The Problem with Microplastics


Microplastics are tiny bits of plastic five millimeters or smaller. Their small size exempts them from most regulations, but makes microplastics a big pollution problem.

Building on SFEI’s major finding that storm-driven runoff from cities is a major pathway for microplastics to enter California’s aquatic ecosystems, this new report synthesizes available information on sources of microplastics to urban runoff, including textile, cigarette filter, and other types of fibers; single-use plastic foodware; and vehicle tires. It illustrates how plastic products and their breakdown microplastic particles move through the environment, traveling through the air, depositing on the urban landscape, and washing into streams, rivers, and coastal locations during storm events. The report also illustrates a broad menu of promising measures that California agencies, the public, and the vehicle industry can use to tackle each of the major sources of microplastic pollution.


Kelly Moran and Ruth Askevold, 2022. Microplastics from Tire Particles in San Francisco Bay Factsheet. San Francisco Estuary Institute: Richmond, CA.
Kelly Moran, et al. 2021. A Synthesis of Microplastic Sources and Pathways to Urban Runoff. San Francisco Estuary Institute: Richmond, CA.

Related Publications

Rebecca Sutton, et al. 2019. Understanding Microplastic Levels, Pathways, and Transport in the San Francisco Bay Region. San Francisco Estuary Institute: Richmond, CA.
Rochman, C. M.; Munno, K.; Box, C.; Cummins, A.; Zhu, X.; Sutton, R. 2020. Think Global, Act Local: Local Knowledge Is Critical to Inform Positive Change When It Comes to Microplastics. Environmental Science & Technology. SFEI Contribution No. 1024.
Miller, E.; Sedlak, M.; Lin, D.; Box, C.; Holleman, C.; Rochman, C. M.; Sutton, R. 2020. Recommended Best Practices for Collecting, Analyzing, and Reporting Microplastics in Environmental Media: Lessons Learned from Comprehensive Monitoring of San Francisco Bay. Journal of Hazardous Materials . SFEI Contribution No. 1023.
Hung, C.; Klasios, N.; Zhu, X.; Sedlak, M.; Sutton, R. 2020. Methods Matter: Methods for Sampling Microplastic and Other Anthropogenic Particles and Their Implications for Monitoring and Ecological Risk AssessmentIntegrated Environmental Assessment and Management 16 (6)SFEI Contribution No. 1014
Miller, E.; Klasios, N.; Lin, D.; Sedlak, M.; Sutton, R.; Rochman, C. 2020. Microparticles, Microplastics, and PAHs in Bivalves in San Francisco Bay. SFEI Contribution No. 976. San Francisco Estuary Institute: Richmond, CA.
Meg Sedlak et. al., 2019 SFEI Microplastics Strategy Update SFEI Contribution No. 951. San Francisco Estuary Institute: Richmond, CA.
Sutton, R.; Sedlak, M. 2017. Microplastic Monitoring and Science Strategy for San Francisco Bay. SFEI Contribution No. 798. San Francisco Estuary Institute: Richmond, CA.
Rebecca Sutton, et al., 2016. Marine Pollution Bulletin. Volume 109, Issue 1. Microplastic contamination in the San Francisco Bay, California, USA.
Rebecca Sutton, 2016. Microplastic Contamination in San Francisco Bay - Fact Sheet. 2015, Revised 2016. SFEI Contribution No. 770.

Project Partners and Funding Sources


The 5 Gyres Institute

UC Davis Center for Watershed Science


Moore Foundation

With Additional Support From:

San Francisco Bay Regional Monitoring Program for Water Quality


City of Palo Alto

East Bay Municipal Water District

Virginia Wellington Cabot Foundation

California Ocean Protection Council


San Francisco Baykeeper

Associated Staff:
SFEI’s 2021 report on microplastics in storm-driven runoff from cities includes a menu of promising measures to prevent pollution, and informed California’s new Statewide Microplastics Strategy. Media highlights include:


San Francisco Chronicle: California adopts plan to tackle microplastic pollution — first state to do so

Kurtis Alexander of the San Francisco Chronicle writes:

California is set to become the first state, and maybe the first place in the world, to limit microplastics at sea.

A state advisory board called the Ocean Protection Council adopted a plan Wednesday for addressing these pesky particles that flake off tires, clothing, plastic bags and countless other items before making their way to the water.

Read More
Los Angeles Times: California officials approve plan to crack down on microplastics polluting the ocean

James Rainey of the Los Angeles Times writes:

California aims to sharply limit the spiraling scourge of microplastics in the ocean, while urging more study of this threat to fish, marine mammals and potentially to humans, under a plan a state panel approved Wednesday.

The Ocean Protection Council voted to make California the first state to adopt a comprehensive plan to rein in the pollution, recommending everything from banning plastic-laden cigarette filters and polystyrene drinking cups to the construction of more green zones to filter plastics from stormwater before it spills into the sea.

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Estuary News: West Coast Salmonids All Tired Out?

Alastair Bland of the San Francisco Estuary Magazine writes:

West Coast salmon and steelhead populations have declined steeply in the past century – a plight that biologists have primarily blamed on habitat loss. Dams, for instance, block adult fish’s access to historic spawning grounds, and juvenile survival is impacted by streamside development and water diversions.

Now, it turns out, microplastic pollution may be a much bigger factor than anyone knew just several years ago.

In 2019, scientists with the San Francisco Estuary Institute and the Los Angeles-based nonprofit 5 Gyres published findings indicating that car tire particles are one of the most prevalent forms of microplastic pollution flowing into San Francisco Bay. Then, in 2020, a team of West Coast scientists discovered that a chemical in these particles is extremely toxic to coho salmon at miniscule concentrations, apparently responsible for abrupt die-offs of adult fish observed over many years in Puget Sound streams. The researchers published their results in the journal Science.

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Chemistry & Engineering News: Urban stormwater presents pollution challenge

Alla Katsnelson, special to C&EN, writes:

On the wildest, stormiest nights in the San Francisco Bay Area, scientists from the San Francisco Estuary Institute (SFEI) go out on the prowl. Nighttime is when storm intensity in the Bay Area is generally highest, and the team gets going only when a storm is predicted to dump more than 2 cm over 6 h at a particular site.

The researchers fan out to different sites where they know stormwater flow is especially strong. At each site, they take samples to assay the levels of five classes of chemicals: tire- and vehicle-derived chemicals such as 6PPD-quinone; bisphenols, a starting material in manufacturing plastics; organophosphate esters, a key component of flame retardants; per- and polyfluoroalkyl substances (PFAS); and ethoxylated surfactants from paints, coatings, and floor polish. Over several hours, they nab some samples in 50 mL tubes and others in 2 L glass jugs.

This year will be the fourth and final wet season that SFEI scientists conduct these night runs before synthesizing their findings. “We’re laying the groundwork for understanding what’s out there in stormwater,” chemist Rebecca Sutton says. SFEI launched the monitoring project after a chemical analysis of samples collected in 2016 revealed untreated stormwater runoff from populated areas as an overlooked source of chemicals that water-monitoring agencies have only recently begun to track (Environ. Sci.: Processes Impacts 2021). “It really opened our eyes to stormwater as an underexplored pathway in terms of emerging contaminants,” Sutton says.

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ABC 7 News: Recent storms washed microplastics into San Francisco Bay, studies show

Dan Ashley and Tim Didion of ABC 7 News report:

Walk along Damon Slough in Oakland and you're likely to see trash heading towards San Francisco Bay. David Lewis of the environmental group Save the Bay, says much of it comes from the nearby 880 freeway and local storm drains.

"Every time it rains, anything that's on the streets goes into the storm drains and straight out into the bay unfiltered. And we see this on all of the freeways and all of our urban road," Lewis explains.

And experts say the pollution you can actually see is only part of the threat. Floating along side, often invisible to the naked eye, are microplastics. They're tiny particles, that can come from clothing, cigarette butts, and even the rubber from car tires.

"And the way it wears off is when the tire hits the road. It wears off these little tiny bits of tires. They're so small, they're practically microscopic," says environmental researcher Kelly Moran, Ph.D. of the San Francisco Estuary Institute.

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KQED Newsroom: 'You Can't Recycle Your Way Out': California's Plastic Problem and What We Can Do About It

Monica Lam of KQED Newsroom reports:

California dumps more than 12,000 tons of plastic into landfills every day — enough to fill 219 Olympic-size swimming pools, according to CalRecycle, the state's recycling and waste management agency. The state boasts one of the highest recycling rates in the country, especially of cans and bottles, but despite decades of investment in infrastructure and machinery, the system remains overwhelmed by plastic.

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Dryer Vents Blow Hot Air & Microplastics

For KneeDeep Times, a new digital magazine focusing on climate resilience, Alastair Bland writes:

New research confirms that air vents on tumble dryers – rather than washing machines – may be a leading source of microplastic fibers from clothing in the environment. The findings, presented in a new report by the San Francisco Estuary Institute, provide convincing reason to hang-dry clothes and to use energy-intensive dryers sparingly, if ever.

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The Mercury News: Study finds California salmon face deadly threat from car tires

WILL HOUSTON of Marin Independent Journal writes:

A highly toxic chemical used in the production of millions of tires every year is killing salmon in the Pacific Northwest, and it is being detected in streams across Northern California, a new study finds.

Scientists have known for decades that stormwater runoff from roads, highways and other urban areas has been linked to high rates of coho salmon deaths in Washington state, where as many as 90% of salmon in the Puget Sound area have died before they could spawn.

The new study published in the research journal Science on Thursday has identified a culprit chemical for the first time — a commonly used preservative called 6PPD used to give tires longer life.

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LA Times: Scientists solve mystery of mass coho salmon deaths. The killer? A chemical from car tires

ROSANNA XIA of LA Times writes:

When officials in Seattle spent millions of dollars restoring the creeks along Puget Sound — tending to the vegetation, making the stream beds less muddy, building better homes for fish — they were thrilled to see coho salmon reappear.

But when it rained, more than half, sometimes all, of the coho in a creek would suffer a sudden death. These mysterious die-offs — an alarming phenomenon that has been reported from Northern California to British Columbia — have stumped biologists and toxicologists for decades. Numerous tests ruled out pesticides, disease and other possible causes, such as hot temperatures and low dissolved oxygen. Now, after 20 years of investigation, researchers in Washington State, San Francisco and Los Angeles say they have found the culprit: a very poisonous yet little-known chemical related to a preservative used in car tires. This chemical is just one of a vast number of contaminants that washes off roads whenever it rains.

Read More
The release of the 2019 San Francisco Bay microplastics report prompted a far-reaching media response. The following list represents some of the significant highlights:


'Everywhere we looked': trillions of microplastics found in San Francisco Bay

Maanvi Singh from the US edition of the Guardian, based in the UK, writes, “It was basically everywhere we looked,” said Rebecca Sutton, an environmental scientist at the San Francisco Estuary Institute, a local institution that led the three-year, $1.1m research effort.

The findings fit with other recent studies that detected microplastics within the deepest reaches of the ocean, flowing through UK lakes and rivers and permeating US groundwater. Scientists have also found plastic in remote regions like the Pyrenees and the Rocky Mountains, suggesting these particles can travel with the wind for hundreds, if not thousands, of kilometers.

Read More

Wired Magazine: A new report shows an astounding amount of microplastics, largely from car tires, are tainting the watershed

Matt Simon from Wired Magazine writes:

San Francisco Bay, like Monterey Bay to its south, is a rare success story in ocean conservation. In the 1960s, three grassroots activists—Sylvia McLaughlin, Kay Kerr, and Esther Gulick—launched Save the Bay, which beat back developers trying to fill in parts of the iconic body of water.

But also like Monterey Bay, San Francisco Bay has all the while been poisoned by an invisible menace—microplastic. Yesterday at a summit in Berkeley on the east shore of the Bay, the San Francisco Estuary Institute and the 5 Gyres Institute presented findings from a three-year survey of microplastics in Silicon Valley’s massive watershed.

The news is grim: an estimated 7 trillion (yes, with a “t”) pieces of microplastic are entering the Bay via stormwater each year, much of the debris likely coming from car tires, with treated wastewater contributing another 17 billion (this time with a “b”) particles, largely from synthetic fibers in clothing. They found particles everywhere—in surface waters, in sediments, in fish. The less grim news: The research inadvertently discovered a way to help stop microplastics from reaching aquatic habitats, and it’s bringing some rigor to the still-nascent field of microplastics research.

Read More

San Jose Mercury News: 7 trillion tiny pieces of plastic wash into San Francisco Bay every year, new study shows

On October 2nd, 2019, Paul Rogers released an article in the San Jose Mercury News regarding this microplastics study, in which he asserted, "The three-year study found that billions of pieces of “microplastic” — particles smaller than 5 millimeters each, or roughly the size of a pencil eraser — pour through the Bay Area’s 40 sewage treatment plants every year. The particles come from synthetic fibers in clothing, like fleece jackets that shed in washing machines or baby wipes flushed down toilets, and then wash down sewer pipes, pass through treatment plant filters and empty into bay waters.

"But 300 times more of the relentless toxic confetti, the study revealed, comes from storm drains, the largest source of the particles. The drains collect plastic litter from roads, foam food packaging, rubber bits from car tires, and other sources, and deliver the debris to creeks and the bay, especially during wet winter months, where it breaks down but never fully disappears."

Read More

LA Times: The biggest likely source of microplastics in California coastal waters? Our car tires

Rosanna Xia of the LA Times writes:

"Driving is not just an air pollution and climate change problem — turns out, it just might be the largest contributor of microplastics in California coastal waters.

"That is one of many new findings, released Wednesday, from the most comprehensive study to date on microplastics in California. Rainfall washes more than 7 trillion microplastics, much of it tire particles left behind on streets, into San Francisco Bay each year — an amount 300 times greater than what comes from microfibers washing off polyester clothes, microbeads from beauty products and the many other plastics washing down our sinks and sewers."

Read More

SF Chronicle: Huge amounts of plastic, much of it from car tires, washing into SF Bay, study finds

Kurtis Alexander of the SF Chronicle writes:

More than 7 trillion tiny pieces of plastic wash from city streets into San Francisco Bay each year, a new study finds, a staggering amount of pollution that researchers weren’t entirely aware of and aren’t prepared to stop.

The microplastic, defined as plastic particles smaller than 5 millimeters, are the remnants of bottles, cigarettes, clothing fibers and a seemingly endless list of plastic products. They’re pushed by rain into storm drains and carried through rivers and creeks into the bay. Nearly half of this pollution, according to the report, consists of black rubbery fragments that the study’s authors believe are from worn tires.

Read More

About the Event

It is possible to view the symposium via live stream. The videos for the Symposium's sections are posted below. 

For more information, please email [email protected].



Welcome and Introduction
Warner Chabot, Executive Director, San Francisco Estuary Institute


Big Picture from the Ocean Protection Council
Mark Gold, Deputy Resources Secretary for Coast and Oceans and Executive Director, Ocean Protection Council

Potential impacts of microplastics on marine, freshwater, and terrestrial organisms:
         What we know and what we need to know to better assess risk

GUEST EXPERT • Susanne Brander, Oregon State University at Corvallis

SESSION 1 • New Findings from the San Francisco Bay Microplastics Project

Science Panel: What’s the Big Picture on these Tiny Contaminants?

  • Study Objectives - Meg Sedlak, SFEI
  • Microplastics in Bay and Ocean Waters - Carolynn Box, 5 Gyres
  • Microplastics in Sediment and Fish - Diana Lin, SFEI
  • Microplastics in Wastewater and Stormwater - Alicia Gilbreath, SFEI

DISCUSSION • Moderated by Rebecca Sutton - SFEI, with Technical Expert Xia Zhu - University of Toronto


From Land to Sea: Models to Trace the Movement of Microplastics in the Bay and Ocean
Don Yee & Rusty Holleman, University of California at Davis

The Future of Microplastic Science
Chelsea Rochman, University of Toronto

Next Steps for Science and Monitoring in the San Francisco Bay and California
Rebecca Sutton, SFEI, and Shelly Moore, Southern California Coastal Water Research Project (SCCWRP)


Focus on Solutions

Airrion Copeland, Executive Director, 5 Gyres


The Big Picture from CalEPA
Jared Blumenfeld, Secretary for Environmental Protection, CalEPA

SESSION 2 • Bay Area Solutions to Reduce Microplastics Pollution

Youth Stakeholders and the Importance of our Influence and Diversity
Cambria Bartlett and Damian Montesinos, Heirs to our Oceans

Data Driven Solutions for Microplastics Pollution in San Francisco Bay
Carolynn Box and Anna Cummins, 5 Gyres

Policy Panel: Local Actions to Drive Change

  • Miriam Gordon, Upstream
  • Jen Jackson, Department of the Environment, San Francisco
  • Martin Bourque, Berkeley Ecology Center
  • Chris Sommers, EOA
  • Sherry Lippiatt, National Oceanic Atmospheric Administration

DISCUSSION • Moderated by Jen Jackson


SESSION 3 • Rising to the Challenge, Microfibers and More

What does Design Change Look like for Textile Industry?
GUEST EXPERT • Krystle Moody Wood, Materevolve, LLC.

Case Study on Effectiveness of Filtration that Could be Applied in Bay Area
Lisa Erdle, University of Toronto

BIG Trends in MICROplastics Legislation in California
Nick Lapis, Californians Against Waste

Highlights from the Plastic Pollution Movement: Bay Area and Beyond
Marcus Eriksen, 5 Gyres


WEBINAR: Microplastics Study Design, Analysis, and Reporting
Sponsored by the California Ocean Protection Council 

Friday, February 21, 2020 
10:00 AM – 12:30 PM 

Description: Researchers at the San Francisco Estuary Institute (SFEI), 5Gyres, and University of Toronto recently completed a three-year project to monitor microplastics in the San Francisco Bay and adjacent national marine sanctuaries, as well as the contaminant pathways of wastewater effluent and urban stormwater. In this webinar, researchers will share lessons learned to guide others who are conducting microplastic research.  In particular, we will cover

  • Factors to consider when designing a study;
  • Brief overview of microplastic sample collection for a range of environmental matrices, including quality assurance/quality control samples;
  • Brief overview of laboratory processing and analysis for the San Francisco Bay study; 
  • Field and laboratory reporting templates;
  • Standardized vocabulary developed for reporting results.

The goal of the webinar is to guide and encourage robust and consistent monitoring of microplastics. This webinar was generously funded by the California Ocean Protection Council.


  Topic Time / Presenter
 1. Introduction and Goals 
  • Share the goals and format of the webinar. 
10:00 am / Diana Lin
 2. Study Design to Address Research Objectives
  • We will review research objectives and other factors to consider in study design, using the San Francisco Bay study as an example.
10:10 am / Liz Miller
 3. Microplastic Data for Transport Modeling
  • Review of microplastic data used to inform microplastic transport model
10:30 am / Rusty Holleman
 4. Field Sampling Methods and Quality Assurance/Quality Control Samples
  • Brief introduction to field sampling methods used for different matrices (surface water, sediment, fish, stormwater, and wastewater).
  • Introduce field sheets with field parameters used for each sampling matrix. 
  • Discuss collection of QA/QC samples including field blanks, field duplicates, and laboratory blanks.
10:40 am / Diana Lin
 5. Short Break 11:05
 6. Processing and Analysis of Samples in the Laboratory
  • Outline laboratory analysis for different matrices, including extraction, counting, polymer characterization using Raman/FTIR analysis, and new tools being developed. 
  • Review microplastic characteristics measured and recorded through laboratory analysis.
  • Introduce laboratory reporting worksheets.
11:10 am / Chelsea Rochman
 7. Reporting Vocabulary
  • Importance of standardized vocabulary 
  • Review the vocabulary and method for summarizing results developed for CEDEN, the California Environmental Data Exchange Network. Example of challenges in datasets and methods to address this.
11:30 am / Adam Wong
 8. Additional Time for Questions 12:00 pm


Field and Laboratory Sampling Templates


Plastic pollution is gaining global recognition as a threat to the resilience and productivity of ocean ecosystems. However, we are only just beginning to understand the scope and impacts of microplastic particles (less than 5 mm) on coastal and ocean resources, and the San Francisco Bay Area is no exception. A preliminary study of nine water sites in San Francisco Bay, published in 2016, showed greater levels of microplastics than the Great Lakes or Chesapeake Bay. Based on these findings, the San Francisco Estuary Institute (SFEI) organized a workshop with stakeholders, scientific experts, and regulatory staff to identify major data gaps and management questions. SFEI developed a Microplastic Strategy to outline the essential scientific studies needed to inform management actions.

With a generous grant of $880,250 from the Gordon and Betty Moore Foundation, $75,000 from the Bay's Regional Monitoring Program, and support from Patagonia, City of Palo Alto, East Bay Municipal Utility District, and San Francisco Baykeeper, scientists from SFEI and The 5 Gyres Institute have embarked on a two-year study to address the highest priority elements identified in the Strategy (3 minute video). 

This project includes multiple scientific components to develop improved knowledge of microplastic in the Bay Area environment and prioritize practical steps to reduce pollution:  

  • Baseline microplastic monitoring in San Francisco Bay surface water, sediment, and fish 
  • Monitoring in National Marine Sanctuary surface waters outside of the Golden Gate
  • Characterization of microplastics in treated wastewater and stormwater flowing into the Bay
  • Rigorous method development and standardization 
  • Development of modeling tools to link Bay contamination to that of adjacent Sanctuaries
  • Data-driven policy options for the Bay Area developed with leading national and regional experts 
  • Sharing findings with regional stakeholders and the public  

The scientific information, tools, and policy recommendations developed via the San Francisco Bay microplastic project are intended to catalyze similar efforts to understand and reduce plastic pollution around the globe. 

Track the latest developments on Instagram and Twitter: #SFBayMicroplastics

Carolynn Box
Programs and Focus Areas: 
Clean Water Program
Data Services
Design and Communications
Location Information