Differences in the bioaccumulation of selenium by two earthworm species (Pheretima guillemi and Eisenia fetida).

Information on the bioaccumulation of selenium (Se) in soil invertebrates (e.g. earthworms) is rather scarce. In the present study, bioaccumulation of Se in two eco-physiologically different earthworms, namely anecic Pheretima guillemi and epigeic Eisenia fetida, was determined after 28 days exposure to a successive doses of Se-spiked soil, specifically 0.5, 5, 50, and 200 μg Se g-1 soil. The results showed that Se concentration in earthworms elevated with increasing exposure levels, and maximums were up to 54.6 and 83.0 μg g-1 dry weight in Pheretima guillemi and Eisenia fetida, respectively, after 4 weeks exposure to 200 μg Se g-1 soil. Exposure to Se caused significant inhibition on earthworm growth, with the fresh weight loss ranging from 8.9% to 80.5%. Bioaccumulation factors (BAFs), empirically-derived and non-steady state, ranged from 0.12 to 4.17 and generally declined at higher exposure levels. Moreover, BAFs of Pheretima guillemi were higher than those of Eisenia fetida in low-dose Se-spiked soils, but the opposite was true in high-dose soils, indicating there is a species-specific response to exposure of Se between different earthworms. Further research is thus needed to reveal the accumulation pattern of Se in a wider range of earthworm species other than Eisenia fetida, which allows a better risk assessment of excessive Se to soil invertebrates and higher order organisms.