The Dutch decision tree for the evaluation of the leaching of plant protection products

Plant protection products can leach into the groundwater and cause problems for the abstraction of drinking water. Leaching into the groundwater is therefore one of the aspects included in the evaluation procedure that precedes the authorization of plant protection products for the Dutch market. In 2005, a decision tree was introduced for performing this evaluation. This decision tree has now been revised based on the latest insights and data. The most important reason for the revision of the decision tree is the insight that the organic matter content of the soil was being overestimated. As a result, the predicted concentration of plant protection products in the groundwater was two to 10 times too low. This is undesirable because this could lead to the unwarranted authorization of a plant protection product. Applicants who want to have a plant protection product authorized in the Netherlands must therefore use the revised decision tree. This decision tree follows a tiered approach, which means that an applicant can start with a simple and conservative calculation procedure. If a plant protection product can be used safely according to this simple calculation procedure, an authorization can be granted without requiring additional work. If an authorization cannot be granted based on this simple calculation procedure, the applicant can provide additional and more precise studies. In the second tier, the applicant can demonstrate a safe use by calculating the leaching in the area in which a plant protection product is planned to be used in the Netherlands. Should the second tier not demonstrate a safe use, the applicant can use groundwater monitoring to show that the product can be safely used in the Netherlands. If groundwater monitoring does not show a safe use as well, the product cannot be authorized for use on the Dutch market.