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The user-friendly software tool DROPLET (acronym for DRinkwater uit OPpervlaktewater-Landbouwkundig gebruik Evaluatie Tool) assists the Dutch Board for the Authorization of Plant Protection Products and Biocides (Ctgb) in evaluating whether pesticides may exceed the 0.1 μg/L standard in one of the Dutch surface water abstraction points for drinking water production. Based upon Good Agricultural Practice DROPLET uses the peak concentration in the FOCUS D3 ditch (with spray drift deposition according to Dutch numbers) as starting point for the final, expected concentration at the abstraction pointssituated in the larger waterbodies downstream. This report compares concentrations in the abstraction points calculated by the old model suite (FOCUS-SWASH 3.1, FOCUS-MACRO 4.4.2, FOCUS-TOXSWA 3.3.1 and DROPLET 1.2) with those calculated by the more recently released model suite (FOCUS-SWASH 5.3, including the substance database SPIN 3.3, FOCUS-MACRO 5.5.4, FOCUS-TOXSWA 4.4.3 and DROPLET 1.3.2). The concentrations in the drinking water abstraction points calculated by the new model suite may be up to a factor of approximately 2.5 higher than the ones calculated by the old model suite. This is practically entirely due to the increased pesticide mass in the drainage fluxes calculated by the new version of the MACRO model. The calculations by the TOXSWA and DROPLET models have not been changed. Because nomeasured water and mass fluxes for drainage are available for the D3 scenario, it is not possible to indicate whether the fluxes calculated by MACRO 4.4.2 or those by MACRO 5.5.4 reflect better reality. Thus no recommendation can be made on the model suite to be used in the Dutch exposure assessment for drinking water production from surface waters. Het gebruikersvriendelijke instrument DROPLET (acroniem voor DRinkwater uit OPpervlaktewater-Land-bouwkundig gebruik Evaluatie Tool) ondersteunt het Nederlandse College voor de toelating van gewas-beschermingsmiddelen en biociden (Ctgb) bij het evalueren of gewasbeschermingsmiddelen de drinkwater norm van 0.1 μg/L overschrijden in één van de negen innamepunten van oppervlaktewater voor drinkwater-bereiding. Uitgaande van Goed Landbouwkundig Gebruik gebruikt DROPLET de piekconcentratie in de FOCUS D3 sloot (met spuitdriftdepositie volgens Nederlandse cijfers) als startpunt voor de berekening van de uitein-delijke concentratie bij de drinkwater innamepunten die benedenstrooms in grotere wateren zijn gesitueerd. Dit rapport vergelijkt de concentraties in de innamepunten zoals berekend door de vorige modellentrein (FOCUSSWASH 3.1, FOCUS-MACRO 4.4.2, FOCUS-TOXSWA 3.3.1 en DROPLET 1.2) met die van de meer recent uitgebrachte modellentrein (FOCUS-SWASH 5.3, inclusief de stoffendatabase SPIN 3.3, FOCUS-MACRO 5.5.4, FOCUS-TOXSWA 4.4.3 en DROPLET 1.3.2). |
