When plastics end up in the environment, they are gradually broken down by all kinds of processes — often the action of ultraviolet rays and/or oxygen, in addition to more mechanical “attacks” like erosion — which will break them into smaller and smaller pieces. Definitions vary here, but we generally speak of “microplastics” when the size is less than 0.5 or 0.1 millimeters.
Now, there are not that many of these microplastics in surface waters in Quebec. In any case, much less than we already thought.
“There have been a lot of studies on microplastics, and it was a bit of a wild west at the beginning,” explains Mathieu Lapointe, water treatment researcher at the École de Technologie Supérieure. There were many methodological errors where researchers themselves contaminated their samples, resulting in concentrations that seemed very alarming. But when we adopted better methods, we realized that there were a lot fewer than we thought.”
Here: in a report published in 2019, the Association for the Protection of Lake Saint-Charles and the Marais du Nord (APEL) collected water samples at 11 points on Lake Saint-Charles, from which Quebec draws a much of its drinking water. On average, this water contained roughly between 0.02 and 0.1 particles of microplastic per liter, which means that between 10 and 50 liters had to be filtered to find a single piece of microplastic.
Comparable concentrations are found in the St. Lawrence, says Mr. Lapointe. And elsewhere in the world too, for that matter.
Microplastics and mesoplastic debris are photographed on Almaciga beach on the north coast of the Canary island of Tenerife. (Desiree Martin/Agence France-Presse Archives)
And again, he adds, “even if there were more, our drinking water plants capture them very well”.
In these factories, we force the precipitation of many contaminants, including plastics, by adding aluminum sulfate which, in contact with water, will precipitate and form a kind of “snowflakes” which will capture contaminants. . This already removes a large part of the (rare) microplastics present, and those that remain have a good chance of being captured by the next step in drinking water treatment, “granular filtration”, where we do pass the water through a sort of fine sand.
In short, there are not many microplastics at the start, and very, very little remains after treatment.
Low toxicity
In any case, these plastics are not particularly toxic — even if we agree that they are not exactly recommended by Canada’s Food Guide… In general, plastics are not digested by our intestines, what enters tends to to just pass through.
There are, of course, still quite a few studies which have found them to have a certain potential for harm. But most tested doses or concentrations that have absolutely nothing to do with real-world conditions.
For example, one of them wanted to see if microplastics were harmful to human colon cells. The authors therefore exposed them, in test tubes, to concentrations of more than 2.5 grams per liter (g/l) of water for 14 days.
By comparison, if we take the average weights per particle found in a 2021 study published in Microplastics and Nanoplasticsthe APEL report measured concentrations of around 0.001 g/l, or 2500 times less than the solution in which human cells were “soaked”…
In short, until proven otherwise, there is really nothing to worry about with the “micro”.
And what about “nanos”?
That said, however, there still remain some gray areas, warns Mr. Lapointe. The first is nanoplastics which, as their name suggests, are also tiny plastic particles, but even finer than “micro”.
“We are less able to measure them,” he said. Even in my lab with all the resources we have, we are more in the semi-quantitative, in the “there is or there is not”. So we don’t know, basically, if we are good or not at removing nanoplastics from water.”
— Mathieu Lapointe, researcher in water treatment at the École de Technologie Supérieure
“And it’s a little more worrying because nanoplastics are smaller than microplastics, so they probably pass more easily through the different barriers of the human body. It’s a general rule in toxicology: the smaller it is, the more it passes.”
In a study recently published in Nature – Water, Mr. Lapointe and his team added fluorescent nanoplastics (easier to detect and measure) in untreated water, to see the performance of current wastewater treatment processes (which are still different from treatment drinking water, it should be noted). Conclusion: these only remove between 40 and 70%, which is undoubtedly better than nothing, but not great either.
“For drinking water, we don’t know yet, we are currently doing the study,” says Mr. Lapointe.
However, in general, he continues, it is especially the treatment of wastewater which raises questions, because we find many more micro- and nanoplastics there when in surface water – largely because of the microfibers of clothes that come apart during washing.
“What worries us from an environmental point of view,” explains the researcher, “is the accumulation in nature. If a pollutant remains stable, we can live with it. But if it accumulates, that worries us more, and that’s what’s happening with microplastics in the River.
“Even though we are good at removing them from wastewater, there still remains 5 to 10% which goes into the rivers. […] And afterward, it’s the St. Lawrence River that becomes a big decanter.”
In some areas of the river, research has found up to 1,000 plastic particles per liter of sediment. The question of their effect on ecosystems therefore arises.
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