Revised greenhouse scenarios for exposure of aquatic organisms to plant protection products : Soil-bound crops in greenhouses

Samenvatting

In 2016 a greenhouse scenario for soil-bound crops has been adopted in the Dutch authorisation procedure for plant protection products to assess the exposure of aquatic organisms. However, two important shortcomings resulting from the parameterisation of the surface water scenario were discovered. These were due to the assumption of an exact repetition of the irrigation scheme for a fully-grown chrysanthemum crop and that of a top layer with a well-developed macropore system. The first assumption resulted in an extreme sensitivity of the exposure concentration to the application date and the second assumptions was considered unrealistic, because the soil in the greenhouse is frequently ploughed. The above two issues were addressed in the revised exposure scenario presented in this report. The first important improvement was the division of the greenhouse into 24 cultivation sections with a description of the sequence and growth development of all crop cycles in each cultivation section. The second shortcoming was remedied by the change of the topsoil layer with a well-developed macropore system into a topsoil layer without macropores. The target concentration for the assessment of the exposure in surface water strongly depends on the half-life of the substance in the greenhouse soil. Should data on the DegT50 obtained from measurements in greenhouse soils not be available, we recommend to apply provisionally the same factor as included in the tiered assessment scheme proposed by Wipfler et al. (2014), i.e. multiplying the DegT50 value derived from measurements in field soils by a factor 10. The new version of the Greenhouse Emission model (GEM) contains the option to specify an application day relative to the date of planting or harvest. If the GAP (Good Agricultural Practice) of a plant protection product specifies a number of applications per crop cycle, this option should be used. If the GAP specifies a number of applications per year, the application option to specify an absolute date should be selected. For the selection of the application date resulting in the required percentile of the PEC90 in surface water, we recommend an update of the SAFE (Select Application For Evaluation) tool. Suggestions are made to increase the validation status of the model and for the further development and use of the GEM model within the EU.