Scientists have discovered microplastics in virtually each part of the human body. Yet many questions remain about exactly how these infinitesimal particles of synthetic polymers impact human health and how they might cause disease.
A new paper investigating chemical reactions between water and decaying plastic offers a potential hypothesis for how microplastics could make us sick.
Plastics were long thought to be chemically inert, meaning they did not react easily with other compounds. This is why they are often used for packaging and why they resist biodegradation so stubbornly.
But a research team from Columbia University has discovered that when water molecules come into contact with plastic surfaces, a key chemical reaction does indeed occur. The meeting of water and plastic creates a third class of molecules called reactive oxygen species.
ROS are a type of free radical, a general term for a class of unstable, high-energy molecules. ROS are known to damage cells and promote inflammation. They “tend to damage nearby materials and molecules,” said Wei Min, a professor of chemistry and biomedical engineering at Columbia and co-author of the study. “For example, if ROS comes into contact with DNA, it will most likely cause a mutation.”
In the first stage of the experiment, the team added water to microscopic pieces of six different types of common plastics: polyethylene; polypropylene; polystyrene; polyvinyl chloride, or PVC; poly(methyl methacrylate), or PMMA; and polyethylene terephthalate (PET), which is used in disposable water bottles. Next, they measured the amount of ROS created by each encounter. Exposure to polyethylene and polypropylene resulted in increased ROS formation. PMMA, commonly called acrylic, generates less.
They then exposed the mice’s red blood cells to each type of plastic. When the cells encountered the microplastics, they changed shape and ruptured. The more plastic type of ROS is generated, the more damage is observed in the cells.
The study authors emphasized that their research does not prove that these chemical reactions are responsible for disease or damage in the human body. But they think this explains why this man-made material seems to become more harmful the smaller it gets.
When a piece of plastic breaks down into microscopically small components, its total surface area increases exponentially. Since these harmful ROS molecules form when water meets the surface of a plastic, and water is present in every cell of the human body, this particular chemical reaction could be a real problem.
The article was published Wednesday in the journal Nature.
By 2024, the Columbia team showed that the amount of microplastics present in commercially available bottled drinking water was 10 to 100 times larger than previously believed. Ninety percent of these particles were small enough to be considered nanoplastics, small enough to cross the blood-brain barrier and be taken up by human cells.
“Ordinary people are exposed to this stuff regularly in their daily lives,” said Beizhan YanColumbia environmental chemist and co-author of the study.
Everyday actions generate billions of these nanoparticles, Yan noted, from washing a load of laundry to reheating a dish in the microwave.
The newer paper is also relevant to understanding plastic pollution in the environment, said Matthew Campen, a professor of pharmaceutical research at the University of New Mexico. Like the authors of the article, he cautioned against drawing premature conclusions about human health. When the researchers added a chemical surfactant called Triton X100, it eliminated ROS production. This could indicate that the presence of other compounds in the body could curb the creation of free radicals.
“This is a fundamental study of the chemistry of plastics interacting with the most common chemical, water, and it is important because it actually shows that these elements are capable of generating hydroxyl radicals,” Campen said.
This comes amid growing concern about the long-term health impacts of these ubiquitous particles. In April, the federal government announced a $144 million effort study the effects of microplastics on the human body and drinking water.
“We know enough that people should take steps to reduce their exposure” to plastic, said Tracey Woodruff, a professor of epidemiology and population health at Stanford. “If we wait to reduce exposures, we could also cause more harm. »
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