Environmental Project No. 1178 2007 – Evaluation of Pesticide Scenarios for the Registration Procedure

Evaluation of Pesticide Scenarios for the Registration Procedure

Summary

The Danish Environmental Protection Agency is currently using mathematical modelling results to support their pesticide approval procedure. Up to now the modelling results derives from the EU scenario Hamburg (sand) as well as the two Danish model scenarios Karup (sand) and Langvad (clay). The data supporting the three scenarios is very limited. Hamburg is thus not supported by any calibration and Karup and Langvad has been calibrated against a large scale yearly water balance only. Recently the Danish Pesticide Leaching assessment Programme (PLAP) has generated extensive data sets and well-parameterized and -calibrated model providing a good description of water and solute transport through unsaturated zone in Denmark. This improved data availability made it possibly to assess the reliability and representativeness of the scenarios hitherto being used in the Danish registration procedure.

The objective of this study was to evaluate the reliability and representativeness of both the existing model scenarios (Langvad, Karup and Hamburg) and the recent PLAP scenarios (Jyndevad, Tylstrup, Silstrup, Estrup and Faardrup), with the purpose of recommending the two scenarios to be used in the coming registration procedure.

The PLAP scenarios Jyndevad (sand) and Silstrup (clay) are proposed for future use in the Danish pesticide approval procedure. This recommendation is based on characterization with respect to precipitation, geology, reliability of field data and conceptual model. Additionally it is based on the authors´ assumption that choosing the worst case scenarios with respect to leaching will best protect the Danish groundwater against pesticides. However, it should be noted that none of the scenarios presented in this report have been validated against pesticide leaching data. While the selected PLAP scenarios provide a good model description of water and conservative solute transport its predicting capability towards pesticide leaching has not yet been assessed. Such assessment would attach further reliability to the model output, and the needed measured pesticide leaching data for the PLAP-scenarios is now available.

This report provides solid documentation on the selected scenarios including result from the calibration made against measured groundwater table, soil water contents, measurements of bromide concentration, and for the clay soils drainage runoff. Moreover soil texture (organic matter, clay, silt), simulated water balance, and simulated leaching from the existing scenarios are compared with those obtained from the PLAP scenarios. Results from the latter showed that the existing scenarios (Karup, Langvad, and Hamburg) were less restrictive with regard to leaching than the PLAP scenarios. For the sandy scenarios, the highest leaching was found at Jyndevad. The somewhat lower leaching at Karup resembles that of Tylstrup, while that of Hamburg was markedly lower. For clay scenarios, the leaching at Langvad was higher than that at Faardrup but considerably lower than that of Silstrup and Estrup. Furthermore, the choice of application date and plant evolution could influence which type of pesticides that will pass the Danish pesticide approval system.