Whole-body accumulation of copper predicts acute toxicity to an aquatic oligochaete (Lumbriculus variegatus) as pH and calcium are varied.
We tested the hypothesis that whole-body accumulation of Cu at 50% mortality (i.e. the median lethal accumulation, LA50 value) in a freshwater oligochaete (Lumbriculus variegatus) is constant across a wide range of water quality, whereas the LC50 values of Cu(total) and the cupric ion (Cu(2+)) in solution are not. We exposed the worms in intermittent-flow, water-only chambers to a series of Cu concentrations at a variety of combinations of pH and water hardness (pH 6.5, 7.5 and 8.5 crossed with hardnesses of 0.5, 2, 4, 6 and 15 mEql(-1)) at 17-20 degrees C. In addition to monitoring mortality at 48 h, we determined whole-body Cu uptake in half of the replicate chambers at 6 h. LC50 values of Cu(total) and Cu(2+) increased as water hardness increased, as expected from traditional LC50 vs. hardness regressions. Moreover, LC50 values of Cu(total) remained approximately constant and LC50 values of Cu(2+) decreased considerably as pH increased, as expected from principles of cation competition and binding by inorganic ligands. However, LA50 values of Cu(body) remained approximately constant (0.17-0.34 micromol Cug(-1) dry wt.) in all pH x hardness combinations. Thus, consistent with the biotic-ligand model, Cu accumulation might be a constant predictor of acute mortality to L. variegatus whereas aqueous Cu concentrations are not.
D000818:Animals; D002118:Calcium / Q000378:metabolism*; D003300:Copper / Q000378:metabolism* / Q000633:toxicity; D005544:Forecasting; D005618:Fresh Water / Q000032:analysis*; D006863:Hydrogen-Ion Concentration; D009835:Oligochaeta / Q000187:drug effects / Q000378:metabolism*; D023382:Toxicity Tests, Acute / Q000379:methods*
D003300:Copper; D002118:Calcium