TP11 Metals in the Environment: Aquatic Biological Perspectives
Tuesday, 15 November 2005: 8:00 AM - 6:30 PM in Exhibit Hall
(GIL-1117-858941) Comparing the effect of varying water chemistry on the acute toxicity of cadmium to Chironomus riparius.
Gillis, P1, Wood, C1, 1 Department of Biology, McMaster University, Hamilton, ON, Canada
ABSTRACT- The Biotic Ligand Model (BLM) is a mechanistically based tool which can be used to predict site-specific metal toxicity based on water chemistry. The majority of data used to develop the BLM were derived from trout, fathead minnow and Daphnia toxicity tests. In an effort to extend the BLM to a wider range of species, we investigated the effect of varying water chemistry on the sensitivity of midge larvae (Chironomus riparius) to waterborne Cd. Standardized toxicity tests with C. riparius use 2nd instar larvae and to sustain the animals during the test, both food and substrate are added. Because organic matter (food) can complex dissolved metals, we chose to avoid feeding during the test and therefore employed 3rd-4th instar larvae, since they were much less susceptible to starvation during the exposure (48 h). Time course uptake experiments using Cd109 demonstrated that larvae accumulate Cd for the duration of the exposure. Initial range-finder Cd exposures were conducted in both moderately-hard water (Ca 1000 
M, Na 600 M, Mg 200 M, pH 7.9, DOC 3 mg/L), and soft water (Ca 50 M, Na 50 M, Mg 20 M, pH 7.2, DOC 0.7 mg/L). The 48 h LC50 in soft water was 260 mg Cd/L versus higher than 400 mg/L in hard water. Tissue Cd concentrations reflected the high level of exposure, reaching 3 mg/g in the soft water exposures. Even in soft water, the larvae were still extremely tolerant to Cd, withstanding concentrations in the millimolar range. At these levels, even extreme changes in water chemistry will result in only minor effects on Cd sensitivity. Therefore, in order to extend the BLM to C. riparius environmentally realistic Cd concentrations need to be investigated. Ongoing studies are addressing the sensitivity of earlier life stages and the potential of using these stages in full BLM-type experiments. Supported by ILZRO, ICA, CDA, NiPERA, Noranda-Falconbridge, Teck Cominco and an NSERC CRD grant.
Key words: Cadmium, Chironomus riparius, Biotic Ligand Model, Acute toxicity