Despite a reduction in the total amounts of pesticides used, the toxicity of commonly used pesticides to nontarget species, partially aquatic invertebrates and pollinators, has increased considerably in recent decades, according to a new study analyzing 25 years of pesticide use. This has been driven by the widespread use of highly toxic pyrethroid and neonicotinoid pesticides. The findings challenge claims suggesting that the overall environmental impacts of pesticide use have declined. The impacts of applied pesticides on humans and the environment are often based on comparisons of use rates (e.g., kilograms per hectare) or the total amounts used (e.g., kilograms per year). However, from an environmental perspective, these weight-based measurements often fail to account for the specific toxicity of applied pesticides, which can vary over several orders of magnitude. While fewer pesticides are routinely used today, the types - and their toxicity - have changed considerably. To better understand the environmental impacts of pesticides over time, Ralf Schulz and colleagues used data from the U.S. Geological Survey and the U.S. Environmental Protection Agency and designed a weight-based assessment of the use of 381 pesticides for the years 1992 to 2016. It evaluated pesticide effects, in terms of toxicity, on eight nontarget species groups. The authors further accounted for the way pesticide use has undergone substantial changes with the implementation of pesticide-tolerant genetically modified crops. Schulz et al. found that, despite decreasing total amounts applied and decreased impacts on vertebrates, the toxicity of pesticides has increased substantially for nontarget aquatic invertebrates, including crustaceans and waterborne insect larvae, as well as pollinator species like bees. These impacts seem to be associated with recent increases in the use of pyrethroid and neonicotinoid insecticides. What's more, the authors discovered increasing toxic effects to nontarget invertebrates and pollinators in genetically modified corn and to terrestrial plants in herbicide-tolerant soybeans over the last decade. "In light of the multiple emergent risks and resistance problems," say the authors, "pesticide risks should be more integrated into policy strategies to develop resilient global production systems."

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