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Document the presence of pharmaceutical products in municipal effluents in the Montréal region and assess their effect on aquatic fauna

Context and project description

The Montréal purification station alone creates half of all wastewater discharged into the St. Lawrence in Quebec. We know that the discharge of these urban effluents constitutes a major source of pollution for the river. We also know that these discharges contain numerous chemical products, to which many new components are added year after year, including many pharmaceutical substances. But we still know too little about what happens to these substances in purification stations and about the risks that they create for the environment and human health once they are discharged into the environment.

It is to mitigate this lack of knowledge that the SLAP has created a project aiming to document the presence of pharmaceutical products in the Montréal region’s effluents and to evaluate their effects on aquatic life. The project includes a whole series of research looking as much at the substances themselves and the products of their degradation as the organisms in the river that may be affected. The researchers will study, among other things, substances from anti-inflammatory medications, antidepressants and antibiotics, and study the effects of their accumulation in the tissues of indicator organisms (mussels, fish and birds).


Knowledge has been acquired regarding effluents and their effects on the St. Lawrence. This project involved designing and testing a multi-level biological approach for assessing the impacts of municipal effluents on yellow perch in the St. Lawrence. The study showed that municipal wastewater discharges have a measurable effect on yellow perch exposed to them. Numerous statistical relationships were identified between the presence of contaminants, such as perfluorinated compounds, flame retardants, metals and trace elements, and certain biological responses in the fish. The findings of this study were published in the journal Science of the Total Environment [1] and in a  St. Lawrence Action Plan fact sheet (PDF, HTML).

The project also led to the publication of a second article in Science of the Total Environment [2] in spring 2016. This article describes the results of the first comparative study of three natural degradation processes for two pharmaceuticals commonly found in surface waters: diclofenac (an anti-inflammatory drug) and sulfamethoxazole (an antibiotic). The results confirm that the degradation processes (photolysis, or exposure to sunlight, and biodegradation in aerobic and anerobic conditions) affect the time it takes for these products to break down in water.

This project helped provide a better understanding of the behaviour of pharmaceuticals and other emerging substances that are present in municipal effluents and of their effects on aquatic fauna. Research is continuing as part of a new project aimed at evaluating the effect of ozone treatment of City of Montreal wastewater.

[1] For more information, see the original article, “A multi-level biological approach to evaluate impacts of a major municipal effluent in wild St. Lawrence River Yellow Perch (Perca flavescens)” (Science of the Total Environment, 2014, No. 497-498, pp. 307–318).

[2] For more information, see the original article, “Degradation of the pharmaceuticals diclofenac and sulfamethoxazole and their transformation products under controlled environmental conditions” (Science of the Total Environment, 2016, No. 557-558, pp. 257–267).

Participating departments

Government of Canada

  • Environment and Climate Change Canada

Government of Quebec

  • Ministère du Développement durable, de l’Environnement et de la Lutte contre les changements climatiques