Pesticide contamination of surface water: assessment of the contribution from atmospheric deposition

As it has now been established that surface water is contaminated by gaseous deposits of pesticides volatilised from treatment areas, tools need to be developed to assess this route of contamination in order to complement the risk assessment associated with pesticide use. The working hypothesis explored here is based on the fact that these deposits, which occur over several weeks, are likely to cause contamination equivalent to, or even greater than, that caused by drift, which lasts only for the duration of the application. This hypothesis is confirmed by the results of initial model tests as well as by experimental findings. This project proposes gas deposition charts (similar to drift charts) derived from simulations carried out using two coupled models across a significant number of scenarios. The key factors controlling the gaseous deposition of pesticides have been identified for both a body of water and a drainage ditch. These results enable the identification of management measures to reduce the risks of contamination.