Survival and Reproductive Effects in the Aquatic Invertebrate Ceriodaphnia dubia Exposed to Uranium Spiked Site Water Collected from Two Creeks in the Yukon, Canada.

Abstract

This study evaluates aqueous uranium (U) toxicity in Ceriodaphnia dubia exposed to surface water collected from two creeks located in U-rich areas of Yukon, Canada. Water for toxicity testing was collected at two times of the year to represent water quality characteristics generally observed during open-water (high flows) and winter baseflow water (low flows) seasons. Collected water was transferred to the toxicological laboratory and spiked with U to achieve nominal concentrations of 50, 150, 350, 500, 650, 800, and 1000µgU/L. Toxicity endpoints included lethal concentrations (LC50) for survival, in addition to no observed effect concentration (NOEC) and lowest observed effect concentration (LOEC) for reproduction. All derived toxicity endpoints were significantly higher than applicable Canadian water-quality guidelines for U (15μg/L [Chronic] and 33μg/L [Acute]). No effects on C. dubia survival were observed at LC50 concentrations > 799μgU/L. Derived NOEC (381μgU/L) and LOEC (524μgU/L) values also were significantly above chronic water quality guidelines. The differences noted in the toxicity response between seasons were mainly due to the presence of toxicity ameliorating factors for U (i.e., dissolved organic carbon). These results highlight the high conservatism in applicable water-quality guidelines and the crucial need to consider site-specific water characteristics when deriving environmentally relevant, yet protective thresholds for uranium in aquatic environments.