Environmental Fate and Exposure Assessments for Pesticides

- Risk assessments and Regional Mass balances –

Andreas Huber, Syngenta Crop Protection AG, Basel

Current registration practices in many OECD countries require the prediction of potential exposure of terrestrial ecosystems as well as ground and surface waters associated with the use of pesticides in agriculture. These estimates are usually based on a predefined realistic worst-case of pollution for each exposure route. In this way regulatory risk assessment schemes avoid dealing with the variability of potential pollution by basing control standards on the realistic worst case. Typically exposure scenarios consist of particularly vulnerable combinations of soil, climate and land use characteristics, which are subject to a location-specific probability of occurrence. More recent risk assessment schemes recognise the need to use a number of scenarios in order to assess adequately the potential exposure of a compound that is applied under a range of natural conditions. Nevertheless the focus of any risk assessment done for regulatory purposes is the compliance with threshold values, in most cases concentrations in environmental compartments.

By way of contrast, a regional mass balance of pesticide pollution aims to reflect the variability inherent in pesticide exposure predictions in order to predict e.g. annual average losses of a compound after normal agricultural use in a country. As a consequence a regional mass balance does not yield realistic worst-case concentrations under certain scenario conditions, but estimates average loadings or masses for combinations of factors as they occur in reality.

Risk assessments and mass balances require thus contrasting methods and are applied for different purposes.