Selenium Speciation in the Sediments and the Oligochaete Lumbriculus Variegatus

Abstract Sediments are the major sink for selenium (Se) in aquatic environments. Se speciation in sediments is crucial for its bioavailability and the toxicity in benthos but this is relatively understudied. In this study, selenite (Se(IV)) and seleno-L-methionine (Se-Met) were respectively added to sediments for 90 and 7 days, and the accumulation and depuration of Se in the oligochaete Lumbriculus variegatus was investigated. The background levels of Se in the river sediments, fish flakes, and L. variegatus were also detected. Without the presence of worms, the levels of Se(IV) in the sediments were relatively stable within 7 d but showed a decreasing trend during the 90 d of aging. In contrast, Se-Met in the sediments showed a sharp decrease within 3 d of aging. The LC50-96h values of Se(IV) and Se-Met in L. variegatus were 372.6 and 9.4 µg/g. Interestingly, the dominant Se species in Se(IV)- or Se-Met-treated L. variegatus was Se-Met, whose levels were increased with time in 7 days of exposure. Se was barely depurated from L. variegatus during the 8 d of depuration period. This study has provided indispensable data on the levels of total Se in the abiotic and biotic matrices and the biodynamics of Se in a representative benthos, which could better understand the ecological risk of Se to the freshwater benthic communities.