Temporal scales in ecological risk assessment.

The process of human health risk assessment (HRA) was formalized in 1983 by the National Research Council to include hazard identification, dose-response analyses, exposure assessment and risk characterization. Risk assessment for ecologic endpoints is emerging as a new discipline. Although environmental impact statements have been conducted for many years, ecologists, managers and policy makers are beginning to formalize the process in terms of risk, and are adapting the HRA paradigm to ecological risk assessment (ERA). In this paper it is suggested that the temporal scales of the two processes differ, and that these differences should be incorporated in ecological risk assessment. Even when HRA techniques are applied to a single non-human species there are temporal variations including: (1) different and often variable life spans, (2) unpredictable lengths of lifestages and different metamorphic stages, and (3) indeterminate growth in some species. When these differences are considered for multispecies assemblages, the impact on the food web will result in exposures of differing magnitudes affecting different species. The challenges for ERA include developing general principles for estimating or predicting exposure to critical life stages of the dominant species in an ecosystem, and establishing the appropriate temporal scales for predicting impacts or evaluating outcomes.