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Combining Agrochemicals More Harmful to Bees than Previously Understood

Combining Agrochemicals More Harmful to Bees than Previously Understood
When multiple agrochemicals are used, their effects on bees can be magnified. Photo courtesy of Emily Bailes.

Bees perform critical services in ecosystems, including by pollinating the plants that humans and other animals rely on for food. According to new research, however, bees exposed to multiple types of agricultural chemicals face much greater risk than previously understood. The finding, published in the journal Nature, has researchers raising the alarm that regulatory approval processes need updating to allow for more consideration of the environmental risks brought about by these chemicals' interactions.

A new study from University of Texas at Austin researcher Harry Siviter and scientists at Royal Holloway, University of London found that bees that were exposed to multiple agrochemicals have a significantly higher mortality rate than would be predicted based on what's known about the impact of each agrochemical on its own.

Bees are routinely exposed to a combination of environmental stressors. The researchers analyzed data from the last two decades and found that when bees are exposed to stressors in combination, the interactions between the various factors increase bee mortality; in particular, exposure to multiple agrochemicals led to a sharp increase in bee mortality.

Worldwide, regulators determine whether agrochemicals are safe to use by focusing on one product at a time; they do not typically consider how agrochemicals interact with one another in relation to animal health. But the new paper's results confirm that exposure to combined stressors can have a far more harmful impact on bees than current environmental risk assessments predict.

"Bees are key to the health of our planet, but the number of stressors they encounter is increasing as a consequence of human activities," said Siviter, a postdoctoral fellow in UT Austin's Muth Laboratory and co-first author of the paper. "Crops are treated with multiple agrochemicals, so bees are routinely exposed to several different chemicals simultaneously. Our analysis found that the interactions between these chemicals significantly increased bee mortality, beyond the levels we would predict if we just added the negative impact of multiple chemicals together."

For this reason, scientists are urging regulators around the globe to consider the combined effects of agrochemicals during the approval process.

"Unfortunately, these interactions are not considered when agrochemicals are licenced for use, and so their impact on bees will be underestimated," Siviter added. He conducted the research at Royal Holloway, University of London alongside his co-first author Emily Bailes, currently at Bangor University, and co-authors Callum Martin, Thomas Oliver, Julia Koricheva, Ellouise Leadbeater and Mark Brown.

Felicity Muth, UT Austin assistant professor of integrative biology, and Siviter are among scientists calling for regulators to give more consideration of the additional impacts of agrochemicals on insects. The pair were among 14 researchers who signed on to a letter in Nature last month calling for decision-makers to change their approach to weighing agricultural chemicals' impacts on bees and other pollinators.

"Stricter laws are needed that are evidence-based, override vested interests and recognize pollinators as essential contributors to food security," wrote Adrian Fisher of Arizona State University along with Muth, Siviter and the other scientists.

Even effects that are not lethal on their own, like causing behavior changes or lower reproductive success, can combine with factors such as parasites, habitat destruction or other chemicals to harm bee health. The researchers also called for long-term environmental monitoring to study how agrochemicals and additives interact.

Adapted with permission from Royal Holloway, University of London.

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Saturday, 23 October 2021

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