in some parts of the netherlands , bog ore - containing soils predominate , which have natural arsenic levels that exceed , by a factor of 10 , existing standards for maximum allowable levels of inorganic arsenic in soil . 
 these standards are based on the assumption that in humans the bioavailability of arsenic from ingested soil is equal to that from an aqueous solution . in view of the regulatory problem that the arsenic levels of these soils present , we questioned the validity of this assumption . to obtain a more realistic estimate , 
 the bioavailability of inorganic arsenic from soil in a suitable animal model was studied . in this 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 120-hr period after administration urine 
 was collected in 24-hr fractions . 
 levels of arsenic were determined using a method of wet digestion , isolation and complexation of arsine , followed by molecule absorption spectrometry . within 120 hr after intravenous administration , 88 + /- 
 16% of the dose was excreted renally . 
 after oral administration of arsenic - containing soil , only 7.0 + /- 
 1.5% was excreted renally . from the urinary excretion data for these two routes of administration , the calculated bioavailability of inorganic 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.imagesfigure 1.figure 2 .