Abstract: The present study assessed the effects of preexposure to Se on the accumulation and toxicity of copper (Cu) in Lumbriculus variegatus. Furthermore, the effects of exposure routes and the Se species were also evaluated. L. variegatus were preexposed to environmentally relevant concentration of Se in sediment (dietary at 20 μg·g^-1 dry wt) or in solution (dissolved at 15 μg·L^-1) for 2 weeks. The Se species included selenite (Se(Ⅳ)), selenate (Se(Ⅵ)) and selenoLmethionine (Se-L-Met). The Se preexposed L. variegatus were subsequently exposed to 15 μg·L^-1 of Cu for 7 days. The accumulation of Cu and the levels of thiobarbituric acid reactive substances (TBARS) were determined. The results showed that mortality did not occur in all the treatments except for the Se-L-Met sediment treatment during the 2 week exposures. Preexposure to all the three forms of Se from both the dietary and dissolved routes significantly decreased the accumulation of Cu in the worms except for preexposure to dissolved Se(Ⅵ). The Se preexposed worms had significantly lower levels of TBARS than the control worms. The protective potential of pre-exposure to Se against Cu toxicity was in the order as Se(Ⅵ) > Se(Ⅳ) ≈ Se-L-Met in the dissolved exposure, while in the dietary exposure, the protective potential of the three species was comparable. The results suggested that preexposure to Se at environmentally realistic concentrations can offer protection against Cu toxicity in L. variegatus. Future research on the interaction of Se and Cu is warranted to better understand the mechanisms underlying this protection in the worm in particular and possibly in other aquatic organisms in general.

Key words: Hulun Buir Grassland, slow-released urea, enzyme activity, microbial biomass C