Pier 32 trash skimmer used in plastic debris collection for study
San Diego Bay’s fish are ending up with plastics in their systems from trash that washes downstream — and the fish are fed more plastic with every rainstorm.
That’s the conclusion of the first comprehensive report on plastics in the bay that was completed in October by researchers from the San Diego Regional Water Quality Control Board, San Diego Coast Keeper, the cities of Imperial Beach and Chula Vista, the port district, the Navy, and the U.S. Fish and Wildlife Service.
“Stingrays had the most plastics,” said Chad Loflen, from the water board. “But other fish had microplastics, too. It’s important to understand that microplastics are sponges for chemicals and toxins.”
Researchers found the plastics in 88 percent of the intertidal zones in the bay, according to the report. The plastics range in size from bottles and bags to the tiny (less than a half millimeter) microbeads found in many personal-care products, including toothpaste, that provide abrasiveness.
As the big objects get tossed around and torn into smaller pieces, more microscopic pieces are created. Food wrappers were the most common find, with plastic bags.
In the water, the microbeads stay in the water column just below the surface, Loflen said. Little fish eat it there and then are consumed by bigger fish.
They found the plastics in bay fish including sea bass, white bass, spotted sand bass, and round stingrays. Round stingrays in particular had the most plastics and the widest variety, Loflen said.
The state’s Office of Environmental Health Hazard Assessment already has issued advisories to try to discourage people from eating those fish if they come from the bay, according to Sam Delson, the agency’s spokesman. (There are also agency advisories on Mission Bay fish.)
“We don’t generally look at microplastics; we focus on chemical contaminants,” Delson said. “To do an advisory, we need a certain amount of data and evidence, and that area of study is emerging.”
The majority of the plastics come from higher ground and move when it rains.
“Most of the plastics were coming down tributaries — the trash you see in curbs and gutters is carried into the bay by storm water,” Loflen said.
Besides the bay, researchers gathered plastics along the three rivers that flow into the bay. They found significant differences between what they found in the watersheds defined by the Sweetwater and Otay rivers and Chollas Creek.
“Chollas Creek tributaries had the highest density of food wrappers and hard and soft plastic pieces when compared with the two rivers. Sweetwater River had greater densities of single use plastic bags, cigarette butts and other items compared with the Chollas Creek tributaries. Otay River had higher densities of foam polystyrene pieces and cigarette butts,” the report says.
The study found that far more of the material ended up in salt marshes and mudflats along the rivers that transport them, at river mouths, and in riprap, than at beaches, where clean-up projects focus.
“It’s harder to hold a cleanup in a salt marsh, because they are sensitive habitat and you need permits,” Loflen said. “We had to get permits to enter these sensitive areas to do our study.”
I Love a Clean San Diego is already orchestrating many cleanups each year, and some of those are creek and inland park efforts, according to Pia Piscitelli, the group’s marketing manager.
“We teach about watershed protection,” Piscitelli said. “But we don’t do a lot of sensitive-habitat cleanup — it’s not our specialty.”
Researchers found polystyrene foam and "persistent" plastics (the most dominant forms of plastic) in every salt marsh and mud flat they looked at. Persistent plastics include single-use bags, food wrappers, and hard plastic pieces.
But plenty made it to the sand.
“Sand samples contained an average of 6,654 pieces of small plastic per cubic meter of sand,” researchers reported.
The take-away recommendations: educating the public on proper disposal of food containers, continuing to push for less polystyrene use, and broadening clean-up efforts to include more upstream areas.
And we need more research in this emerging area of study, according to Brian Collins of the U.S. Fish & Wildlife Service.
"This tells us that plastics are a huge issue for the bay," he said. "And the sources aren't boats."