Glyphosate a threat to freshwater ecosystems, research suggests — even when used according to guidelines

Scapholeberis mucronata is one of the few zooplankton species that showed resistance to glyphosate throughout the research. (Marie-Pier Hébert)

MONTREAL -

Glyphosate, commonly sold under the brand name Roundup, is a popular herbicide sprayed everywhere from industrial crops to backyard gardens.

It’s also an herbicide that’s highly controversial, with some research linking it to cancer, although the extent of this risk is inconclusive. Many experts, including authorities at Health Canada, say glyphosate isn’t harmful to human health if used according to label directions.

But human health aside, new research from McGill University suggests the herbicide has alarming consequences for an entirely different kind of life form: zooplankton.

Zooplankton are tiny, often microscopic organisms that are fed on by fish and insects.

“Because plankton form the foundation of the food chain in freshwater ecosystems, it is very important to understand how plankton communities respond to widely used pesticides,” said Jesse Shapiro, a researcher and professor of microbiology and immunology at McGill.

The research was presented within two papers, one published in Molecular Ecology and the other in Ecological Applications.

The studies found that glyphosate levels as low as 0.1 mg/L can cause diversity loss within zooplankton communities. This finding is particularly concerning, says Shapiro, as it shows communities can be "impaired under currently acceptable North American water quality guidelines."

The effects of nutrient fertilizers and a pesticide called “imidacloprid” were also studied, but glyphosate packed the biggest punch.

“We found that when we applied the pesticides and fertilizers alone and in combination, at a wide range of concentrations, that glyphosate was the most influential driver of community structure among the agrochemicals,” said researcher and McGill biology professor Andrew Gonzalez.

After glyphosate was introduced to a zooplankton community, the abundance of these microscopic organisms eventually recovered within three weeks. However, the diversity of this recovered population was significantly lowered — and diversity is key to a healthy ecosystem.

“Long-lasting species loss and compositional shifts have clear implications for the functioning and stability of freshwater ecosystems, even when zooplankton abundance appears unaffected,” said researcher Marie-Pier Hébert, a PhD candidate in McGill’s Department of Biology.

But how can a community’s population restabilize when the diversity of that same population has been slashed?

According to researchers, it likely comes down to which zooplankton are more sensitive to glyphosate’s toxicity. Fragile species will die out at higher rates, allowing more tolerant species to dominate, homogenizing the population as a result.

Although a lack of diversity is never a good thing, the extent to which real-world glyphosate use has impacted zooplankton communities is not yet fully understood, according to Hébert.

“How the effects of glyphosate cascade through freshwater ecosystems to affect their health in the long-term deserves much more study,” she said.

Earlier this year, the federal government set forth a proposal to increase the amount of glyphosate residue allowed on certain foods imported into Canada.

Health Canada told CTV News the amounts of glyphosate used by Canadian farmers is not expected to increase, as they must follow label instructions.