Microplastics: Adapting to Emerging Legal Challenges with Proper Risk Assessment

Microplastics are the breakdown product of various polymers including the deterioration of plastic bottles, containers and many other consumer products. Due to their size and perceived non-toxicity of plastics, for the past few decades they have been considered relatively harmless to aquatic species and humans.

However, a February 2025 PubMed search for “microplastics” resulted in 16,572 hits and 4,803 new publications in 2024 alone. A similar search for “nanoplastics” produced 3,285 hits and 1,133 publications in 2024. This surge in research highlights the scientific community’s concern about the potential impacts of microplastics, prompting further investigations into their presence, distribution and effects on human and environmental health.

Although these microplastics may very well be fundamentally inert and no different from nuisance dusts, concern over their increasing presence in the environment and the human body persists. To ensure that regulators, the public and juries reach accurate decisions about the potency of microplastics, it is important to conduct an exhaustive health risk assessment evaluating a diversity of toxicological endpoints across differing doses.

Current Research Highlights Emerging Concerns

Studies have shown that microplastics are pervasive in the environment, found in rivers, precipitation, soil and wildlife. Notably, microplastics have also been detected in the human body, including the lungs (Jenner et al. 2022), digestive system (Fournier et al. 2023), blood (Leslie et al. 2022; Leonard et al. 2024), and reproductive organs (Ragusa et al. 2021; Liu et al. 2022; Codrington et al. 2024). A recent article by the Washington Post suggested that some amount of microplastics may be present in the ambient air due to the release from clothing, car tires, plastic packaging, AstroTurf and cosmetic exfoliating agents (Ducroquet and Osaka 2024).

The World Health Organization (WHO) stated in 2019 that “based on the limited information we have, microplastics in drinking water don’t appear to pose a health risk at current levels…” (WHO 2019). In fact, the weight of evidence indicates that existing sources of microplastics are generally believed to present no risk, or at least no measurable risk, to humans (Burton Jr. 2017; Cox et al. 2019; Backhaus and Wagner 2020; Hwang et al. 2020).

Although there is no definitive evidence that the presence of these tiny plastic particles have the potential to adversely affect human health, several studies have “linked” or found weak associations between their presence and health issues including cancer, heart disease and other chronic illnesses (Ducroquet and Osaka 2024). A recent study by Nihart et al. (2025) received widespread media coverage, including headlines suggesting that “[y]our brain may have a plastic spoon’s worth of microplastics…”. While the study reported a median concentration of 4,917 µg/g in postmortem brain tissue, the findings were based on pyrolysis–gas chromatography–mass spectrometry (Py-GC/MS), an analytical method with known limitations when applied to lipid-rich matrices such as the brain. As a result, it remains uncertain whether the detected signal reflects synthetic polymers or, alternatively, pyrolysis artifacts from the breakdown of endogenous lipids. It is difficult, if not impossible, to draw conclusions on disease causation from these studies, due to the presence of confounding factors including smoking, aging or other exposures, that the authors were unable to account for.

While some studies in rodents have suggested that high concentrations of microplastics in the blood may result in neurotoxic effects, such results are difficult to extrapolate to humans; especially when exposures are hundreds of fold less than what the animals received (Li et al. 2020; Estrela et al. 2021; Jin et al. 2021; Liu et al. 2022; Shan et al. 2022).

Given that cellular irritation could be an important mechanism, the type, size, shape and concentration of microplastics almost certainly affect their toxicity. For those not directly excreted from the body, the immune system (macrophages) can engulf microplastics. The ability to then degrade the material is likely dependent on the type of plastic (Hwang et al. 2020; Kuroiwa et al. 2023; Adler et al. 2024).

It has been suggested that microplastics, on a case by case basis, can contain and leach toxic chemicals, depending on the origin of the plastic and, on their own, can potentially cause some level of inflammation (Jeong et al. 2016; Kadac-Czapska et al. 2024).

A comprehensive, globally accepted risk assessment of microplastics is necessary to draw accurate conclusions on what health hazards, if any, are posed at current or predicted concentrations.

Legal and Regulatory Action Are Rising

Litigation related to microplastics has surged in recent years, with claims against plastics producers under both environmental and consumer protection laws. In a landmark case, Formosa Plastics Corporation was required to pay $50 million to fund environmental remediation projects after violating its discharge permit by releasing plastic pellets into a water body (plasticpollutioncoalition 2019).

On the regulatory front, the European Union has proposed measures to curb microplastics pollution, including bans on microplastics in cosmetics and detergents and mandates for companies to cover the costs of removing microplastics from urban wastewater. These regulations aim to significantly reduce human and environmental exposure to microplastics by 2030, supporting the broader zero-pollution action plan (Tsang and Kvedar 2024). In the United States, legislative actions such as the Microbead-Free Waters Act of 2015 have set the stage for further regulatory efforts to address microplastics pollution (National Association of Clean Water Agencies (NACWA) 2024). In 2020, the California State Water Resources Control Board became the first regulatory body to define microplastics in drinking water (Baroni and Henke 2022).

TRC Can Help

TRC’s tested practitioners, like Dr. Dennis Paustenbach PhD, CIH, DABT, and Michael Stevens, provide scientifically sound risk assessments for complex cases. Our team applies exposure science and the health risk assessment methodology embraced by the National Academies of Science to characterize the possible risks and have conducted more than 1,000 targeted risk assessments. To learn more about our capabilities or discuss a specific need, please contact Michael Stevens at mstevens@trccompanies.com.