Microplastics in Great Lakes Drinking Water: Latest Research and Health Implications

Microplastic contamination in the Great Lakes has emerged as one of the most pressing environmental research priorities in freshwater science. Since the first comprehensive surveys in 2012, researchers have documented widespread microplastic pollution across all five Great Lakes, raising questions about drinking water safety, aquatic ecosystem health, and the effectiveness of current wastewater treatment technologies.

What the Research Shows

The Rochester Institute of Technology (RIT) has operated the most extensive microplastic monitoring program in the Great Lakes since 2012. Their surface water surveys, using standardized trawl methods at over 100 sampling sites, have documented an average concentration of 43,000 microplastic particles per square kilometre across the Great Lakes surface. This makes the Great Lakes among the most microplastic-contaminated freshwater systems globally in terms of surface concentration.

Contamination levels vary significantly among the lakes. Lake Erie and Lake Ontario, which receive the highest urban and industrial wastewater inputs relative to their volume, consistently show the highest surface concentrations, with some nearshore areas exceeding 100,000 particles per square kilometre. Lake Superior, with its lower population density and larger volume, shows the lowest concentrations but is not free from contamination.

A 2024 study published in Water Research by researchers at McGill University analyzed sediment cores from Lake Ontario and found that microplastic deposition has increased approximately tenfold since the 1970s, with the most rapid increase occurring after 2000. The study identified polyester fibres from synthetic clothing as the most common microplastic type in sediment samples, followed by fragments of polyethylene and polypropylene from degraded plastic packaging.

Sources of Microplastic Pollution

Research has identified several primary pathways through which microplastics enter the Great Lakes. Municipal wastewater treatment plants represent the single largest documented point source. A study conducted by the Ontario Ministry of the Environment at 12 Great Lakes wastewater treatment plants found that treated effluent discharged an average of 6 million microplastic particles per facility per day. While modern tertiary treatment removes approximately 95 to 99 percent of microplastics from incoming wastewater, the sheer volume of wastewater processed means that significant quantities still reach the lakes.

Stormwater runoff from urban areas carries microplastics from road surfaces (tire wear particles), building materials, and litter into tributaries and directly into the lakes. A monitoring study of Toronto’s Don River watershed found microplastic concentrations in stormwater runoff that were 10 to 100 times higher than concentrations in treated wastewater.

Atmospheric deposition is an increasingly recognized pathway. Researchers at the University of Western Ontario have documented microplastic particles in rain and snow samples collected at rural sites across the Great Lakes basin, indicating that wind-transported microplastics can travel hundreds of kilometres from urban source areas before being deposited on water or land surfaces.

Drinking Water Implications

The Great Lakes supply drinking water to over 40 million people in Canada and the United States. Studies of treated drinking water from Great Lakes municipal systems have detected microplastics, though at concentrations far lower than those found in untreated lake water.

A 2023 analysis by the Ontario Drinking Water Surveillance Program tested finished drinking water from 15 Great Lakes municipal treatment plants and found detectable microplastics in all samples, with concentrations ranging from 0.5 to 8.2 particles per litre. These concentrations are comparable to levels found in treated drinking water systems worldwide.

The World Health Organization’s 2023 assessment of microplastics in drinking water concluded that current evidence does not indicate a significant health risk from microplastic ingestion at the concentrations typically found in treated drinking water. However, the WHO noted significant knowledge gaps regarding the toxicity of microplastic-associated chemicals and the potential health effects of long-term, low-level exposure, and recommended continued monitoring and research.

Regulatory Response

Canada has taken several regulatory actions to address microplastic pollution sources. The federal government banned the manufacture and import of plastic microbeads in toiletries in 2018 under the Canadian Environmental Protection Act. In 2024, Environment and Climate Change Canada added “plastic manufactured items” to Schedule 1 of CEPA, providing the legal basis for additional regulations targeting plastic pollution sources.

Ontario’s proposed regulations under the Resource Recovery and Circular Economy Act include provisions for reducing textile microfibre releases through standards for washing machine filtration. France has already mandated microfibre filters on new washing machines sold after January 2025, and similar requirements are under discussion in Canada and several U.S. states.

Ongoing Research

The International Joint Commission identified microplastics as a chemical of mutual concern under the Great Lakes Water Quality Agreement in 2024, triggering a requirement for both countries to develop coordinated monitoring and management strategies. A binational science team is currently developing standardized monitoring protocols to enable consistent comparison of microplastic data across the Great Lakes.

The Canadian government committed 6.7 million dollars in Budget 2024 to fund a five-year Great Lakes Microplastics Research Program, based at the Canada Centre for Inland Waters in Burlington, Ontario. The program will conduct systematic monitoring of microplastic concentrations, types, and sources across the Canadian Great Lakes and assess the effectiveness of existing and emerging treatment technologies.