Effects of chronic uranium exposure on life history and physiology of Daphnia magna over three successive generations.

Daphnia magna was exposed to waterborne uranium (U) at concentrations ranging from 10 to 75 microgL(-1) over three successive generations (F0, F1 and F2). Progeny was either exposed to the same concentration as mothers to test whether susceptibility to this radioelement might vary across generations or returned to a clean medium to examine their capacity to recover after parental exposure. Maximum body burdens of 17, 32 and 54 ng U daphnid(-1) were measured in the different exposure conditions and converted to corresponding internal alpha dose rates. Low values of 5, 12 and 20 microGy h(-1) suggested that radiotoxicity was negligible compared to chemotoxicity. An increasing sensitivity to toxicity was shown across exposed generations with significant effects observed on life history traits and physiology as low as 10 microgL(-1) and a capacity to recover partially in a clean medium after parental exposure to