Relationships between surface-bound and internalized copper and cadmium and toxicity in Chlamydomonas reinhardtii

In the present study, the adsorption and uptake of copper (Cu) and cadmium (Cd) in Chlamydomonas reinhardtii were examined to establish fundamental toxicity relationships to glutathione and cell-growth endpoints. Establishing these fundamental relationships of metal accumulation and toxicity metrics is necessary to subsequently implement an algal biotic ligand model. The glutathione response was similar to the response measured from growth endpoints for both internal and adsorbed Cu, indicating that glutathione may be a useful biomarker of toxicity. The glutathione response with Cd contrasted markedly with that observed with Cu and was therefore observed to be a metal-specific biomarker. The density of sites binding metals and the related stability constants for the algal cell surface were also determined. Short exposures to metals (2 h) were conducted, and we determined 6.0 × 10(-6) mol/g sites binding Cu and 2.0 × 10(-6) mol/g sites binding Cd and conditional stability constants as log K' = 7.2 and log K' = 6.7 for Cu and Cd, respectively. Experiments were also conducted to determine the effect on toxicity endpoints of varying nitrate concentrations and different humic acids (HA) in the exposure media. Varying nitrate concentrations did not have an effect on cell growth over 24 h. The surface-adsorbed Cu measurements from the experiments with HA depended on the type and concentration of HA.