A Study of the Waterborne and Dietary Toxicityof Cadmium to \u3cem\u3eHydra attenuata\u3c/em\u3e and \u3cem\u3eDaphnia plux\u3c/em\u3e in Soft Waters and the Development of Biotic Ligand Models to predict such toxicity

The goal of this thesis was to compare the effects of waterborne Cd exposures and dietary Cd exposures to Hydra attenuata. Before the Hydra could be exposed to dietborne exposures of Cd, the effects of waterborne exposures had to be understood. This was done by looking at the sensitivity of D. pulex to Cd and then understanding the accumulation of Cd. After bioaccumulation patterns of Cd. to D. pulex were known, we could then feed the prey to the Hydra and comapre the effects to waterborne effects of Cd to Hydra. To understand the waterborne effects of Cd to D. pulex 48 h toxicity tests were done using a lethal endpoint. It was found that Cd toxicity was most strongly affected by Ca2+ followed by Mg2+ activity. D. pulex in soft waters were more sensitive to the effects of Ca and Mg relative to C. dubia in hard waters. Na+, K+, H+, and Cl- did not have any significant effects on Cd toxicity, however both sources were able to complex Cd, rendering Cd un-bioavailable to D. pulex. The waterborne effects of Cd to H. attenuata were similar to what was seen in waterborne exposures of Cd to D. pulex. From this study, Ca proved to have a protective effect on Cd toxicity, while the other ions manipulated in toxicity tests (Mg, Na, K, Cl) did not. DOC also did not show any signs of decreasing Cd toxicity in the concentrations tested. When Cd toxicity was assessed by lethality, LC50s varied from 0.39-1.53μM, and when Cd toxicity was assessed using the sub-lethal end point of clubbed tentacles, the EC50s ranged from 0.18-0.79μM. The latter concentrations may not be associated with immediate death, however the impairment of feeding capabilities would ultimately affect of the population of H. attenuata. From the above tests of waterborne Cd toxicity to D. pulex and H. attenuata it was found that Hydra are more sensitive and thus Daphnia can be used as a vector for dietborne exposures. To quantify the effects of dietary CD to H. attenuata we chose an exposure concentration of Cd with a known toxicological effect: the EC50, which is marked by the presence of clubbed tentacles. In hardness’ of 40 and 140 mg CaC03/l the EC50 for Hydra has been determined to be approximately 35 and 90 μg/l, respectively. The percentage of surviving Hydra after being exposed to dietborne exposures will allow for a comparison to waterborne effects and determine which pathway is more sensitive. Waterborne and dietary exposures can also be combined into a co-exposure that will mimic the exposures in a natural setting where the food is exposed to the same concentration and the Hydra. After determining that Hydra are more sensitive to Cd than Daphnia, we were able to use Daphnia as the dietborne exposure vector. When we compared the waterborne and dietborne exposures of Cd to Hydra, it was clear that when the exposure concentrations of the Hydra and the prey were consistent the dietborne effects were not significantly affecting teh Hydra relative to the waterborne exposures