Arsenic in drinking-water
Background document for development of WHO Guidelines for Drinking-water Quality
Environmental levels and human exposure
Arsenic concentrations measured in remote or rural areas range from 0.02 to 4 ng/m3 (US NRC, 1999). In urban areas, arsenic concentrations of 3–200 ng/m3 have been measured. Much higher concentrations (>1000 ng/m3) are present in the vicinity of industrial sources (Ball et al., 1983; WHO, 1987; US NRC, 1999).
The level of arsenic in natural waters, including open ocean seawater, generally ranges between 1 and 2 µg/litre (Hindmarsh & McCurdy, 1986; US NRC, 1999). Concentrations may be elevated, however, in areas with volcanic rock and sulfide mineral deposits (Hindmarsh & McCurdy, 1986); in areas containing natural sources, where levels as high as 12 mg/litre have been reported (Grinspan & Biagini, 1985); near anthropogenic sources, such as mining and agrochemical manufacture (US NRC, 1999); and in geothermal waters (mean 500 µg/litre, maximum 25 mg/litre) (US NRC, 1999). Mean arsenic concentrations in sediment range from 5 to 3000 mg/kg; the higher levels occur in areas of contamination (US NRC, 1999) but are generally unrelated to arsenic concentrations in water.
The total estimated daily dietary intake of arsenic may vary widely, mainly because of wide variations in the consumption of fish and shellfish. Most data reported are for total arsenic intake and do not reflect the possible variation in intake of the more toxic inorganic arsenic species. Limited data indicate that approximately 25% of the arsenic present in food is inorganic, but this is highly dependent upon the type of food (Hazell, 1985; US EPA, 1988; IPCS, 2001).
Fish and meat are the main sources of dietary intake of arsenic (Gartrell et al., 1986a); levels ranging from 0.4 to 118 mg/kg have been reported in marine fish sold for human consumption, and concentrations in meat and poultry can be as high as 0.44 mg/kg (Health and Welfare Canada, 1983).
The mean daily intake of arsenic in food for adults has been estimated to range from 16.7 to 129 µg (Hazell, 1985; Gartrell et al., 1986a; Dabeka et al., 1987; Zimmerli et al., 1989); the corresponding range for infants and children is 1.26–15.5 µg (Nabrzyski et al., 1985; Gartrell et al., 1986b). In preliminary studies in North America, the estimated daily intake of arsenic from the diet was 12–14 μg of inorganic arsenic (Yost et al., 1998).
4 Estimated total exposure and relative contribution of drinking-water
Except for individuals who are occupationally exposed to arsenic, the most important route of exposure is through the oral intake of food and drinking-water, including beverages made from drinking-water. The mean daily intake of arsenic from drinking-water will generally be less than 10 µg; however, in those areas in which drinking-water contains elevated concentrations of arsenic, this source will make an increasingly significant contribution to the total intake of inorganic arsenic as the concentration of arsenic in drinking-water increases. Since the estimated daily intake of arsenic from food in preliminary studies of diets in North America is 12–14 µg of inorganic arsenic (Yost et al., 1998), consumption of 2 litres of drinking-water containing 10 µg/litre would make drinking-water the dominant source of intake. In circumstances where soups or similar dishes are a staple part of the diet, the drinking-water contribution through preparation of food will be even greater. The estimated intake from air is generally less than 1 µg.