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.
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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 –Glassy and brittle –Low conductor
More About Arsenic Isotopes –Stable: 75 As –33 radioisotopes synthesized; 60-92 73 As –Most stable –half-life = 80.3 days; 73 Ge 74 As –Half-life = 17.78 days; 74 Ge or 74 Se –10 nuclear isomers; 66-84 Ex: 68m As ; 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 –As 2 O 3 and As 2 O 5 ; 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: –As 2 S 3 and As 4 S 4 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),
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 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