Pesticide usage in the US has declined by more than 40 percent over the last three decades, and some organisms, including mammals and birds, have benefitted from the reduction in pesticide usage and improvements in product design, according to a study published April 2 in Science. But an increase in pesticide potency has come at the expense of other species’ health.
“Compounds that are particularly toxic to vertebrates have been replaced by compounds with less vertebrate toxicity, and that is indeed a success,” coauthor Ralf Schulz, an ecotoxicologist at the University Koblenz and Landau in Germany, tells The Guardian. “But at the same time, pesticides became more specific, and therefore, unfortunately, also more toxic to ‘non-target organisms’, like pollinators and aquatic invertebrates.”
Schulz and his team combined self-reported US Geological Survey data on farmers’ use of 381 pesticides between 1992 and 2016 with data from the Environmental Protection Agency (EPA) on the toxic dosage effects of these chemicals on eight types of animals and plants: fish, mammals, birds, pollinators, terrestrial and aquatic invertebrates, and terrestrial and aquatic plants. Using the two data streams, the authors calculated a “total applied toxicity” value for each group to assess changes in pesticide usage and their effects over time.
Taken together, the results show that despite the drop in their usage, pesticides continue to negatively affect many different forms of life. The toxicity level of pesticides doubled for aquatic invertebrates such as plankton and insect larvae, and the same was true of important pollinators such as bees. Mammals and birds were the only groups to benefit over the course of the study—their toxicity values dropped by more than 95 percent—but even these groups may be negatively affected through changes to the food web.
“The bottom line is that these pesticides, once believed to be relatively benign and so short-lived that they would not damage ecosystems, are anything but,” Lynn Goldman, a former EPA scientist who was not part of the study, tells the Associated Press.
The results are largely a reflection of how technology has changed the landscape of pesticide design. Pesticides have become stronger, sometimes requiring only 6 grams per hectare compared with several kilograms of older chemicals such as organophosphates and carbamate pesticides, Science reports. And companies have also gotten better at tailoring their products to target particular agricultural pest species while minimizing unintended damage to other organisms, although they aren’t so specific that they can distinguish between pests and potentially beneficial insects.
This tradeoff between vertebrates and invertebrates could have unintended consequences for the health and functioning of ecosystems, says Schulz. Aside from their importance as pollinators, many insect species are food for other animals, and the current study does not measure the accumulation of toxins up the food web, something Schulz tells the AP he would like to see followed up on in future research.
In the current study, plants also registered increasing levels of toxicity, even among species that have been genetically modified to reduce their need for pesticides. One strain of corn, for example, had been modified to produce an insect-killing chemical, but as the insects have evolved a tolerance to the chemical, farmers have responded with more-frequent applications of other pesticides. Wild plants are also susceptible to pesticide toxicity, especially from commonly used weed killers, and their use risks reducing the overall plant diversity in undeveloped areas surrounding agricultural fields.
To avoid this future, countries around the world will need to think more critically about their use of pesticides, John Tooker, an entomologist at Penn State who was not involved in the research, tells Science. “The patterns in the US pesticide use and toxicity data should be a cautionary tale for the rest of the world, much of which seems to be leaning more heavily on pesticide use rather than ecological interactions for pest control.”