Arsenic

Laura Stanton

Properties• As

– Atomic number: 33

– Relative Mass: 74.92

– Metalloid

– Grey or Yellow or Black color• Grey

– Density: 5.73 grams per meters cubed

– Semiconductor and solid

• Yellow (As4)– Soft and waxy; density: 1.97 grams per meters cubed

– Volatile and toxic

• Black– Glassy and brittle

– Low conductor

More About Arsenic

• Isotopes

– Stable: 75As

– 33 radioisotopes synthesized; 60-92

• 73As– Most stable

– half-life = 80.3 days; 73 Ge

• 74As– Half-life = 17.78 days; 74 Ge or 74 Se

– 10 nuclear isomers; 66-84

• Ex: 68mAs; half-life = 111 seconds

Even More• Chemical

+ heat when in an air medium

→ arsenic oxidizes to Arsenic Trioxide

• Heat of Fusion = 24.44 kJ/mol

• Heat of Vaporization = 34.76 kJ/mol

• Specific Heat Capacity = 24.64 J/mol*K

• Inorganic arsenic– As2O3 and As2O5; soluble in water

– Acutely toxic

• Arsenic(V) Acid is a weak acid

• Arsenate is an arsenic salt; many used in agriculture

History

• Discovered by Albertus Magnus, 1250

• Used for strengthening metals: copper and lead

– Automotive batteries

– Semiconductor in electronic devices

• Used in production of pesticides:

– To treat wood products

– Also herbicides and insecticides

• In painting pigments:

– As2S3 and As4S4

Also used in medicine as antibiotic (past)

Into Environment

• Runoff from agriculture

• Industrial waste

• Into ground water

• Volcanic ash

• Weathering of the arsenic-containing mineral

Arsenic contents of surface sediments vary in the range 6-40 mg/kg; fine sand and sediments tend to have higher levels of arsenic than coarser fractions (Safiullah 2007).

What contains Arsenic?• Arsenic was detected in fruits, vegetables, grain

products, fast foods, dairy products, BUT mostly seafoods

– Arthropods (shrimp)

– Fish

– Bivalves (clams)

– Algae

• Arsenic concentration for all seafoods in fast food sandwiches was 2.1 μg/g (dry weight). (Nielson et al. 1991)

• Average intake is about 10–50 µg/day (humans)

– More if seafood is consumed

Arsenic into the Body• Arsenite is more toxic than arsenate

– Arsenite (0) accumulation in cells is faster than arsenate (-).

– It can pass through the cell membrane, but also actively transported into cells

• Arsenite = aquaglycoporins 7 and 9– Which also transports water and

glycerol

• Arsenate = phosphate transporter

• Metabolized by methylation

– Then excreted in the urine.

– Methylation occurs in liver, kidney and lungs.

More on Methylation

Reduce arsenite (via purine nucleoside phosphorylase) to arsenate then methylation (via enzymatic transfer of the methyl group from S-adenosylmethionine (SAM) to arsenite to form monomethylarsonic acid (MMAV) )

• Gene that codes for the enzyme responsible for this reaction is just like Cyt 19

arsenite+SAM→MMAV

MMAV+thiol→MMAIII

MMAIII+SAM→DMAV

DMAV+thiol→DMAIII

• DMA III = Dimethylarsinous Acid

• Most humans exposed to arsenic excrete 10–30% inorganic arsenic, 10–20% MMA(V+III) and 60–80% DMA(V+III),

It’s Effects

Arsenic In Ground Water!

Figure of Arsenic concentration from United States Geological Survey

Ground Water

• Arsenic in ground water is largely the result of minerals dissolving from weathered rocks and soils.

– Arsenic concentrations in ground water generally are highest in the West (Welsh, et. al 2008).

• Several types of cancer have been linked to arsenic in water. (National Research Council, 1999)

• 2001: EPA lowered the maximum level of As permitted in drinking water 50 ug/L → 10 ug/L.

What can it cause?

• Can contribute to skin, bladder, and other cancers (National Research Council, 1999).

• Arsenicosis

• Sugestions on how to fix:

– Mitigation options include use of alternative groundwater sources, use of microbiologically safe surface water (e.g. rainwater harvesting), or use of arsenic removal technologies.

Works CitedUSGS

National Research Council

WHO

Nielson, Kirk K., et al. 1991. Occurance of arsenic in seafoods from fast foods analyzed by X-ray fluorescence. Journal of Food Composition and Analysis. 4.4.pg:285-292.

Obinaju, Blessing E. 2009. Mechanisms of arsenic toxicity and carcinogenesis. African Journal of Biochemistry Research. 3.5.232-237.

Rossman, Toby G. 2003. Mechanism of Arsenic Carcinogensis. Metals and Human Cancer. 553.1-2.pg: 37-65.

Safiullah, Syed. 2007. Arsenic pollution in the groundwater in Bangladesh: An Overview. Asian Journal of Water, Environment, and Pollution. 4.1.47-59

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