Accumulation and chronic toxicity of uranium over different life stages of the aquatic invertebrate Chironomus tentans.

Limited data are available on the effects of uranium (U) exposures on benthic macroinvertebrates, something that would be needed before national or provincial water quality guidelines could be developed. The goal of this study was to evaluate chronic U toxicity and accumulation in the aquatic invertebrate Chironomus tentans. Test organisms were exposed to three aqueous U concentrations (40, 200, and 1,000 microg/L) and an untreated control. Larval growth, adult emergence, and U tissue concentrations at different life stages were evaluated. The measured no-observed-effect concentration (NOEC) and lowest-observed-effect concentration (LOEC) for growth of C. tentans larvae after 10 days of U exposure were 39 and 157 microg/L, respectively. At U concentrations >157 ug/L, there was reduced larval growth of 30% to 40%, which corresponded to reduced adult emergence of 40% to 60%. Despite significant delays in time to adult emergence, there were no significant effects on reproductive output of successfully emerged adults. The F(1) generation C. tentans larvae that were never directly exposed to U, but originated from adult males and females exposed to U during their immature life stages, displayed a significant decrease in 10-day growth that was similar to that observed for the F(0)-exposed larvae. This suggests that the environment of the parental generation can significantly influence the development of the next generation through environmentally induced parental effects. Uranium accumulated in C. tentans immature stages was partially excreted during molting and metamorphosis to the adult stage. However, the elimination of U was not complete and some was still measured in adult midges. Consequently, a minor transfer of U from the aquatic to the terrestrial environment could be expected to occur.