This article was written by Kevin Jiang and was published in the Toronto Star on April 22, 2024.
We are living in an increasingly plastic world. Microplastics, tiny shards of polymers less than five millimetres in length, have been found everywhere from the far reaches of the arctic to the depths of our lungs and bloodstreams.
Now, researchers have discovered that microplastics in our food and water are able to cross the intestinal barrier to reach our most sensitive organs — and were among the first to detect their presence in the brain.
“It’s currently estimated that us as humans consume about five grams of microplastics per week, the equivalent of a credit card,” the study’s lead author Dr. Marcus Garcia, a pharmacist and postdoctoral fellow at the University of New Mexico, told the Star.
“We’re in a kind of rough situation where almost everything that we consume, there’s some type of microplastics present.”
But while unaffiliated experts appreciated the study for its novel insights, they noted potential flaws in the research — including that five gram figure: “There isn’t a consensus on how much plastic we are exposed to,” said Lindsay Cahill, a professor of chemistry at the Memorial University of Newfoundland and Labrador.
Microplastics detected in the brain, other organs after ingestion
Over a period of four weeks, Garcia and his team laced the drinking water of a group of mice with varying microplastic concentrations, up to the equivalent of five grams per week in humans.
They tested polystyrene particles, but also a batch of mixed plastics similar to what might be encountered in nature.
The results were dramatic. On dissecting and analyzing the animals’ organs, plastics were detected deep inside their brains, livers and kidneys — signalling a spread across the intestinal barrier and far into the body.
“We were really intrigued to find out that there were microplastics actually crossing into the brain,” Garcia said. It’s especially concerning that particles may have crossed the blood-brain barrier — a tightly regulated membrane vital to protecting the brain from germs or toxins — given the relatively large size of the plastics, he continued.
Particles were “more apparent” in the liver compared with the animals’ brains and blood sera. Far fewer were found in the kidneys, the paper read.
Unfortunately, the researchers weren’t able to measure the exact amount of plastics present in the organs, Garcia noted: “That was one of our limitations.”
A flurry of papers have emerged in recent years that found microplastics in other organs, including the human heart. Garcia previously detected the particles in placenta as well, and devised a method to count the number of plastics present.
Are microplastics bad for you?
Over the period of just four weeks, the researchers detected significant metabolic changes in the microplastic-affected organs, as well as the mice’s colons.
“The large metabolic changes observed in this study may be associated with chronic diseases later in life including diabetes, non-alcoholic fatty liver disease and cardiovascular diseases,” noted Cahill, who is unaffiliated with the study. “However, we need to be cautious about overstating the health impacts until we know more about human exposure levels.”
In the brain, studies suggest micro and nano-plastic accumulation could lead to worsened brain development or even trigger neurodegenerative diseases like Alzheimer’s over time.
“The accumulation of metabolic changes that we did see, that was just over a four week period” — so imagine the impacts of a human lifespan spent ingesting microplastics, Garcia said.
All that said, there are still “more questions than answers about the health impacts of ingesting microplastics,” Cahill noted. Far more research is needed to suss out its true toll on public health.
How many microplastics are we really eating?
The study was not without its flaws. Studies suggest the figure of five grams of microplastics consumed per week, often cited in the media and by other researchers, may have overexaggerated the levels of our actual exposure by several magnitudes.
The truth is we don’t know how many microplastics we’re eating, drinking and breathing in, Cahill explained. It’s possible the effects seen by Garcia and his team are different at lower exposure levels.
But given our exponential production of plastics since the 1950s, from two million to over 450 million tonnes today, Garcia believes his results are still relevant in our increasingly polluted world.
“After we use those products and they end up in the landfill, they continue to break down into these microplastics,” he said.
These can then leach into our groundwater and air, into the irrigation for our crops and, eventually, our vegetables and livestock as well.
“Almost every food product that we’re thinking about we’re getting some microplastic exposure from,” he continued.
“These are still the early stages — it will take infrastructure and also policies (to mitigate our exposure).”
In the brain, studies suggest micro and nanoplastic accumulation could lead to worsened brain development or even trigger neurodegenerative diseases like Alzheimer’s over time
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