Microplastics are ubiquitous and persistent pollutants in the ocean, and a pervasive and preventable threat to the health of marine ecosystems. Microplastics, defined as particles less than 5 mm, come in a wide variety of shapes, sizes, and plastic types, each with unique physical and chemical properties and toxicological impacts. Accurate measures of the occurrence of microplastics in the environment and identification of likely sources are necessary to form an understanding of the magnitude of the problem, identify the highest priorities for mitigation, and inform effective management actions.
The findings of the study made headline news on the front cover of the LA Times and the Mercury News. Those news stories focused on one of the findings from the study which was the total estimated microplastic loads going into the bay. Prior to the study, there wasn’t any data to make that type of estimate.
Microplastics were in the news several years ago with microbeads, a common ingredient in facial products that went down the drain, through wastewater treatment plants, with some of it escaping into the environment. In 2015, legislation was passed to address microbeads in large part because of the data that the Regional Monitoring Program had collected. A previous study in 2015 also made the news because the microplastics measured in San Francisco Bay were higher than what had been measured in other areas.
Microplastics are much more than microbeads; they come in different shapes and sizes, including fragments, fibers, spheres, films, and foams.
“Essentially these microplastics are the detritus of modern day society for over 350 million tons of plastic are produced annually,” said Dr. Lin.
The shape of the microplastic is a clue as to where it might have come from. For example, a piece of foam piece have come from polystyrene food packaging litter that has broken down into smaller microplastics.
“We’re concerned about microplastics in the environment because organisms that ingest them might be harmed from physical blockage or from chemicals that are embedded in the plastic itself,” said Dr. Lin.
The study of microplastic is still in the early stages so the ecological impacts are unknown. In the meantime, plastic use is only going to increase, which in turn means that microplastic is likely going to continue to increase. Once in the environment, microplastics are persistent and logistically impossible to remove, and so over time, microplastic is likely to continue to accumulate, especially in places like San Francisco Bay. Recently the concern for microplastics in San Francisco Bay was elevated to the moderate concern category, largely due to the results from the recent study.
The most recent study is the first comprehensive regional study of microplastic in the San Francisco Bay, and from the start, it was designed to inform pollution prevention efforts. “We had many ambitious objectives, including to improve methods to insure the quality of our data results,” said Dr. Lin. “Additionally, another major objective was to evaluate current concentrations of microplastics so we can understand the magnitude of the problem, as well as to track future trends. For example, did the microbead ban reduce microplastics over time? We also wanted to characterize pathways so we could understand how microplastics were getting to the bay and how we can stop it.”
For the study, they collected many different types of samples, from water samples and fish samples, specifically prey fish such as anchovies and top smelt, as well as sediment samples. Researchers collected samples from the nearby oceans, as well as characterizing pollution pathways. They sampled final treated wastewater effluent, untreated stormwater runoff, and surface water using a special collector to collect particles on the surface.
Wastewater samples were collected from 8 wastewater treatment facilities throughout the bay which represent 70% of total effluent flows going into the bay. For stormwater, they sampled 12 different watersheds that represent 11% of the watershed drainage area in the bay; the watersheds that were sampled vary in geography, their size, as well as their land use.
The hundreds of samples were then sent to the University of Toronto for analysis where Dr. Chelsea Rochman’s group of over 20 graduate and undergraduate students counted the hundreds and hundreds of particles in the samples and characterized them as to color, morphology, and dimensions. They were then further analyzed to confirm that they were plastic.
Even with over 20 students counting, there wasn’t enough time to analyze all of the samples, so a subset of the microparticles was analyzed for microplastic and then they extracted the percentage of the total microparticle count for microplastic. The percentage varied based on the matrixes but varied between 7% and 66% for different types of samples, Dr. Lin said.
“What we found was that microparticles were really abundant in surface water and sediment,” she said, presenting a bubble chart showing surface water concentrations in the bay as well as the adjacent ocean. “As you can see from the blue circles being bigger than the red circles, the wet season concentrations were ten times greater than the dry season. And the Bay concentrations were 30 times greater than the nearby oceans.”
“Concentrations in the sediment were also abundant with the highest concentrations in the lower South Bay which is heavily influenced by stormwater and wastewater discharges. These concentrations were higher than what has been measured in other areas. One footnote to that comparison is that studying microplastic is still being developed; there are not standard methods, and there are limited studies. But even despite those limitations, what we measured was much higher than what has been measured in other studies.”
Microplastics were also identified in anchovies and top smelt; these species are really important because they form the foundation of the food web in the bay and this means that the microplastic in the water and the sediment is making it’s way through the food web, Dr. Lin said.
Most of the particles identified were fibers and fragments. Some of the fibers were polyester and acrylic fibers, likely from textiles; others were fragments of polypropelene and polyetheline fragments which are commonly used in single use food-ware items. Polyethelene spears were identified which could come from microbeads.
Half of the stormwater samples contained black and rubbery fragments that were hard to analyze which were sent to another lab and confirmed that some of them were rubber. One possible source of these rubbery particles is tire wear.
“When we take our wastewater and stormwater results and extrapolate it to the whole bay, the total estimated loads of microplastic coming from wastewater treatment plants going to the bay is 17 billion,” said Dr. Lin. “When we take the number for our stormwater, this number is 7 trillion. That’s a lot of zeroes, but the punch line is the stormwater loads is 300 times greater than the wastewater load.”
“And remember those black rubbery particles? This means that half of that could be coming from tire wear particles, and identifying tire wear as a source of microplastic is a huge challenge, not only for microplastic but also for climate change.”
This stormwater load was part of what made the headlines. Prior to this, there was no stormwater data, so this has shifted the focus of the Regional Monitoring Program to more studies looking at the sources of microplastic.
Dr. Lin noted that a colleague from SFEI, Dr. Sutton, had spent a week meeting with tire manufacturers to talk about the study results and start discussions on potential solutions.
“From the start, our project was designed to link our science with policy decisions that can help find solutions,” she said. “This effort was led by our partners at Five Gyres who are very active in environmental advocacy as well as policy discussion on reducing plastic use. They led an effort to convene a committee of diverse stakeholders to discuss policy options and different recommended actions informed from the scientific results from our study. And they came up with a report with many recommendations about what are the next steps.”
The first recommendation is to support policies that reduce single use plastic and packaging. “Much of the litter items that are identified on shorelines and beaches were from food-ware and each of these have the potential to fragment thousands and thousands of microplastic, so addressing single use plastic is a good start.”
The next recommendation is to explore green stormwater infrastructure as a tool for treating microplastics in urban stormwater runoff which is largely untreated. SFEI studies of rain gardens ound that they were quite effective at removing microplastic from urban runoff, removing over 90% of the microparticles that flowed through it.
The next recommendation is to explore policy options to install fiber filtration in laundry machines, which is meant to address the abundance of the fibers that were detected in all of the samples.
During the discussion period, the question was asked if the research methods used were biased towards the buoyant particles. “For surface water, we are collecting more of the more buoyant particles and collecting sediment, so we are missing a large part of the water column when we’re collecting surface and sediment samples, so different matrixes are biased towards the buoyancy of different particles that we identified,” said Dr. Lin.
“So this could still be an underestimate of particles in the Bay?” asked the audience member.