|
(70-24) Chronic toxicity of uranium to aquatic invertebrates. Liber, Karsten*,1, Muscatello, Jorgelina1, George, Tara1, 1 Toxicology Centre, Saskatoon, SK, Canada ABSTRACT- The northern part of the Canadian province of Saskatchewan is home to some of the top- producing uranium mines in the world. The higher uranium concentrations found in water and sediment in downstream areas indicate that these are important areas of potential impact of uranium released from mines and mills to the aquatic environment. However, limited data are available on the chronic effects of uranium exposure on aquatic invertebrates. Data from chronic/life-cycle toxicity studies are therefore needed to help develop sound guidelines for acceptable uranium levels in Canadian waters. This work evaluated the effect of uranium over the full life cycle of the midge, Chironomus tentans, and the effect of water hardness on chronic uranium toxicity to the daphnid, Ceriodaphnia dubia. For C. tentans, there was a significant decrease in larval growth at uranium concentrations >157 ug/L. Larval growth retardations correlated with emergence reductions and significant delays in time to adult emergence. Reductions of 35-40% in larval growth corresponded to decreases of 40-60% in adult emergence, indicating that reductions in adult C. tentans emergence under laboratory conditions can be predicted from 10-d growth retardation data. Uranium that accumulated in C. tentanslarval stages was partially excreted during metamorphosis to the adult stage. Mass balance calculations showed that uranium in exuvia represented 40-60% of the uranium measured in the pupae, suggesting that a detoxification/elimination mechanism may be occurring. Separate experiments with C. dubia showed that reproductive performance was affected at uranium concentrations as low as 45 ug/L and that uranium toxicity decreased significantly with increasing water hardness and alkalinity; there was an approximately 10-fold decrease in uranium toxicity with doubling in water hardness. Key words: Uranium, Chronic toxicity, Chironomus tentans, Ceriodaphnia dubia |
