Comparative studies on the uptake and effects of cadmium and zinc on the cellular energy allocation of two freshwater gastropods.

The uptake and effects of cadmium (Cd) and zinc (Zn) as free metal ions were compared in the freshwater gastropods Melanoides tuberculata and Helisoma duryi. The Langmuir isotherm model was applied to determine the uptake of Cd, Zn, and a mixture of the metals at five different concentrations (Cd: 0.25, 0.51, 0.77, 1.03, 1.29 microM; Zn: 0.17, 0.43, 0.86, 2.17, 4.34 microM). The model gave a good description of metal uptake over a short exposure period (6 h). The gastropods showed interspecies differences in the uptake of Zn. The linear uptake of Cd was similar in these species, although the data did not yield a good fit to the model. No clear Cd/Zn interaction was observed with the mixed metal exposures and both species showed a reduced net uptake for the metals. Cellular energy allocation as a biomarker of exposure provided a measure of the net energy budget (total available energy reserves and total energy consumption). The gastropods were exposed to 0.51 microM Cd, 0.43 microM Zn, and mixture of the metals for a 2-week period. Both species elicited similar decreased net energy budgets following the metal exposures. A combined study on metal uptake and biomarker responses in organisms allows the ability to make interspecies sensitivity comparisons in ecotoxicological studies.