The contribution of arsenic in food to total human arsenic intake has not been extensively studied, but there is evidence that water is not the sole source of this toxic element. Fish and shellfish are a recognized source of total arsenic, and while these sources may be particularly high in organoarsenicals, this represents the least toxic form of arsenic. The contribution of food crops to total arsenic intake, particularly the more toxic inorganic forms, is poorly understood.
Dietary selenium status has been shown to influence arsenic excretion in animal models. Gregus et al. (1998) noted that selenium facilitates the excretion of inorganic arsenic metabolites in rats. Selenium supplementation (organic forms of selenium) has been shown to be helpful against poisoning from arsenic and other toxic elements in mice (Andersen and Nielsen, 1994). Similar results have been noted among humans. Recently, Hsueh et al. (2003) found that, in a Taiwanese population exposed to inorganic arsenic via drinking water, urinary arsenic levels significantly increased as urinary selenium levels increased. These observations were recently confirmed in another independent study conducted in Chile from a population exposed to moderate levels of arsenic in their drinking water (~40 µg L−1) (Christian et al., 2006). The results from these studies suggest that, in populations exposed to arsenic, dietary selenium intake may be correlated with urinary arsenic excretion and may alter arsenic methylation.
Arsenic from Coal in China
Domestic coal combustion has had profound adverse effects on the health of millions of people worldwide. In China alone, several hundred million people commonly burn raw coal in unvented stoves, a process that permeates their homes with high levels of toxic metals and organic compounds. At least 3,000 people in Guizhou Province in southwest China, where coal samples contain up to 35,000 ppm arsenic, suffer from severe arsenic poisoning. Although fresh chili peppers contain less than 1 ppm arsenic, Zheng et al. (1996) showed that chili peppers dried over open coal-burning stoves have on average more than 500 ppm arsenic and therefore may be the principal vector for the arsenic poisoning (Figure 5.1). Significant amounts of arsenic may also come from other tainted foods, from dust ingestion (samples of kitchen dust contained as much as 3,000 ppm arsenic), and from inhalation of indoor arsenic-polluted air. In this area, the arsenic content of drinking water samples was below the Environmental Protection Agency’s drinking water standard of 10 ppb and does not appear to be an important factor.
Data describing the concentrations and distributions of potentially toxic elements in coal may assist people dependent on local coal sources to