Ecological risk assessment: Implications of hormesis

Hormesis is a widespread phenomenon across many taxa and chemicals, and, at the single species level, issues regarding the application of hormesis to human health and ecological risk assessment are similar. For example, convi ncing the public of a 'beneficial' effect of environmental chemicals may be problematic, and the design and analysis of laboratory studies may require modifications to detect hormesis. However, interpreting the significance o f hormesis for even a single species in an ecological risk assessment can b e complicated by considerations of competition with other species, predatio n effects, etc. Ecological risk assessments involve more than a single spec ies; they may involve communities of hundreds or thousands of species as we ll as a range of ecological processes. Applying hermetic adjustments to thr eshold effect levels for chemicals derived from sensitivity distributions f or a large number of species is impractical. For ecological risks, chemical stressors are frequently of lessor concern than physical stressors such as habitat alteration or biological stressors such as introduced species, but the relevance of hormesis to non-chemical stressors is unclear. Although e cological theories such as the intermediate disturbance hypothesis offer so me intriguing similarities between chemical hormesis and hermetic-like resp onses resulting from physical disturbances, mechanistic explanations are la cking. Further exploration of the relevance of hormesis to ecological risk assessment is desirable. Aspects deserving additional attention include dev eloping a better understanding of the hermetic effects of chemical mixtures , the relevance of hormesis to physical and biological stressors and the de velopment of criteria for determining when hormesis is likely to be relevan t to ecological risk assessments.