Pesticide contamination across drinking water sources in the Netherlands

Pesticides have been found in surface water and groundwater sources for decades. They are not only widely considered as a major threat for these waters, but also for drinking water. Not only pesticides that are still authorized by the European Commission can be found in the sources for drinking water, also banned compounds, such as atrazine (banned in 2007), still cause exceedances of environmental threshold values (as measured in 2020).

A comprehensive study was conducted in Dutch drinking water sources analyzing pesticides and their metabolites in both surface water and groundwater. Observations in surface water sources were divided in intake water and pre-treated water. For groundwater sources, observations were divided in observation wells, individual abstraction wells and all abstraction wells per particular drinking water abstraction station. Dutch drinking water standards were used as a measure of the implications for drinking water production processes.

This study shows that 156 different pesticides or metabolites were found at the nine surface water intake points considered. The standard for this substance group was exceeded on several occasions at all intake points. Pesticide residues have also been found in 40% of groundwater abstractions for drinking water production, particularly in phreatic ones (77%). This also involves a diversity of different substances. Pesticide residues exceeded the standard in 20% of groundwater abstractions. The pressure on surface water quality due to pesticides as indicated by the Removal Requirement Index seems to decrease slightly in recent years, whereas the pressure on groundwater intended for drinking water production seems to increase. Due to the diversity of pesticides found in ground- and surface water, trends are not obvious. Which and how many pesticides were observed differs between observation wells, abstraction wells and the combined abstraction wells, as well as aquifer properties.