T3 PM Aquatic Ecotoxicology (Part 2)
Tuesday, 15 November 2005: 1:50 PM - 5:30 PM in Ballroom 3

(SOU-1117-839612) Chloride and hardness influence the acute and chronic toxicity of sodium sulfate to freshwater crustaceans.

Soucek, D¹, ¹ Illinois Natural History Survey, Champaign, Illinois, USA

ABSTRACT- Based on the results of previous research indicating that dilution water plays an important role in the toxic response of Hyalella azteca to sodium sulfate, the purpose of this study was to quantify the influence of both chloride and water hardness on acute and chronic toxicity endpoints for Hyalella and Ceriodaphnia dubia. When chloride concentration was held constant, increasing hardness, tested at six levels ranging from 100 to 600 mg/L (as CaCO₃) at constant Ca:Mg ratios, was related to decreased toxicity of sodium sulfate (increased LC50s) in a linear fashion for both Hyalella (R²= 0.706) and Ceriodaphnia (R²= 0.720). The response of these two organisms was consistent to the degree that similar increases in mean LC50s (in terms of SO₄^2-) were observed when testing at hardness level of 300 mg/L compared to 100 mg/L. For Ceriodaphnia, the mean LC50 increased from 2,050 (hardness = 100 mg/L) to 2,946 mg/L (at hardness = 300), an increase of 896 mg/L, while for Hyalella the mean LC50 increased from 1,854 to 2,841 mg/L (an increase of 987 mg/L) at the same hardness levels. This suggests that hardness has a similar mechanism of toxicity reduction for both organisms, perhaps tightening of epithelial cells by calcium. The response to increasing levels of chloride was not the same for the two crustaceans. In the range of 5 to 33 mg Cl/L, sulfate LC50s for Hyalella were positively correlated (R²= 0.685, p = 0.042) with chloride concentrations. Over the same range of chloride concentrations, sulfate LC50s for Ceriodaphnia were not related to chloride (R²= 0.171, p = 0.486). This suggests, that Hyalella may be more dependent on chloride than Ceriodaphnia for osmoregulation. Sulfate LC50s progressively decreased for both organisms when chloride was increased to 100, 300, and 500 mg/L.

Key words: sodium sulfate, crustaceans, osmoregulation, total dissolved solids