Policy choices concerning the use of GEM for application of plant protection products in greenhouses
Since March 2016 the guidance document on protected crops and the model GEM (Greenhouse Emission Model) is used for the risk assessment of plant protection products in greenhouses. This model contains options for national policy choices regarding the target percentile related to flow velocity and the application of a safety factor for degradation of substances in greenhouse soil. The responsible Dutch ministries have chosen to implement an average flow velocity and no safety factor.
- With regard to the flow velocity percentile for the substrate scenario the choice was between the 50thpercentile (approximately the average flow velocity) and the 90thpercentile (low flow velocity). The use of the 50th percentile flow velocity was chosen because for other sensitive scenario parameters the 90th percentile is selected. This decision is defensible in line with the European assessment methodology that aims at a realistic worst-case assessment, corresponding to an overall 90th percentile exposure concentration.
- With regard to the degradation half-life in soil for the soil-bound scenario the choice was whether a safety factor of 10 should be applied. There were indications that the degradation of substances would be slower in greenhouse than in field due to the disinfection of greenhouse soil. Newer information appears to indicate that this effect is less than expected. It was therefore decided that a safety factor is not required.
Ctgb will apply these policy choices at once. Both decisions have already been described in the Evaluation Manuals for groundwater and surface water (NL part), version 2.1, October 2016.
The policy choices were made for a period until 2018 and will be evaluated and reconsidered.