June 23, 2021 | Small streams are prone to excessively high levels of pesticide contamination that are even more hazardous than once thought, according to a pilot study by a team of German researchers and published in Water Research. The results indicate significant risks for the health of aquatic ecosystems and should be used as evidence for establishing greater protections from toxic pesticide use, researchers say. Scientists established monitoring sites at more than 100 streams throughout Germany over the course of two years. Most sites were established near farm fields, where chemical farmers will use highly toxic pesticides that often make their way into local waterways. The results are significantly worse than researchers anticipated. “We have detected a significantly higher pesticide load in small water bodies than we originally expected,” said Matthias Liess, PhD, ecotoxicologist and coordinator of the water monitoring project. The regulatory standards are exceeded in 81% of streams tested. For nearly one in five streams, regulatory limits are exceeded for over 10 different pesticide compounds. For the most sensitive aquatic species, such as caddisflies and dragonflies, researchers say that these species require 1,000x lower threshold values than less sensitive animals like snails and worms. “For sensitive insect species, the pesticide concentration in the small lowland streams is the most relevant factor that determines their survival. 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 researcher said. [Liess, Matthias et al. Pesticides are the dominant stressors for vulnerable insects in lowland streams, Water Research, 201:117262, 2021.]
