Microplastics are everywhere. They are in the air we breathe, the water we drink, and the food we eat. They worm their way into the roots of lettuce and fall out of the sky when raindrops condense around them.
These tiny particles, with diameters ranging in size from as big as a fingernail and as small as a hundredth of the width of a human hair, break off of plastic products as they are used or as they are exposed to the elements.
Plastic is everywhere
Microplastics are in the streets and air of Nashville, and they reach as far as the depths of Mammoth Cave, Kentucky, where Vanderbilt researchers have measured microplastic pollution in cave streams. Researchers have also found microplastics in the Cumberland River, where runoff from Nashville contributes additional particles as the river passes through the city. Often paired with the water cycle, microplastics are now participating in their own “plastic cycle,” traveling between ocean, atmosphere, people, plants and animals.
The ubiquity of microplastics does not mean they are harmless. Scientists agree that exposure to microplastics and their smaller counterpart, nanoplastics, is associated with some level of toxicity and that severity increases with exposure.
Microwaving releases billions of nanoplastics
College students without time or kitchen equipment frequently throw microwaveable plastic containers, plates, and food packaging into the microwave to heat up a meal. These products are common at the Munchie Marts, where microwaveable soup, rice and pasta are all packaged in plastic.
Heating plastics produces the highest risk of food contamination. When food comes into contact with plastic wrappers and containers, it takes on micro- and nanoplastics that break or leech off, but microwaving food in plastic accelerates that process and causes micro- and nanoplastic concentration to skyrocket.
Microwaving food plastic containers releases tens to hundreds of millions of microplastics and billions of nanoplastics per square centimeter of surface area. This is 400 times as much as when food is stored in plastic at room temperature for a month.
Microwaves heat the plastics themselves, weakening the bonds in plastic polymers, therefore accelerating breakdown. They also promote hydrolysis reactions, in which water breaks apart plastic molecules and contributes to the breakdown of miniscule pieces of plastic: micro- and nanoplastics. On top of that, toxic additives leech out of the plastics when exposed to the same conditions.
Type of plastic dictates risk
Plastic is a broad category, defined by molecular structure: plastic molecules are long chains, and they can be made up of a variety of substances, but most plastics in consumer products are made of petrochemicals.
However, certain plastics release more microplastics than others. Most food packaging is made of low-density polyethylene, which is flexible and degrades more easily than polypropylene, a rigid material that is used in some plastic dishware.
A 2023 study at the University of Nebraska-Lincoln microwaved mildly acidic solutions in plastic containers for three minutes, and it found differences between polypropylene containers. One container released 200 to 400 times as many microplastics into food than another, meaning billions of particles instead of tens of millions.
Plastic additives, found in all consumer products, including microwave-safe food containers, are known to be endocrine disruptors. Phthalates and BPA, two common additives regulated by the FDA, can act like estrogen in the body and are currently being studied for long-term effects of exposure. Phthalates are found in food containers, the liners of wrappers, and some plastic wraps.
Health risks of micro- and nanoplastic exposure
The Vanderbilt Drinking Water Justice Lab is mapping water sources throughout Tennessee to identify communities at risk for contamination of plastic additives in drinking water. These chemicals are associated with health risks throughout the body. Micro- and nanoplastics are, too.
Microplastics are known to disrupt food webs and to kill human embryonic cells. Inhalation of microplastics may cause lung lesions, and embryonic kidney cells have died after microplastic exposure in in vitro studies. However, the long-term health effects of micro- and nanoplastics and the mechanisms causing them are not fully understood.
Last year, researchers at the University of Campania in Naples, Italy, found a correlation between microplastics and cardiovascular disease. In an observational study, researchers measured the abundance of micro- and nanoplastics in plaque removed from the blood vessels of 312 patients undergoing surgery to clear artery blockages. Over half of patients had polyethylene in their arteries, and these patients were at a higher risk of cardiac events in the 34 months of follow-up after surgery.
Since then, studies have found microplastics in bone marrow and the brain.
For now, it is clear that micro- and nanoplastics are not good for the body. While the specific mechanisms of how these materials interact with cells and systems are still being studied, experts, including physicians at Vanderbilt University Medical Center, recommend limiting micro- and nanoplastic exposure as much as possible.
References
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