HA10 Environmental Toxicology, Environmental Assessment
D135-136
8:00 AM - 12:00 PM, Thursday
() On the Potential for Using the Free Ion Activity Model to Describe Toxicity within Ephemeral Wetlands.
Boeckman, C1, Bidwell, J1, 1 Oklahoma State University, Stillwater, OK, US
ABSTRACT- Ephemeral wetlands may exhibit fluctuations in physico-chemical parameters such as temperature, dissolved oxygen and suspended solids that may either ameliorate or exacerbate contaminant effects on resident species. The goal of this study was to determine the effects of differing environmental conditions on the response of two wetland species, Daphnia pileata and the calanoid Diaptomus clavipes, to a copper reference toxicant. Organisms were exposed to the metal in 48-h static renewal tests using either reconstituted laboratory water or water from the wetland that had elevated levels of both suspended solids and organic carbon. We used an ion selective probe to measure cupric ion concentrations in both diluents prior to exposure. Based on the Free Ion Activity Model (FIAM), which states the free available ion drives toxicity, we hypothesized that LC50 values based on nominal concentrations would differ between diluents, but those generated using the free ion concentrations would be similar. This hypothesis was not supported for either species. LC50 values based on the free ion for D. pileata were significantly lower when using wetland water as the diluent, indicating a possible synergistic effect of the suspended solids, while increased toxicity occurred in the soft water diluent as compared to the wetland water for D. clavipes. Additional bioassays are underway to determine if these results are indicative of interspecies variation and to further evaluate the applicability of the FIAM under conditions common to ephemeral wetlands.
Key words: ephemeral wetlands, free ion activity model, copper, multiple stressors