Before a pesticide is approved for use, risk assessments must be carried out to indicate that no unacceptable acute or longer-term harm will occur to non-target wildlife. The assessment of long-term harm relies on standard toxicological studies of the organisms’ reproductive health. In these chronic studies a variety of toxic endpoints are assessed eg number of eggs laid per hen, mean egg-shell thinning, weight of chicks). The current approach takes only the single most sensitive of these endpoints, and compares it with the expected long term exposure. This is a deliberately conservative approach and it often leads to the conclusion that the pesticide poses an unacceptably high risk.
The draft revised EU Guidance Document for assessing pesticide risks to birds and mammals proposes to implement a more realistic approach, a phase-specific long-term risk assessment. This divides reproduction into a series of phases (eg courtship, egg-laying, incubation, nestling growth etc) of different durations and the most appropriate toxicological endpoint (eg number of eggs hatched, or chick weight) is then compared with the exposure during a particular phase. Scientifically, this is a substantial improvement over the current approach which uses only the most sensitive endpoint, but there are concerns that it will still be over-conservative if implemented as currently proposed, because it assumes that every phase of every reproductive attempt is maximally exposed to pesticide. In reality, pesticide spraying may take place long before or long after any given nesting attempt so that only a proportion of broods will be exposed. Furthermore, for those which are exposed, the peak exposure may not occur during the most sensitive phase. We will take account of these factors by developing and evaluating models that estimate the proportion of broods or litters at risk, based on the extent of temporal overlap between individual pesticide applications and individual reproductive attempts. The most suitable model will then be implemented for a selection of species-crop scenarios commonly encountered in regulatory assessment.