Microplastic pollution discovered in St. Lawrence River sediments

Previously undocumented in North American rivers, concentrations of microplastic particles found in the St. Lawrence have proven to be as high as in the world’s most contaminated ocean sediments.
The microbeads found at the bottom of the St Lawrence River likely originate from cosmetics, household cleansers or industrial cleansers – all products in which they are commonly used as abrasives.

By Cynthia Lee

A team of researchers from McGill and the Quebec government has discovered microplastics (in the form of polyethylene ‘microbeads,’ less than 2 mm in diameter) widely distributed across the bottom of the St. Lawrence River, the first time such pollutants have been found in freshwater sediments.

The microbeads likely originate from cosmetics, household cleansers or industrial cleansers – all products in which they are commonly used as abrasives. Owing to their small size and buoyancy, they may readily pass through sewage treatment plants. Microplastics are a global contaminant in the world’s oceans, but have only recently been detected in the surface waters of lakes and rivers.

Researchers lowered a steel grab from a boat to collect sediment from ten locations along a 320-km section of the river from Lake St. Francis to Québec City. Microbeads were sieved from the sediment, and then sorted and counted under a microscope. “We found them in nearly every grab sample taken. The perfect multi-coloured spheres stood out from natural sediment, even though they were the size of sand grains,” said the lead author of the study, Rowshyra Castañeda, a former McGill MSc student (now at University of Toronto).

At some locations, the researchers measured over a thousand microbeads per liter of sediment, a magnitude that rivals the world’s most contaminated ocean sediments. “We were surprised to find such concentrations at the bottom of a river,” says McGill professor Anthony Ricciardi, who supervised the study. “It was previously assumed that floating microplastics are flushed through rivers to the sea. Now we have evidence that rivers can act as a sink for this pollution.”

The prevalence of microplastics in the St. Lawrence River raises the possibility that they are being consumed by fish and other animals. The environmental effects of microplastics are poorly known; but the surfaces of such particles attract chemical pollutants, including PCBs, which can be transferred to animals that ingest the plastics. “At present, we cannot predict the consequences of the accumulation of these non-biodegradable particles in freshwater ecosystems,” added Ricciardi, whose lab is investigating whether the microbeads are being consumed by fish in the river.

With growing recognition of microplastics as an emerging threat to waterways, some U.S. states (Illinois, New York, Minnesota, Ohio, California) have recently adopted or are considering legislation that bans the use of plastic microbeads in cosmetics. No such legislation has yet been proposed in Canada.

Read the full article in the Canadian Journal of Fisheries and Aquatic Sciences here.


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Oona Houlihan
9 years ago

2 mm is already “big” for a “micro”bead. The really problematic kind is, though not a nano particle by definition, too small to be seen with the naked eye. Most seem to come from cosmetics where they are used as “exfoliants” to “clean” (i.e. damage!) skin although there are inorganic alternatives that would not float, would form silt in the sewage treatment plant and be inert in any case anyhow. These smaller microbeads then are incorporated into aquatic organisms and in the last analysis eaten by those who caused them – the “health-conscious” humans …