COMPARATIVE ACUTE TOXICITY AND BIOCONCENTRATION OF SELENIUM BY THE MIDGE CHIRONOMUS-DECORUS EXPOSED TO SELENATE, SELENITE, AND SELENO-DL-METHIONINE

The increased flux of selenium into aquatic ecosystems due to anthropo genic activities has resulted in the degradation of several systems. I nitial experiments examined the comparative acute toxicity of waterbor ne selenate, selenite, and seleno-DL-methionine to fourth instar Chiro nomus decorus larvae resulting in 48-h LC50 concentrations of 23.7, 48 .2, and 194 mg Se/L, respectively. The relative toxicities of the sele nium 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 a nd subsequent plateauing with maximum concentrations attained by 16 h. The final whole body selenium levels were approximately 63 mg Se/kg f or selenate and 85 mg Se/kg for selenite. Comparative bioconcentration experiments demonstrated that after 48 h selenium accumulation was gr eater in larval C. decorus exposed to 25 mg Se/L as seleno-DL-methioni ne than in those exposed to 25 mg Se/L as selenate and selenite.