Environmental Chemistry

Chapter 11:Arsenic

Copyright © 2005 by DBS

Arsenic

• Chemistry:– extremely complex because it can exist in metallic form, can be in trivalent and

pentavalent state (charge of 3+ or 5+), and can be organic or inorganic– widely distributed in nature (variety of forms)

• Sources:– smelting of gold, silver, copper, lead and zinc ores– combustion of fossil fuels– agricultural uses as herbicides and fungicides– cigarette smoke– occupational: largest source is manufacture of pesticides and herbicides

• Environmental fate:– found in surface and groundwater through runoff– accumulates in plants if soil conditions are right– bioaccumulates in aquatic ecosystems (so fish consumption is a source)

Source: http://www.webelements.com

Sources

• Eating food, drinking water, or breathing air containing arsenic. – Herbal medicines (India/Pakistan Ayurvedic” remedies

• Breathing contaminated workplace air. • Breathing sawdust or burning smoke from wood

treated with arsenic. • Living near uncontrolled hazardous waste sites

containing arsenic. • Living in areas with unusually high natural levels of

arsenic in rock.

• Arsenic is widespread in the environment • Occupational exposures can occur

– Smelting industry– Coal fired power plants

• Epidemiological studies implicate arsenic as a carcinogen• Inhalation is a common route of exposure• Drinking water exposure can also lead to cancer

• pharmacokinetics and dynamics:– absorbed via inhalation, ingestion and dermal exposure– mimics phosphate in terms of uptake by cells– Detoxified by methylation: decreased rates lead to increased toxicity

(individual susceptibility)– Can cross placenta– accumulates in liver, kidney, heart and lung - later in bones, teeth, hair,

etc.– half-life is 10 hr, excretion via kidneys

Arsenic Toxicity Mechanisms

• binds to sulfhydryl groups (and disulfide groups), disrupts sulfhydryl-containing enzymes (As (III))– inhibits pyruvate and succinate

oxidation pathways and the tricarboxylic acid cycle, causing impaired gluconeogenesis, and redu

ced oxidative phosphorylation

• targets ubiquitous enzyme reactions, so affects nearly all organ systems

• substitution for phosphorus in biochemical reactions– Replacing the stable phosphorus

anion in phosphate with the less stable As(V) anion leads to rapid hydrolysis of high-energy bonds in compounds such as ATP. That leads to loss of high-energy phosphate bonds and effectively "uncouples" oxidative phosphorylation.

Arsenic Toxicity

• organic arsenicals>inorganic arsenicals>metallic forms

• trivalent>pentavalent• acute: severe abdominal pain, fever,

cardiac arrhythmia • chronic: muscle weakness and pain,

gross edema, gastrointestinal disturbances, liver and kidney damage, swelling of peripheral nerves (neuritis), paralysis

– liver injury: jaundice– peripheral vascular disease -

blackfoot disease• chronic drinking water exposure in

Taiwan and Chile– cancer (skin, lung, kidney bladder)

Black Foot Disease

• skin disease:– keratosis of hands and feet, and hyperpigmentation

Blisters

Arsenic Problems: Bangladesh

• Arsenic is found in groundwater of many countries: particularly South East Asia and Bangladesh

• As leached from underground sources into village wells of 1 million people, levels of 1000 ppb

– 62% of wells tested exceeded WHO standard

– ~ 35 million people exposed above US EPA standard

• 200,000 people suffering from As-induced skin lesions

• problem may have been exacerbated by large scale withdraw of groundwater for irrigation or by extensive use of fertilizers

Skin pigmentation, keratoses andskin cancers were found amongpeople who drank from arseniccontaminated wells

http://phys4.harvard.edu/~wilson/arsenic/arsenic_project_introduction.htmlSee Prof. Wilson at Harwad’s Arsenic page From: Klaassen et al., Chap. 19, Philp, Chap. 6

Toxic Hazards Associated with Poultry Litter Incineration

What Goes In, Must Come Out“One of the most basic principles of incineration is that what goes in, must come out. There is no alchemy going on, so if there are toxic heavy metals like lead, mercury or arsenic going in one end, they must come out in the form of toxic ash and toxic air emissions.”

http://www.energyjustice.net/fibrowatch/

Arsenic Use in Chicken & Turkey FeedRoxarsone, or 3-nitro-4-hydroxyphenylarsonic acid, is currently the most commonly used arsenical compound in poultry feed in the United States, with a usage of 23 to 45 grams of chemical per ton of feed for broiler chickens for increased weight gain, feed efficiency, improved pigmentation, and prevention of arasites. Roxarsone is used in turkeys as well as chickens. By design, most of the chemical is excreted in the manure.

• Setting the Standard• 1992: California toxicologist argues that US EPA

standard for As in drinking water would constitute a 1:100 risk of cancer for lifetime consumption

• EPA standard not originally based on cancer as an endpoint

• achieving a 1:1,000,000 risk would require dropping standard from 50 ppb to 2 ppt

• EPA revising standard to from 50 to 10 ppb in 2006– consider cost to small communities

Arsenic in US Drinking Waters

• In the U.S. the arsenic for drinking water was lowered from 50 ppb (μg/L) to 10 ppb – to be complied by 2006

Source: http://water.usgs.gov/nawqa/trace/arsenic

Removal of As from Water

• Pass over alumina (Al2O3)

• Anion exchange or reverse osmosis• Precipitation

In treatment facilities by precipitating it in the form of insoluble arsanate, AsO4

3-

Fe3+ + AsO43- → FeAsO4(S)

GW As is usually reducing so As(III) must first be oxidized to As(V)

Steady-State of As in Water

Arsenic in Lake OntarioThe lake receives 161 tonnes of As per year through river and lake flows that originate in land based sources

Thompson et al, 1999

Input = Output

158 + 3.6 = 161.6 t = 119 + (91-49) t

Toxicology

• LD50 values for some common forms of As

Meat and seafoodConverted by bio-methylation → excreted

Toxicology

• As(III) compounds arsine (AsH3) and trimethylarsince (As(CH3)3) are most toxic

Chromated Copper Arsenate (CCA)

• Chromated copper arsenate (CCA) used to protect decks (45% As2O3)

• Concern over leaching of As especially in childrens playgrounds

• 76 mg/kg found in soil 10x control

Pressure treated wood

CCA: 22 percent pure arsenic

A 12-foot section of pressure-treated lumber contains about an ounce of arsenic, or enough to kill 250 people.

"In less than two weeks, an average five-year-old playing on an arsenic-treated playset would exceed the lifetime cancer risk considered acceptable under federal pesticide law." EPA, 2004, banned from residential use

Source: http://www.sptimes.com/News/031101/State/The_poison_in_your_ba.shtml

• End Baird

As Concentrations in Natural Waters

• As

Global Arsenic Cycle and Reservoir Sizes

oceans

lithosphere

Global As cycle and reservoir sizes from Matschullat, 2000

800-1,740 t As

τ = 0.022-0.027 yr = 8 – 10 d

4.01 x 1013 t As in the earth’s crust 1.5 – 2 mg kg-1 upper crust

1 – 1.8 mg kg-1 bulk crust

As in Western PA

• As in Western PA

Senior Theseis: Local Sites of Interest

• Breslube Penn Superfund site

• Clever Park CCA structures

Cadmium

• Relatively new metal in terms of humans• Sources:

– natural rock weathering– copper, lead and zinc smelting auto

exhaust– cigarette smoke (a cigarette contains 1-2

ug Cd)• Uses:

– metal plating – nickel-cadmium batteries– solders– paint pigments (blue)– plastic stabilizers– photographic chemicals– fungicides

• Readily absorbed and accumulated in plants• Food as most common route of exposure for

general population

From: Klaassen et al., Chap. 19, Philp, Chap. 6 http://www.cadmium.org

Pharmacokinetics

pharmacokinetics:• inhalation:

– smelters, cigarette smoke– 15-50% absorbed

• ingestion:• main source is liver and kidney of

meats• 6% absorbed, greater if deficient

in calcium, zinc or iron

Shenyang Copper Smelter

Toxicity Mechanisms

• Mechanisms – binding to –SH groups – competing with Zn and Se for

inclusion into metalloenzymes– competing with calcium for binding

sites (calmodulin)• Kidney toxicity• Lung toxicity• Skeletal effects

– Osteoporosis and osteomalacia • Cancer

– carcinogenic in animal studies– ~8% of lung cancers may be

attributable to Cd

Cadmium (Cd)Epidemics/case studies

Japan (1940s)• effluent (outflow) from a lead-

processing plant washed over adjacent rice paddies for many years– rice accumulated high level

of Cd– community was poor (and

therefore malnourished with respect to calcium)

– acute toxicity: renal failure,anemia, severe muscle pain

• named "Itai-Itai" disease ("ouch, ouch")

Itai-itai victim

Further Reading (Baird)

• Hingston, J.a. et al (2001) Leaching of Chromated Copper Arsenate Wood Preservatives. Environmental Pollution, Vol. 111, pp. 53.

• Lykknes, A. and Kvittingen, L. (2003) Arsenic: Not So Evil After All?. Journal of Chemical Education, Vol. 80, pp. 497.

• Pearce, F. (2003) Arsenic’s Fatal Legacy Grows. New Scientist. August 9, pp. 4.

• Smith, A.H. et al. (1992) Cancer Risks from Arsenic in Drinkng Water. Environmental Health Perspecives. Vol. 97, pp. 259.

Further Reading

• Smith, A.H. et al (2002) Science• Welch, A., Ryker, S., Helsel, D., and Hamilton, P.

(2001) Arsenic in Ground Water of the United States: A Review. Well Water Journal. February, pp. 30-33.