Municipal wastewater effluents are one of the largest sources of pollution to Canadian waters

What are wastewater effluents?

"Wastewater" means a mixture of liquid wastes primarily composed of domestic sewage, that can also include other liquid wastes from industrial, commercial and institutional sources. "Effluent" means untreated or treated wastewater that is released from the outfall(s) of a wastewater system.

Wastewater may contain a large number of potentially harmful pollutants, including some that are the result of biological activity (e.g. human wastes) and others such as the over 200 identified chemicals from industries, institutions, households, and other sources.

Across Canada, a high proportion of the population is served by municipal wastewater collection and treatment systems. Throughout Canada, the level of treatment to remove pollutants prior to discharge varies, ranging from no treatment to very sophisticated and thorough treatments. Wastewater effluents are released to a wide variety of receiving environments: lakes, ponds, streams, rivers, estuaries and oceans. Accordingly, effluents released from wastewater systems do contain pollutants of concern since even advanced treatment systems are unable to remove all pollutants and chemicals. Furthermore, some sewer collection and treatment systems are combined with stormwater collection systems that can become overloaded during heavy rainfalls, resulting in the release of partially treated effluents.

The 2001 report "The State of Municipal Wastewater Effluents in Canada" descibes the sources and the nature of contaminants entering municipal sewer systems, levels of municipal wastewater treatment across Canada, the impacts that municipal wastewater effluents can have on water quality, plant and animal life and the implication of impacts for human health and beneficial water uses, such as shellfish harvesting and recreation.

Impacts of Pollutants in Wastewater on Ecosystems and Human Health

Several environmental and health impacts of wastewater effluents have been identified in the scientific literature and actions need to be taken to reduce these impacts. These impacts include negative effects on fish and wildlife populations, oxygen depletion, beach closures and other restrictions on recreational water use, restrictions on fish and shellfish harvesting and consumption and restrictions on drinking water consumption.

Some examples of pollutants that can be found in wastewater and the potentially harmful effects these substances can have on ecosystems and human health include:

decaying organic matter and debris can use up the dissolved oxygen in a lake so fish and other aquatic biota cannot survive;
excessive nutrients, such as phosphorus and nitrogen (including ammonia), can cause eutrophication, or over-fertilization of receiving waters, which can be toxic to aquatic organisms, promote excessive plant growth, reduce available oxygen, harm spawning grounds, alter habitat and lead to a decline in certain species;
chlorine compounds and inorganic chloramines can be toxic to aquatic invertebrates, algae and fish;
bacteria, viruses and disease-causing pathogens can pollute beaches and contaminate shellfish populations, leading to restrictions on human recreation, drinking water consumption and shellfish consumption;
metals, such as mercury, lead, cadmium, chromium and arsenic can have acute and chronic toxic effects on species.
other substances such as some pharmaceutical and personal care products, primarily entering the environment in wastewater effluents, may also pose threats to human health, aquatic life and wildlife.

For more information refer to our list of Reference Documents

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ETAD

About Wastewater

What are wastewater effluents?

Impacts of Pollutants in Wastewater on Ecosystems and Human Health