Dependency of copper toxicity to polychaete larvae on algal concentration

Algae are often used as food in aquatic metal toxicity tests to maintain the well-being of test animals. Such food addition may change metal bioavailability because of the reduction of aqueous metal concentration and the increase in particle-bound metal concentration. While the importance of aqueous exposure pathway is widely recognized, few studies have determined the contribution of the dietary pathway to the overall metal toxicity to aquatic invertebrates. In this study, we determined the toxicity of both algal-bound copper alone and copper solution containing algae to the larvae of marine polychaete Hydroides elegans. Algae that had been pre-exposed to copper at up to 1024 μg l−1, when fed to the larvae, did not cause significant abnormal larval development. However, when larvae were exposed to algal-copper mixture, percentage of normal larvae could be modeled as a logistic function of aqueous copper concentration, with a 48-h EC50 (mean ± S.E.) of 64.9 ± 4.8 μg Cu l−1. When the toxicity was expressed using total copper concentration, the EC50 ranged from 58.4 ± 4.5 μg l−1 in the control to 121.9 ± 9.9 μg l−1 in the 106 cells ml−1 algal treatment. This study highlights the dependency of copper toxicity on the aqueous exposure pathway in this polychaete and the importance of considering algal binding of the metal in larval toxicological tests.