Arsenic is a naturally occurring element in the earth’s crust with a long history of use as a constituent of commercial and industrial products, as a component in pharmaceuticals, and as an agent of deliberate poisoning. Recent commercial applications of arsenic include its use in the manufacture of semiconductors, wood preservatives for industrial applications (eg, marine timbers or utility poles), nonferrous alloys, glass, and the turf herbicide monosodium methane arsonate (MSMA). The use of phenyl-arsenic compounds as feed additives for poultry and swine was terminated in the United States in 2015. In some regions of the world, groundwater may contain high levels of arsenic that has leached from natural mineral deposits. Arsenic in drinking water in the Ganges delta of India and Bangladesh is now recognized as one of the world’s most pressing environmental health problems. Environmental risk assessments have suggested that arsenic migrating from coal combustion wastes (eg, coal ash) deposited in unlined landfills may contaminate underlying groundwater. Arsine, an arsenous hydride (AsH3) gas with potent hemolytic effects, is manufactured predominantly for use in the semiconductor industry but may also be generated accidentally when arsenic-containing ores or scrap gallium arsenide semiconductors come in contact with acidic solutions.
It is of historical interest that Fowler’s solution, which contains 1% potassium arsenite, was widely used as a medicine for many conditions from the eighteenth century through the mid-twentieth century. Organic arsenicals were the first pharmaceutical antimicrobials * and were widely used for the first half of the twentieth century until supplanted by sulfonamides and other more effective and less toxic agents.
Other organoarsenicals, most notably lewisite (dichloro[2-chlorovinyl]arsine), were developed in the early 20th century as chemical warfare agents. Arsenic trioxide was reintroduced into the United States Pharmacopeia in 2000 as an orphan drug for the treatment of relapsed acute promyelocytic leukemia and is finding expanded use in experimental cancer treatment protocols. Melarsoprol, another trivalent arsenical, is used in the treatment of advanced African trypanosomiasis (see Chapter 52).
Soluble arsenic compounds are well absorbed through the respiratory and gastrointestinal tracts (Table 57–1). Percutaneous absorption is limited but may be clinically significant after heavy exposure to concentrated arsenic reagents. Most of the absorbed inorganic arsenic undergoes methylation, mainly in the liver, to monomethylarsonic acid and dimethylarsinic acid, which are excreted, along with residual inorganic arsenic, in the urine. When chronic daily absorption is <1000 mcg of soluble inorganic arsenic, approximately two thirds of the absorbed dose is excreted in the urine within 2–3 days. After massive ingestions, the elimination half-life is prolonged. Inhalation of arsenic compounds of low solubility may result in prolonged retention in the lung and may not be reflected by urinary arsenic excretion. Arsenic binds to sulfhydryl groups present in keratinized tissue, and following cessation of exposure, hair, nails, and skin may contain elevated levels after urine values have returned to normal. However, arsenic in hair and nails as a result of external deposition may be indistinguishable from that incorporated after internal absorption.
Arsenic compounds are thought to exert their toxic effects by several modes of action. Interference with enzyme function may result from sulfhydryl group binding by trivalent arsenic or by * Paul Ehrlich’s “magic bullet” for syphilis (arsphenamine, Salvarsan) was an arsenical.