Microplastics Occurrence, Health Effects, and Mitigation Policies: An Evidence Review for the California State Legislature
January 2023 | California State Policy Evidence Consortium (CalSPEC)
This report responds to a joint request from the California Senate Committee on Environmental Quality and the Assembly Committee on Natural Resources for evidence concerning human health effects of microplastics and public policies related to microplastics prevention and mitigation. Research was conducted by the California State Policy Evidence Consortium (CalSPEC), an independent program administered through the University of California Center Sacramento (UCCS) and composed of faculty, staff, and graduate student researchers across UC campuses who evaluate evidence to inform public policy deliberations. This report addresses three overarching questions:
What are microplastics and how abundant are they in the environment?
What are the human health effects from microplastics exposure?
What government actions have addressed microplastics, and to what extent have the policies succeeded in reducing microplastics in the environment?
Overview of Microplastics
Plastics persist and accumulate in the environment regardless of whether disposal is managed or unmanaged.
Annual global plastic production, increasing exponentially since 1990, will reach an estimated 1.1 billion metric tons by 2050.
Degradation studies estimate the half-lives of plastics in the natural environment range from 50 to 1200 years, depending on the plastic’s composition and environmental exposures.
Plastics generated 1.8 billion metric tons of greenhouse gas (GHG) emissions in 2019, which represents 3.4% of global GHG (more than the percentage of C02 contributed by the global aviation industry); annual emissions from plastics will exceed 4.3 billion metric tons by 2060.
Once plastics enter the environment (air, water, soil, food, flora/fauna), they break into smaller fragments — microplastics — enabling long-range transport, which increases environmental and human interactions. A growing body of evidence shows increasing human exposure to microplastics due to accumulation in the ecosystem.
The packaging and textiles sectors are the largest contributors to microplastics waste.
Microplastics are small particles, generally defined as <5 mm (5,000 microns)1 in one dimension. They are either:
Primary microplastics: intentionally manufactured microplastics, such as preproduction feedstock (pellets) for plastics manufacturing, microbeads (for abrasion in cosmetic personal care products and industrial cleaners), particles for air-blasting technology and printer toner; or films or resins (coatings for seeds or fertilizers).
Secondary microplastics: fragments degraded from larger products that contain plastics including packaging, tires, and textiles.
Microplastics differ in size, shape (beads, pellets, fibers, fragments, films, etc.), and chemical composition. These characteristics affect transport, fate, and persistence in the environment.
Microplastics cross geographic and environmental boundaries and have been found everywhere they have been studied, including Arctic glaciers and deep-sea sediment. The totality of their prevalence globally and environmental and health impacts remain unknown. However:
Secondary microplastics are thought to comprise the majority of microplastics in the environment. For example, two-thirds of microplastics in the global marine environment are from fragmentation of virgin plastics such as tires, synthetic textiles, packaging, road markings, and marine coatings. Virgin plastics are polymers or resins that have never been used or processed before.
Microplastics annually released to land are estimated to be 4 to 23 times greater than microplastics released to oceans.
Microplastics research is an emerging field dominated more by studies of occurrence and polymer type than intermediate and long-term environmental and health effects. The field is working to standardize scientific definitions, research methods, and units of measurement.
Health Effects of Microplastics
CalSPEC conducted a rapid systematic review of evidence from the peer-reviewed literature to answer: “What are the human health effects from microplastics exposure?” A comprehensive search in July 2022 found no human studies of microplastics exposure; therefore, CalSPEC used a wellestablished scientific method to evaluate mammalian rodent studies of microplastic exposures. This process allowed CalSPEC to draw conclusions about human health effects.
Of the multiple biologic systems studied, this rapid review used a stepped approach to evaluate the effects of microplastics on human digestive, reproductive, and respiratory systems. CalSPEC evaluated the quality and strength of the evidence for outcomes related to biological changes (e.g., immunologic responses, inflammatory responses, hormonal changes) and observable outcomes (e.g., colon shortening, sperm damage) measured in studies meeting the search criteria.
CalSPEC then characterized the evidence into one of three human health hazard level classifications based the animal data: 1. Presumed to be a hazard to humans; 2. Suspected to be a hazard to humans; 3. Not Classifiable using the Hazard Identification Scheme from the National Toxicology Program as guidance.
Key Findings
The evaluated evidence was of primarily moderate quality based on criteria from the UCSF Navigation Guide methodology.
Exposure to microplastics is suspected to be a digestive hazard to humans, including cancer.
Exposure to microplastics is suspected to be a hazard to the human reproductive system.
Although the evidence from the respiratory studies did not undergo as rigorous of an evaluation, the findings in the five studies on the respiratory system are also indicative of health harm.
Limitations: This rapid review did not evaluate all health outcomes in the digestive and reproductive systems and did not evaluate plastic chemical additives known to increase the risk of negative health effects. There may also be adverse health outcomes in systems not evaluated. CalSPEC recognizes that the conclusions of the rapid review can be an underestimation of the true harm of microplastic exposure given these limitations.
The full study is available here to view or download (PDF)
