Crop protections safeguard agricultural yields by controlling harmful insects, fungi, and weeds. However, they also enter neighboring streams and damage the aquatic communities, which are crucial for maintaining biodiversity, are part of the food web and support the self-purification of water. In a nationwide monitoring program, a consortium of scientists led by the Helmholtz Centre for Environmental Research (UFZ) has shown that the governmental thresholds for pesticides are generally too high and that even these excessively high levels are still exceeded in over 80% of water bodies. As they published in the scientific journal Water Research the loss of biodiversity can only be halted if the environmental risk assessment of pesticides is radically revised.
For two years, the researchers studied contamination at more than 100 monitoring sites on streams flowing through predominantly agricultural lowland regions in 12 federal states in Germany. They found significant exceedances of the RAC value – the concentration of an active ingredient specified in the official approval procedure for a crop protection, which should not be exceeded in the water body in order to prevent negative effects on aquatic organisms. In most of the small streams investigated, the RAC values were exceeded (81%). In 18% of the streams, such exceedances were detected for more than 10 crop protections.
"We have detected a significantly higher crop protection load in small water bodies than we originally expected," says Prof. Matthias Liess, ecotoxicologist at the UFZ and coordinator of the small water monitoring project. For example, in three water bodies, the insecticide thiacloprid exceeded the RAC value by more than 100-fold. In 27 streams the insecticides clothianidin, methiocarb, and fipronil as well as herbicides such as terbuthylazine, nicosulfuron, and lenacil exceeded the RAC value 10- to 100-fold.
In the course of the project, the scientists also found that the type of sampling has a drastic influence on the concentrations measured. In addition to the scoop sample specified as standard by the EU Water Framework Directive, they also took an "event sample." Here, an automatically controlled sampler takes water samples from the water body after a rain event. "The event sample provides much more realistic results because the crop protections enter the water bodies as a result of the increased surface run-off from the field, especially during rain," says Liess.
Compared to the scoop samples, the event-related samples show a 10-fold higher load. "In order to realistically depict the water pollution, samples must therefore be taken after rainfall events. That's why we need an official regular environmental monitoring to be able to assess the amount and the effects of chemical crop protections," says Matthias Liess. He and his colleagues also demand that new scientific findings be incorporated into the approval process for new crop protections more quickly. "We are still using crop protections that were approved many years ago based on an outdated risk assessment. This must therefore change as soon as possible. Only in this way can we preserve the biodiversity in our waters and with it the services that these biotic communities provide for our ecosystems."
Matthias Liess, Liana Liebmann, Philipp Vormeier, Oliver Weisner, Rolf Altenburger, Dietrich Borchardt, Werner Brack, Antonis Chatzinotas, Beate Escher, Kaarina Foit, Roman Gunold, Sebastian Henz, Kristina L. Hitzfeld, Mechthild Schmitt-Jansen, Norbert Kamjunke, Oliver Kaske, Saskia Knillmann, Martin Krauss, Eberhard Küster, Moritz Link, Maren Lück, Monika Möder, Alexandra Müller, Albrecht Paschke, Ralf B. Schäfer, Anke Schneeweiss, Verena C. Schreiner, Tobias Schulze, Gerrit Schüürmann, Wolf von Tümpling, Markus Weitere, Jörn Wogram, Thorsten Reemtsma. Pesticides are the dominant stressors for vulnerable insects in lowland streams. Water Research, 2021; 201: 117262 DOI: 10.1016/j.watres.2021.117262