The current Dutch authorisation procedure for calculating the exposure of aquatic organisms to plant protection products needs to be revised. For this reason, Wageningen UR, RIVM and PBL Netherlands Environmental Assessment Agency were asked to develop a new exposure assessment methodology for various crops and application methods. This report describes the methodology for upward and sideways spraying in Dutch fruit crops. In contrast to the current procedure, the new procedure calculates the exposure concentration based on a statistical distribution of the exposure concentration in all relevant Dutch watercourses. The methodology results in a so-called 90 th percentile exposure concentration considering all watercourses alongside fields grown with fruit crops. The new methodology takes input of plant protection products by spray drift, drainage and atmospheric deposition into account. Agronomic practices in Dutch apple and pear orchards were considered representative for all (high) pome and stone fruit orchard crops in the Netherlands. An important part of the new methodology is the option to mitigate spray drift deposition by using drift-reducing technologies in a higher spray drift reducing class or by including a wider crop-free buffer zone.
An innovative model has been developed for downwind deposits of pesticides due to spray drift next to an orchard of pome fruit trees (apple, pear). The SPEXUS model (spray drift exposure for upward and sideways directed sprays) is an empirical model based on 20 years of experimental data of spray drift deposits for conventional cross-flow pesticide applications. The major factors affecting the deposits are downwind distance, wind speed, wind direction, air temperature, density of the tree canopy and size of the orchard. Modelling the canopy density of the trees as a continuous function of time of year is a new approach. Canopy density is uniquely related to the phenological growth stage (identified by the BBCH index). Experimentally observed features of the effects of the mentioned factors are modelled by selecting appropriate sub-models. These effects are discussed and interpreted. Modelled deposits and measured deposits were compared and gave a correlation coefficient of 86%. Drift reducing techniques were implemented using experimental data on reductions of downwind spray deposits as a function of downwind distance. The SPEXUS model forms the basis for risk assessment for exposure of aquatic organisms concerning all edge-of-field water bodies next to fruit orchards in the Netherlands.
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