Toxicity of copper to Chlamydomonas reinhardtii (Chlorophyceae) and Ceriodaphnia dubia (Crustacea) in relation to changes in water chemistry of a freshwater pond

Chlamydomonas reinhardtii and Ceriodaphnia dubia were used to evaluate effects of seasonal changes in the water chemistry (DOC, alkalinity, hardness) of a freshwater pond on the toxicity of copper. Chlamydomonas was much more sensitive to copper than was Ceriodaphia. The only correlation between copper toxicity and water chemistry was a positive correlation between DOC concentrations and algal density after a 72-h exposure to copper. Because freshwater DOC changes qualitatively as well as quantitatively over time, it is postulated that these qualitative changes result in unpredictable differences in copper-binding affinity of the DOC which makes it impossible to use DOC concentrations to predict environmentally safe concentrations of copper.