High levels of pesticide pollution found in streams in German agricultural landscapes
The use of pesticides to control insects, fungi and plants which threaten agricultural production has soared globally in recent decades. One recent study suggests that that around one-third of the planet’s agricultural land is at ‘high risk’ of pesticide pollution, and that aquatic ecosystems are particularly vulnerable to the harmful effects of pesticide run-off.
The 2019 UN Global Environment Outlook states that food production is a major driver of global biodiversity loss, and a significant pollution source for aquatic environments. This is particularly the case where intensified agricultural practices are heavily reliant on chemical pesticides and fertilisers.
A newly-published study suggests that small streams in agricultural landscapes across Germany are heavily polluted with pesticides, causing significant effects on aquatic biodiversity. Over two years, a team of scientists led by the Helmholtz Centre for Environmental Research (UFZ) studied pesticide contamination at more than 100 monitoring sites on streams flowing through agricultural lowland regions across Germany.
The research team found that government ‘safe’ thresholds for pesticides were exceeded in over 80% of the streams. In 18% of the streams, these thresholds were exceeded by more than ten different pesticides, showing the ‘cocktail’ of chemical stressors the small stream ecosystems are subject to.
“We have detected a significantly higher pesticide load in small water bodies than we originally expected,” says Professor Matthias Liess, ecotoxicologist at the UFZ and coordinator of the small water monitoring project.
In some streams the pesticide loads were significantly higher than government thresholds. In three water bodies, the insecticide thiacloprid was detected at concentrations over one hundred times the threshold. In twenty-seven streams, the insecticides clothianidin, methiocarb, and fipronil, as well as herbicides such as terbuthylazine, nicosulfuron, and lenacil, exceeded the threshold 10 to 100-fold.
Image: André Künzelmann / UFZ
The researchers’ detailed datasets revealed that pesticides negatively impact stream insect communities at much lower concentrations than previously assumed in government risk assessments. “For sensitive insect species, the pesticide concentration in the small lowland streams is the most relevant factor that determines their survival,” says Professor Liess. “In contrast, other environmental problems such as watercourse expansion, oxygen deficiency, and excessive nutrient content are less important. For the first time this study allows a ranking of environmental problems.”
The study suggests that German government thresholds for the management of aquatic pesticide pollution are insufficient for protecting invertebrate communities. The researchers suggest that this is because, until now, the ecological risk posed by pesticides has been predicted using laboratory studies, artificial ecosystems and computer simulations.
“In addition to pesticides, many other stressors act on organisms in the ecosystem,” states Professor Liess. “These make them much more sensitive to pesticides. Natural stressors such as predation pressure or competition between species are not sufficiently taken into account in the risk assessment. But these obvious problems often go unnoticed because the degree of pesticide contamination and the effect of this have not been validated in the field – neither in Germany nor in other countries.”
The scientists found that the type of sampling method use significantly influenced their measurements of pesticide concentrations. Scoop samples of water are standard for water quality monitoring under the EU Water Framework Directive. However, the scientists found that ‘event samples’, which automatically collect water samples after rainfall, provide much higher concentrations of pesticides entering the stream ecosystems.
“The event sample provides much more realistic results because the pesticides enter the water bodies as a result of the increased surface run-off from the field, especially during rain,” says Professor Liess. “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 pesticides.”
The study has significant implications for the management of aquatic ecosystems within agricultural landscapes in Germany. ”We are still using pesticides that were approved many years ago based on an outdated risk assessment,” argues Professor Liess. “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.”
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