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on the form of arsenic absorbed. As mentioned in Chapter 3, some foods, especially those of marine origin, often have high concentrations of arsenic mainly in the form arsenobetaine, which is not metabolized in the body but is rapidly excreted in the urine (Vahter et al. 1984; Vahter 1994). Thus, ingestion of such foods results in a rapid increase in the concentration of total arsenic in the urine; that increase would invalidate urinary arsenic as an indicator of exposure to inorganic arsenic. One serving of seafood might give rise to urinary arsenic concentrations of more than 1,000 µg/L (Norin and Vahter 1981). In comparison, concentrations of 5-50 µg/L are found in the urine of subjects with no intake of seafood arsenic or excessive exposure to inorganic arsenic in drinking water or in the working environment. Certain other foods (e.g., chicken) also might contain arsenobetaine if fish meal is used as a source of protein in the feed.
A better measurement of the intake of inorganic arsenic can be obtained from the concentration of inorganic arsenic and its metabolites monomethylarsonic acid (MMA) and dimethylarsinic acid (DMA) in the urine (see Chapters 3 and 5). Exposure to MMA, DMA, or both will influence the estimate, but other than occupational exposure to pesticides containing DMA, such exposure seems to be very low in most countries. However, certain types of seafood, especially seaweed and some shellfish, might contain DMA (Mohri et al. 1990; Arbouine and Wilson 1992; Yamauchi et al. 1992) or arsenosugars, which are partly metabolized in the body to DMA (Le et al. 1994; Ma and Le 1998). Thus, consumption of such foods might result in increased urinary concentrations of DMA, and those increases might be interpreted as exposure to inorganic arsenic. In fact, consumption of seafood has been shown to cause a slight increase in the concentration of metabolites of inorganic arsenic in the urine (Norin and Vahter 1981; Vahter and Lind 1986; Arbouine and Wilson 1992; Mürer et al. 1992; Larsen et al. 1993; Buchet et al. 1994). Therefore, the intake of seafood, especially seaweed, should be investigated when urinary metabolites of arsenic are to be used for evaluation of exposure to inorganic arsenic. If such food is common, people should be asked to refrain from eating seafood a couple of days before urine sampling.
Reported data on average background concentrations of metabolites of inorganic arsenic (inorganic arsenic + MMA + DMA) in the urine are generally below 10 µg/L in European countries (Apel and Stoeppler 1983; Valkonen et al. 1983; Foà et al. 1984; Vahter and Lind 1986; Andrén et al. 1988; Jensen et al. 1991; Buchet et al. 1996; Trepka et al. 1996; Kristiansen et al. 1997; Kavanagh et al. 1998), somewhat higher in some parts of the United States (Smith et al. 1977; Morse et al. 1979; Binder et al. 1987), and around 50 µg/L in Japan (Yamauchi and Yamamura 1979; Yamauchi et al.