Concentrations of pharmaceutical products in the St. Lawrence River sometimes exceed thresholds at which toxic effects on fauna and flora are observed, according to a new Montreal study. Rivers that flow into the river have the same problem.
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“Other studies have shown that there are pharmaceutical products in waterways, including in Quebec, but we have five years of data that show that this is a chronic situation and not a one-off problem,” explains Sébastien Sauvé, Chemist at the University of Montreal, the lead author of the study published in the journal Science of the Total Environment.
However, the only Canadian standard for a pharmaceutical product is adhered to. This is carbamazepine, an anticonvulsant. “But for many other drugs there are toxicity studies in the scientific literature,” says Mr. Sauvé. We calculated a risk quotient from these studies. » High levels of caffeine have also been detected.
A significant proportion of water samples exceed this risk quotient for ibuprofen (28% of samples) and the anti-inflammatory diclofenac (59% of samples).
PHOTO PROVIDED BY MARC-ANTOINE VAUDREUIL
The vessel used during the sampling campaign
The ozonation plant planned for the Montreal wastewater treatment plant in 2028 is intended to eliminate pharmaceutical molecules. However, according to Sauvé, under certain conditions an ozonation plant can produce byproducts of these pharmaceutical molecules that are even more toxic. “If there is a strong flow, for example during heavy rain, the treatment in the ozonation plant may not last long enough to remove these byproducts. » It would then be necessary to interrupt the ozonation for a certain period of time or to create retention basins in front of the system.
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Sampling was carried out downstream and upstream of the discharges of wastewater from the Montreal wastewater treatment plant. Upstream, drug concentrations are slowly increasing due to wastewater from water treatment plants in suburban cities. Then they have a peak opposite where Montreal's wastewater is released in the east of the island.
“We can see the place where the wastewater from the sewage treatment plant rises to the surface,” explains Marc-Antoine Vaudreuil, doctoral student and co-author of the study. “It is visible and it smells. » The wastewater is visible on the surface for several kilometers and the pharmaceutical products can be measured over 70 km to Lake Saint-Pierre.
In Quebec, a more distant peak is noticeable and concentrations of pharmaceutical molecules are measurable up to the location where the influence of salt water is felt. “With salt, organic material precipitates very quickly,” says Mr. Sauvé.
The next step is to measure the effects of these drugs on river organisms. Due to the high flow speed of the river, there is no large accumulation of these molecules in the sediments. But organisms still come into contact with these pharmaceutical products in the water, argues Mr. Sauvé.
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7200 nanograms per liter Maximum caffeine concentration observed in the St. Lawrence River near Montreal
SOURCE: WHOLE ENVIRONMENT SCIENCE