The effect of temperature on environmental risk assessment using species sensitivity distributions
Summary
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.