SEDIMENT TOXICITY AND HEAVY-METALS IN 11 LIME REFERENCE LAKES OF SWEDEN

Sediments from an eutrophic reference lake (L. Hjalmaren) and eleven oligotrophic Swedish lakes were analyzed for heavy metals (Cd, Cr, Cu, Hg. Ni, Pb, and Zn) and tested for whole sediment toxicity to Daphnia magna. Whole sediment toxicity, expressed as 48-hr EC50 on a wet weight basis in reconstituted dilution water, ranged from 2.8% (most toxic) to > 32% (least toxic). Correlations between bulk sediment heavy metal concentrations and toxicity were significant (P less-than-or-equal-to 0.05) for Hg, Pb, and Zn. However, a causal connection between the concentrations of these metals and toxicity was not supported by the results from metal-spiked sediment toxicity tests. In addition sediment toxicity was not affected by the addition of EDTA, which is a strong chelator known to reduce metal toxicity. After storage for several months test sediments either remained nontoxic, toxic, or increased in toxicity. These results illustrate some of the difficulties in the interpretation of bulk sediment chemistry data and the release of toxic chemicals from sediment samples, highlighting the effect of sediment storage on toxicity.