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

摘要

Daphnia magna was exposed to waterborne uranium (U) at concentrations ranging from 10 to 75I14gLa degree 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 54ngUdaphnida degree 1 were measured in the different exposure conditions and converted to corresponding internal alpha dose rates. Low values of 5, 12 and 20I14Gyha degree 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 10I14gLa degree 1 and a capacity to recover partially in a clean medium after parental exposure to a[control]陇25I14gLa degree 1. Using a 14C-labelled food technique, the study showed that uranium affected carbon assimilation in F0 at concentrations of 25 and 75I14gLa degree 1 (34 and 80% reduction respectively) and as low as 10I14gLa degree 1 in F1 and F2 (40 and 36% reduction respectively). Consequences were strong for both somatic growth and reproduction and increased in severity across generations. Maximum size was reduced by 12% at 75I14gLa degree 1 in F0 and 23% at 25I14gLa degree 1 in F2. Reduction in 21-day fecundity ranged from 27 to 48% respectively at 25 and 75I14gLa degree 1 in F0 and from 43 to 71% respectively at 10 and 25I14gLa degree 1 in F2. Growth retardation caused a delay in deposition of first brood of 1.3 days at 75I14gLa degree 1 in F0, of 1.9 days at 25I14gLa degree 1 in F1 and of 5 days at 25I14gLa degree 1 in F2. Differences in respiration rates and egg dry mass between the control and exposed daphnids were mainly an indirect result of uranium effect on body size. The observed increase in toxic effects across generations indicated the necessity of carrying out multigeneration tests to assess environmental risk of uranium in daphnids.