Pesticide contamination is associated with invertebrate community change in non-agricultural streams

Pesticides are frequently detected in protected regions, including biosphere reserves, but their ecological impacts within these ecosystems remain insufficiently studied. Here, we examined the presence and effects of pesticides in 13 streams situated in catchments without adjacent agricultural land use, where contamination was presumed to result solely from atmospheric transport. 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. Although mean pesticide levels were associated with distance weighted proportions of agricultural land use, the peaks of potential toxicity (TU_max) linked to ecological effects could not be associated with such quantitative measures of agricultural activity. They were mainly linked to insecticides and biocides not approved for agricultural use in Germany or phased out during the time of study, such as fipronil and neonicotinoids, and to a lesser extent also pyrethroids currently in use. We conclude that ecotoxicological impacts cannot be predicted by modelling aerial transport based on agricultural land use. Environmental monitoring is key to reveal impacts of pesticides and biocides in non-agricultural streams. Our results highlight the need for further investigation into non-agricultural entry pathways of pesticides and biocides in order to mitigate pesticide effects in these critical refuge biotopes.