ECOLOGICAL CONSIDERATIONS IN PESTICIDE RISK ASSESSMENT FOR AQUATIC ECOSYSTEMS

Risk assessment of pesticides for aquatic ecosystems is typically base d on comparisons of exposure and effect concentrations at a variety of levels (tiers). At the highest tier, effects assessment can involve g enerating data under field conditions, typically in mesocosm experimen ts. However, interpreting the ecological significance of effects measu red in these studies can be difficult because ecological factors can i nfluence the outcome of perturbations in the real world. The influence of ecological factors is not readily addressed experimentally and so a strategic modelling approach is proposed which may aid in defining a cceptability of effects.