In brief
· On October 1, California will add microplastics to its Candidate Chemicals List, an initial step in the state’s process for assessing chemicals for potential regulation.
· The move is the most recent in a decade-old regulatory approach that began with a ban on plastic microbeads in cosmetics.
· With a binding international plastics treaty stalled, a Stanford-led paper describes how California has managed to make progress on the plastic pollution problem, potentially serving as a model for other states and countries to follow.
While talks on an international plastics treaty remain deadlocked, California is kickstarting a process for potentially regulating microplastics. On October 1, the state will add microplastics to a list of substances that evidence suggests may be harmful to people or the environment and are candidates for increased regulation.
A recent Stanford University-led paper traces California's approach to microplastic regulation over the past decade, and draws lessons for other states and countries looking to regulate a synthetic material found in our water, food, and bodies. The paper, published in Frontiers in Environmental Science , was supported by the Stanford Center for Human and Planetary Health . Below, paper coauthors Amelia Meyer , Kara Meister , and Sarina Patel explain what can be learned from the state's decade-long regulatory experiment.
Meyer is an environmental scientist who co-leads Stanford’s Plastics and Health Working Group , which focuses on the health and policy dimensions of microplastic pollution. Meister is a pediatric otolaryngologist and head-and-neck surgeon whose lab at the Stanford School of Medicine has documented microplastics in children's tonsil tissue and is developing new methods to measure microplastic burden in the body. Patel is a policy program manager at the Stanford Woods Institute for the Environment and a former California Legislature science fellow who works to connect Stanford research with state policymakers.
(Read more about how Stanford scholars are approaching the plastic problem from many angles: https://woods.stanford.edu/planet-versus-plastic-earth-day-2024 )
Listing microplastics in the Candidate Chemicals List doesn't mean a product is restricted in any way. It's the procedural step California's Department of Toxic Substances Control takes before it can designate specific products for regulation. The process still requires public comment and formal review.
“While microplastics have been measured in the environment for a while, there hasn’t been a coherent way, legally, to treat them as pollution that needs to be mitigated,” Patel said. “Classing microplastics as a chemical of concern opens an important legal door.”
In 2015, California banned microbeads in wash-off cosmetics like facial scrubs because the tiny plastic pieces can slip through wastewater treatment systems and accumulate in waterways. It was a relatively straightforward law, according to Meyer, because microbeads "were intentionally manufactured, had a clear source, the same general shape and texture, and were largely non-essential."
Today's biggest microplastic sources, such as tire dust and clothing fibers, are harder to address; when particles shed continuously from millions of cars and washing machines, the interventions must go beyond manufacturing. California has slowly been chipping away at the issue with an expanding body of regulations.
Microplastics have been found in human blood, organs, and other bodily fluids. Some published studies and ongoing research link their presence to significantly higher rates of heart attack, stroke, and death, but finding microplastics in the body doesn't prove they are the cause of that harm.
"Detecting microplastics in the body does not by itself tell us what level of exposure causes harm," Meyer said. "Uncertainty is a reason to continue research and reduce unnecessary exposure at the source, not a reason to wait until every question has been answered."
Meister is equally concerned about what travels with the plastic. "Microplastics are Trojan horses," she said. "There are potentially thousands of other chemicals and polymers conjugated to microplastics," including plasticizers like BPA with well-documented health effects. "We are just at the beginning of understanding the reach, scope, and impact of these exposures."
Since the 2015 microbead ban, California has created a statewide microplastics strategy, drinking-water standards, and a law, SB 54, that assigns producers responsibility for the full life cycle of their products, not just their creation. It includes plans for a $5 billion mitigation fund fed by manufacturer fees. "This is a public facing, tangible step to raise awareness and mitigate the impacts of plastics in our state," Meister said.
“By taking a variety of regulatory approaches, California gives itself tools to tackle microplastic pollution across the scope of the problem, from production to waste management to environmental cleanup,” Patel said.
Despite years of effort, UN negotiators have failed to agree a binding plastics treaty, largely due to a deadlock over production caps. In that vacuum, states and other governmental bodies are charting their own course.
“There are some strident voices speaking up in support of the plastics industry, pushing back against regulation supposedly in the name of affordability,” Patel said. “While systemic change does cost money, the damage plastic has done to the environment, to wildlife, and potentially to human health also has a cost associated and right now there is no accountability for those costs.”
"Because plastics are rooted in the petroleum industry, there will be strong pushback to regulation,” Meister said. “That makes it necessary to have a concentrated, cohesive effort that is okay with baby steps. Otherwise, there is a risk of regrettable substitutions.” For example, the U.S. Food and Drug Agency and some states restricted the use of Bisphenol A (BPA), a chemical once used in various food and drink packaging. Manufacturers replaced it with chemicals that pose similar health dangers, according to various studies .
In the meantime, California shows how other states and countries can make inroads on the issue. “It is experimenting with policies, generating evidence, and demonstrating what stronger regulation can look like in practice,” Meyer said.
Coauthors of the paper also include Desiree LaBeaud , a professor of pediatrics (infectious diseases) at the Stanford School of Medicine, a senior fellow at the Stanford Woods Institute for the Environment , co-lead of the Plastics and Health Working Group hosted by the Stanford Center for Human and Planetary Health, and a professor, by courtesy, of epidemiology and population health and of environmental social sciences; and Chloe Smith, a policy officer at the London School of Economics Sustainability Regulation Observatory and Sustainability Law & Policy Clinic, and formerly a policy officer at the Sustainability Law and Policy Clinic & Regulation Observatory of the University of California, Berkeley.
Related:
https://news.stanford.edu/stories/2026/06/pregnant-women-chemicals-risk-research
Frontiers in Environmental Science
Microplastic pollution policy and one health: a critical perspective on California legislation as a case study
5-Aug-2026