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Arsenic

Laura Stanton. Arsenic. 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 (As 4 ) Soft and waxy; density: 1.97 grams per meters cubed Volatile and toxic Black

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Arsenic

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  1. Laura Stanton Arsenic

  2. 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

  3. 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

  4. 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

  5. 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)

  6. 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).

  7. 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

  8. 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.

  9. 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),

  10. It’s Effects

  11. Arsenic In Ground Water! • Figure of Arsenic concentration from United States Geological Survey

  12. 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.

  13. 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.

  14. Works Cited • USGS • 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 • More

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