Toxicokinetics and Biotransformation of As(III) and As(V) in Eisenia fetida

Earthworms, Eisenia fetida, were exposed to soils spiked with As(III) and As(V), to understand the response of earthworms to As in terms of both toxicity and accumulation using toxicokinetics, and to explain As metabolism and bioavailability. As(III) showed higher toxicity than As(V), in all toxicity endpoints of burrowing time, survival, growth, and cocoon production. Bioconcentration occurred at both As(III) and As(V) treatments during 28-d exposure. Worms did not show the elimination of As for consecutive 28 d of exposure to clean soils. Biotransformation of As was characterized using HPLC-ICP-MS and XANES, showing the reduction of As in worms regardless of the As species to which worms were exposed. Metabolism of As in worms that formed As-thiol complex is thought to limit the excretion of As, and thus induce bioconcentration in worms. Uptake rates by one-compartment model indicated that pore water was the bioaccessible pool of As, and directly controlled the uptake of As by worms. The study suggests that higher uptake rate and bioaccumulation of As(III) than of As(V) are among the factors that make As(III) more toxic than As(V).