Scientists May Have Discovered One Way Microplastics Could Harm the Body

Plastics are present throughout our everyday lives. As a result, so are microplastics, tiny particles that get shed as plastics break down.

“These radicals can potentially damage important biological molecules such as proteins, lipids [fats in the body], and DNA,” says the senior author, Wei Min, PhD, a professor of chemistry and biomedical engineering at Columbia University in New York City.

“I think one of the most important messages from our study is that we may need to rethink how we evaluate the chemical safety of plastics,” says Dr. Min.

A Possible Missing Link Between Microplastics and Health Risks

Microplastics have been found in blood, placentas, breast milk, babies’ first poop, and arteries, says Lisa Patel, MD, a clinical associate professor of pediatrics at Stanford School of Medicine in California, and the executive director of the Medical Society Consortium on Climate and Health, who wasn’t involved in the study.

“We’ve long assumed that plastic itself is inert, and that any harm from microplastics comes from the chemicals added to plastics or the pollutants that stick to them,” she says. Plastic has been thought of and treated like glass, for example, something that just sits there and doesn’t react with anything, says Dr. Patel.

“This study suggests the surface of the plastic particle can be chemically active on its own,” she says. That activity can create free radicals, the same kind of unstable molecules behind oxidative stress, which are connected with aging and disease, says Patel.

How Scientists Uncovered the Reaction

Researchers at Columbia University and the University of California in Berkeley studied six common plastics, including polyethylene, polypropylene, polystyrene, PVC, PET, and acrylic, in the form of microplastics mixed with water.

The first clue came when a yellow dye in water slowly lost its color over 10 days after being stirred with plastic particles. The dye remained stable when the particles were mixed into other liquids, such as alcohol, which pointed to water as a key player, the authors wrote.

Further tests showed that the plastic surfaces were producing hydroxyl free radicals, a highly reactive form of oxygen, in the absence of light or added chemicals. Computer simulations helped explain why, and the team then tested what those molecules did to proteins and to red blood cells from mice.

Plastics Common in Food Containers and Bottle Caps Did the Most Damage

All six plastics produced free radicals when exposed to water, but some produced far more than others. The most water-repelling plastics, polyethylene and polypropylene, were the most reactive, and PET and acrylic were the least reactive.

When the researchers tested what the hydroxyl radicals could do, a common protein clumped together at the plastic surfaces — a sign that its structure had been damaged.

Adding a substance that neutralizes free radicals reduced clumping, suggesting that the radicals caused the damage.

Water Molecules Behave Differently at the Surface of Plastic

“The surprising part is that neither the plastic nor the water needs to be chemically unusual. What matters is the boundary where they meet,” says Min.

Water molecules behave differently when they’re in contact with the surface of plastic, and that shift creates conditions where reactive molecules can form, he says. “You can think of this as a special chemical environment that emerges when two otherwise familiar materials come into contact,” says Min.

Findings Suggest Not All Plastics Are Equal

Researchers already know microplastics are everywhere, says Patel. “What we’re still figuring out is how they might cause harm. This study offers one explanation: The particle’s surface may generate damaging molecules directly,” she says.

“It also suggests that not all plastics are equal. The more reactive types caused more damage. That could eventually help us prioritize which plastics to phase out of food contact and products used by children,” she says.

Strengths and Limitations of the Study

The findings of the study were consistent: The lab experiments and computer simulations pointed to the same explanation, and the effect showed up in all six common plastics tested.

But it’s also important to be clear about what the study is and isn’t, says Patel. “These are lab experiments. They don’t show this is happening in people’s bodies, or at what doses,” says Patel.

“It is also important to emphasize that science has not yet established exactly what levels of microplastic exposure cause harm in humans,” says Min.

Next, researchers want to learn whether these reactions cause damage in living cells and tissues, and if the effects depend on the type of plastic and the size of the particles, he says.

Simple Ways to Reduce Microplastic Exposure

Microplastics are so widespread that avoiding them completely probably isn’t realistic, says Min. “I would encourage people to take reasonable precautions without becoming unnecessarily alarmed,” he says.

“This study doesn’t change what I do so much as reinforce it. If anything, it suggests that even ‘clean’ plastic without BPA or other additives may not be harmless, so ‘BPA-free’ shouldn’t be the end of the conversation,” she says. BPA, or bisphenol A, is a chemical used in some plastics that has been linked to fertility issues.

When asked what they do in their own lives, both experts described a few simple steps they take to reduce their exposure to microplastics.

Don’t Reheat Food in Plastic

“I try to take simple, practical steps to reduce unnecessary plastic exposure, particularly where plastics come into direct contact with food and drinking water,” says Min. He generally prefers reusable glass or stainless steel containers when it’s convenient and avoids heating food in plastic containers, he says.

Patel, “as a pediatrician and a mom,” says she follows a similar strategy. “I don’t microwave food in plastic. Heat increases how much plastic sheds, and studies have found polypropylene baby bottles release large numbers of particles when heated,” she says. She also keeps plastic out of the dishwasher.

Children are likely to bear more of whatever risks microplastics pose, she says, because relative to their size, they eat, drink, and breathe more than adults, and their bodies are still developing.

Avoid Bottled Water When You Can

Still, individual choices only go so far; the real solution is to produce less plastic and set stronger safety standards, says Patel.