Pesticides fly under the radar of official monitoring

The governmental monitoring under the Water Framework Directive (WFD) shall monitor the status of European water bodies. By carrying out a refined monitoring, a group of scientists from Leipzig and Landau now showed that pesticide risk in surface waters remains widely unnoticed in the WFD monitoring.

The WFD requires EU member states to monitor their water bodies and provides guidance on how to do so. A recently publishedarticle in Water Research authored by scientists from the Helmholtz Centre for Environmental Research – UFZ and the University of Landau classifies the WFD monitoring approach incapable to assess pesticide risk in surface waters. They conducted a refined monitoring of streams designed to specifically assess pesticide risk (the so-called Kleingewässer-Monitoring) and compared the results to those a WFD-compliant monitoring would have yielded.

The results differed distinctly: The WFD-compliant monitoring only identified 28 % of pesticides posing a risk and 43 % of streams that were at risk due to pesticides (see figure below).

Caption 1: Differences in risk assessment of streams and pesticides by WFD and more realistic pesticide monitoring (CC André Künzelmann / UFZ)

The study emphasizes three major reasons for this underestimation of pesticide risk under the WFD-compliant monitoring:

The sampling approach

The current timing of surface water sampling following a regular sampling schedule is unable to adequately capture the periodic occurrence of pesticides. Furthermore, the monitoring site selection mainly focuses on larger rivers while small streams particularly susceptible to pesticide risks are mostly disregarded.

The measuring method

Chemical analysis of water samples focuses on a too narrow and outdated analyte spectrum that excludes most current-use pesticides. In Germany, for example, only 6 % of pesticides currently approved have to be analyzed. This is accompanied by analytical limitations impeding the measurement of ecologically harmful concentrations. Both issues lead to the fact that several pesticides posing a risk are not identified as such under the WFD.

The assessment method for measured concentrations

The limited availability of regulatory thresholds, particularly with respect to short-term concentration maxima, is not sufficient to assess measured pesticide concentrations. In addition, the authors estimate existing thresholds too high to ensure a good ecological status based on ecological effects observed in the field. Compliance with current regulatory thresholds is therefore unlikely to ensure a good ecological status in the field.

The authors therefore expect pesticides to play a more important role in the widely insufficient ecological status of surface waters than estimated so far. Legal and practical refinements were necessary, they state, to gain a more realistic picture of pesticide pollution and to ultimately improve the status of European waters.For other findings from the Kleingewässer-Monitoring, see earlier blog posts describing the ecological effects of pesticides in streams or the risk due to environmental pesticide mixtures.