Comparative acute toxicity and bioconcentration of selenium by the midge Chironomus decorus exposed to selenate, selenite, and seleno-DL-methionine

Abstract

The increased flux of selenium into aquatic ecosystems due to anthropogenic activities has resulted in the degradation of several systems. Initial experiments examined the comparative acute toxicity of waterborne selenate, selenite, and seleno-DL-methionine to fourth instar Chironomus decorus larvae resulting in 48-h LC₅₀ concentrations of 23.7, 48.2, and 194 mg Se/L, respectively. The relative toxicities of the selenium forms are reversed compared to previous studies on other species and demonstrate that relative waterborne selenium toxicity is species specific. Studies examining the kinetics of selenate and selenite (the dominant waterborne forms) accumulation by C. decorus larvae exposed to the 48-h LC₅₀ selenium concentrations showed initial rapid uptake and subsequent plateauing with maximum concentrations attained by 16 h. The final whole body selenium levels were approximately 63 mg Se/kg for selenate and 85 mg Se/kg for selenite. Comparative bioconcentration experiments demonstrated that after 48 h selenium accumulation was greater in larval C. decorus exposed to 25 mg Se/L as seleno-DL-methionine than in those exposed to 25 mg Se/L as selenate and selenite.