Pesticide Contamination of Nonagricultural Streams Underscores Further Threats to Biodiversity

(Beyond Pesticides, July 1, 2025) Published in Water Research, a study highlights the various routes for pesticide contamination, with the results identifying the presence of over 80 substances in streams without adjacent agricultural land use. “Our findings underscore the necessity of further investigating the non-agricultural entry pathways of pesticides and biocides to effectively mitigate their impacts on streams in non-agricultural catchments,” the authors state. They continue, “These streams often serve as critical refuge habitats and sources of recolonization, making their protection essential for biodiversity conservation.”

In analyzing nonagricultural streams, the researchers find pesticide contamination that, while lower than levels found in streams directly next to agricultural land, can occur through various routes and threatens biodiversity in essential ecosystems. As the authors describe: “Although pesticide concentrations were lower than in agricultural streams, the potential toxicity of pesticides was associated with a significant reduction in sensitive insect populations, as indicated by the SPEAR_pesticides index. Notably, 40% of the studied streams did not achieve a good status according to the pesticide specific SPEAR_pesticides indicator.”

The SPEAR_pesticides indicator is used “to identify pesticide effects on the aquatic invertebrate community. It measures the abundance of pesticide-sensitive species (“species at risk”) in relation to the abundance of all taxa,” the study explains. The calculated value then correlates with “five quality classes (high, good, moderate, poor and bad) following the ecological status classes laid out under the WFD [European Union (EU) Water Framework Directive].”

The study focuses on examining “13 streams located predominantly in protected areas with no agricultural land use in their catchments,” which leads to the hypothesis that, “Given the absence of direct pesticide input via runoff, any detected pesticide contamination is likely attributable to atmospheric deposition.” These areas were chosen due to the role of protected areas in contributing to biodiversity conservation.