Recent research indicates that fish fillets caught along the waterfront in Toronto have up to 12 times more microplastic compared to common store-bought alternatives.

While scientists are still trying to determine whether microplastics pose a direct risk to human health, the study co-authored by researchers from the University of Toronto and the Ontario Ministry of the Environment offers insight into how tire wear and other microplastic debris end up in fish — and on dinner plates.

The study stated, "The high number of particles observed in fish from Humber Bay highlights the need for extensive geographic monitoring, especially near microplastic sources."

Microplastics, no larger than the width of a pencil eraser down to the size of a mitochondrion, are ubiquitous, appearing everywhere from human blood to Arctic sea ice. In fish, these broken pieces of larger plastics have been linked to reduced growth and reproductive levels, among a host of other issues.

The researchers examined a total of 45 fish caught in Humber Bay, where the Humber River flows into Lake Ontario along the Toronto waterfront.

The study noted that microplastics appeared, in varying sizes and concentrations, at an average of 138 particles per fish, which is significantly higher than averages reported in other studies. For example, the U of T Research Lab found only 17 particles per fish in Lake Simcoe.

Madeline Milne, a co-author of the latest study, remarked that the findings show how microplastic pollution has become "a widespread environmental issue."

Milne, who conducted the study as part of an honors thesis at the University of Toronto with Professor Chelsea Rochman, said, "It's time for us to start thinking about how to fix this, whether through policy to reduce single-use plastics or thinking about solutions in the environment to clean up microplastics, and other types of solutions like that."

Despite the pollution, the study found no evidence that microplastics were accumulating in the bodies of fish as they aged.

Milne, now a graduate student at the University of Manitoba, added, "I think it's promising. I think we just need to understand why this is happening."

The authors note that the findings likely represent a "worst-case scenario" for freshwater fish contamination because they examined both the gastrointestinal tracts and fitness of the fish, whereas studies often look only at the intestines, and they discovered fish in a part of the lake known to be heavily polluted.

Milne, who recently co-authored a study examining common store-bought foods, indicated that Humber Bay fish had about nine to 12 times the microplastic per serving in their fillets compared to minimally processed Alaskan pollock. The study noted that the number of particles per gram of Humber Bay fish fillet, at about 0.5, was still within the range identified by a systematic review of other studies examining microplastics in seafood.

The study pointed out that the fillets are still pale compared to some other common ways humans are exposed to microplastics. The authors estimated that a person consuming two servings of Humber Bay fish fillets a week would ingest about 12,800 particles annually, compared to about 90,000 particles annually from bottled water.

The federal study, published on Wednesday, was described as "an important step."

Kahail, an associate professor at Memorial University in Newfoundland, said, "We are starting to get actual numbers so we can look at what our exposure is and then decide, is our exposure harmful or not."

However, he noted that further research is needed to determine whether this exposure is harmful and to what extent it is actually harmful.

Some studies have raised concerns.

A study published earlier this year in the New England Journal of Medicine, with notable limitations, found more evidence of inflammation in patients with microplastics in their bloodstream. Another from 2021 found that people with inflammatory bowel disease had higher levels of microplastics in their stool than healthy individuals.

Among the Great Lakes, microplastics were found to be most concentrated in Lake Ontario, according to an environmental report from the Ontario Auditor General last year.

In a statement via email, a spokesperson for the Ontario Ministry of the Environment, Conservation and Parks said it is studying microplastics in fish to provide "baseline information to help understand the degree of concern with available risk information."