Microplastics are in our bodies. How much do they harm us?

As plastic garbage becomes more prevalent across the world, one key issue remains unanswered: what harm, if any, does it cause to human health?

When microplastics were discovered in the intestines of fish and shellfish a few years ago, there was a lot of anxiety about seafood safety. Shellfish were especially concerning because, unlike fish, we consume the entire animal—stomach, microplastics, and all. Belgian scientists reported in 2017 that eating mussels, a popular meal in the nation, might result in the consumption of up to 11,000 plastic particles per year.

Scientists have previously discovered that plastics break in the environment, shredding into fibers as thin as a strand of human hair over time – particles so minute that they readily become airborne. The University of Plymouth in the United Kingdom chose to compare the risk of eating infected wild mussels in Scotland to the risk of inhaling air in a normal house. People will inhale or swallow more plastic fibers floating in the air around them, fibers shed by their own garments, carpets, and upholstery, during a mussels supper than they will by eating the mussels.
This spriing scientists from the Netherlands and the United Kingdom claimed that they had discovered small plastic particles in living humans in two previously unseen locations: deep inside the lungs of surgery patients and in the blood of anonymous donors. Neither of the two studies addressed the issue of potential injury. But, taken together, they signified a change in worry about plastics from the plastics themselves to the cloud of airborne dust particles we live in, some of which are so minute that they can penetrate deep within the body and even inside cells in ways that bigger microplastics can't.

Dick Vethaak, a co-author of the blood research and a professor emeritus of ecotoxicology at the Vrije Universiteit Amsterdam, doesn't think his findings are alarming— "but, yes, we should be concerned. Plastics should not be in your blood.”

“We live in a multi-particle world,” he continues,  referring to the dust, pollen, and soot that humans inhale on a daily basis. “The trick is to figure out how much plastics contribute to that particle burden and what does that mean.”

Harm is the hard part

Scientists have been studying microplastics, defined as particles measuring less than five millimeters (a fifth of an inch) across, for a quarter century. Richard Thompson, a marine scientist at the University of Plymouth, coined the term in 2004 after finding piles of rice-sized plastic bits above the tideline on an English beach. In the ensuing years, scientists located microplastics all over the globe, from the floor of the Mariana Trench to the summit of Mount Everest.

Salt, alcohol, fresh fruits and vegetables, and drinking water all contain microplastics. Airborne particles can travel around the world in a couple of days and shower down from the sky. Seagoing missions to count microplastics in the water create unfathomable statistics, which have grown exponentially over time as more plastic garbage reaches the oceans each year and disintegrates. In 2014, a peer-reviewed estimate put the sum at $5 trillion. Last year, Japanese scientists from Kyushu University calculated that there are 24.4 trillion microplastics in the world's top seas, which is the equivalent of about 30 billion half-liter water bottles.

“When I started doing this work in 2014, the only studies being done involved looking for where they are,” says Alice Horton, a microplastic pollution expert at the UK's National Oceanography Center. “We can stop looking now. We know wherever we look, we will find them.”

However, assessing whether they do harm is far more difficult. Plastics are made up of a complicated mixture of chemicals, as well as additives that provide strength and flexibility. Plastics and chemical additions can also be harmful.The most recent analysis has identified more than 10,000 unique chemicals used in plastics, of which more than 2,400 are of potential concern, says Scott Coffin, a research scientist at the California State Water Resource Control Board.

According to the report, many chemicals are "not adequately regulated" in several nations, and 901 compounds are not allowed for use in food packaging in some jurisdictions.

Chemicals can also seep into water, with one research finding that up to 88 percent might leach depending on conditions like sunshine and time. According to the same study, a single plastic product might include up to 8,681 different chemicals and additives. It's not simple to figure out which chemical combinations are dangerous and what degree and period of exposure causes harm in such a complicated mix.

“You may find a correlation, but you would be hard pressed to find causation because of the sheer number of chemicals we’re exposed to in our daily lives,” says Denise Hardesty, a research scientist at Australia's Commonwealth Scientific and Industrial Research Organization who has studied plastic waste for 15 years.

Janice Brahney, a scientist at Utah State University who studies how dust distributes nutrients, viruses, and pollutants, is worried that plastic manufacturing is increasing rapidly when so much about microplastics is unknown. Plastics were created in 367 million metric tons in 2020, with that number expected to quadruple by 2050.

“It is alarming because we are far into this problem and we still don’t understand the consequences, and it is going to be very difficult to back out of it if we have to,” she adds.

The American Chemical Council (ACC), an industry trade association, has a long list of comments on its website that describe the chemical composition of various plastics and refute study assertions that some plastics are harmful.

“No, microplastics are not the ‘New Acid Rain.’ Not even close,” the council said in response to media coverage of Brahney’s 2020 paper, published in Science, which estimated that 11 billion metric tons of plastic will accumulate in the environment by 2025. 

The ACC also criticized that finding, saying, “The amount of microplastics in the environment represents only 4 percent of particles collected on average… The other 96 percent is comprised of natural materials like minerals, dirt and sand, insect parts, pollen and more.”

Meanwhile, the ACC announced through a spokesman that it has launched a research program to help answer outstanding questions about microplastics, including those relating to household dust, and to facilitate a global exchange of microplastics research between universities, research institutions, and industry. Examining the environmental destiny and potential routes of exposure to microplastics, identifying potential hazards, and building a framework to assess risk are all part of the plan. The results will be released over the following few years.

According to Hardesty, the subject is so convoluted and contentious that even the concept of injury is a point of contention. Should we simply be concerned about the health implications of microplastics? What about the potential consequences for animals and ecosystems?

Plastics in animals

Marine researchers examining the diets of seabirds discovered plastic in their stomachs 40 years ago, sparking a quest for possible damage from plastics. As more marine creatures were entangled or ingested plastics, research extended to include additional marine species, as well as rats and mice.

In 2012, the Convention on Biological Diversity in Montreal determined that eating or being entangled in plastic harmed all seven sea turtle species, 45 percent of marine mammal species, and 21% of seabird species. In the same year, ten experts attempted unsuccessfully to have the world's governments legally categorize the most dangerous plastic as hazardous, giving their regulatory bodies the "the power to restore affected habitats."

The number of animals killed and the hazards they face have increased in the decade since. Plastics have an impact on over 700 species. Scientists estimate that hundreds of millions of wild birds have swallowed plastic, and that by the middle of the century, all seabird species on the globe will be consuming it. Widespread exposure to endocrine-disrupting chemicals found in plastics is already suspected to be threatening certain bird species. Plastics have been demonstrated to impair fish reproductive systems and stress the liver in laboratory experiments.

Plastic garbage is everywhere, according to animal studies, which has aided study into its possible physiological and toxicological impacts in people.

Although plastic toxins can harm birds, an Australian study published in 2019 revealed the opposite: the chicks experienced slight delays in development and maturity but were not more likely than unexposed chicks to become sick, perish, or have difficulties reproducing. The researchers were taken aback by the findings, which they described as “first experimental evidence” that the toxicological and endocrine effects “may not be as severe as feared for the millions of birds” carrying small loads of plastics in their stomachs.

One of the co-authors, Hardesty, believes the quail research serves as a reminder that measuring the hazard posed by microplastic exposure is "not that simple". The difficulties in discovering strong evidence of harm in quails, she adds, “really highlights that we are still not able to answer the question of what the impact of eating plastic is for humans in a definitive way.”

Plastics in humans

Human beings, unlike quail and fish, cannot be purposely fed a diet of plastics, making measuring any negative effects of plastics significantly more challenging. Microplastics have been found to cause harm to human cells in laboratory testing, including allergic responses and cell death. However, no epidemiologic studies have yet been published that show a link between microplastic exposure and health effects in a broad population of people.

Instead, studies have focused on small groups of people, which restricts the conclusions that can be reached beyond identifying the presence of microplastics in various bodily areas. Microplastics were discovered in the feces of eight persons in a 2018 research. Another research discovered microplastics in the placentas of newborn babies.

Plastics were identified in the blood of 17 of 22 healthy blood donors in a recent research by Vethaak and colleagues, while microplastics were found in 11 of 13 lung samples obtained from 11 patients. Almost nothing is known about each group that may assist identify the dose and duration of exposure, two critical factors in determining danger.

The plastic particles discovered in both investigations were mostly nanoplastics, which are smaller than one micrometer. The ones discovered in the blood analysis were tiny enough to have been breathed, but Vethaak adds they may also have been swallowed. It's unclear if such particles may move from the bloodstream into other organs, particularly the brain, which is protected by a thick network of cells that acts as a barrier.

“We know particles can be transported throughout the body via the river of blood,” Vethaak explains. The Dutch National Organization for Health Research and Development is conducting 15 microplastics research investigations.

The lung research, conducted at the University of Hull in the United Kingdom, demonstrated how dangerous airborne particles may be. While the researchers expected to detect plastic fibers in surgery patients' lungs since previous studies had found them in cadavers, they were astounded to find the greatest number, in diverse shapes and sizes, implanted deep in the lower lung lobe. Two millimeters was the length of one of the fibers.

“You would not expect to find microplastics in the smallest parts of the lung with the smallest diameter,” says Jeannette Rotchell, a Hull environmental scientist. According to her, the study allows her team to go on to the next level of questioning and perform lab investigations employing cells or tissue cultures of lung cells to learn more about the microplastics they discovered.

“There are many more questions,” she continues. “I would like to know what levels are we exposed to in the course of our lives. What microplastics are we breathing in every day, whether working at home, going to the office, outdoors, cycling, running, in different environments. There’s a big knowledge gap.”

The question of harm

Scientists aren't completely lost in the dark. There is a lot of study on plastic toxins, as well as lung disorders including asthma and chronic obstructive pulmonary disease (COPD) and cancer, which kill millions of people each year and have been connected to other pollutants. COPD, which is caused by chronic inflammation, is the fourth greatest cause of mortality in the United States, according to the American Lung Association's newest study.

Humans have been inhaling a variety of foreign particles every day since the beginning of the Industrial Revolution. The body's first reaction is to try to eliminate them. Large particles in the lungs are usually coughed up. Mucus accumulates around particles deeper down the respiratory system, generating a mucus "elevator" that drives them back up to the upper airway, where they may be evacuated. Immune cells encircle and isolate those who remain

Over time, such particles might irritate the skin, causing a cascade of symptoms ranging from inflammation to infection to cancer. They might also just be a passive presence.

According to Kari Nadeau, a physician and director of allergy and asthma research at Stanford University, the particles found in the lung study are made of polymers that are known to be hazardous to people and have caused lung irritation, dizziness, migraines, asthma, and cancer. She ticked off the symptoms as she read through the study's list of fibers.

“We know this already from other published articles,” she explains. “It takes one minute of breathing in polyurethane and you could start wheezing.”

What scientists don't know is whether the plastic particles in the lungs would satisfy the required quantity and duration of exposure to cause injury.

It would be difficult to show if such particles "directly caused asthma for someone's whole life," she argues. “I am not saying we should be afraid of these things. I am saying we should be cautious. We need to understand these things that are getting into our body and possibly staying there for years.”

According to Albert Rizzo, chief medical officer of the American Lung Association, the evidence is too obscure to draw judgments.   “Are the plastics just simply there and inert or are they going to lead to an immune response by the body that will lead to scarring, fibrosis, or cancer? We know these microplastics are all over the place. We don’t know whether the presence in the body leads to a problem. Duration is very important. How long you are exposed matters.”

The most appropriate connection, he claims, is the decades-long campaign to persuade the authorities that smoking causes cancer. “By the time we got enough evidence to lead to policy change, the cat was out of the bag,” he adds. “I can see plastics being the same thing. Will we find out in 40 years that microplastics in the lungs led to premature aging of the lung or to emphysema? We don’t know that. In the meantime, can we make plastics safer?”