The effect of temperature on environmental risk assessment using species sensitivity distributions
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The toxicity of a chemical depends on environmental factors such as temperature through a change in bioavailability, toxicokinetics and toxicodynamics of the chemical and indirect by a change in the biology of an organism. Although many studies confirm the interaction between temperature and toxicity, the effect is usually not included in toxicological risk assessment. The purpose of the current study is to assess the effect of temperature on species sensitivities towards compounds using the species sensitivity distribution (SSD) approach. Two model compounds have been selected for this study. Toxicity data for a broad range of aquatic species were collected for the heavy metal cadmium (Cd) and the organic biocide pentachlorophenol (PCP). The results were divided per compound into a high- and low temperature group (respectively ≤20°C and >20°C) based on the median test temperature. Per temperature group, geometric mean 96h-LC50 values were calculated for each species. The values were used to construct temperature group-dependent SSDs. A comparison of toxicant sensitivity between the temperature groups was made by means of the 5% and 50% hazardous concentration (HC5 and HC50). This was done twice for each compound, using all available species and only species tested at both high and low temperature. For Cd, the HC5 and HC50 were significantly decreased by a factor 2 in the high temperature group compared to the low temperature group. When the same species were used in the temperature-specific SSDs, the HC5 for high temperature was a factor 5 lower although the HC50 was only decreased by a factor 1.4. For PCP, the differences between the HC5 and HC50 of different temperature groups were a factor 0.65 and 1.80 respectively and were not statistically significant. Results suggest that in cases where temperatures of water bodies are (temporarily) elevated above 20°C, the effect of temperature on sensitivity should be taken into account. When upholding a precautionary principle it would be advisable to apply a safety factor of minimal 2 to environmental quality standards for chemical pollution in waters with increased temperature when striving to protect 95% of the species. By taking relevant environmental conditions such as temperature into account, environmental risk assessment can become more realistic.