity is largely dependent on its chemical speciation in the environ-ment In oxic and anoxic subsurface environments inorganic iodine is observed in three different valence states (iodide I(minus1)minus) iodine (I(0)2)) and iodate (I(+5)O minus

3 )) (Fuge and Johnson 1986 Hu et al 2005) The reduced inorganic I(minus1) species is recognized as the most mobile iodine species in soils as oxidized


I(+5)O minus3 ) has a greater affinity for geomedia at neutral pH (Couture and Seitz

1983 Yamada et al 1999 2002 Yuita 1992) Iodate (I(+5)O minus3 ) was found to be

strongly hydrated with a Bader charge of +483 which could allow iodate to strongly sorb to the negatively charged mineral surfaces Bader charge analysis is often used to define the hardness of atoms or molecules This property of iodate could explain why iodate is more strongly sorbed to colloids (eg illite hematite) than iodide or other iodine species do (Couture and Seitz 1983 Kaplan et al 2000) The results are summarized below

There are several macroscopic investigations reporting different affinities of iodate iodide and iodine on geomedia Iodate (I(+5)O minus

3 ) is known to be retained in soils (eg andisols) and on phyllosilciates (epidote chlorite) metal oxyhydroxide surfaces (eg aluminum oxide biotite hydrous ferrous oxide and hematite) at near neutral pH (Couture et al 1979 Couture and Seitz 1983 Dai et al 2004 Fuhrmann et al 1998 Kaplan et al 2000 Nagata and Fukushi 2010 Ticknor and Cho 1990 Yoshida et al 1992) Our iodate sorption experiments on activated alumina also show the pH depen-dent sorption behavior sorption decreases with increasing pH (Figure 23) Because of high point-of-zero charge (sim9) of activated alumina the surface charge of minerals become more negative with increasing pH that repel

Figure 23 Iodate sorption envelope on activated alumina [iodate]total 3 mg Lminus1 and solidndashsolution ratio 5 g Lminus1 of 80ndash200 mesh chromatographic grade activated alumina Matheson Coleman and Bell Norwood OH


anionic iodate species in solution It also shows lack of ionic strength effect on iodate sorption indirectly suggesting the presence of inner-sphere sur-face complexation mechanisms A recent surface complexation study sup-port our finding that iodate sorbs on variable charge mineral surfaces via a bidentate mononuclear at low pHs (Nagata and Fukushi 2010)

Conversely iodide (I(minus1)minus) adsorption is very weak Iodide shows near negligible sorption on bentonite calcite chlorite epidote goethite kaolin-ite magnetite montmorillonite quartz and vermiculite (Fuhrmann et al 1998 Kaplan et al 2000 Raja and Babcock 1961 Ticknor and Cho 1990 Whitehead 1974) only illite exhibits some sorption capacity for iodide at pH sim7 (Kaplan et al 2000 Vinogradov 1959) pH-dependent iodide retention behavior has been reported in both soils (eg glacial tills marine clay and andisols) and soil constituents (eg bentonite hematite and zeo-lite) (Katz et al 1996 Whitehead 1973b Yoshida et al 1992) In other research the strong reactivity of soft-acid-based minerals (cinnabar and copper sulfide) for iodine has been reported (Sazarashi et al 1994 Lefevre et al 2003) Iodide sorption on variable charge mineral surfaces generally decreases with increasing pH from 4 to 8 in these materials Based on a positive correlation between the amount of iodide sorption and the iron and aluminum oxide content in 23 English soils Whitehead (1973ab) sug-gested an important role for FeAl oxyhydroxides with respect to the iodide fixation in soils Our sorption experiment using kaolinite (carbonate and iron oxide removed KG-1a) shows a decrease in iodine sorption at alkaline pH (Figure 24) Interestingly sorption was affected by the ionic strength With increasing ionic strength from 001 to 01 M NaNO3 the sorption decreased at pH 35ndash6 suggesting the presence of outer-sphere surface complexes at low ionic strength This supports the results of a triple-layer model to describe the weak adsorption of iodide on kaolinite surfaces in considering an outer-sphere complexation mechanism (Weerasooriya and Wickramarathna 1999)

The recent investigation by Fox et al (2009) showed pH dependent iodide oxidation during iodide (Iminus) reaction with birnessite The iodide oxidation rate by birnessite was significantly less with increasing pH in the range of 450ndash63 The pseudo first order rate constant kprime decreased from 325 plusmn 03 to 0064 plusmn 0003 hminus1 with increasing pH from 45 to 625 There are few molecular-scale studies probing in situ iodine speciation (ie valence state) at the mineralndashwater interface eg (Fuhrmann et al 1998 Yamaguchi et al 2006) Fuhrmann et al (1998) conducted XANES analysis on iodide- andor iodate-reacted pyrite magnetite and biotite mineral slurries at pH 26ndash93


While iodate was reduced to I2 upon reaction with the pyrite suspensions iodate-biotite and iodide-magnetite systems showed no changes in iodine valence state Yamaguchi and co-workers recently investigated iodine valence speciation in paddy field soils using a XANES technique (Yamaguchi et al 2006) They reported significant iodate reduction in anoxic systems no iodide re-oxidation was observed in these systems

8 REMEDIATION OF IODINE CONTAMINATION

Iodine remediation is generally applied to the remediation of radio-iodine-129 because of its toxicity associated with a long half-life in the aquatic and terrestrial environment The following three remediation tech-niques have been considered (1) volatilization (2) immobilization and (3) phytoremediation

81 VolatilizationWhitehead (1981) earlier reported the iodine volatilization from soil which was associated with soil properties Because of the sorption reaction of iodine in different soil components the content of inorganic and organic soil components (eg iron oxide and OM) can retard the volatilization process

Figure 24 Iodide sorption envelope on kaolinite [iodide]total 3 mg Lminus1 and solidndash solution ratio 15 g Lminus1 of KG1a kaolinite Clay Mineral Society Chantilly VA


In a sandy soil sim100 of the iodine can be volatilized due to lack of sorp-tion whereas other finer texture soils with some organic matter as well as montmorillonite kaolinite and iron oxide showed only 10 of iodine loss to atmosphere The study was followed by several investigators to better elu-cidate the volatilization mechanisms (Amachi et al 2004 2005 Farrenkopf et al 1997 Muramatsu and Yoshida 1999 Sheppard et al 1994 Zhang et al 2011) They have shown that soil microorganisms are responsible for the major iodine loss to the atmosphere They facilitated the conversion of inorganic iodide to organic iodine methyl iodide (CH3I) Amachi et al (2001) showed that the source of the methyl group in methyl iodide is com-ing from a compound known as S-adenosyl-methionine (SAM) It was also found that methylation was preferentially occurring at the interface of oxic and anoxic environments Zhang et al (2011) have recently reported the importance of sulfur and iron-reducing bacteria that can contribute to the initial reduction step from iodate to iodine prior to the methylation process

82 Immobilization and PrecipitationAs discussed in the previous section soft acids in adsorbentssoil solution facilitate the formation of surface complexes and various solubility prod-ucts making iodine less bioavailable

In a study by Atkins et al (1990) researchers found that adding silver to a new cement slurry containing radioactive iodide precipitated most of the radioiodine Although this method works in new cement slurries over time anoxic portions of the cement begin to develop In addition to bind-ing to iodide ions silver binds more preferentially to reduce sulfur (S2minus) In the cement if there is reduced sulfur the silver ions will bind to them and make the iodide ions soluble Reduced sulfur also has the ability to reduce silver cations to elemental silver (Ag(0)) which would also remo-bilize iodide ions (Atkins et al 1990) Silver can be also added to drinking and or ground water as silver chloride The silver iodide is known to readily precipitate out allowing the radioactive iodine to be removed from solution (Denham et al 2008) However the reaction is perturbed by the activity of sulfide since it competitively binds with silver cations causing the iodide to become soluble again (Atkins et al 1990)

Mattigod et al (2003) has shown that synthetic ldquogettersrdquo can sorb vast amounts of radioiodine the getters can sorb 104ndash105 mL gminus1 of radioio-dine These ldquogettersrdquo are self-assembled monolayers on mesoporous support (SAMMS) These SAMMS have high surface areas (800ndash1000 m2 gminus1) and pore spaces that allow them to sorb different cations anions and oxyanions


In addition these ldquogettersrdquo also have soft acids embedded into their struc-ture such as silver-thiol that iodide preferentially binds with ( Mattigod et al 2003 Wulfsberg 1991) These SAMMS have been shown to also adsorb radioiodine selectively as opposed to other halide ions such as chloride flu-oride and bromide A disadvantage of this SAMMS adsorbent technology is the reality that they can only adsorb iodide Radioiodine exists in many other oxidation states in the soil solution such as elemental iodine (I2) and iodate (IOminus

3 ) therefore it is highly selective for iodide

83 PhytoremediationResearchers have also tested various plant species as a potential for remedia-tion of radioactive iodine However the results are inclusive among plant species Dai et al (2006) found that iodate was preferentially taken up by spinach plants than iodide from the soil The study found a high root to leaf transfer of iodate but the researchers also noted that iodide was being lost to the atmosphere as gaseous methyl iodide (CH3I) but no iodine was volatilized as inorganic iodine (I2) The fact that iodide can leave the plant as a vapor may account for the higher values of iodate in the plant (Dai et al 2006) A study by Soudek et al (2006) showed that iodine was being sorbed by hydroponically cultivated sunflower (Helianthus annuus L) but the radioiodine was not making it much further than the roots The researchers observed no volatilization of iodine which may be a species-specific ability (Soudek et al 2006)

9 CONCLUSION AND FUTURE CHALLENGES

Approximately 70 of global iodine budget resides in ocean whereas geogenic iodine supply is limited This remains as the critical source of iodine in sustaining terrestrial life In general iodine deficiency is more concerned to human health (Soumlderlund et al 2011) than its direct toxicity unless radioiodine is released into the environment Due to the short-lived I-131 I-129 is a focus of radioiodine in the environmental remediation Unlike other radionuclides (eg U and Tc) immobilization of radioio-dine in geomedia is difficult It rarely forms stable solubility products with common cations in groundwater and soil solutions Furthermore the par-titioning of iodate and iodine is greatly affected by pH and ionic strength In general iodate shows much stronger retention to soil minerals than iodide at environmentally relevant pH values (4ndash75) Sorption of both ions decreases with increasing pH and ionic strength (Kaplan 2011 Soumlderlund


et al 2011 Whitehead 1984) making the stabilization of iodine in soils and sediments difficult at near neutral pH Volatilization of radioiodine as methyl iodine or elemental iodine has been considered at the DOE sites However its complex environmental chemical cycle involving multiple valence states (iodide iodine and iodate) makes the development of in situ remediation technology challenging The complexation of iodide and iodate with humic substances seem to be one of the most important reaction paths in assessing the fate of radio-iodine as long as enough carbon sources (eg soil humic substances natural organic matter) are available In (sub)surface environ-ment development of in situ remediation technology for radioiodine might require a better understanding of the retention mechanism of organo-iodine species in soils and sediments and the transport process

REFERENCESAimoz Laure Curti Enzo Maumlder U 2011 Iodide interaction with natural pyrite Journal

of Radioanalytical and Nuclear Chemistry 288 (2) 517ndash524Aldahan A Kekli A Possnert G 2006 Distribution and sources of 129-I in rivers of the

baltic region J Environ Radioact 88 49ndash73Allinger NL Cava MP De Jong DC Johnson CR Lebel NA Stevens C 1976

Organic Chemistry Worth Publishers Inc New YorkAmachi S Kamagata Y Kanagawa T Muramatsu Y 2001 Bacteria mediate methyla-

tion of iodine in marine and terrestrial environments Appl Environ Microbiol 67 2718ndash2722

Amachi S Mishima Y Shinoyama H Muramatsu Y Fujii T 2005 Active transport and accumulation of iodide by newly isolated marine bacteria Appl Environ Microbiol 71 741ndash745

Amachi S Kasahara M Fujii T Shinoyama H Hanada S Kamagata Y Ban-nai T Muramatsu Y 2004 Radiotracer experiments on biological volatilization of organic iodine from coastal seawaters Geomicrobiol J 21 481ndash488

Anschutz P Sundby B Lefranccedilois L Luther III GW Mucci A 2000 Interactions between metal oxides and species of nitrogen and iodine bioturbated marine sediments Geochim Cosmochim Acta 16 2751ndash2763

Ashworth DJ Shaw G Butler AP Ciciani L 2003 Soil transport and plant uptake of radio-iodine from near-surface groundwater J Environ Radioact 70 99ndash114

Ashworth DJ Shaw G 2006 A compaction of the soil migration and plant uptake of radioactive chlorine and iodine from contaminated groundwater J Environ Radioact 89 61ndash80

Atkins M Kindness A Glasser FP Gibson I 1990 The use of silver as a selective precipi-tant for 129I in radioactive waste management Waste Manage 10 303ndash308

Baldwin RM 1986 Chemistry of radioiodine Int J Radiat Appl Instrum Part A Appl Radiat Isot 37 817ndash821

Bartholomay RC 2009 Iodine-129 in the Snake River Plain aquifer at and near the Idaho National Laboratory Idaho 2003 and 2007 US Geological Survey Scientific Investigations Report 2009ndash5088 (DOEID-22208) 28 p httppubsusgsgovsir20095088

Benes J 1985 Establishing of equilibrium between radioiodine and soil Coll Czech Chem Commun 50 1033ndash1038


Bringmann G Kuumlhn R 1980 Comparison of the toxicity thresholds of water pollutants to bacteria algae and protozoa in the cell multiplication inhibition test Water Res 14 (3) 231ndash241

Bors J Martens R 1992 The contribution of microbial biomass to the adsorption of radioiodine in soils J Environ Radioact 15 35ndash49

Burgi H Schaffner T Seiler JP 2001 The toxicology of iodate a review of the literature Thyroid 11 (5) 449ndash456

Burgot JL 2012 Ionic equilibria in analytical chemistry Springer New YorkChristiansen JV Carlsen L 1989 Iodine in the Environment Revisited An Evaluation

of the Chemical and Physico-Chemical Processes Possibly Controlling the Migration Behaviour of Iodine in the Terrestrial Environment Riso National Laboratory Roskilde Denmark

Councell TB Landa ER Lovley DR 1997 Microbial reduction of iodate Water Air Soil Pollut 100 99ndash106

Couture RA Seitz MG Steindler MJ 1979 Adsorption of iodate by hematite (Fe2O3) T Am Nuc Soc 32 397

Couture RA Seitz MG 1983 Sorption of anions of iodine by iron oxides and kaolinite Nucl Chem Waste Manage 4 301ndash306

Dai JL Zhang M Zhu YG 2004 Adsorption and desorption of iodine by various Chi-nese soils -I Iodate Environment International 30 525ndash530

Dai J Zhu Y Huang Y Zhang M Song J 2006 Availability of iodide and iodate to spinach (Spinacia oleracea L) in relation to total iodine in soil solution Plant Soil 289 301ndash308

Dalke C Holzimmer G Calzada-Wack J Quintanella-Martinez L Atkinson MJ Rosemann M 2012 Differences in the susceptibility to iodine 131-induced thyroid tumours amongst inbred mouse strains J Radiat Res 53 343ndash352

de Benoist B Anderson M Egli I Takkouche B Allen HE 2004 Iodine status world-wide WHO global database on iodine deficiency World health Organization Geneva Switzerland

Denham M Nichols R Bach M Millings M 2008 Removal of Iodide from Ground-water Using Silver Chloride Rep SRNL-STI-2008-00459 Savannah River National Laboratory Aiken South Carolina

Downs AJ Adams CJ 1973 The Chemistry of Chlorine Bromine Iodine and Astatine Pergamon Press Oxford England

Dushman S 1904 The rate of the reaction between iodic and hydriodic acids J Phys Chem 8 453ndash482

Edwards R Rey P 1969 Terrestrial Occurrence and Distribution of Iodine-129 United States Army Environmental Control-Report Rep NYO-3624ndash3

Farrenkopf AM Dollhopf ME Chadhain SN Luther GW Nealson KH 1997 Reduction of iodate in seawater during Arabian sea whipboard incubations and in labo-ratory cultures of the marine bacterium Shewanella putrefaciens strain MR-4 Mar Chem 57 347ndash354

Fawcett DM Kirkwood S 1953 The mechanism of antithyroid action of iodide ion and the ldquoaromaticrdquo thyroid inhibitors J Biol Chem 205 (2) 795ndash802

Fetter G Ramos E Olguin MT Bosch P Lopez T Bulbulian S 1996 Sorption of 131I-by hydrotalcites J Radioanal Nucl Chem 221 63ndash66

Fox PM Davis JA Luther III GW 2009 The kinetics of iodide oxidation by the manga-nese oxide mineral birnessite Geochim Cosmochim Acta 73 2850ndash2861

Fuge R Johnson CC 1986 The geochemistry of iodinendasha review Environ Geochem Health 8 31ndash54

Fuge R 1988 Sources of halogens in the environment influences on human and animal health Environ Geochem Health 10 51ndash61


Fuhrmann M Bajt S Schoonen MAA 1998 Sorption of iodine on minerals investi-gated by Xray absorption near edge structure (XANES) and 125I tracer sorption exper-iments Applied Geochem 13 127ndash141

Gephart RE 2010 A short history of waste management at the Hanford site Phys Chem Earth Pts ABC 35 298ndash306

Goldschmidt VM 1956 Geochemistry Q J R Meteorol Soc 82 547Grogan K 2012 Development and Application of Novel Detection Methods for Aqueous

Radioactive Iodine All Dissertations Paper 926Grossman CM Morton WE 1996 Hyperthyroidism and spontaneous abortions among

Hanford Washington downwinders Arch Environ Health 51 175ndash176Guichardon P Falk L Villermaux J 2000 Characterisation of micromixing efficiency by

the iodidendashiodate reaction system Part II kinetic study Chem Eng Sci 55 4245ndash4253Hansen V Yi P Hou X Aldahan A Roos P Possnert G 2011 Iodide and iodate (129I

and 127I) in surface water of the Baltic Sea Kattegat and Skagerrak Sci Total Environ 15 412ndash413 296ndash303

Hird FJR Yates JR 1961 The oxidation of protein thiol groups by iodate bromate and persulphate Biochem J 80 612ndash616

Hu Q Zhao P Moran JE Seaman JC 2005 Sorption and transport of iodine in sedi-ments from the Savannah River and Hanford sites J Contam Hydrol 78 185ndash205

Jirosek L Pritchard ET 1971 On the chemical iodination of tyrosine with protein sulfe-nyl iodide and sulfenyl periodide derivatives the behaviour of thiol protein-iodine sys-tems Biochem Biophys Acta 243 230ndash238

Kaplan DI Roberts KA Schwehr KA Lilley MS Brinkmeyer R Denham ME DiPrete D Li H Powell BA Xu C Yeager CM Zhang S Santschi PH 2011 Evaluation of a radioiodine plume increasing in concentration at the Savannah River Site Environ Sci Technol 45 489ndash495

Kaplan D Yeager C Denham ME Zhang S Xu X Schwehr KA Li HP Brinkmeyer R Santschi PH 2012 Biogeochemical Considerations Related to the Remediation of 129-I Plumes Rep SRNL-STI-2012-00425 Savannah River National Laboratory Aiken SC

Kaplan DI Serne RJ Parker KE Kutnyakov IV 2000 Iodide sorption to subsurface sediments and illitic minerals Environ Sci Technol 34 399ndash405

Katz LE Humphrey DN Jankauskas PT DeMascio FA 1996 Engineered soils for low-level radioactive waste disposal facilities Effects of additives on the adsorptive behavior and hydraulic conductivity of natural soils Hazard Waste Hazard 13 283ndash306

Kuumlpper FC Carpenter LJ McFiggans GB Palmer CJ Waite TJ Boneberg E Woitsch S Weiller M Abela R Grolimund D 2008 Iodide accumulation provides kelp with an inorganic antioxidant impacting atmospheric chemistry P Natl Acad Sci 105 6954ndash6958

Laverock M Stephenson M Macdonald C 1995 Toxicity of iodine iodide and iodate to Daphnia magna and rainbow trout (Oncorhynchus mykiss) Arch Environ Contam Toxicol 29 344ndash350

Lefegravevre G Bessiegravere J Ehrhardt J Walcarius A 2003 Immobilization of iodide on copper (I) sulfide minerals J Environ Radioact 70 73ndash83

Lehr J Wybenga J Rosanow M 1958 Iodine as a micronutrient for tomatoes Plant Physiol 33 421ndash427

Lewis JC Powers WL 1941 Iodine in relation to plant nutrition J Agric Res 63 623ndash637MacLean LCW Martinez RE Fowle DA 2004 Experimental studies of bacteria-

iodide adsorption interactions Chem Geol 212 229ndash238Mattigod SV Serne RJ Fryxell GE Pacific Northwest National Laboratory (US) and

United States Dept of Energy 2003 Selection and Testing of ldquoGettersrdquo for Adsorption of Iodine-129 and Technetium-99 A Review Pacific Northwest National Laboratory Richland WA


Michel R Handl J Ernst T Botsch W Szidat S Schmidt A Jakob D Beltz D Romantschuk LD Synal H Schnabel C Loacutepez-Gutieacuterrez JM 2005 Iodine-129 in soils from Northern Ukraine and the retrospective dosimetry of the iodine-131 expo-sure after the Chernobyl accident Sci Total Environ 340 35ndash55

Morgan K 1954 Some reactions of inorganic iodine compounds Q Rev Chem Soc 8 123ndash146

Moriarty RM Prakash O 1986 Hypervalent iodine in organic synthesis Acc Chem Res 19 244ndash250

Muramatsu Y Yoshida S 1999 Effects of microorganisms on the fate of iodine in the soil environment Geomicrobiol J 16 85ndash93

Muramatsu Y Yoshida S Fehn U Amachi S Ohmomo Y 2004 Studies with natural and anthropogenic iodine isotopes iodine distribution and cycling in the global environ-ment J Environ Radioact 74 221ndash232

Nagata T Fukushi K 2010 Prediction of iodate adsorption and surface speciation on oxides by surface complexation modeling Geochim Cosmochim Acta 74 6000ndash6013

Nishimaki K Satta N Maeda M 1994 Sorption and migration of radioiodine in satu-rated sandy soil J Nucl Sci Technol 31 828ndash838

Otosaka S Schwehr KA Kaplan DI Roberts KA Zhang S Xu C Li H Ho Y Brinkmeyer R Yeager CM Santschi PH 2011 Factors controlling mobility of I-127 and I-129 species in an acidic groundwater plume at the Savannah River Site Sci Total Environ 409 3857ndash3865

Ou SH 1985 Rice Diseases Commonwealth Mycological Institute Great BritainRaisbeck GM Yiou F 1999 129I in the oceans origins and applications Sci Total Environ

237ndash238 31ndash41Raja ME Babcock KL 1961 On the Sod Chemistry of Radio-Iodine Soil Sci 91Sander R 1999 Compilation of Henryrsquos Law Constants for Inorganic and Organic Species

of Potential Importance in Environmental Chemistry Max-Planck Institute of Chem-istry Mainz Germany

Sazarashi M Ikeda Y Seki R Yoshikawa H 1994 Adsorption of Iminus ions on minerals for 129I waste management J Nucl Sci Technol 31 620ndash622

Schink DR Santschi PH Corapcioglu O Sharma P Fehn U 1995 129I in Gulf of Mexico waters Earth Planet Sci Lett 135 131ndash138

Schlegel ML Reillerb P Mercier-Biona F Barreacutea N Moulinc V 2006 Molecular envi-ronment of iodine in naturally iodinated humic substances insight from X-ray absorp-tion spectroscopy Geochim Cosmochim Acta 70 5536ndash5551

Schmitz G 1999 Kinetics and mechanism of the iodatendashiodide reaction and other related reactions Phys Chem Chem Phys 1 1909ndash1914

Schwehr KA Santschi PH Kaplan DI Yeager CM Brinkmeyer R 2009 Organo-iodine formation in soils and aquifer sediments at ambient concentrations Environ Sci Technol 43 7258ndash7264

Sekimoto Hitoshi 2009 Higher Plants Have the Ability to Reduce Iodate to Iodide UC Davis Department of Plant Sciences UC Davis Retrieved from httpescholarshiporgucitem23r7j0kw

Sheppard MI Thibault DH Smith PA Hawkins JL 1994 Volatilization a soil degas-sing coefficient for iodine J Environ Radioact 25 189ndash203

Sheppard SC Evenden WG 1995 Toxicity of soil iodine to terrestrial biota with implica-tions for 129I Journal of Environmental Radioactivity 27 99ndash116

Shetaya WH Young SD Watts MJ Ander EL Bailey EH 2012 Iodine dynamics in soils Geochim Cosmochim Acta 77 457ndash473

Sillen LG Martell AE Bjerrum J 1964 Stability Constants of Metal-Ion Complexes Chemical Society London

Soumlderlund M Lusa M Lehto J Hakanen M Vaaramaa K Lahdenperauml AM 2011 Sorp-tion of Iodine Chlorine Technetium and Cesium in Soil Rep 4 Posiva Eurajoki Finland


Soudek P Tykva R Vaňkovaacute R Vaněk T 2006 Accumulation of radioiodine from aque-ous solution by hydroponically cultivated sunflower (Helianthus annuus L) Environ Exp Bot 57 220ndash225

Sparks DL 2003 Environmental Soil Chemistry Academic Press AmsterdamSteinberg SM Kimble GM Schmett GT Emerson DW Turner MF Rudin M

2008 Abiotic reaction of iodate with sphagnum peat and other natural organic matter J Radioanal Nucl Chem 277 185ndash191

Steinhauser G Merz S Kabber-Heiss A Katzlberger C 2012 Using animal thyroids as ultra-sensitive biomonitors for environmental radioiodine Environ Sci Technol 46 12890ndash12894

Szczepaniak W Koscielna H 2002 Specific adsorption of halogen anions on hydrous γ-Al2O3 Analytica Chimica Acta 470 (2) 263ndash276

The Chernobyl Forum 2006 Chernobylrsquos Legacy Health Environmental and Socio- Economic Impacts International Atomic Energy Agency Vienna Austria

Ticknor K Cho YH 1990 Interaction of iodide and iodate with granitic fracture-filling minerals J Radioanal Nucl Chem 140 75ndash90

Tikhomirov FA Kasparov SV Prister BS Salrsquonkov VG 1980 Role of organic matter in iodine fixation in soils Sov Soil Sci 12 64ndash72

Truesdale VW Watts SF Rendell AR 2001 On the possibility of iodide oxidation in the near-surface of the Black Sea and its implications to iodine in the general ocean Deep Sea Res Part I Oceanogr Res Pap 48 2397ndash2412

Um W Serne RJ Krupka KM 2004 Linearity and reversibility of iodide adsorption on sediments from Hanford Washington under water saturated conditions Water Res 38 2009ndash2016

Vinogradov AP 1959 The Geochemistry of Rare and Dispersed Chemical Elements in Soils 2nd ed Consultants Bureau New York

Vitti P Delange F Pinchera A Zimmermann M Dunn JT 2003 Europe is iodine deficient Lancet 361 1226

Warner JA Casey WH Dahlgren RA 2000 Interaction kinetics of I2(aq) with substi-tuted phenols and humic substances Environ Sci Technol 34 3180ndash3185

Weerasooriya R Wickramarathna HUS 1999 Modeling anion adsorption on kaolinite J Colloid Interf Sci 213 395ndash399

Weng H Hong C Xia T Bao L Liu H Li D 2013 Iodine biofortification of vegetable plants-An innovative method for iodine supplementation Chinese Science Bulletin 1-7

Whitehead DC 1973a The sorption of iodide by soils as influenced by equilibrium condi-tions and soil properties J Sci Food Ag 24 547ndash556

Whitehead DC 1973b Studies on iodine in British soils J Soil Sci 24 260ndash270Whitehead DC 1974 The sorption of iodide by soil components J Sci Food Ag 25 73ndash79Whitehead DC 1981 The volatilization from soils and mixtures of soil components of

iodine added as potassium iodide J Soil Sci 32 97ndash102Whitehead DC 1984 The distribution and transformations of iodine in the environment

Environ Int 10 321ndash339Wong G 1991 The marine geochemistry of iodine Rev Aquat Sci 4 45ndash73Wulfsberg G 1991 Hard-soft acid base theory In Principles of Descriptive Inorganic

Chemistry first ed University Science Books Sausalito California p 273Xiangke W Wenming D Yingchun G Changhui W Zuyi T 2001 Sorption character-

istics of Radioeuropium on Bentonite and Kaolinite J Radioanal Nucl Chem 250 267ndash270

Yamada H Kiriyama T Onagawa Y Hisamori I Miyazaki C Yonebayashi K 1999 Speciation of iodine in soils Soil Sci Plant Nutr 45 563ndash568

Yamada H Hisamori I Yonebayashi K 2002 Identification of organically bound iodine in soil humic substances by size exclusion chromatographyinductively coupled plasma mass spectrometry (SECICP-MS) Soil Sci Plant Nutr 48 379ndash385


Yamada H Takeda C Mizushima A Yoshino K Yonebayashi K 2005 Effect of oxidizing power of roots on iodine uptake by rice plants Soil Sci Plant Nutr 51 141ndash145

Yamaguchi N Nakano M Tanida H Fujiwara H 2006 Redox reaction of iodine in paddy soil investigated by field observation and I K-edge XANES spectroscopy J Envi-ron Radioact 86 212ndash226

Yamaguchi N Nakano M Takamatsu R Tanida H 2010 Inorganic iodine incorpora-tion into soil organic matter evidence from iodine K-edge X-ray absorption near-edge structure J Environ Radioact 101 451ndash457

Yoshida S Muramatsu Y Uchida S 1992 Studies on the sorption of Iminus(iodide) and IOminus3

(iodate) onto andosols Water Air Soil Pollut 63 321ndash329Yuita K 1992 Dynamics of iodine bromine and chlorine in soil II chemical forms of

iodine in soil solutions Soil Sci Plant Nutr 38 281ndash287Zhang S Du J Xu C Schwehr K Ho YF Li HP Roberts K Kaplan D Brinkmeyer

R Yeager C 2011 Concentration-dependent mobility retardation and speciation of iodine in surface sediment from the Savannah River Site Environ Sci Technol 45 5543ndash5549

Zhu Y Huang Y Hu Y Liu Y 2003 Iodine uptake by spinach (Spinacia oleracea L) plants grown in solution culture effects of iodine species and solution concentrations Environ Int 29 33ndash37

Two - Environmental Chemistry and Toxicology of Iodine

1 Introduction

2 Indigenous Sources

21 The Global Iodine Cycle

22 Marine Iodine

23 Iodine in Soils

3 Anthropogenic Sources

31 Radioactive Iodine Sources

32 Radioiodine Contamination

4 Iodine Toxicity

41 Radioiodine Toxicity

42 Ecotoxicology

5 Impacts on Human Health

51 Iodine Deficiency

52 Excessive Iodine

6 Environmental Chemistry of Iodine

61 IodateIodide and the Hard Soft Acid Base Theory

62 ReductionOxidation Reactions of IodideIodate in Solution and Soils

63 Metal-IodateIodide Complexation and Solubility Products

64 Volatilization of Iodine Species

65 Hypervalent Iodine

7 Iodine Sorption in Humic Substances and Soil Minerals

71 Iodine Interactions with Humic Substances

72 Iodine Sorption in Clays and Clay Minerals

8 Remediation of Iodine Contamination

81 Volatilization

82 Immobilization and Precipitation

83 Phytoremediation

9 Conclusion and Future Challenges

References


Abstract

Iodine is a trace halide found in the environment A majority of global iodine budget resides in ocean while lithosphere and pedosphere contain the rest limiting the bio-availability of iodine in terrestrial environment Iodine cycles involve the multivalence state chemical speciation at the airndashwaterndashsediment interfaces The mobility and reactivity of these inorganic and organic iodine species are impacted by changes in physicochemical factors (eg pH and ionic strength) and macro- and micro-biological activities Although iodine aqueous biogeochemistry has been extensively investi-gated in marine systems in the past the partitioning mechanisms of iodine at the geomediandashwater interface remained poorly understood This chapter covers environ-mental soil chemistry of iodine and the impact to human and ecological health

1 INTRODUCTION

Iodine belongs to the group of elements known as halogens It is the least reactive of the halogens because of its large atomic size besides asta-tine but can exist in several different chemical states in low- temperature geochemical environment namely iodide (Iminus) elemental iodine (I2) iodate (IOminus

3 ) and periodate (IO minus4 ) This redox sensitive chemical speciation makes

the iodine cycle in environment extremely complex Among 37 isotopes nonradioactive iodine-127 is the most stable and common isotope Approxi-mately 70 of global iodine is present in marine systems and iodine in litho-sphere and pedosphere is often limited causing iodine deficiency in some parts of world The two most common radioactive isotopes are iodine-129 (t12 16 million years) and iodine-131 (around 13 days) (Downs and Adams 1973 Grogan 2012) that are anthropogenically produced through the fission of uranium and plutonium at nuclear reactors (Michel et al 2005) Many attempted to understand the environmental chemistry of iodine in predict-ing the transport of radioiodine in subsurface environment and in develop-ing the best remediation technologies This chapter provides an overview of iodine environmental chemistry and toxicity as well as an extensive review of iodine sorption reaction in inorganic and organic soil components

2 INDIGENOUS SOURCES

As a trace nutrient iodine is scarce in the environment The concentra-tions of other halogens fluorine chlorine and bromine greatly outnumber iodine concentrations Iodine can be found naturally in minerals known as lautarite (Ca(IO3)2) and dietzeite (7Ca(IO3)28CaCrO4) These minerals occur naturally in the Caliche beds of Chile where they are mined and sold The





Unit

Iodine Chlorine




ment590 times 1012 682 338 times 1011 092

Mafic oceanic crust

540 times 1010 062 420 times 1011 11


240 times 1012 277 440 times 1012 119


230 times 1011 27 510 times 1012 138








Emission

CH3Ihv

I2IndashIO3

ndashI2 HIO

Brine

SoilBacteria

CH3ICH3IHIOEmission

Deposition Rainfall

Plants

River

Magma

Hydrothermalwater

(iodine rich)


Oceanic PlateBasalt

SeawaterBacteria


IO3ndash




















































deg

deg



















3079



After Burgot (2012)













PI2(g)











(aq) 658Silver Ag+


2 (aq)117



131



89



94



97






(aq) rarr CdI02(aq)

392



50



60




(aq) rarr PbI02(aq)

32



39



119








110



089





072







190





100



190



100
















(aq) minus726










After Sander (1999)




3 (aq)minus764


3 (aq)minus615


3 (aq)minus1086


3 (aq)minus163


3 (aq)minus40


minus713


3 (aq)minus1261


3 (aq)minus636


3 (aq)minus1371


3 (aq)minus1789


3 (aq)minus433


3 (aq)343


3 (aq)minus894


3 (aq)minus751


3 (aq)minus694


3 (aq)minus551


3 (aq)minus995


3 (aq)minus541








66





background






pH sim4 6 and 7

Radiotracer studies










Environmental Chem











Perudic ferrisols




pH 37 63 and 10




Continued


68










raphy






Environmental Chem






















Continued


70





























Column experiment


125I radiotracer



decreasing pH



Environmental Chem







pH 15ndash95












Column experiments













Continued


72







Reaction time 24 h

















Environmental Chem





1000 mg Lminus1




XANES spec-troscopy












Redox experi-ments



Continued


74






Column experi-ments



















Environmental Chem






01ndash10 g Lminus1


010 M NaClO4








1 g Lminus1



Reaction time 22 h



Continued


76














Environmental Chem



























Continued


78





























Environmental Chem
















Continued


80















Environmental Chem









pH 45 55 65 75 and 85















175 mg Lminus1





Continued


82



pH = 69 and 67









01 g Lminus1









Environmental Chem












Redox experi-ments











01 g Lminus1








Continued


84








Redox experi-ments































































































































































1 Introduction



22 Marine Iodine

23 Iodine in Soils




4 Iodine Toxicity


42 Ecotoxicology



52 Excessive Iodine











81 Volatilization


83 Phytoremediation


References





Unit

Iodine Chlorine




ment590 times 1012 682 338 times 1011 092

Mafic oceanic crust

540 times 1010 062 420 times 1011 11


240 times 1012 277 440 times 1012 119


230 times 1011 27 510 times 1012 138








Emission

CH3Ihv

I2IndashIO3

ndashI2 HIO

Brine

SoilBacteria

CH3ICH3IHIOEmission

Deposition Rainfall

Plants

River

Magma

Hydrothermalwater

(iodine rich)


Oceanic PlateBasalt

SeawaterBacteria


IO3ndash




















































deg

deg



















3079



After Burgot (2012)













PI2(g)











(aq) 658Silver Ag+


2 (aq)117



131



89



94



97






(aq) rarr CdI02(aq)

392



50



60




(aq) rarr PbI02(aq)

32



39



119








110



089





072







190





100



190



100
















(aq) minus726










After Sander (1999)




3 (aq)minus764


3 (aq)minus615


3 (aq)minus1086


3 (aq)minus163


3 (aq)minus40


minus713


3 (aq)minus1261


3 (aq)minus636


3 (aq)minus1371


3 (aq)minus1789


3 (aq)minus433


3 (aq)343


3 (aq)minus894


3 (aq)minus751


3 (aq)minus694


3 (aq)minus551


3 (aq)minus995


3 (aq)minus541








66





background






pH sim4 6 and 7

Radiotracer studies










Environmental Chem











Perudic ferrisols




pH 37 63 and 10




Continued


68










raphy






Environmental Chem






















Continued


70





























Column experiment


125I radiotracer



decreasing pH



Environmental Chem







pH 15ndash95












Column experiments













Continued


72







Reaction time 24 h

















Environmental Chem





1000 mg Lminus1




XANES spec-troscopy












Redox experi-ments



Continued


74






Column experi-ments



















Environmental Chem






01ndash10 g Lminus1


010 M NaClO4








1 g Lminus1



Reaction time 22 h



Continued


76














Environmental Chem



























Continued


78





























Environmental Chem
















Continued


80















Environmental Chem









pH 45 55 65 75 and 85















175 mg Lminus1





Continued


82



pH = 69 and 67









01 g Lminus1









Environmental Chem












Redox experi-ments











01 g Lminus1








Continued


84








Redox experi-ments































































































































































1 Introduction



22 Marine Iodine

23 Iodine in Soils




4 Iodine Toxicity


42 Ecotoxicology



52 Excessive Iodine











81 Volatilization


83 Phytoremediation


References






Emission

CH3Ihv

I2IndashIO3

ndashI2 HIO

Brine

SoilBacteria

CH3ICH3IHIOEmission

Deposition Rainfall

Plants

River

Magma

Hydrothermalwater

(iodine rich)


Oceanic PlateBasalt

SeawaterBacteria


IO3ndash




















































deg

deg



















3079



After Burgot (2012)













PI2(g)











(aq) 658Silver Ag+


2 (aq)117



131



89



94



97






(aq) rarr CdI02(aq)

392



50



60




(aq) rarr PbI02(aq)

32



39



119








110



089





072







190





100



190



100
















(aq) minus726










After Sander (1999)




3 (aq)minus764


3 (aq)minus615


3 (aq)minus1086


3 (aq)minus163


3 (aq)minus40


minus713


3 (aq)minus1261


3 (aq)minus636


3 (aq)minus1371


3 (aq)minus1789


3 (aq)minus433


3 (aq)343


3 (aq)minus894


3 (aq)minus751


3 (aq)minus694


3 (aq)minus551


3 (aq)minus995


3 (aq)minus541








66





background






pH sim4 6 and 7

Radiotracer studies










Environmental Chem











Perudic ferrisols




pH 37 63 and 10




Continued


68










raphy






Environmental Chem






















Continued


70





























Column experiment


125I radiotracer



decreasing pH



Environmental Chem







pH 15ndash95












Column experiments













Continued


72







Reaction time 24 h

















Environmental Chem





1000 mg Lminus1




XANES spec-troscopy












Redox experi-ments



Continued


74






Column experi-ments



















Environmental Chem






01ndash10 g Lminus1


010 M NaClO4








1 g Lminus1



Reaction time 22 h



Continued


76














Environmental Chem



























Continued


78





























Environmental Chem
















Continued


80















Environmental Chem









pH 45 55 65 75 and 85















175 mg Lminus1





Continued


82



pH = 69 and 67









01 g Lminus1









Environmental Chem












Redox experi-ments











01 g Lminus1








Continued


84








Redox experi-ments































































































































































1 Introduction



22 Marine Iodine

23 Iodine in Soils




4 Iodine Toxicity


42 Ecotoxicology



52 Excessive Iodine











81 Volatilization


83 Phytoremediation


References



















































deg

deg



















3079



After Burgot (2012)













PI2(g)











(aq) 658Silver Ag+


2 (aq)117



131



89



94



97






(aq) rarr CdI02(aq)

392



50



60




(aq) rarr PbI02(aq)

32



39



119








110



089





072







190





100



190



100
















(aq) minus726










After Sander (1999)




3 (aq)minus764


3 (aq)minus615


3 (aq)minus1086


3 (aq)minus163


3 (aq)minus40


minus713


3 (aq)minus1261


3 (aq)minus636


3 (aq)minus1371


3 (aq)minus1789


3 (aq)minus433


3 (aq)343


3 (aq)minus894


3 (aq)minus751


3 (aq)minus694


3 (aq)minus551


3 (aq)minus995


3 (aq)minus541








66





background






pH sim4 6 and 7

Radiotracer studies










Environmental Chem











Perudic ferrisols




pH 37 63 and 10




Continued


68










raphy






Environmental Chem






















Continued


70





























Column experiment


125I radiotracer



decreasing pH



Environmental Chem







pH 15ndash95












Column experiments













Continued


72







Reaction time 24 h

















Environmental Chem





1000 mg Lminus1




XANES spec-troscopy












Redox experi-ments



Continued


74






Column experi-ments



















Environmental Chem






01ndash10 g Lminus1


010 M NaClO4








1 g Lminus1



Reaction time 22 h



Continued


76














Environmental Chem



























Continued


78





























Environmental Chem
















Continued


80















Environmental Chem









pH 45 55 65 75 and 85















175 mg Lminus1





Continued


82



pH = 69 and 67









01 g Lminus1









Environmental Chem












Redox experi-ments











01 g Lminus1








Continued


84








Redox experi-ments































































































































































1 Introduction



22 Marine Iodine

23 Iodine in Soils




4 Iodine Toxicity


42 Ecotoxicology



52 Excessive Iodine











81 Volatilization


83 Phytoremediation


References


















3079



After Burgot (2012)













PI2(g)











(aq) 658Silver Ag+


2 (aq)117



131



89



94



97






(aq) rarr CdI02(aq)

392



50



60




(aq) rarr PbI02(aq)

32



39



119








110



089





072







190





100



190



100
















(aq) minus726










After Sander (1999)




3 (aq)minus764


3 (aq)minus615


3 (aq)minus1086


3 (aq)minus163


3 (aq)minus40


minus713


3 (aq)minus1261


3 (aq)minus636


3 (aq)minus1371


3 (aq)minus1789


3 (aq)minus433


3 (aq)343


3 (aq)minus894


3 (aq)minus751


3 (aq)minus694


3 (aq)minus551


3 (aq)minus995


3 (aq)minus541








66





background






pH sim4 6 and 7

Radiotracer studies










Environmental Chem











Perudic ferrisols




pH 37 63 and 10




Continued


68










raphy






Environmental Chem






















Continued


70





























Column experiment


125I radiotracer



decreasing pH



Environmental Chem







pH 15ndash95












Column experiments













Continued


72







Reaction time 24 h

















Environmental Chem





1000 mg Lminus1




XANES spec-troscopy












Redox experi-ments



Continued


74






Column experi-ments



















Environmental Chem






01ndash10 g Lminus1


010 M NaClO4








1 g Lminus1



Reaction time 22 h



Continued


76














Environmental Chem



























Continued


78





























Environmental Chem
















Continued


80















Environmental Chem









pH 45 55 65 75 and 85















175 mg Lminus1





Continued


82



pH = 69 and 67









01 g Lminus1









Environmental Chem












Redox experi-ments











01 g Lminus1








Continued


84








Redox experi-ments































































































































































1 Introduction



22 Marine Iodine

23 Iodine in Soils




4 Iodine Toxicity


42 Ecotoxicology



52 Excessive Iodine











81 Volatilization


83 Phytoremediation


References













PI2(g)











(aq) 658Silver Ag+


2 (aq)117



131



89



94



97






(aq) rarr CdI02(aq)

392



50



60




(aq) rarr PbI02(aq)

32



39



119








110



089





072







190





100



190



100
















(aq) minus726










After Sander (1999)




3 (aq)minus764


3 (aq)minus615


3 (aq)minus1086


3 (aq)minus163


3 (aq)minus40


minus713


3 (aq)minus1261


3 (aq)minus636


3 (aq)minus1371


3 (aq)minus1789


3 (aq)minus433


3 (aq)343


3 (aq)minus894


3 (aq)minus751


3 (aq)minus694


3 (aq)minus551


3 (aq)minus995


3 (aq)minus541








66





background






pH sim4 6 and 7

Radiotracer studies










Environmental Chem











Perudic ferrisols




pH 37 63 and 10




Continued


68










raphy






Environmental Chem






















Continued


70





























Column experiment


125I radiotracer



decreasing pH



Environmental Chem







pH 15ndash95












Column experiments













Continued


72







Reaction time 24 h

















Environmental Chem





1000 mg Lminus1




XANES spec-troscopy












Redox experi-ments



Continued


74






Column experi-ments



















Environmental Chem






01ndash10 g Lminus1


010 M NaClO4








1 g Lminus1



Reaction time 22 h



Continued


76














Environmental Chem



























Continued


78





























Environmental Chem
















Continued


80















Environmental Chem









pH 45 55 65 75 and 85















175 mg Lminus1





Continued


82



pH = 69 and 67









01 g Lminus1









Environmental Chem












Redox experi-ments











01 g Lminus1








Continued


84








Redox experi-ments































































































































































1 Introduction



22 Marine Iodine

23 Iodine in Soils




4 Iodine Toxicity


42 Ecotoxicology



52 Excessive Iodine











81 Volatilization


83 Phytoremediation


References







110



089





072







190





100



190



100
















(aq) minus726










After Sander (1999)




3 (aq)minus764


3 (aq)minus615


3 (aq)minus1086


3 (aq)minus163


3 (aq)minus40


minus713


3 (aq)minus1261


3 (aq)minus636


3 (aq)minus1371


3 (aq)minus1789


3 (aq)minus433


3 (aq)343


3 (aq)minus894


3 (aq)minus751


3 (aq)minus694


3 (aq)minus551


3 (aq)minus995


3 (aq)minus541








66





background






pH sim4 6 and 7

Radiotracer studies










Environmental Chem











Perudic ferrisols




pH 37 63 and 10




Continued


68










raphy






Environmental Chem






















Continued


70





























Column experiment


125I radiotracer



decreasing pH



Environmental Chem







pH 15ndash95












Column experiments













Continued


72







Reaction time 24 h

















Environmental Chem





1000 mg Lminus1




XANES spec-troscopy












Redox experi-ments



Continued


74






Column experi-ments



















Environmental Chem






01ndash10 g Lminus1


010 M NaClO4








1 g Lminus1



Reaction time 22 h



Continued


76














Environmental Chem



























Continued


78





























Environmental Chem
















Continued


80















Environmental Chem









pH 45 55 65 75 and 85















175 mg Lminus1





Continued


82



pH = 69 and 67









01 g Lminus1









Environmental Chem












Redox experi-ments











01 g Lminus1








Continued


84








Redox experi-ments































































































































































1 Introduction



22 Marine Iodine

23 Iodine in Soils




4 Iodine Toxicity


42 Ecotoxicology



52 Excessive Iodine











81 Volatilization


83 Phytoremediation


References









After Sander (1999)




3 (aq)minus764


3 (aq)minus615


3 (aq)minus1086


3 (aq)minus163


3 (aq)minus40


minus713


3 (aq)minus1261


3 (aq)minus636


3 (aq)minus1371


3 (aq)minus1789


3 (aq)minus433


3 (aq)343


3 (aq)minus894


3 (aq)minus751


3 (aq)minus694


3 (aq)minus551


3 (aq)minus995


3 (aq)minus541








66





background






pH sim4 6 and 7

Radiotracer studies










Environmental Chem











Perudic ferrisols




pH 37 63 and 10




Continued


68










raphy






Environmental Chem






















Continued


70





























Column experiment


125I radiotracer



decreasing pH



Environmental Chem







pH 15ndash95












Column experiments













Continued


72







Reaction time 24 h

















Environmental Chem





1000 mg Lminus1




XANES spec-troscopy












Redox experi-ments



Continued


74






Column experi-ments



















Environmental Chem






01ndash10 g Lminus1


010 M NaClO4








1 g Lminus1



Reaction time 22 h



Continued


76














Environmental Chem



























Continued


78





























Environmental Chem
















Continued


80















Environmental Chem









pH 45 55 65 75 and 85















175 mg Lminus1





Continued


82



pH = 69 and 67









01 g Lminus1









Environmental Chem












Redox experi-ments











01 g Lminus1








Continued


84








Redox experi-ments































































































































































1 Introduction



22 Marine Iodine

23 Iodine in Soils




4 Iodine Toxicity


42 Ecotoxicology



52 Excessive Iodine











81 Volatilization


83 Phytoremediation


References







66





background






pH sim4 6 and 7

Radiotracer studies










Environmental Chem











Perudic ferrisols




pH 37 63 and 10




Continued


68










raphy






Environmental Chem






















Continued


70





























Column experiment


125I radiotracer



decreasing pH



Environmental Chem







pH 15ndash95












Column experiments













Continued


72







Reaction time 24 h

















Environmental Chem





1000 mg Lminus1




XANES spec-troscopy












Redox experi-ments



Continued


74






Column experi-ments



















Environmental Chem






01ndash10 g Lminus1


010 M NaClO4








1 g Lminus1



Reaction time 22 h



Continued


76














Environmental Chem



























Continued


78





























Environmental Chem
















Continued


80















Environmental Chem









pH 45 55 65 75 and 85















175 mg Lminus1





Continued


82



pH = 69 and 67









01 g Lminus1









Environmental Chem












Redox experi-ments











01 g Lminus1








Continued


84








Redox experi-ments































































































































































1 Introduction



22 Marine Iodine

23 Iodine in Soils




4 Iodine Toxicity


42 Ecotoxicology



52 Excessive Iodine











81 Volatilization


83 Phytoremediation


References

Environmental Chem











Perudic ferrisols




pH 37 63 and 10




Continued


68










raphy






Environmental Chem






















Continued


70





























Column experiment


125I radiotracer



decreasing pH



Environmental Chem







pH 15ndash95












Column experiments













Continued


72







Reaction time 24 h

















Environmental Chem





1000 mg Lminus1




XANES spec-troscopy












Redox experi-ments



Continued


74






Column experi-ments



















Environmental Chem






01ndash10 g Lminus1


010 M NaClO4








1 g Lminus1



Reaction time 22 h



Continued


76














Environmental Chem



























Continued


78





























Environmental Chem
















Continued


80















Environmental Chem









pH 45 55 65 75 and 85















175 mg Lminus1





Continued


82



pH = 69 and 67









01 g Lminus1









Environmental Chem












Redox experi-ments











01 g Lminus1








Continued


84








Redox experi-ments































































































































































1 Introduction



22 Marine Iodine

23 Iodine in Soils




4 Iodine Toxicity


42 Ecotoxicology



52 Excessive Iodine











81 Volatilization


83 Phytoremediation


References


68










raphy






Environmental Chem






















Continued


70





























Column experiment


125I radiotracer



decreasing pH



Environmental Chem







pH 15ndash95












Column experiments













Continued


72







Reaction time 24 h

















Environmental Chem





1000 mg Lminus1




XANES spec-troscopy












Redox experi-ments



Continued


74






Column experi-ments



















Environmental Chem






01ndash10 g Lminus1


010 M NaClO4








1 g Lminus1



Reaction time 22 h



Continued


76














Environmental Chem



























Continued


78





























Environmental Chem
















Continued


80















Environmental Chem









pH 45 55 65 75 and 85















175 mg Lminus1





Continued


82



pH = 69 and 67









01 g Lminus1









Environmental Chem












Redox experi-ments











01 g Lminus1








Continued


84








Redox experi-ments































































































































































1 Introduction



22 Marine Iodine

23 Iodine in Soils




4 Iodine Toxicity


42 Ecotoxicology



52 Excessive Iodine











81 Volatilization


83 Phytoremediation


References

Environmental Chem






















Continued


70





























Column experiment


125I radiotracer



decreasing pH



Environmental Chem







pH 15ndash95












Column experiments













Continued


72







Reaction time 24 h

















Environmental Chem





1000 mg Lminus1




XANES spec-troscopy












Redox experi-ments



Continued


74






Column experi-ments



















Environmental Chem






01ndash10 g Lminus1


010 M NaClO4








1 g Lminus1



Reaction time 22 h



Continued


76














Environmental Chem



























Continued


78





























Environmental Chem
















Continued


80















Environmental Chem









pH 45 55 65 75 and 85















175 mg Lminus1





Continued


82



pH = 69 and 67









01 g Lminus1









Environmental Chem












Redox experi-ments











01 g Lminus1








Continued


84








Redox experi-ments































































































































































1 Introduction



22 Marine Iodine

23 Iodine in Soils




4 Iodine Toxicity


42 Ecotoxicology



52 Excessive Iodine











81 Volatilization


83 Phytoremediation


References


70





























Column experiment


125I radiotracer



decreasing pH



Environmental Chem







pH 15ndash95












Column experiments













Continued


72







Reaction time 24 h

















Environmental Chem





1000 mg Lminus1




XANES spec-troscopy












Redox experi-ments



Continued


74






Column experi-ments



















Environmental Chem






01ndash10 g Lminus1


010 M NaClO4








1 g Lminus1



Reaction time 22 h



Continued


76














Environmental Chem



























Continued


78





























Environmental Chem
















Continued


80















Environmental Chem









pH 45 55 65 75 and 85















175 mg Lminus1





Continued


82



pH = 69 and 67









01 g Lminus1









Environmental Chem












Redox experi-ments











01 g Lminus1








Continued


84








Redox experi-ments































































































































































1 Introduction



22 Marine Iodine

23 Iodine in Soils




4 Iodine Toxicity


42 Ecotoxicology



52 Excessive Iodine











81 Volatilization


83 Phytoremediation


References

Environmental Chem







pH 15ndash95












Column experiments













Continued


72







Reaction time 24 h

















Environmental Chem





1000 mg Lminus1




XANES spec-troscopy












Redox experi-ments



Continued


74






Column experi-ments



















Environmental Chem






01ndash10 g Lminus1


010 M NaClO4








1 g Lminus1



Reaction time 22 h



Continued


76














Environmental Chem



























Continued


78





























Environmental Chem
















Continued


80















Environmental Chem









pH 45 55 65 75 and 85















175 mg Lminus1





Continued


82



pH = 69 and 67









01 g Lminus1









Environmental Chem












Redox experi-ments











01 g Lminus1








Continued


84








Redox experi-ments































































































































































1 Introduction



22 Marine Iodine

23 Iodine in Soils




4 Iodine Toxicity


42 Ecotoxicology



52 Excessive Iodine











81 Volatilization


83 Phytoremediation


References


72







Reaction time 24 h

















Environmental Chem





1000 mg Lminus1




XANES spec-troscopy












Redox experi-ments



Continued


74






Column experi-ments



















Environmental Chem






01ndash10 g Lminus1


010 M NaClO4








1 g Lminus1



Reaction time 22 h



Continued


76














Environmental Chem



























Continued


78





























Environmental Chem
















Continued


80















Environmental Chem









pH 45 55 65 75 and 85















175 mg Lminus1





Continued


82



pH = 69 and 67









01 g Lminus1









Environmental Chem












Redox experi-ments











01 g Lminus1








Continued


84








Redox experi-ments































































































































































1 Introduction



22 Marine Iodine

23 Iodine in Soils




4 Iodine Toxicity


42 Ecotoxicology



52 Excessive Iodine











81 Volatilization


83 Phytoremediation


References

Environmental Chem





1000 mg Lminus1




XANES spec-troscopy












Redox experi-ments



Continued


74






Column experi-ments



















Environmental Chem






01ndash10 g Lminus1


010 M NaClO4








1 g Lminus1



Reaction time 22 h



Continued


76














Environmental Chem



























Continued


78





























Environmental Chem
















Continued


80















Environmental Chem









pH 45 55 65 75 and 85















175 mg Lminus1





Continued


82



pH = 69 and 67









01 g Lminus1









Environmental Chem












Redox experi-ments











01 g Lminus1








Continued


84








Redox experi-ments































































































































































1 Introduction



22 Marine Iodine

23 Iodine in Soils




4 Iodine Toxicity


42 Ecotoxicology



52 Excessive Iodine











81 Volatilization


83 Phytoremediation


References


74






Column experi-ments



















Environmental Chem






01ndash10 g Lminus1


010 M NaClO4








1 g Lminus1



Reaction time 22 h



Continued


76














Environmental Chem



























Continued


78





























Environmental Chem
















Continued


80















Environmental Chem









pH 45 55 65 75 and 85















175 mg Lminus1





Continued


82



pH = 69 and 67









01 g Lminus1









Environmental Chem












Redox experi-ments











01 g Lminus1








Continued


84








Redox experi-ments































































































































































1 Introduction



22 Marine Iodine

23 Iodine in Soils




4 Iodine Toxicity


42 Ecotoxicology



52 Excessive Iodine











81 Volatilization


83 Phytoremediation


References

Environmental Chem






01ndash10 g Lminus1


010 M NaClO4








1 g Lminus1



Reaction time 22 h



Continued


76














Environmental Chem



























Continued


78





























Environmental Chem
















Continued


80















Environmental Chem









pH 45 55 65 75 and 85















175 mg Lminus1





Continued


82



pH = 69 and 67









01 g Lminus1









Environmental Chem












Redox experi-ments











01 g Lminus1








Continued


84








Redox experi-ments































































































































































1 Introduction



22 Marine Iodine

23 Iodine in Soils




4 Iodine Toxicity


42 Ecotoxicology



52 Excessive Iodine











81 Volatilization


83 Phytoremediation


References


76














Environmental Chem



























Continued


78





























Environmental Chem
















Continued


80















Environmental Chem









pH 45 55 65 75 and 85















175 mg Lminus1





Continued


82



pH = 69 and 67









01 g Lminus1









Environmental Chem












Redox experi-ments











01 g Lminus1








Continued


84








Redox experi-ments































































































































































1 Introduction



22 Marine Iodine

23 Iodine in Soils




4 Iodine Toxicity


42 Ecotoxicology



52 Excessive Iodine











81 Volatilization


83 Phytoremediation


References

Environmental Chem



























Continued


78





























Environmental Chem
















Continued


80















Environmental Chem









pH 45 55 65 75 and 85















175 mg Lminus1





Continued


82



pH = 69 and 67









01 g Lminus1









Environmental Chem












Redox experi-ments











01 g Lminus1








Continued


84








Redox experi-ments































































































































































1 Introduction



22 Marine Iodine

23 Iodine in Soils




4 Iodine Toxicity


42 Ecotoxicology



52 Excessive Iodine











81 Volatilization


83 Phytoremediation


References


78





























Environmental Chem
















Continued


80















Environmental Chem









pH 45 55 65 75 and 85















175 mg Lminus1





Continued


82



pH = 69 and 67









01 g Lminus1









Environmental Chem












Redox experi-ments











01 g Lminus1








Continued


84








Redox experi-ments































































































































































1 Introduction



22 Marine Iodine

23 Iodine in Soils




4 Iodine Toxicity


42 Ecotoxicology



52 Excessive Iodine











81 Volatilization


83 Phytoremediation


References

Environmental Chem
















Continued


80















Environmental Chem









pH 45 55 65 75 and 85















175 mg Lminus1





Continued


82



pH = 69 and 67









01 g Lminus1









Environmental Chem












Redox experi-ments











01 g Lminus1








Continued


84








Redox experi-ments































































































































































1 Introduction



22 Marine Iodine

23 Iodine in Soils




4 Iodine Toxicity


42 Ecotoxicology



52 Excessive Iodine











81 Volatilization


83 Phytoremediation


References


80















Environmental Chem









pH 45 55 65 75 and 85















175 mg Lminus1





Continued


82



pH = 69 and 67









01 g Lminus1









Environmental Chem












Redox experi-ments











01 g Lminus1








Continued


84








Redox experi-ments































































































































































1 Introduction



22 Marine Iodine

23 Iodine in Soils




4 Iodine Toxicity


42 Ecotoxicology



52 Excessive Iodine











81 Volatilization


83 Phytoremediation


References

Environmental Chem









pH 45 55 65 75 and 85















175 mg Lminus1





Continued


82



pH = 69 and 67









01 g Lminus1









Environmental Chem












Redox experi-ments











01 g Lminus1








Continued


84








Redox experi-ments































































































































































1 Introduction



22 Marine Iodine

23 Iodine in Soils




4 Iodine Toxicity


42 Ecotoxicology



52 Excessive Iodine











81 Volatilization


83 Phytoremediation


References


82



pH = 69 and 67









01 g Lminus1









Environmental Chem












Redox experi-ments











01 g Lminus1








Continued


84








Redox experi-ments































































































































































1 Introduction



22 Marine Iodine

23 Iodine in Soils




4 Iodine Toxicity


42 Ecotoxicology



52 Excessive Iodine











81 Volatilization


83 Phytoremediation


References

Environmental Chem












Redox experi-ments











01 g Lminus1








Continued


84








Redox experi-ments































































































































































1 Introduction



22 Marine Iodine

23 Iodine in Soils




4 Iodine Toxicity


42 Ecotoxicology



52 Excessive Iodine











81 Volatilization


83 Phytoremediation


References


84








Redox experi-ments































































































































































1 Introduction



22 Marine Iodine

23 Iodine in Soils




4 Iodine Toxicity


42 Ecotoxicology



52 Excessive Iodine











81 Volatilization


83 Phytoremediation


References

























































































































































1 Introduction



22 Marine Iodine

23 Iodine in Soils




4 Iodine Toxicity


42 Ecotoxicology



52 Excessive Iodine











81 Volatilization


83 Phytoremediation


References

[advances in agronomy] volume 128 || environmental chemistry and toxicology of iodine

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