Interpretatie van metingen van gewasbeschermingsmiddelen in grondwater in Noord- en Oost- Nederland : Vergelijking van metingen met berekeningen (Dutch only, English synopsis)
RIVM Report 2016-0163
Provinces in the northern and eastern parts of the Netherlands and water companies in the same regions detect residues of plant protection products in their monitoring networks. This raised the question whether the authorisation procedure sufficiently protects the drinking water function of the groundwater. This report investigates whether the occurrences indicate flaws in the authorisation procedure of plant protection products.
Starting point of the investigation was the combined database on findings in groundwater in the region. Six parent substances and six metabolites were selected for further investigation, based on the relative number of detects above the value of 0.1 µg/L and difficulties in removing these substances from water. Vulnerability maps were calculated for each of the substances and the relative vulnerability of the sampling locations established. A further selection of groundwater samples was made on the estimated age of the groundwater and the land use in the infiltration areas. The leaching estimates were compared with the measurements.
Although for a number of samples the opposite was found, for most samples measurements were below estimated leaching concentrations. For mecoprop and the metabolite chloridazon-desfenyl, however, a relatively large number of samples showed the opposite. For bentazone, approximately 10% of the selected samples showed a concentration above the threshold limit. It should be investigated further whether these findings also reflect current label prescriptions.
Selected metabolites all appeared to have the status 'non-relevant', indicating that a value of 10 µg/L (instead of 0.1 µg/L) is used as criterion in the authorisation decision.
The study revealed a number of issues. With regard to the monitoring networks attention should be paid to completing meta-information, the age of the groundwater, the establishment of the infiltration area of each of the sampling filters and the use of substances in the infiltration area. With regard to the substance dossiers, more attention should be paid to the establishment of the transformation routes and the derivation of the fate characteristics of the substances, especially the metabolites.
Last but not least, the requirements and criteria for decision making on monitoring results should be clarified.