MP13 Aquatic Ecotoxicology
Monday, 14 November 2005: 8:00 AM - 6:30 PM in Exhibit Hall

(LAS-1117-132326) Effects of hardness and alkalinity in culture and test waters on reproduction of Ceriodaphnia dubia.

Lasier, P¹, Winger, P¹, Hardin, I², ¹ US Geological Survey, Athens, Georgia, USA² The University of Georgia, Athens, Georgia, USA

ABSTRACT- Ceriodaphnia dubia is a freshwater organism often used for testing the chronic toxicity of municipal and industrial effluents. Standard procedures for testing whole effluent toxicity (WET) call for their culture in moderately-hard water, but many effluents and receiving waters in the southeastern United States are low in hardness concentrations. This study examined the effects of water hardness and alkalinity in culture waters and test waters on the responses of C. dubia to toxic levels of chloride, sulfate and bicarbonate. Animals were cultured for a minimum of eleven months prior to testing in one of four different laboratory-water formulations that provided waters with the following hardness and alkalinity concentrations (mg/L as CaCO3): 40/40, 40/100, 100,70 and 100/100. Two chronically toxic concentrations of each anion were evaluated with animals from each culture in each of the four test waters. Three replicate tests were conducted for each solution using the standard 7-day, 3-brood C. dubia reproduction test often mandated for permit compliance for the discharge of effluents. When C. dubia cultured in moderately-hard water were exposed to test waters with low hardness, their reproduction was significantly reduced. Animals cultured in low-hardness waters exhibited no reduction when exposed to waters with moderate hardness. The hardness of the water in which C. dubia was cultured did not significantly affect their sensitivity to the three anions. However, increased hardness in the test waters significantly ameliorated the toxicities of chloride and sulfate, but not the toxicity of bicarbonate. Differences in alkalinity among the formulated base waters had no observable effect on reproduction. The physiological stress associated with a sudden decrease in solution hardness may contribute to marginal failures of otherwise non-toxic soft-water effluents. The standard WET protocol should be broadened to allow the culture of C. dubia under site-specific criteria such as hardness that are characteristic of receiving waters.

Key words: Ceriodaphnia dubia, water hardness, anion toxicity, culture