environmental monitoring of chromium in air, soil, and water

REGULATORY TOXICOLOGY AND PHARMACOLOGY 26, S80–S85 (1997)ARTICLE NO. RT971144

Environmental Monitoring of Chromium in Air, Soil, and Water

Rock J. Vitale, CPC, George R. Mussoline, and Kelly A. Rinehimer

Environmental Standards, Inc., 1140 Valley Forge Road, P.O. Box 911, Valley Forge, Pennsylvania 19482-0911

Received May 20, 1997

dium nitrate, NaNO3, or manganese dioxide, MnO2

(Stokinger, 1978).Historical uses of chromium have resulted in itswidespread release into the environment. In recent Chromium chemicals (chromates) are manufacturedyears, a significant amount of research has evaluated by alkaline roasting finely ground chromite ore at highthe impact of chromium on human health and the envi- temperatures, followed by water leaching and acidifi-ronment. Additionally, numerous analytical methods cation to obtain Na2CrO4 or Na2Cr2O7, from which nu-have been developed to identify and quantitate chro- merous other Cr compounds can be derived. Chromatesmium in environmental media in response to various and dichromates have many applications in lithogra-state and federal mandates such as CERCLA, RCRA, phy, textile printing, tanning, dyeing, photography,CWA, CAA, and SWDA. Due to the significant toxicity and manufacture of dyes, pigments, glues and adhe-differences between trivalent [Cr(III)] and hexavalent sives, electric cells, explosives, matches, and rubber[Cr(VI)] chromium, it is essential that chromium be

goods (Sax and Lewis, 1987).quantified in these two distinct valence states to assessBecause of its widespread and long-term use, chro-the potential risks to exposure to each in environmen-

mium contamination of soils and groundwater has beental media. Speciation is equally important because ofidentified at thousands of sites in the United Statestheir marked differences in environmental behavior.and around the developed world. In fact, Cr has beenAs the knowledge of risks associated with each valencecited as a contaminant at over one-third of the Su-state has grown and regulatory requirements have

evolved, methods to accurately quantitate these spe- perfund sites on the national priority list (NPL). Incies at ever-decreasing concentrations within environ- view of this, it is essential that reliable methods bemental media have also evolved. This paper addresses available to accurately quantify chromium contamina-the challenges of chromium species quantitation and tion wherever it is encountered, particularly since Crsome of the most relevant current methods used for has significantly different toxicity between its two mostenvironmental monitoring, including ASTM Method common valence states, Cr(III) and Cr(VI).D5281 for air, SW-846 Methods 3060A, 7196A and 7199 A number of analytical techniques are available tofor soils, sediments, and waste, and U.S. EPA Method characterize environmental samples for total metals218.6 for water. q 1997 Academic Press

content in water, soils, and air media. As toxicity datahave been generated for specific valences for total chro-mium, analytical techniques have also been developed

INTRODUCTION for use by the analytical chemists. Generally speaking,valence-specific analyses of total chromium are usuallysomewhat more complex than the analysis of the totalChromium exists in the natural environment pri-measurement, in that either valence-specific analysesmarily as the mineral chromite, FeOCr2O3, with impu-are indirectly measured or there are interferences in-rities such as Mg and Al present. It is a valuable metalherent to the analytical technique. This paper ad-that has been widely used in the industrialized worlddresses the analytical techniques routinely used tofor more than a century with the most extensive usesmeasure total chromium and the methodologies devel-for plating and alloying with iron to form stainlessoped over the past several years for the analysis forsteels. Chromium is typically produced in the form ofCr(VI) in environmental media, including ASTMan iron alloy, ferrochromium, by the reaction of chro-Method D5281 for air; SW-846 Methods 3060A, 7196A,mite ores with carbon or silicon in an electric furnace.and 7199 for soils, sediments, and solid waste; and U.S.Ferrochromium is also produced from chromite by aEnvironmental Protection Agency (EPA) Methodssilicothermic reaction in the presence of a suitable oxi-

dizing agent, such as calcium chromate, CaCrO4, so- 218.6 and 1636 for water (U.S. EPA, 1992, 1995c).

S800273-2300/97 $25.00Copyright q 1997 by Academic PressAll rights of reproduction in any form reserved.

AID RTP 1144 / 6e10$$$621 08-27-97 10:27:01 rtpas AP: RTP

S81CHROMIUM SYMPOSIUM

DISCUSSION ods 218.6, 1636, and 7199 are currently relevant basedon modifications that have made it possible to separate

Total Chromium—Sample Preparation and Analysis many of the interfering substances that plagued thehistorically used manual uv/vis colorimetric procedure,Regulatory-approved methods for the preparation of while simultaneously achieving much lower detectionaqueous, soil/sediment/solid wastes, and air samples limits (e.g., 0.3 mg/liter versus 500 mg/liter) (U.S. EPA,for total chromium analysis have been in existence for 1992, 1995a). Aqueous sample preparation techniquesquite some time (U.S. EPA, 1983, 1986; NIOSH, 1984). for these methods involve filtering through a 0.45-mmThe methods are designed to analyze for chromium as filter and adjusting the filtrate pH to 9 to 9.5 with aa total metal and do not distinguish between the differ- buffer solution. A measured volume of the sample (50–ent valence states [i.e. Cr(III) and Cr(VI)]. Aqueous 250 ml) is introduced into an ion chromatograph. Apreparatory techniques typically involve the heated di- guard column removes organics from the sample beforegestion of a known volume of sample with a known the Cr(VI), as CrO4

20, is separated on an anion-ex-volume and concentration of acid(s) for a defined period change separator column. Postcolumn derivatization ofof time and adjusting the digestate to a final volume the Cr(VI) with diphenylcarbazide (DPC) is followed byprior to analysis. Similarly, soil/sediment/solid waste detection of the colored complex at 530 nm. All colori-and air/dust collection media (e.g., cellulose filter disks) metric methods utilized for Cr(VI) use DPC as an indi-sample preparation techniques typically involve the di- cator. The use of DPC is highly selective for Cr(VI) andgestion of a known weight of a sample (or a collection has been used since the turn of the century for thisfilter disk for air samples) with acid(s) and hydrogen purpose (Cazeneuve, 1900).peroxide for a defined period of time and adjusting the With respect to air collection media (e.g., PVC fil-digestate to a final volume prior to analysis. Microwave ters), the recently reissued NIOSH sample preparationdigestion has recently become more prominent as an technique (NIOSH, 1994) involves the digestion of analternative to conventional hot-plate digestion (U.S. exposed PVC filter in 5 ml of extraction solution, 2%EPA, 1990b). NaOH–3% Na2CO3. The headspace above the solutionThe analysis of total Cr in sample digestates can is purged with nitrogen to avoid oxidation of Cr(III).be accomplished using various analytical techniques, The beaker is covered with a watch glass and heatedincluding graphite furnace atomic absorption (GFAA), to near boiling point on a hot plate with occasionalinductively coupled plasma/mass spectrometry (ICP/ swirling for 30 to 45 min. The solution is heated for upMS), and ICP—the most widespread analytical tech- to 45 min and is not allowed to evaporate to dryness,nique. The basic premise of the analytical process for because Cr(VI) may be lost due to reaction with thetotal Cr by ICP is that sample digests are nebulized PVC filter. The solution is cooled and, if cloudy, it isand the aerosol that is produced is transported to a filtered through a PVC filter in a vacuum filtrationplasma torch where excitation occurs. Characteristic apparatus. Sulfuric acid is added to the solution alongatomic-line emission spectra are produced by a radio- with DPC and it is mixed thoroughly. An aliquot of thefrequency ICP. The spectra are dispersed by a grating solution is placed in a cuvette and the absorbance isspectrometer and the intensities of the line are moni- recorded. The working range is 0.001 to 5 mg/m3 for atored by photomultiplier tubes. The photocurrents from 200-liter air sample (NIOSH, 1994).the photomultiplier tubes are processed and controlled NIOSH methods have been historically designed toby a computer system. A background correction tech- monitor air concentrations of Cr(VI) in the workplace;nique is required to compensate for the variable back- however, the detection limits have generally not beenground contribution to the determination of trace ele- sufficiently sensitive to assess ambient air exposures.ments. Background emissions are measured adjacent Accordingly, after an extensive developmental effort,to the analyte line of interest during sample analysis ASTM Method D 5281-92 was accepted in 1992 as a(U.S. EPA, 1990b). standard for the collection and measurement of Cr(VI)in ambient, workplace, or indoor atmospheres. ThisCr(VI)—Sample Preparation and Analysistest method is applicable in the range of 0.2 to 100 ng/m3 of Cr(VI) in the atmosphere assuming 20 m3 of airSimilar to the preparatory methods for total chro-

mium, regulatory-approved methods for the prepara- sample. This method draws air at a rate of 15 liters/min over a continuous 24-hr period through three 500-tion of aqueous and air samples for Cr(VI) analysis

have been in existence for quite some time (U.S. EPA, ml glass Greenburg–Smith impingers (in-line) filledwith 0.02 N sodium bicarbonate (NaHCO3) buffer solu-1983; NIOSH, 1984). However, within the past several

years aqueous and air sample preparation/analysis tion. A target air volume of 20 m3 is sampled. Figure1 is an illustration of a triple impinger sampling trainmethods have been refined with the advances of instru-

mental techniques such as ion chromatography coupled for airborne Cr(VI). A 1-ml volume of the filtered im-pinger solution is injected into an eluant flow path andwith postcolumn reaction. For aqueous samples, Meth-


S82 CHROMIUM SYMPOSIUM

pH of the digestate must be carefully adjusted andmonitored during the digestion procedure. The sampleis digested using 0.28 M Na2CO3/0.5 M NaOH solutionat 90–957C for 60 min to solubilize the Cr(VI). Further-more, Method 3060A includes the addition of MgCl2

to the alkaline digestion solution to help suppress theoxidation of soluble Cr(III) which may be present(Zatka, 1985). Although large amounts of soluble formsof Cr(III) in samples have been shown to impart anoxidation artifact, the forms of Cr(III) typically ob-served in environmental samples are insoluble, suchas Cr2O3 or crystallized Cr(OH)3, notwithstanding afresh spill of soluble Cr(III). Consequently, Method3060A specifies a water extraction test to ascertain ifsamples contain soluble Cr(III) to confirm or rule outthe possibility of a positive-bias artifact.

Once Cr(VI) is solubilized in solution, there are sev-eral regulatory-approved methods that are available.Some of the available analytical methods are rarelyused because the measurement process involves an in-direct measurement of Cr(VI) after various pretreat-ment techniques. Specifically, SW-846 Method 7195 isbased on the separation of Cr(VI) from solution by co-precipitation of lead chromate with lead sulfate in asolution of acetic acid. After separation, the superna-FIG. 1. Triple impinger sampling train for airborne Cr(VI).tant [containing Cr(III)] is drawn off and the precipi-tate is washed to remove occluded Cr(III). The Cr(VI)is then reduced and resolubilized in nitric acid andseparated by anion exchange. After this separation, the

sample is reacted with an acidic solution of DPC, the quantified as Cr(III) by either flame or furnace atomicabsorption spectroscopy. The amount determined iseluant stream is passed through a photometric detec-

tor, and the sample absorbance is measured at 520 nm considered to be Cr(VI). Method 7195 may be used toanalyze samples containing more than 5 mg of Cr(VI)(ASTM, 1993).

A regulatory-approved method for the preparation per liter (U.S. EPA, 1986b).SW-846 Method 7197 is based on the chelation ofof solid samples for Cr(VI) analysis has not been in

existence since 1986 when U.S. EPA removed an alka- Cr(VI) with ammonium pyrrolidine dithiocarbamate(APDC) and extraction with methyl isobutyl ketoneline digestion procedure (SW-846 Method 3060) from

its manual for the preparation of solid samples for (MIBK). The extract is aspirated into the flame of anatomic absorption spectrophotometer and the resultantCr(VI) analysis. The removal of this method was due

primarily to a U.S. EPA-funded research study that total chromium concentration is assumed to representCr(VI). Method 7197 may be used to analyze samplesdid not achieve consistent results with SW-846 Method

3060 (U.S. EPA, 1984, 1986a). The researchers con- containing from 1.0 to 25 mg of Cr(VI) per liter (U.S.EPA, 1986b). SW-846 7196A is most often used to de-cluded that the Cr oxidation state is matrix specific and

may be unstable and unpredictable (in environmental termine the concentration of dissolved Cr(VI) in soilextracts and aqueous samples. Method 7196A may besamples) once it is solubilized in either an acidic or

basic aqueous extraction medium (U.S. EPA, 1986a). used to analyze samples containing from 0.5 to 50 mgof Cr(VI) per liter. SW-846 Method 7196A colorimetri-Refinements from the original Method 3060 for the

extraction of total Cr(VI) have been reevaluated cally determines the amount of dissolved Cr(VI) pres-ent in the sample through a reaction with DPC. A red–through a significant amount of research performed

over the past 4 years (Vitale et al., 1993, 1994; James violet color is produced through the complexation withDPC in an acidic environment. The reaction is ex-et al., 1995). Based primarily on these refinements, the

alkaline digestion method, SW-846 Method 3060A, has tremely sensitive, however, as turbidity and color canimpart false positives. The absorbance is measuredrecently been proposed by the U.S. EPA (U.S. EPA,

1995b). photometrically at 540 nm (U.S. EPA, 1992).SW-846 Method 7199 introduces a known volume ofProposed Method 3060A uses an alkaline digestion

solution to solubilize both water-insoluble and water- a pH of 9.0- to 9.5-adjusted sample into an ion chroma-tograph. A guard column removes organics from thesoluble Cr(VI) compounds in solid matrix samples. The



sample before the Cr(VI) as CrO420 is separated on an

anion-exchange separator column. Postcolumn derivat-ization of the Cr(VI) with DPC is followed by detectionof the colored complex at 530 nm (U.S. EPA, 1995a).Method 7199 is designed to separate interfering sub-stances (i.e., turbidity, color) while simultaneouslyachieving lower detection limits than the uv/vis colori-metric procedures (0.3 mg/liter versus 500 mg/liter)(U.S. EPA, 1992, 1995a). The basic chemistry of U.S.EPA Methods 218.6 and 1636 is similar to that of SW-846 Method 7199 (U.S. EPA, 1991a).

Interpretation of Matrix Spike Data for Cr(VI)

Historically, analytical chemists have utilized ma-trix spiking techniques to assess the quality of analyti-cal data. For total metals, the assessment of matrixspike recoveries is a routine process. However, for theanalysis of valence-specific species such as Cr(III) andCr(VI), the interpretation of matrix spike recoveriesrequires a thorough understanding of the matrix chem-istry associated with the specific environment fromwhich the sample is collected. For example, certain re-ducing sample types (e.g., anoxic sediments) cannotsupport chromium in the hexavalent state regardlessof whether the Cr(VI) was added in the natural field

FIG. 2. Eh/pH phase diagram. The dashed lines define Eh/pHconditions or during chemical analysis. boundaries commonly encountered in soils and sediments. Note thatA major enhancement of proposed Method 3060A the Eh values plotted in this diagram are corrected for the reference

electrode voltage: 244 mV units must be added to the measured valueover its predecessor is the assessment of ancillary pa-when a separate calomel electrode is used, or 199 mV units must berameters to determine if a sample exhibits a reducingadded if a combination platinum electrode is used.capacity. The analysis of ancillary parameters such as

pH, oxidation reduction potential (ORP), total sulfides,and total organic carbon (TOC) provides quantitative

Such data are distinctly different from conventionaldata (1) to assess the tendency of Cr(VI) to exist in anQC data requirements for total metals analysis, whichenvironmental sample and (2) to assist in the interpre-is also a major enhancement over prior extraction pro-tation of quality control (QC) data for predigestion ma-cedures for Cr(VI).trix spike recoveries, particularly in situations where

low or 0% matrix spike recoveries are observed (Vitale pH. In general, soil samples need to be alkaline inet al., 1994). The four major redox-indicating ancillary nature (pH ú 7.0) in order to sustain chromium in theparameters are pH (using U.S. EPA SW-846 Method hexavalent state. It appears that the higher the pH of150.1M), ORP (using ASTM D1498-76), sulfides (using the soil, the less likely Cr(VI) will be reduced to Cr(III).U.S. EPA SW-846 Method 9030), and TOC (using the Based on the research data evaluated and thermody-U.S. EPA Region II method in which organic com- namic predictions (U.S. EPA, 1991b), samples with pHpounds are decomposed by pyrolysis in the presence of values õ7.0 tend to exhibit lower spike recoveries.O2 or air) (U.S. EPA, 1983, 1990a; ASTM, 1976; U.S.EPA Region II, personal communication). ORP. Generally, the larger the negative ORP value,

the stronger the reducing environment. In addition, theThe collective research that established the basis forproposed Method 3060A demonstrated that (1) method- more positive the ORP, the greater the tendency for

Cr(VI) to be sustained in the soils and the likelihoodinduced reduction of Cr(VI) to Cr(III) does not contrib-ute to low or 0% matrix spike recoveries and (2) soils of obtaining ‘‘acceptable’’ predigestion matrix spike re-

coveries. As shown in the chromium Eh/pH diagramthat exhibit high reducing properties cannot maintainCr(VI) spikes in the 6/ valence state. Proposed SW- (Fig. 2), a reducing environment may exist at a high

pH (10) if the ORP value is between 0600 and 0 mV.846 Method 3060A contains a detailed decision tree toassist the user in interpreting QC data, including the In addition, a reducing environment can exist at higher

ORP values (Ç/300 mV) provided the pH of the soil isancillary parameters discussed below, that are neededto substantiate the quantification of Cr(VI) results. acidic (Ç4.0).


S84 CHROMIUM SYMPOSIUM

TOC. Chromium may exist in a number of oxida- REFERENCEStion states; however, they are not all of the same stabil-

American Society for Testing and Materials (1976). Standard Prac-ity. Although CrO420 (a hexavalent form of chromium)

tice for Oxidation–Reduction Potential of Water, ASTM Desig.is relatively stable, its high positive reduction potential D1498-76. ASTM, Philadelphia, PA.denotes that it is strongly oxidizing and is unstable in American Society for Testing and Materials (1993). Standard Testan acid solution, as well as in the presence of organic Method for Collection and Analysis of Cr(VI) in Ambient, Work-molecules with oxidizable groups (alkanes, alkenes, al- place or Indoor Atmospheres, ASTM Desig. D5281-92. ASTM, Phil-

adelphia, PA.cohols, aldehydes, ketones, carboxylic acids, etc.).Cazeneuve, P. (1900). Sur la diphenylcarbazide, reactif tres sensibleTherefore, the greater the levels of TOC in the soil,

de quelques composes matelliques: Cuivre, mercure, fer au maxi-the more likely that Cr(VI) will be reduced to Cr(III)mum, acide chromique. Bull. Soc. Chim. Paris 23, 701–706.(Wiley–Interscience, 1988).

James, B. R., et al. (1995). Cr(VI) extraction from soils: A comparisonof five methods. Environ. Sci. Technol. 29, 2377–2381.Sulfides. The presence of sulfides in soils is a strong

National Institute for Occupational Safety and Health (1984).indicator that the soil is reducing in nature. A water- NIOSH Manual of Analytical Methods, 3rd ed. Cincinnati, OH.soluble reagent such as sodium sulfide can readily re-

National Institute for Occupational Safety and Health (1994).duce Cr(VI) and precipitate it to Cr(OH)3. This reduc- NIOSH Manual of Analytical Methods, 4th ed. Cincinnati, OH.tion seems to occur in nature when a secondary metal Sax, N. I., and Lewis, Sr. (Eds.) (1987). Hawley’s Condensed Chemi-such as iron is present. Not surprisingly, one method cal Dictionary, 11th ed. Van Nostrand Reinhold, New York.used in wastewater treatment plants for removing Stokinger, H. E. (1978). The metals. In Patty’s Industrial Hygiene

and Toxicology, 3rd ed., p. 1589.heavy metals (i.e., chromium) from water samples isthrough sulfide precipitation (Wiley–Interscience, 1988). U.S. Environmental Protection Agency (1983). Methods for Chemical

Analysis of Water and Wastes, U.S. EPA Rep. 600/4-79-020. U.S.If the collective data indicate that a sample exhibits aEPA Environmental Monitoring and Support Laboratory, Office ofreducing environment, poor Cr(VI) predigestion matrixResearch and Development, Cincinnati, OH.spike recoveries are predictable and not indicative of

U.S. Environmental Protection Agency (1984). Test Methods for Eval-method-induced reduction or technical error. Charac- uating Solid Wastes, Physical/Chemical Methods, SW-846, 2nd ed.terization of the ancillary parameters is essential in Office of Solid Waste and Emergency Response, Washington, DC.establishing the sample’s oxidation/reduction propen- U.S. Environmental Protection Agency (1986a). Determination ofsity. However, each of these parameters by itself may Stable Valence States of Chromium in Aqueous and Solid Waste

Matrices—Experimental Verification of Chemical Behavior, U.S.not be sufficient to determine whether or not a sampleEPA Rep. 600/4-86-039. U.S. EPA, Cincinnati, OH.has reducing properties.

U.S. Environmental Protection Agency (1986b). Test Methods forEvaluating Solid Wastes, Physical/Chemical Methods, SW-846,3rd ed. Office of Solid Waste and Emergency Response, Washing-CONCLUSIONton, DC.

U.S. Environmental Protection Agency (1990a). Test Methods forEvaluating Solid Wastes, Physical/Chemical Methods, SW-846,Due to the significant toxicity differences between3rd ed. Office of Solid Waste and Emergency Response, Washing-Cr(III) and Cr(VI), it is essential that chromium beton, DC.quantified in these two distinct valence states to assess

U.S. Environmental Protection Agency (1990b). U.S. EPA Contractthe potential risks of exposure to each in environmentalLaboratory Program Statement of Work for Inorganic Analysis,

media. Speciation is equally important because of their Multi-Media, Multi-Concentration, Statement of Work Contractmarked differences in environmental behavior. As the Solicitation, Doc. ILM03.0. U.S. EPA, Washington, DC.knowledge of risks associated with each valence state U.S. Environmental Protection Agency (1991a). Determination of

dissolved hexavalent chromium in drinking water, groundwaterhas grown, analytical methods have also been devel-and industrial wastewater effluents by ion chromatography. Inoped which have assisted decision makers in realisticTest Methods for Evaluating Solid Wastes, Physical/Chemicalassessment of risk with respect to chromium and itsMethods, SW-846, 2nd ed. Office of Solid Waste and Emergency

compounds. Within the past several years, significant Response, Washington, DC.advances have been made in the sample preparation U.S. Environmental Protection Agency (1991b). MINTEQA2/PRO-and instrumental analysis of total Cr and Cr(VI) in DEFA2. A Geochemical Assessment Model for Environmental Sys-

tems: Version 3.0, EPA/600/3-91/021. U.S. EPA, Washington, DC.environmental media. In particular, for Cr(VI), detec-U.S. Environmental Protection Agency (1992). Test Methods for Eval-tion limits have been reduced significantly through the

uating Solid Wastes, Physical/Chemical Methods, SW-846, 3rd ed.use of instrumental techniques such as ion chromatog-Office of Solid Waste and Emergency Response, Washington, DC.raphy coupled with postcolumn reactions. Equally im-

U.S. Environmental Protection Agency (1993). IRIS: A Continuouslyportant, advances in the characterization of samplesUpdated Electronic Database Maintained by the U.S. Environmen-to determine the inability to maintain Cr(VI) under tal Protection Agency. National Library of Medicine, Bethesda, MD.

environmental conditions have aided in the appro- U.S. Environmental Protection Agency (1995a). Determination ofpriate interpretation of laboratory matrix spike data Cr(VI) in drinking water, groundwater and industrial wastewater

effluents by ion chromatography. In Test Methods for Evaluatingand the validity of quantitative Cr(VI) results.



Solid Wastes, Physical/Chemical Methods, SW-846, 2nd ed. Office Q: I just wondered if you could clarify the digestionof Solid Waste and Emergency Response, Washington, DC. method of lead and the chromium in the samples.

U.S. Environmental Protection Agency (1995b). Test Methods for A: The top method has been used in the context ofEvaluating Solid Wastes, Physical/Chemical Methods, SW-846, purely field screening and depending on the type ofthird update to the 3rd ed. Office of Solid Waste and Emergency sample, you may get erratic results. To answer the firstResponse, Washington, DC. [U.S. EPA (1995). Fed. Reg. 60, 37974.]

question. This method is for total hexavalent chro-U.S. Environmental Protection Agency (1995c). Determination of

mium. You do get the barium chromates, the lead chro-Hexavalent Chromium by Ion Chromatography, EPA 821/R/95/029.mates, and the other sparingly soluble chromates. Tri-U.S. EPA Office of Water, Engineering and Analysis Division,

Washington, DC. valent chromium, by the way, is not soluble at pH 11.8or greater. So looking at trials where we were actuallyVitale, R. J., et al. (1994). Cr(VI) extraction from soils: Evaluation of

an alkaline digestion method. J. Environ. Qual. 23, 1249–1256. preparing and trying effectively to analyze total chro-mium in the alkaline solution, then also I must useVitale, R. J., et al. (1995). Hexavalent chromium quantification in

soils: An effective and reliable procedure. Am. Environ. Lab. 7, that same solution for hex. The numbers pretty muchDoc. No. 3. stay consistent but it is difficult to do total chrome

Wiley–Interscience (1988). Chromium in the Natural and Human analysis in that strong of an alkaline solution.Environments, pp. 25, 237. Wiley, New York. Q: Your holding-time studies were done with field

Zatka, V. J. (1985). Speciation of Cr(VI) in welding fumes: Interfer- soils. Would you expect to see different results if youence by air oxidation of chromium. Am. Ind. Hyg. Assoc. J. 46, were working with spiked soils? You made a comment327–331. on the differences in holding time for the different types

of chromium you might find under environmental con-ditions.QUESTIONS AND ANSWERS

A: This raises a very interesting philosophical ques-tion. Given a choice between looking at samples that

A, DR. ROCK J. VITALE have hexavalent chromium present in them and doingM, MODERATOR a liquid spike to a soil sample, I obviously would preferQ, QUESTIONER (AUDIENCE) the former. In the latter, you’re not actually measuring

M: Thank you, Dr. Vitale. We have time for some the soil particulate itself or solid particulate itself.short questions. What you’re measuring is the spiked liquid that has

Q: The samples you showed here, were they site sam- now coated the outside. I do believe that there’s a differ-ples or were they taken from the environment? ent chemistry going on when you’re looking at certain

contamination versus true mineral content.A: Those were actually field-collected samples.


environmental monitoring of chromium in air, soil, and water

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