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Micro- and Nanoplastics: Fatal Material Flaws

by Ted Schettler, SEHN science director

The United Nations convened international treaty negotiations in 2022 to address the growing global crisis of plastic pollution, a crisis that is most visible in littered streets, overflowing landfills, fouled rivers and streams, oceanic gyres and beaches. Plastics production is projected to double by 2050 and triple by 2060, promising to make the desecration worse. Whether the UN effort will have any success remains to be seen. Petro-states and chemical industry lobbyists vigorously oppose any curbs on plastic production and want to focus solely on waste management and recycling. Higher ambition countries recognize that this mess cannot meaningfully be addressed without turning down the production tap. 

Less visible than the grotesque images that sparked this sense of urgency, tiny plastic particles and their embedded hazardous chemicals flow through ecosystems everywhere. Persistent and pervasive, they are in the atmosphere, in soil across the land including farms and mountaintops, within glaciers, streams, lakes, rivers, oceans, deep-sea beds, wildlife, and people. 

Most microplastics (MPs, less than 5 millimeters in size) and nanoplastics (NPs, less than one micrometer) are degraded fragments of bottles, bags, surface coatings, tires, clothing, and other plastic products that we use daily—often only once before throwing them away, not knowing where they go. Some are purposely added to paints and personal care products.   

Inhaled, ingested, and potentially absorbed through the skin, micro- and nanoplastics (MNPs) contaminate human blood, urine, feces, breast milk, and semen. Human brains, hearts, blood vessels, livers, intestines, testicles, lungs, and placentas are flecked with MNPs. They affect our health in ways that we are just beginning to understand. 

Beginning to understand health effects, confronting complex challenges

Early studies of ecosystem impacts of plastic fragments were triggered by photographs of dead seabirds on remote North Pacific islands and marine mammals whose intestinal tracts had been blocked by colorful pieces of degraded debris mistaken for food. Beginning in 2016, when it became apparent that smaller MNPs were far more pervasive, published studies of impacts of exposure in many different species of aquatic and terrestrial wildlife rapidly increased. They documented physical, physiologic, and behavioral impacts in shellfish and other invertebrates, fish, birds, amphibians, and various other terrestrial wildlife.  

As it became apparent that people were also contaminated with MNPs, a number of scientists began using cell culture and laboratory animal models to predict human responses. An extensive literature already documented adverse effects of exposure to many of the chemicals that leach from plastic products, but studying MNPs added new challenges.   

Studying the potential health effects of MNP exposures is complicated because of the immense diversity of the size and shape of the fragments, the polymers that comprise them, their chemical additives, and chemicals or microbes adsorbed to the fragments from the surrounding environment. 

Some of the most common polymers in MNPs are polyethylene, polypropylene, and polystyrene. Others include polyvinylchloride (PVC), polyethylene terephthalate (PET), polyamide (nylon), polyester, and acrylic. Tire wear fragments come from styrene butadiene rubber (SBR).

Macro- and nanoplastics carry diverse combinations of chemicals purposely added to the polymer when each product was manufactured. Recently, the Norwegian Research Council reported that over 16,000 chemicals are potentially used or present in various plastic products. Of those, at least 26 percent are of concern because of their high hazards to human health and the environment. Disturbingly, 66 percent have no hazard information available. More than 400 chemicals of concern can be present in each major plastic type and all tested plastics leached hazardous chemicals. 

Macro- and nanoplastics can also carry toxic metals, various chemical pollutants, and microbes that they pick up from the environment. Thus, MNP exposures carry strikingly diverse combinations of physical, chemical, and biological hazards that will influence the cellular, tissue, and organ response in different ways, making a standardized research agenda difficult.  

The growing body of knowledge 

The majority of studies of impacts of MNP exposures use laboratory animals (rats or mice) or cell cultures, but observations in human populations are becoming more common. Most of the adverse impacts seen in laboratory studies involve biochemical and structural damage causing harmful effects in the gastrointestinal system, lungs, and reproductive systems in males and females. For example, in animal studies, inflammation, oxidative stress, immunosuppression, and other characteristics of carcinogens are reported in the intestines after exposure to MNPs; sperm and ovarian abnormalities in the reproductive tracts; and inflammation, oxidative stress, and other evidence of injury in the lungs.   

A rapid systematic review of the expanding literature on health effects of MNPs was recently published in Environmental Science and Technology by authors from the University of California, San Francisco. They narrowed their analysis to mammalian laboratory studies and available human data, focusing on the gastrointestinal, reproductive, and respiratory systems. Their goal was to integrate the findings and draw conclusions about human health implications from currently available evidence. After screening over 1,800 published studies and excluding those that did not meet inclusion criteria, they focused on 28 animal and 3 human studies, following a strict protocol for evaluating the quality and strength of evidence.   

With respect to gastrointestinal studies, they concluded that “exposure to microplastics is ‘suspected’ to be a digestive hazard to humans, including a suspected link to colon cancer.” This was based on MNP-related evidence of inflammation in the colon, oxidative stress, changes in mucous secretion, anatomic changes in the lining of the colon, immunosuppression, and changes in cellular proliferation and cell death.  

They concluded that respiratory exposures to MNPs are “suspected” to induce chronic inflammation and lung fibrosis in humans.  

Finally, they determined that exposure to microplastics is “suspected” to adversely impact sperm quality and testicular health in humans on the basis of the “high” quality of the body of evidence. They found other reproductive impacts, including birth outcomes, “not classifiable” for humans because of few studies and limits to the quality of evidence.  

This review was limited to MNPs of only three primary polymers—polystyrene, polyethylene, and polypropylene—and one study of tire wear particles. The shape of the MNPs in the animal studies were generally homogeneous and spherical, unlike the irregular fragments of various polymers encountered in the real world. These studies also could not account for chemical additives to polymers in real-world plastic fragments. These constraints make it likely that their conclusions underestimate the impacts of MNPs on the gastrointestinal, respiratory and reproductive systems. This synthesis adds to growing concern about public health impacts of MNP exposures. 

Another human study published in the New England Journal of Medicine in 2024 looked at a different health impact. Over three years, the authors followed 257 asymptomatic patients who had undergone removal of plaques in their carotid arteries because of arterial narrowing. Those whose plaques contained MNPs were 4.5 times more likely to have a heart attack, stroke, or death from any cause during follow up than those in whom MNPs were not detected. Here too, there was evidence of inflammation in the plaques containing MNPs, which may explain why remaining plaques were more susceptible to rupture and cause heart attack or stroke.

Vast health implications and the need for increased, multi-level action

How big a problem is this? Despite the need for more research, harmful impacts related to MNP exposures in validated animal studies and people are already clearly demonstrated. Documented increases in colon cancer in younger people and lung cancer in non-smokers are plausibly related to MNP ingestion and inhalation. The observation of increased risk of heart attack and stroke in people whose arterial plaques contain MNPs is more strong evidence of health risks. Moreover, MNPs are so widely distributed throughout the body, it’s highly likely that there are other harmful impacts. Existing evidence is sufficient to trigger action to reduce exposures, which are virtually ubiquitous. 

Some decision-makers have taken early policy steps. For example:

  • Some countries, states, and cities have banned frequently littered single-use plastic items like shopping bags, clamshells, and plastic drink accessories.

  • Several countries have restricted the sale of personal care and cosmetic products containing microplastics.

  • Australia and France have introduced measures to phase in microfiber filters on new washing machines. (Microfibers from synthetic textiles are discharged from washing machines without filters into the waste water. MNPs migrate into sewage sludge, which is often spread on farm land.)

  • California has adopted a comprehensive two-track MP strategy. The first track outlines immediate, ‘no regrets’ actions and multi-benefit solutions to reduce and manage microplastic pollution. The second track outlines a research strategy to enhance the scientific foundation for MP monitoring, source identification, risk assessment, and development of management solutions.

  • The California State Water Resources Control Board is establishing guidelines for acceptable levels of microplastics in drinking water. Public water systems must monitor MPs in drinking water.

The authors of the recent review of health effects of MNP exposures note that the US EPA has the authority under the Toxic Substances Control Act (TSCA) to assess the risk of MNP exposures. Given the marked heterogeneity of MNPs, they conclude that a risk evaluation should consider MNPs as a single class during the assessment, as provided for in TSCA. 

The Food and Drug Administration (FDA) says the agency “continues to monitor the research on MNPs. If the FDA determines, based on scientific evidence, that MNPs in food, including packaged food and beverages, adversely affect human health, the FDA can take regulatory action to protect public health.” One might wonder just how much evidence is necessary to meet that threshold and how long the agency will wait.  

Upstream interventions are available to product manufacturers. Some plastic polymers and products are inherently less toxic throughout their life cycles than others and require fewer hazardous chemical additives. For example, flexible PVC products contain hazardous plasticizers that can leach out during product use and also contaminate PVC MNPs. Alternative polymers not requiring plasticizers can readily be substituted for most purposes. In many cases, plastics of any kind can be replaced with alternative materials.   

Interventions are also available to institutional consumers. For example, hospitals rely far more than necessary on single use plastic items for many different purposes like surgical gowns. Reusable surgical gowns are shown to be as safe and effective as single use disposables make of plastic polymers. Hospital offices and cafeterias also have many opportunities to move away from single-use disposable plastics to alternative materials. 

Some actions can be undertaken by individuals to reduce their MNP exposures. They include: 

  • Avoid using plastic cutting boards. These are a source of MNPs during use. 

  • Avoid plastic water bottles.

  • Avoid microwaving food in plastic containers.

  • A number of water filters will remove MPs from drinking water (check specifications).

  • Reduce plastic food packaging as much as possible while maintaining food safety. For example, recent studies report billions of MP particles released from plastic polymer tea bags when heated in hot water. Loose leaf tea brewed without plastic is an alternative.   

  • Vacuum and dust more frequently to reduce MNPs in indoor air.

This unfolding story reveals human and ecosystem experimentation on a global scale and what increasingly appear to be fatal flaws in large portions of the materials on which we have come to rely. The FDA may want to wait for unequivocal evidence of harm before acting, but some states and cities are undertaking actions now based on what we already know. While there are some steps that individuals can take to reduce their MNP exposures, material scientists and product manufacturers must contribute with redesign and detoxification of the plastics that make up so much of today’s material economy. 

Fossil fuel companies and plastic product manufacturers spin the narrative that we can solve this crisis with better waste management and recycling. While that will help, it will fall far short of what is needed, and the crisis will worsen. We must also significantly limit production by eliminating non-essential uses of plastics. Beverage bottles, some packaging, and single use plastics would be good places to start. 

Mo Banks