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(12-02) Joint effects of cadmium and temperature on Daphnia magna related to accumulation rates. Heugens, E.H.W.*,1,2, Creyghton, R.1, Hendriks, J.2, Kraak, M.H.S.1, Admiraal, W.1, 1 University of Amsterdam, Amsterdam, The Netherlands2 Institute for Inland Water Management and Waste Water Treatment, RIZA, Lelystad, The Netherlands ABSTRACT- Most aquatic organisms are ectotherms, which makes temperature an important environmental factor controlling physiological processes. Standard toxicity tests are regularly performed at one constant, optimal temperature (usually 20°C), while in the field variable and suboptimal temperatures may occur. Knowledge of the interactions between chemicals and temperature is useful for the extrapolation of toxicity data obtained in the laboratory to natural ecosystems and for the development of site-specific quality criteria for toxicants. The influence of temperature on acute metal toxicity was studied by exposing Daphnia magna to cadmium at temperatures ranging from 10 to 35°C. The effect of a temperature rise combined with cadmium exposure caused more severe effects than could be expected from the effects of the separate factors. However, above 26°C, temperature did not further enhance toxicity, while survival in the control group decreased drastically. Cadmium accumulation rates at 10, 20 en 26°C indicated that the thermal effects on cadmium toxicity were caused by an increased cadmium accumulation at higher temperatures and that temperatures within this range mainly accelerated toxicokinetics. Temperatures above this range caused such a severe stress that additional cadmium effects were masked. The outcomes of both experiments were combined to calculate infinite LC50 values, that appeared to be temperature dependent. This reveals that beside accelerating cadmium uptake, temperature influenced the sensitivity of the daphnids to the metal. It is concluded that the outcomes of standard toxicity tests performed at 20°C may not be representative for field situations. Therefore, a way to correct for this discrepancy is presented, that may improve the extrapolation of results of these tests to natural ecosystems. Key words: multiple stressors, cadmium, temperature, accumulation |
