Arsenic compounds

Arsenic has been used as both poison and medicine for millennia — in 18th-century Europe, arsenic trioxide was a fashionable poison, and Fowler's Solution (1% potassium arsenite) was prescribed for a century as a tonic and cancer treatment [1]. The modern crisis is geological rather than industrial: in Bangladesh and West Bengal, India, aquifer sediments release inorganic arsenic (arsenite, As III; arsenate, As V) into groundwater that tens of millions of people drink daily [2]. This geological catastrophe — arguably the largest mass poisoning in human history — was ironically triggered by a well-intentioned public health campaign in the 1970s that drove people from cholera-contaminated surface water to 'safe' groundwater without testing for arsenic. Similar geogenic contamination affects parts of Chile, Argentina, Taiwan, Mexico, and the western United States. Industrial arsenic compounds come from copper and gold smelting (arsenic is a byproduct of sulfide ore processing), wood preservative CCA (chromated copper arsenate, used in pressure-treated lumber until 2003), herbicides (monosodium methyl arsenate, MSMA), and glass manufacturing [1].

The primary pathway globally is drinking water from arsenic-contaminated wells, most severely in South and Southeast Asia, Latin America, and parts of the United States [1]. In the U.S., parts of New England, the Great Plains, and the Southwest have naturally elevated groundwater arsenic — private well users are not covered by the EPA 10 µg/L drinking water standard and must test their own wells [2]. Dietary intake is significant: rice and rice-based products (rice milk, rice cereal, brown rice) accumulate inorganic arsenic from soil and irrigation water — brown rice has 80% more arsenic than white rice [1]. Seafood contains arsenobetaine and organic arsenicals generally considered less toxic. Workers in copper smelting, pesticide production, and wood treatment face occupational inhalation [2]. Children are exposed through soil contact near former orchards (where lead arsenate pesticide was historically used) and CCA-treated wooden playground equipment [1].

Inorganic arsenic is metabolized by methylation (As III → MMA III → DMA V) in the liver, but the intermediate MMA(III) is more reactive and toxic than the parent compound [1]. Arsenic inhibits key enzymes in the pyruvate dehydrogenase complex and the citric acid cycle, disrupting cellular energy production. It generates reactive oxygen species, causes DNA strand breaks, inhibits DNA repair, and disrupts telomerase function — explaining its multi-organ carcinogenicity [2]. IARC classifies inorganic arsenic as a Group 1 carcinogen for bladder, lung, and skin cancers; associations with kidney, prostate, and liver cancer are also documented [1]. Chronic arsenic also causes characteristic skin lesions (keratosis, hyperpigmentation, 'raindrop' depigmentation), peripheral neuropathy, and cardiovascular disease at lower doses than cancer [2].

Private well users in arsenic-endemic regions of the U.S. (New England bedrock aquifers, Great Plains alluvial deposits, Southwest volcanic deposits) are a major at-risk group [1]. Infants and young children fed rice cereal or rice milk have disproportionately high dietary arsenic per body weight. Workers in copper, gold, and lead smelting; pesticide manufacturing; and glass production face occupational inhalation exposure [2]. In South Asia, 200+ million people drink water exceeding the WHO guideline of 10 µg/L. Individuals who are poor methylators (those lacking MTHFR capacity or those with inadequate folate) metabolize arsenic to more toxic intermediates [1].

1. Test your private well annually for arsenic — contact your state health department or use an NSF-certified lab; many New England and western states have high bedrock arsenic [1]. 2. Use a certified reverse osmosis filter for drinking and cooking water if your arsenic exceeds 10 µg/L [2]. 3. Diversify grain intake — replace some rice with quinoa, oats, or other grains, and don't feed infants exclusively rice cereal [1]. 4. Cook rice in a large volume of water (6:1 water:rice ratio) and drain — this reduces inorganic arsenic by up to 57% [2]. 5. Avoid old CCA-treated wood playgrounds, and seal existing CCA-treated wood decks with penetrating sealant every year or two [1]. 6. If occupationally exposed in smelting or pesticide production, use appropriate respiratory protection and biological monitoring programs [2].