PH08 Metals in the Environment: Aquatic Biological Perspectives
Exhibit Hall
8:00 AM - Thursday
(PH105) Influence of water hardness on uranium toxicity to freshwater organisms.
Serben, K1, Eickhoff, C1, Bird, G2, Munger, S2, 1 Vizon SciTec Inc., Vancouver, British Columbia, Canada2 Canadian Nuclear Safety Commission, Ottawa, Ontario, Canada
ABSTRACT- Uranium (U) toxicity was examined at low alkalinity (5-14 mg/L as CaCO3) and various hardnesses (5 to 252 mg/L as CaCO3) for six freshwater species using Environment Canada test methods. Tests included 7-d survival and growth tests with fathead minnows (FHM) (Pimephales promelas), 96-h acute lethality and 30- and 31-d embryo/alevin (EA) tests with rainbow trout (RBT) (Oncorhynchus mykiss), 3-brood survival and reproduction tests with Ceriodaphnia dubia, 14-d water-only survival and growth tests with Hyalella azteca, 72-h growth inhibition tests with Selenastrum capricornutum, and 7-d static growth inhibition tests with Lemna minor. Modifications were made to the recommended reconstituted water recipes in order to achieve low alkalinity and Ca:Mg molar ratios of 1:1 (or 3:1 for H. azteca). In general, H. azteca, C. dubia, and S. capricornutum were the most sensitive species to U with LC/IC50s (based on mortality, reproduction, and growth inhibition, respectively) that ranged between 0.017 and 0.34 mg U/L. RBT alevins were the next most sensitive, with EC50s (based on alevin viability) between 0.46 and 0.64 mg U/L. In the FHM tests, 7-d LC50s were 1.5 to 2.1 mg U/L, whereas the 96-h LC50s were 1.8 to 2.1 mg U/L. These 96-h LC50s were about half of those (3.8 to 4.2 mg U/L) for RBT fry. L. minor was the least sensitive species tested, with IC50s starting at 7.4 mg U/L (frond increase). A decrease in toxicity with an increase in hardness was only observed in the H. azteca, L. minor and RBT EA tests. This was most pronounced for H. azteca where the 14-d LC50 increased from 0.017 mg U/L in soft water to 0.34 mg U/L in hard water, a decrease in toxicity by a factor of 20. Toxicity remained relatively constant with increased hardness for the tests conducted with other species.
Key words: hardness, uranium, alkalinity, freshwater