Effects of aqueous, dietary and combined exposures of cadmium to Ceriodaphnia dubia.

While effects of water-borne metal exposures on freshwater animals have been well documented, the effect of dietary metal exposure is less understood but is gaining importance. However, little attention has been given to the importance of combining both exposure pathways. In this study, we compared effects of aqueous ('water only'), dietary ('food only') and combined ('water+food') exposures of cadmium to the freshwater cladocerans, Ceriodaphnia dubia. Major test endpoints included survival, feeding rate and reproduction. The C. dubia three-brood reproduction tests were conducted according to the United States Environmental Protection Agency (U.S. EPA) methods. Three exposure scenarios were used: aqueous, dietary, and combined aqueous and dietary exposures. Results showed that all three exposures affected survival, feeding rate and reproduction of C. dubia. Interestingly, combined exposure showed contribution effects of aqueous and dietary exposures. Lower cadmium concentrations were needed in combined exposure to produce effects as compared to higher concentrations in aqueous or dietary exposure alone. These results demonstrated the potential importance of dietary and combined exposures for consideration of cadmium regulation and risk assessment of metals.