Speciation of arsenic in Dutch total diets: methodology and results

In the last decade 311 duplicate portions of the 24-h diet of Dutch citizens were collected and lyophilized. All samples were assayed for total arsenic and, in addition, the 20 samples which ranked highest in total arsenic were selected for arsenic speciation i.e., the separate determination of organic-bound arsenic and inorganic arsenic. For the determination of total arsenic, the test portion is wet-digested and the digest reduced with KI/SnCl2/Zn to give AsH3 which is measured by molecular absorption spectrometry. Inorganic arsenic is also measured as AsH3 after acid extraction of the test portion and subsequent NaBH4 reduction of the extract. The residue of the acid extraction and the NaBH4-reduced extract are combined, wet-digested and the digest reduced with NaBH4 to give AsH3 originating from organic-bound arsenic. Samples spiked at different levels with inorganic and organic-bound arsenic were analysed and gave recoveries for inorganic arsenic of 94% to 122% (n = 6) and for organic-bound arsenic of 87% to 104% (n = 6). On average, the inorganic fraction is 30% of the total arsenic intake; range 3% to 50% (n = 14). The inorganic arsenic fraction decreases with increasing level of total arsenic intake. The highest oral inorganic arsenic intake was 60 micrograms; the tolerable daily intake (TDI) for a 60-kg individual is 120 micrograms inorganic arsenic. Organic and inorganic arsenic measured were summed and compared with the results of the total arsenic determination; differences were less than 15%. (Since inorganic arsenic is a contaminant and not an additive, the abbreviation TDI is preferred here over ADI (acceptable daily intake) which is retained for additives.)