Credit: Ferris842/Wikimedia

Pesticides are all over the St. Lawrence River — many at levels that hurt fish and invertebrates

Scientists tested the river system and found nearly one-third of the samples had neonicotinoid pesticides at levels higher than the threshold to protect aquatic creatures. Glyphosate and atrazine were in more than 80% of samples.

Harmful pesticides such as glyphosate, atrazine and neonicotinoids were found in nearly all samples of water from the St. Lawrence River and its tributaries, with many samples containing levels higher than the guideline to protect aquatic life, according to new research.


The St. Lawrence River is one of North America's major water systems—draining a 500,000 square mile watershed that contains the Great Lakes.

"The freshwater inputs of the St. Lawrence provide a source of drinking water production for more than half of the population of the province of Quebec," the authors wrote.

The study, published in Environmental Pollution, found that 99 percent of 68 water samples collected from the large water system contained at least one of the 10 pesticides researchers tested for and 31 percent of the samples contained neonicotinoids at levels higher than Canada allows.

"I wasn't that surprised to find that [the pesticides] are ubiquitous, it's difficult to find water not covered with them," Sébastien Sauvé, senior author of the study, researcher and Vice Dean at the Faculty of Arts and Science at the Université de Montréal, told EHN. "What did surprise me was the number of times the environmental guidelines were exceeded."

Neonicotinoids—widely used on corn, cotton, sorghum, soybeans and on some other fruits and vegetables—are thought to be at least partially behind bee declines in recent years and also have been linked to widespread impacts on aquatic insects and invertebrates.

Scientists in 2016 concluded "the decline of many populations of invertebrates, due mostly to the widespread presence of waterborne residues and the extreme chronic toxicity of neonicotinoids, is affecting the structure and function of aquatic ecosystems."

The chemicals are "really taxing the biodiversity in those rivers and waterways," Sauvé said.

Consistently contaminating water

Credit: Canadian Geographic

The new research adds to evidence that neonicotinoids, along with glyphosate and atrazine, are increasingly contaminating freshwater—and people's drinking water—in farming regions.

In the new study, researchers tested for glyphosate, atrazine and a suite of neonicotinoids. Glyphosate was found in 84 percent of the samples and atrazine was found in 82 percent.

However, concentrations of both compounds were "well below the Canadian water quality guidelines for the protection of aquatic life," the authors wrote.

In a companion paper to the new study, the scientists found atrazine and one of its metabolites in all 450 water samples taken from 2015 to 2018 from drinking water in Quebec.

"This signals the potential exposure of a large portion of the population of Quebec to low yet chronic levels of these herbicides in drinking water produced from the river," the authors wrote.

Sauvé said they saw two spikes in the pesticides—one in early summer and another in fall.

In the U.S., atrazine, another widely used herbicide most often found in Midwest water, contaminates an estimated 7.6 million Americans' tap water, according to a 2017 report from the environmental nonprofit Environmental Working Group.

It's not just atrazine showing up in people's water: In recent years, scientists have reported neonicotinoids in multiple sites in the Great Lakes region including: southern Ontario, Canada, drinking water, New York and Pennsylvania streams, and central Wisconsin groundwater.

Another U.S. study found glyphosate in about 60 percent of surface waters sampled, though most were lower than U.S. and Canadian human health and aquatic life thresholds.

Glyphosate is the main ingredient in Monsanto's Roundup herbicide. Monsanto is now a unit of Bayer AG, which suffered one of its worst losses in 16 years after a court ruled Roundup caused a man's cancer. The herbicide, which is one of the most widely used in history, is the current focus of more than ten thousand lawsuits from people alleging Roundup and other glyphosate products caused them to develop non-Hodgkin lymphoma.

Glyphosate, though long touted as safe for wildlife, has been linked to changes in metabolism, growth, behavior and reproduction of certain fishes, mollusks and insects.

Atrazine is also classified as a possible carcinogen to humans by Health Canada, and has been associated with impacts to the human endocrine system as well.

An assessment last year by the the U.S. EPA last year found atrazine was unlikely to cause cancer, a determination widely skewered by health researchers and advocates as the assessment relied heavily on industry studies.

It's not clear what consistent exposure to these chemicals through drinking water might be doing to people. Sauvé said that they did not find any pesticides at levels higher than what is allowed in drinking water. "But are the guidelines for drinking water protective enough? That's another conversation," he said.

As countries increasingly scrutinize, ban or limit neonicotinoids, Sauvé and colleagues are currently examining some of the proposed alternatives.

He said there needs to be more independent research on the alternatives—when they did a literature review, they found most of the studies so far are tied to industry.

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