Toxicity of metals to green algae and Ceriodaphnia dubia: The importance of water column and dietary exposures.

摘要

The main purpose of this study was to determine the relative importance of water and dietary metal exposures to aquatic organisms. The test organisms for this study were Pseudokirchneriella subcapitata (formerly known as Selenastrum capricornutum), Chlorella vulgaris, Scenedesmus acutus, Straurastrum cristatum, and Ceriodaphnia dubia, whereas the metals used were cadmium (Cd), chromium (Cr), copper (Cu), and silver (Ag). This research was divided into three main studies. The first examined the sensitivity of green algae in terms of metal effects and the capability of green algae to bioconcentrate metals from aqueous solution. The second study examined the relative importance of water and dietary exposures on metal uptake by C. dubia. The last study was designed to compare relative importance of water and dietary metal on C. dubia reproduction, survival, and feeding rates. Results of the first study showed that green algae mobilized significant amount of metal from solution. Furthermore, C. vulgaris and P. subcapitata were observed to be more sensitive than S. acutus and S. cristatum to metal toxicity. Results of the second study indicated that metals were accumulated from both water and diet. While the results showed that uptake from water was more rapid than from diet, both uptakes occurred independently and BB were additive from both sources. Furthermore, metal trophic transfer between primary producers (i.e., P. subcapitata ) and primary consumers (i.e., C. dubia) were observed. However, the biomagnification was observed to be minimal. Results of the third study showed that both water and dietary cadmium and copper were toxic to all three endpoints, while dietary silver was less toxic than water column silver to survival. Chromium was the least toxic metal both on water and dietary route of exposures. Reproduction was the most sensitive endpoint observed. In addition, water, dietary, and combination exposure of cadmium were toxic to all three endpoints. These results suggested that the response was independent of exposure types, and the effects in combined exposures were additive. Moreover, these results demonstrated the importance of dietary metal exposure to be included in development of new water quality criteria (WQC) and risk assessment.