Quebec study finds 'cocktail of different pesticides' in treated tap water

A recent Quebec study shows that a multitude of pesticides can be found in tap water, even after being treated at a water treatment plant.

Sébastien Sauvé, an environmental chemistry professor at Université de Montréal, supervised the study that was published in the June issue of the scientific journal Water Research. 

For more than two years, from 2021 to 2023, researchers collected water samples twice a week from the Châteauguay River in Quebec's Montérégie region. 

The samples were collected from the river as water was being pumped into a water treatment plant and were compared to treated water samples leaving the plant for distribution as drinking water.

The river was chosen because it runs through areas of intensive agriculture activity, where pesticides used by farmers eventually make their way from the fields into waterways. 

The objective, Sauvé said, was to look at how pesticide concentrations in the water varied over time, as well as before and after processing at a water treatment plant. 

Highest concentrations of pesticides occurred in June and July at the beginning of growing season, and while none of the samples collected exceeded Quebec guidelines for safe drinking water, researchers discovered that the treatment process did not effectively filter out pesticides.

Traces of at least 50 different kinds of pesticides and metabolites were found in tap water, in some cases in higher concentrations than the source water. Metabolites are molecules that result from the degradation or breakdown of pesticides.

"There is quite a bit," Sauvé said, adding some pesticides were found in almost all the samples, while others weren't detected as often.

"One of the main ones, or the highest concentration, was for glyphosate," Sauvé said, which is the main active ingredient used in many herbicide formulations. 

It is used to kill weeds and is commonly sold under the brand name Roundup.

In Quebec, many municipalities, including Montreal, have banned its sale and use for domestic purposes over concerns for the environment and possible impact on human health.

In 2015, the World Health Organization's International Agency for Research on Cancer (IARC) concluded that glyphosate was probably carcinogenic to humans. 

Health Canada, however, says it does not cause any harmful effects if used properly.