Arsenic (As)
Definition
Metalloid; trivalent arsenite (As III) is 60 times more toxic than pentavalent arsenate (As V). Thiol-group blocker that poisons mitochondrial enzymes (pyruvate dehydrogenase). Sources: contaminated groundwater (West Bengal arsenicosis belt), Paris green pesticide, opium adulteration, traditional Ayurvedic and Unani preparations.
- Symbol
- As
- Element type
- Metalloid
- Relative toxicity
- Arsenite (As III) about 60x more toxic than arsenate (As V)
- Mechanism
- Blocks thiol groups, inhibits pyruvate dehydrogenase
- Common source
- Contaminated groundwater, e.g. West Bengal belt
Common questions
Why does the oxidation state of arsenic matter forensically?+
Arsenite binds thiol groups far more readily than arsenate, so the two forms differ sharply in toxicity and in tissue distribution. A toxicology report distinguishing As III from As V, not just total arsenic, better supports a poisoning timeline.
Where besides deliberate poisoning does arsenic exposure commonly arise?+
Chronic low-level exposure from contaminated groundwater is a recognised public health issue in parts of South Asia, and historical exposure also came from Paris green pesticide residues and some traditional Ayurvedic or Unani preparations, complicating attribution of a single acute case to malice.
Related terms
- Dry Ashing
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- Hydride Generation (HG-AAS)
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- Lead (Pb)
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- Marsh Test (1836)
- Confirmatory test for arsenic devised by James Marsh after the Bodle case (1832), in which Marsh was unable to convince a jury...
- Mercury (Hg)
- Three toxic forms: elemental (vapour from broken thermometers, dental amalgam), inorganic salts (mercuric chloride, corrosive sublimate), and organic (methylmercury from biomagnification, ethylmercury...
- Reinsch Test
- Classical screen for arsenic, antimony, mercury and bismuth. A clean copper strip is immersed in the acidified sample (concentrated HCl, near-boiling) for...
- Thallium (Tl)
- The 'poisoner's poison' because thallium sulphate is tasteless, odourless and colourless. Substitutes for potassium in cellular transport. Alopecia at 2 to 3...
- Wet Digestion
- Viscera is digested with HNO3 + H2SO4 + HClO4 (or HNO3 + H2O2) at controlled temperature. Closed-vessel microwave-assisted digestion in Teflon bombs...