The toxic burden of pesticides is growing all around the world

More than 60 years after Rachel Carson warned of the dangers of pesticides in her book Silent Springthe damage they cause to wildlife could be more severe than ever.

“In almost all countries, the trend is towards an increase in applied toxicity,” says Ralf Schulz of RPTU Kaiserslautern-Landau University in Germany.

The potential harm caused by any pesticide depends on both the amount applied and its toxicity, which can vary greatly between species. To assess the overall burden of pesticides, Schulz and his colleagues developed a measure called applied toxicity.

The researchers began by examining the quantities of 625 pesticides used in 201 countries from 2013 to 2019. The list includes some pesticides used by organic farmers as well as conventional farmers.

They then averaged data from regulators in several countries on the toxicity of each pesticide to eight major groups of organisms: aquatic plants, aquatic invertebrates, fish, terrestrial arthropods, pollinators, soil organisms, terrestrial vertebrates and land plants. This allowed the team to estimate the total applied toxicity by country or group of organisms.

Globally, total applied toxicity increased from 2013 to 2019 for six of eight organism groups. For example, for pollinators it increased by 13 percent, for fish by 27 percent, and for terrestrial arthropods, such as insects, crustaceans and spiders, by 43 percent.

“This does not mean that this toxicity necessarily results in toxic actions on these organisms,” explains Schulz. “But it’s at least an indicator that shows you whether the pesticides we use are more or less toxic to pollinators or to fish, or whatever.”

Many other studies have shown that pesticide concentrations in various environments, such as rivers, are higher than what regulators assessed when approving pesticides.

“It’s not included in this index, but there is plenty of evidence,” says Schulz. There’s a problem with risk assessments that significantly underestimate exposure, he says.

The increase in total applied toxicity is due to two things: an increase in the quantities of pesticides used and the replacement of older pesticides with even more toxic ones. This is mainly due to the evolution of resistant pests. “Resistance is, in my opinion, something that can only increase if chemical pesticides are used,” says Schulz.

Pesticides called pyrethroids are particularly problematic, especially for fish and aquatic invertebrates, he says, even though they are only supposed to be applied at low levels. Neonicotinoids are another problematic group, particularly for pollinators.

There have been calls to ban the herbicide glyphosate, also known as the weedkiller Roundup. Although its toxicity is not high, because large amounts of glyphosate are used, it contributes to the total toxicity applied, says Schulz. A ban could also have the opposite effect: applied toxicity would increase if more toxic herbicides were used instead.

Reducing pesticide use more broadly could also have unintended consequences. If this reduced farm productivity, more agricultural land would be needed, leading to a loss of biodiversity if cleared.

At a United Nations biodiversity summit in 2022, countries agreed to reduce the “overall risk” from pesticides by at least half by 2030. Exactly what “risk” means has never been defined, Schulz says, but he thinks total applied toxicity would be one way to measure it.

The approach has its limitations, but no measure of overall pesticide use will be perfect, says Roel Vermeulen of Utrecht University in the Netherlands. “Even in a context of uncertainty, the trends it reveals are troubling,” he says. “The world is currently moving further away from the UN target than towards it. This is bad news for ecosystems and, ultimately, for human health.”

“Importantly, the study also shows that a relatively small number of highly toxic pesticides cause most of the overall risk, meaning there are clear and practical goals for which action could have an outsized benefit,” says Vermeulen.

Transforming agriculture will require broader societal change, he says. “Consumers must be prepared to accept changes in their diet, reduce food waste and pay fair prices that reflect the true environmental costs of production. »