Développement durable, Environnement, Faune et Parcs Bandeau du ministère du Développement durable, de l'Environnement, de la Faune et des Parcs
Accueil Plan du site Pour nous joindre Portail gouvernemental A propos du site Recherche English

Press releases


Quebec, August 9, 2001 – Environment Canada and the Quebec Environment Department have today issued a report titled, Toxic Potential Assessment of Municipal Wastewater Treatment Plants in Quebec. This study, conducted under the aegis of the Canada-Quebec St. Lawrence Vision 2000 Action Plan (SLV 2000), provides a snapshot of the potential toxicity of effluents generated by 15 municipal wastewater treatment plants in Quebec.

Sampling campaigns were carried out from 1996 to 1999 at 15 different wastewater treatment plants, in winter and summer operating conditions. The plants are representative of the treatment methods most commonly used in Quebec and service over 50% of the population. The effluent discharges of the 15 plants were compared to assess their potential toxicity, identify the substances that are likely responsible for this toxicity, and determine the causes and the factors at play.

A main finding of the report is that the toxic potential of municipal wastewater treatment plants varies from one facility to an other, and that both the toxicity and the concentrations of substances measured change greatly on a daily basis. A seasonal variation was also noted for certain substances, including ammonia nitrogen.

The toxicity test results show that the treated wastewaters of the majority of plants exhibit a certain degree of toxicity before being diluted in the receiving water. Given the low amplitude of these toxicity values, however, municipal effluents are not, with only a few exceptions, harmful to the test organisms. The substances mainly responsible for the post-treatment toxicity are ammonia nitrogen, followed by the surfactants contained in household and industrial cleaning agents. This is the case for aerated lagoons, for example, which generate ammonia nitrogen at concentrations exceeding 10 mg/L in winter. Other substances like certain pesticides and metals could also be responsible for the recorded toxicity.

Further, our evaluation of values exceeding the water quality criteria points up the presence of organic substances that had rarely ever been quantified in municipal effluents till now. These substances, PCBs and chlorinated dioxins and furans, are occasionally found at concentrations that could lead to the contamination of fish, which could nonetheless be consumed within certain restrictions. To determine the real impact of these substances, however, we must consider the quantity discharged daily relative to the capacity of the receiving water.

Furthermore, the result of the study show that municipal treatment plants that do respect the discharge requirements set by the Quebec Environment Department might have a difficult time further reducing the toxicity of their effluents. The introduction of additional equipment to this end would likely be costly and relatively ineffective given the volume of effluents discharged and the dilution of contaminants in receiving waters. Nonetheless, solutions must be found to some of the problems inherent to certain treatment types in order to reduce effluent toxicity.

The report also recommends that the focus should rather be on at-source reduction, where such efforts would be much more effective and much less costly, particularly for industry. Public awareness campaigns could also help to reduce the use of certain contaminants (pesticides and surfactants) in household applications.

To reduce the toxicity of municipal effluents, the Quebec Environment Department plans to identify and rank, in order of priority, the potentially problematic treatment plants. Toxicity tests and analyses of toxic substances could then be added to the regular monitoring activities of treatment plants, and the problem plants would be subject to a toxicity-reduction plan.

Toxic Potential Assessment of Municipal Wastewater Treatment Plant Effluents in Quebec is available on the SLV 2000 web site (www.slv2000.qc.ec.gc.ca).




Guy Gagnon
Ministère de l’Environnement du Québec
(418) 521-3823

Thérèse Drapeau
Environnement Canada
(514) 283-2343


Jean Maurice Latulippe
Ministère de l’Environnement du Québec
(418) 521-3860

Marie-France Bérard
Environnement Canada
(514) 283-0178

  Retour aux communiqués

Gouvernement du Québec
© Gouvernement du Québec, 2018