Short range transport and deposition of volatilised pesticides

Plant protection products are widely used in agriculture. They are needed by farmers to protect their crops from attacks of pests, fungal diseases and weeds. A further improved understanding of the behaviour of these products in the environment also helps to increase the safety of the populations of non target organisms in off crop areas close to treated fields. Volatilisation, short-range transport and deposition of pesticides from air had recently been identified as a potentially relevant entry path into the habitats of aquatic and terrestrial nontarget organisms. The German Federal Consumer Protection and Food Safety Agency (BVL, formerly BBA) published in 2002 a guideline for the assessment of volatilisation, short-range transport and deposition of plant protection products from air. It was intended to include this path into the exposure assessment for the authorisation of plant protection products. The guideline describes a tiered assessment consisting of model calculations and field experiments. Both assessment methods, model calculations as well as field experiments, showed some uncertainties in their predicted estimated concentrations. This was due to the fact that volatilisation, transport and deposition of volatilised pesticides are a highly complex processes consisting of several mass transfer and transport phenomena. A need for additional research in this area was concluded. The main objective of this research project was the development of a large-scale outdoor wind tunnel test system for reproducible measurements of the atmospheric short-range transport and dry deposition of volatilised pesticides in order to improve models and test systems. The volatilisation, short range transport and deposition behaviour of ten pesticides, representing a wide range of physical and chemical properties, was investigated in fifteen semi-outdoor wind tunnel experiments. The studies also covers a wide range of experimental boundary conditions. The results formed the basis for an empirically derived correlation describing the deposition after volatilisation as a function of vapour pressure and downwind distance from the treated crop.