BIOAVAILABILITY OF INORGANIC ARSENIC FROM BOG ORE-CONTAINING SOIL IN THE DOG

In some parts of The Netherlands, bog ore-containing soils predominate , which have natural arsenic levels that exceed, by a factor of 10, ex isting standards for maximum allowable levels of inorganic arsenic in soil. These standards are based on the assumption that in humans the b ioavailability of arsenic from ingested soil is equal to that from an aqueous solution. In view of the regulatry problem that the arsenic le vels of these soils present, we questioned the validity of this assump tion. To obtain a more realistic estimate, the bioavailability of inor ganic arsenic from soil in a suitable animal model was studied. In thi s report, a study performed in six dogs in a two-way cross-over design is presented. The dogs received orally, in random order, arsenic both as an intravenous solution and as arsenic-containing soil. During a 1 20-hr period after administration, urine was collected in 24-hr fracti ons. Levels of arsenic were determined using a method of wet digestion , isolation and complexation of arsine, followed by molecule absorptio n spectrometry. Within 120 hr after intravenous administration, 88 +/- 16% of the dose was excreted renally. After oral administration of ar senic-containing soil, only 7.0 +/- 1.5% was excreted renally. From th e urinary excretion data for these two routes of administration, the c alculated bioavailability of inoganic arsenic from soil was 8.3 +/- 2. 0%. The results from this study demonstrate the need to reconsider the present risk assessment for arsenic in soil.