Small streams are important refuges for biodiversity, yet knowledge of the effects of agricultural pesticides on these freshwater bodies is limited.
Researchers have used national monitoring data to determine the number of small streams in Germany where regulatory acceptable concentrations (RACs) of pesticides are exceeded. An analysis of data covering almost 500 pesticides and over 2 000 small streams suggests that agricultural land use is a major contributor of pesticides to streams. Overall, RACs were exceeded at 26% of sampled streams, and exceedances were 3.7 times more likely if a stream was near agricultural land.
“This finding may have implications for environmental monitoring and agrienvironmental measures”,
Science for Environment Policy explains, 5 June 2018.
Small streams are important refuges for biodiversity. In agricultural areas, they may be at risk from pesticide pollution. However, most related studies have been limited to a few streams on the regional level, hampering extrapolation to larger scales.
We quantified risks as exceedances of regulatory acceptable concentrations (RACs) and used German monitoring data to quantify the drivers thereof and to assess current risks in small streams on a large scale. The data set was comprised of 1 766 104 measurements of 478 pesticides (including metabolites) related to 24 743 samples from 2301 sampling sites. We investigated the influence of agricultural land use, catchment size, as well as precipitation and seasonal dynamics on pesticide risk taking also concentrations below the limit of quantification into account. The exceedances of risk thresholds dropped 3.7-fold at sites with no agriculture. Precipitation increased detection probability by 43%, and concentrations were the highest from April to June.
Overall, this indicates that agricultural land use is a major contributor of pesticides in streams. RACs were exceeded in 26% of streams, with the highest exceedances found for neonicotinoid insecticides. We conclude that pesticides from agricultural land use are a major threat to small streams and their biodiversity. To reflect peak concentrations, current pesticide monitoring needs refinement.