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Physiology of Absorption, Metabolism, and Excretion

The absorption of inorganic arsenic is related to the solubility of the compound ingested (Vahter, 1983). In humans, more than 90 percent of inorganic arsenite and arsenate from water is absorbed (Vahter, 1983), and approximately 60 to 70 percent of dietary arsenic is absorbed (Hopenhayn-Rich et al., 1993). Once absorbed, inorganic arsenic is transported to the liver where it is reduced to arsenite and then methylated. The majority of ingested arsenic is rapidly excreted in the urine. The proportion of the various forms of arsenic in urine can vary; however, the common forms present are inorganic arsenic, monomethylarsonic acid, dimethylarsinic acid, and trimethylated arsenic (Yamato, 1988).

FINDINGS BY LIFE STAGE AND GENDER GROUP

Because of the lack of human data to identify a biological role of arsenic in humans, neither an Estimated Average Requirement, Recommended Dietary Allowance, nor Adequate Intake were established.

INTAKE OF ARSENIC

Food Sources

Dairy products can contribute as much as 31 percent of arsenic in the diet; meat, poultry, fish, grains and cereal products collectively contribute approximately 56 percent (Mahaffey et al., 1975). Based on a national survey conducted in six Canadian cities from 1985 to 1988, it was reported that foods containing the highest concentrations of arsenic were fish (1,662 ng/g), meat and poultry (24.3 ng/g), bakery goods and cereals (24.5 ng/g), and fats and oils (19 ng/g) (Dabeka et al., 1993). The substantial portion of arsenic present in fish is in the organic form. The major contributors of inorganic arsenic are raw rice (74 ng/g), flour (11 ng/g), grape juice (9 ng/ g), and cooked spinach (6 ng/g) (Schoof et al., 1999).

Dietary Intake

Results of the analysis of 265 core foods conducted by the Food and Drug Administration (1991–1997), and analysis of foods and intake data from the U.S. Department of Agriculture Continuing Survey of Food Intakes by Individuals (1994–1996), indicate that



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