In this blogpost, Jakob Wolfram talks about his recent study “Pesticide occurrence in protected surface waters in nature conservation areas of Germany”. In the study, he analyzed millions of records detailing the occurrence of pesticides in surface waters. The study showed that pesticides frequently occur in strictly protected nature conservation areas and could jeopardize their ecological integrity. 

Nature conservation areas (NCA) are strictly protected landscapes in Germany with minimal agricultural activity (<4.5 %). Their protection aims at safeguarding conservation, development or restoration efforts but also to sustainably protect the biological diversity, ecosystem performance and functionality. Thus, NCA serve as vital ecological refuges in an otherwise highly intensified landscape. Yet, nobody actually investigated comprehensively if pesticides occur in these pivotal aquatic systems. Hence, we used a large monitoring dataset, describing the occurrence of 208 pesticides from 1998 to 2020 in Saxony with > 3.7 million records, to find out if pesticides occur in NCA.

Protected equals uncontaminated?

First of all, pesticides do occur in NCA, although ca. 40% less often compared to the unprotected areas. Thus, the direct protection of nature conservation areas has a positive influence on the occurrence of contaminants. On the other hand, it also shows that these pivotal ecosystems are not free from anthropogenic contaminants, which can directly violate the established protection goals. Interestingly, we were able to show that the detection frequencies between protected and unprotected areas were strongly correlated (R² = 0.7 – 0.92) over time for all major pesticide classes (i.e., herbicides, fungicides, insecticides and metabolites). This suggested that a larger landscape-context (e.g., the watershed-context) may be relevant for the occurrence of contaminants. A similar result was found when comparing the actual concentrations of pesticides between protected and unprotected areas. Here, the differences were even smaller; amounting only to 1.29 – 1.77 higher concentrations in unprotected areas. Hence, if contaminants occur in protected areas, then their magnitude is highly similar to those unprotected areas.

Persistently present?

We also explored how regularly pesticides occur in both protected and unprotected areas. Again, the situation was highly similar between both groups (ρ = 83.5 %). Several substances appear to occur “pseudo-persistently”, meaning that they are detected in >50% of samples at each site. Especially certain metabolites, such as metazachlor sulfonic acid, metolachlor ESA and metazachlor OA showed such persistent behavior. These metabolites were pseudo-persistent in 84.1%–92.9% of sites overall, meaning they are detected nearly permanently. This can of course have detrimental impacts on various organism groups but in particular to aquatic plants, which are most susceptible to the toxic modes of action of herbicides.

Reason to worry?

Without going too much into detail, the ecological risks for aquatic invertebrates, aquatic plants and fish were rather similar between protected and unprotected areas. Here, the exceedance of so-called regulatory threshold levels were ~30% lower in protected areas. As such, the results underscored again that the direct protection of these areas has a positive influence on contaminant occurrence but at the same time dues not drastically reduce the resulting environmental risks. However, there were substantial differences between the organism groups that we assessed. Aquatic plants (20.4%) and aquatic invertebrates (14.7%) had similar threshold exceedances, when comparing them to the European average, whereas risks for fish were very low, i.e. a maximum of 1.8% of samples exceeded their thresholds. Additional analyses of the risk metrics provided further evidence that the ecotoxicological pressures are not substantially between protected and unprotected areas (please refer to the study for details). There is one important thing to note though. As we previously noted, the average concentrations were highly similar between both areas. However, that was not the reason why the ecological risks were similar. Rather, the infrequently, sporadically occurring pesticides drove individual risks, such as highly toxic insecticides (cypermethrin, chlorpyrifos-ethyl) or herbicides (e.g. diflufenican, metazachlor). Interestingly, these were also the substances with the highest applied toxicities in Germany (see Schulz et al.), showing how you can combine application data and ecotoxicology data to identify potential high-risks substances.

But why?

At this stage you may ask yourself how it can be that pesticides occur so frequently and in relevant concentrations in nature protection areas. One thing to keep in mind is that these areas are particularly small in Germany with only 2.5-3 km² on average. The directly surrounding landscape (1 km distance), however, is already very similar to all unprotected areas (R²= 0.92). Thus, high-intensity agriculture and urban areas can be spatially very close to these small protection areas. This also means that the catchment of nature conservation areas is only partially protected (21.9% on average). Thus, when we analyzed the land-use of the contributing catchment for all sites in nature protection areas, we found that agriculture directly explains the observed risks (Fig. 2). In other words, the unprotected upstream areas, which are defined by high-intensity agriculture, serve as pesticide sources. Pesticides simply flow into these small protection areas from the unprotected upstream reaches. To achieve a sufficient protection status, future land-management thus has to account for the fact that aquatic systems are connected over large scales and so is the contaminant transport.

In closing, we analyzed for the first time an extensive data set to answer the question if pesticides occur in nature conservation areas (find the study here for details). We found that pesticides occur less frequently there but still regularly enough to cause noteworthy environmental risks. The reason for it is that they appear to flow into these protected areas, because the upstream areas are intensively used. This work was done as part of the research team “Meta-analysis of Global Impacts of Chemicals” (MAGIC) and if you are interested in our work, you can get in touch.

The paper “Pesticide occurrence in protected surface waters in nature conservation areas of Germany” was published by Jakob Wolfram, Sebastian Stehle, Sascha Bub, Lara Petschick, Anna Schemmer and Ralf Schulz in Science of the Total Environment and will be in print in 2023.