Bioavailability and biomethylation of arsenic in contaminated soils and solid wastes

Scope and method of study. The objective of the bioavailability study was to evaluate alternative methods to estimate the bioavailable fraction of arsenic in soils and solid wastes. A method was developed to simulate the human gastrointestinal environment to estimate arsenic absorbed through the soil ingestion pathway (in-vitro, IVG). Chemical speciation methods were also evaluated in their ability to estimate bioavailable arsenic in soils and solid wastes. The IVG and speciation methods were compared with in-vivo arsenic measured by soil feeding trials using the immature swine model. The objective of the bioremediation study was to evaluate the effectiveness of enhanced biomethylation as a method of lowering soil arsenic. Biomethylation experiments were performed under controlled conditions and biomethylated (volatilized) arsenic was measured over a 20 week incubation period.; Findings and conclusions. The IVG method was highly correlated (r2 = 0.69) with the in-vivo results (P < 0.01). The slope of the linear regression line was 0.88, suggesting that the IVG method measures nearly as much arsenic as the in-vivo method. All of the chemical speciation extractant results for arsenic were positively correlated, however the extractants which measure non-occluded surficial arsenic were found to underestimate in-vivo arsenic and the more aggressive extractants which dissolve the oxide fractions overestimated in-vivo arsenic. Biomethylation experiments showed that calcine, under aerobic conditions, demonstrated 5.31 μg of volatilized arsenic. Stabilizing the lead in the calcine resulted in an increase of >17-fold in the amount of arsenic volatilized.