PARENT SESSION
PT5 - Fate & Effects of Metals: Aquatic Biology
Tuesday, 19 November 2002
8:00 AM to 6:30 PM
Exhibit Hall
(P630) Deriving meaningful effects concentrations from algal bioassays with time-varying contaminant concentrations.
Simpson, Stuart1, Roland, Marie2, Stauber, Jennifer1, Batley, Graeme*,1, Fox, David3, 1 Centre for Advanced Analytical Chemistry, CSIRO, Bangor, NSW, Australia2 Chalmers University of Technology, Gothenburg, Sweden3 CSIRO Land and Water, Floreat Park, WA, Australia
ABSTRACT- The ecotoxicological significance of laboratory bioassays is dictated by how well they reproduce conditions in the field with respect to organism sensitivity and contaminant exposure. In the field, contaminant exposure is rarely constant with time, however this is a requirement of standard toxicity testing procedures. The analysis of toxicity test data assumes that constant exposure occurs, yet in bioassays, this assumption is rarely satisfied as the processes of adsorption to container walls and uptake by test organisms result in significant losses of contaminants from test solutions. For metals such as copper and cadmium, losses are commonly 10-40% during a standard 72-h algal bioassay procedure, whereas for organic compounds (e.g. PAHs), losses can be up to 100%. This decline in contaminant concentration during testing results in an underestimation of toxicity (i.e. higher EC50 and NOEC values). In this study, a laboratory algal bioassay procedure was designed that maintained constant copper concentrations, and the results were compared with those from a standard algal bioassay procedure. A model was developed to calculate the effect that declining concentrations should have on test outcomes for a range of scenarios. The model permits estimation of constant exposure ICx values from test data with a range of time-varying contaminant concentrations. In our experiments, the IC50 for copper toxicity to the test algae copper toxicity was overestimated by as much as a factor of 2. The degree to which toxicity is underestimated (IC50 overestimated) will be significantly greater with increasing concentration decline. Where several toxicants having different rates of decline are being tested, their relative toxicities can only be compared using the constant-exposure ICx values. Extensions of this model will have ultimate value in using laboratory data to predict toxicity in field situations where there is natural concentration change, and the pattern of change is known.
Key words: algal bioassays, metal toxicity, declining toxicant concentrations