Sarah Rennie – LJI reporter
The Société de Conservation et d’Aménagement du Bassin de la Rivière Châteauguay (SCABRIC) held a conference prior to its annual general meeting, in order to unpack recent research that reveals pesticide levels persist in treated municipal drinking water drawn from the Chateauguay River.
Sébastien Sauvé, a Université de Montréal environmental chemistry professor and lead author on the study, presented his findings to a crowded room in Sainte-Martine on May 29. His work, which was published in the June edition of the scientific journal, Water Research, found that over 50 different kinds of pesticides and metabolites, which are transformation products that result from the breakdown of pesticides, remain in tap water even after it has been processed at a water treatment plant.
Sauvé has been focusing his research on the Montérégie Ouest for several years because of the intensive agricultural activity that takes place along waterways, including the Chateauguay River. His previous work established that pesticides such as glyphosate and neonic are present in the region’s surface waters. This new study aimed to determine the temporal trends of pesticide concentrations in the surface water, and the associated health risks of human exposure from drinking water.
Over 838 days between 2021 and 2023, Sauvé and his team collected water samples twice a week from the Chateauguay River near where its waters were being pumped into a treatment facility. The samples were then compared with ones taken from the water as it was leaving the plant to be consumed as drinking water.
Researchers found that peak concentration for pesticides occurred in June and July, and that some transformation products were found in higher concentrations than their parent compounds in the surface water. Sauvé noted that while most pesticides remained in the treated water, up to 11 pesticides and one transformation product showed higher levels in drinking water than the raw sample. He attributed this to some compounds transforming during the treatment process that allowed them to become measurable.
“Roughly speaking, there was no difference in terms of pesticides in the water before and after treatment,” said Sauvé, who explained this does not mean the water treatment facilities are not working properly; they are just designed to remove bacteria.
Sauvé pointed out that his was the first study to investigate the health risks of parent pesticides and their transformation products in drinking water by using long-term sampling. His research argues for the regulation of acceptable levels of metabolites in drinking water, and the need to integrate more advanced treatment technologies into water treatment plants.
“There are a number of parameters that are well measured and well controlled,” Sauvé said, noting that there are specific Quebec standards for pesticides. “When we compare ourselves with the toxicity thresholds that are recognized and used in Quebec, we are not in a risk zone,” he confirmed.
“However, these are all individual risk levels. In toxicology, we know there are multiplier effects when we are exposed to several toxic elements at the same time,” he cautioned, noting they are not presently able to calculate or estimate these effects.