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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.

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The assessment of chemical degradation rates from water-sediment experiments like for instance OECD 308 is challenging due to parallel occurrence of processes like degradation, sorption and diffusive transport, at different rates in water and sediment or at their interface. To systematically and quantitatively analyze this limitation, we generated artificial experiment data sets using model simulations and then used these data sets in an inverse modeling exercise to estimate degradation half-lives in water and sediment (DegT50 and DegT50), which then were evaluated against their true values. Results were visualized by chemical space diagrams that identified those substance property combinations for which the OECD 308 test is fundamentally inappropriate. We show that the uncertainty in estimated degradation half-lives in water increases as the process of diffusion to the sediment becomes dominant over degradation in the water. We show that in theory the uncertainty in the estimated DegT50 is smaller than the uncertainty in the DegT50. The predictive value of our chemical space diagrams was validated using literature transformation rates and their uncertainties that were inferred from real water-sediment experiments.