Arsenic in drinking-water
Background document for development of WHO Guidelines for Drinking-water Quality
Kinetics and metabolism in laboratory animals and humans
Ingested elemental arsenic is poorly absorbed and largely eliminated unchanged. Soluble arsenic compounds are rapidly absorbed from the gastrointestinal tract (Hindmarsh & McCurdy, 1986); arsenic(V) and organic arsenic are rapidly and almost completely eliminated via the kidneys (Buchet et al., 1981a; Luten et al., 1982; Tam et al., 1982). Inorganic arsenic may accumulate in skin, bone, liver, kidney and muscle (Ishinishi et al., 1986); its half-life in humans is between 2 and 40 days (Pomroy et al., 1980). Inorganic arsenic is eliminated from the body by the rapid urinary excretion of unchanged arsenic in both the trivalent and pentavalent forms and by sequential methylation to MMA and DMA in both 3 and 5 valence states (Buchet & Lauwerys, 1985; Lovell & Farmer, 1985). Limited short-term studies on humans indicate that the capacity to methylate inorganic arsenic is progressively, but not completely, saturated when daily intake exceeds 0.5 mg (Buchet et al., 1981b).
The internal dose of inorganic arsenic in individuals can be determined by measuring the arsenic species in urine. The concentrations of metabolites of inorganic arsenic in urine from individuals with no known exposure to arsenic are reported to be generally below 10 µg/litre in European countries; however, in West Bengal and Bangladesh, urinary arsenic concentrations above 1 mg/litre have frequently been observed (IPCS, 2001).
In humans, inorganic arsenic does not appear to cross the blood–brain barrier; however, transplacental transfer of arsenic in humans has been reported (Gibson & Gage, 1982).