The interplay between chemical speciation and physiology determines the bioaccumulation and toxicity of Cu(II) and Cd(II) to Caenorhabditis elegans.

Using the well-documented model organism Caenorhabditis elegans, a combined analysis of metal speciation in the exposure medium and body burdens of metals (Zn, Cu and Cd) was performed, and factors that are predictive of toxicological endpoints in single metal and mixed metal exposures were identified. Cu, and to a lesser extent Cd, is found to associate with Escherichia coli in the exposure medium (the food source for C. elegans) as evidenced by the observed decrease in both their dissolved and free metal ion concentrations. Together with a critical analysis of literature data, our results suggest that free metal ion concentrations and thus aqueous uptake routes are the best predictor of internal concentrations under all conditions considered, and of metal toxicity in single metal exposures. Additional factors are involved in determining the toxicity of metal mixtures. In general, the eventual adverse effects of metals on biota are expected to be a consequence of the interplay between chemical speciation in the exposure medium, timescale of exposure, exposure route as well as the nature and timescale of the biotic handling pathways.