By Alastair Bland
Long ago, the quiet shores of southern San Francisco Bay featured rich wetlands, streams thick with salmon and steelhead, and a bounty of other fishes and invertebrates which fed wildlife and people alike. Perhaps more than anything else, there was clean water.
But after nearly two centuries of Western occupation and the steady pollution that has become a signature of our time, the South Bay has become a toxic sink. Fish still live here, and people still catch and eat species like striped bass, white croaker and leopard shark, but emerging research suggests they should reduce their portions.
In a study published in May, sport fish captured in a remote backwater between Alviso and Milpitas called Artesian Slough topped the charts for concentrations of perfluoroalkyl and polyfluoroalkyl substances, or PFAS. Other sites in the South Bay also ranked high in contamination for multiple species of frequently eaten fish – especially common carp, largemouth bass, leopard shark, shiner surfperch and striped bass – with some of the same species showing lower PFAS concentrations in the northern realms of San Francisco Bay.
PFAS are a family of man-made chemicals widely used in manufacturing and associated with a range of serious health problems, including cancer. They are increasingly appearing in our environment, food sources and our bodies. The new research, published in the journal American Chemical Society ES&T Water, found 20 types of PFAS in fish throughout San Francisco Bay. Dominating the spectrum of PFAS was perfluorooctanesulfonic acid, or PFOS, a possible carcinogen linked to numerous health threats.
The study’s senior author Rebecca Sutton, a senior scientist and emerging contaminant expert with the San Francisco Estuary Institute, attributed the regional PFAS distribution patterns her team recorded to the unique hydrodynamics of different parts of the bay.
The northern and central parts of the estuary are flushed by freshwater inflow and heavy tidal action, while the South Bay is a comparatively enclosed area. The southern part o
the estuary is also ringed by dense cities that produce urban storm runoff and wastewater treatment effluent.
“So we see contaminants, especially the persistent ones like PFAS, building up in that part of the bay,” she said.
More than 80% of samples from the southern bay, compared to just 8% from elsewhere in the estuary, exceeded a one-meal-per-week threshold for PFAS consumption established by the state of Massachusetts, which has the strongest such guidelines in the country.
Sutton said the results of her team’s study likely reflect global trends.
“Much of San Francisco Bay’s contaminant burden is from typical urban use, typical consumer product use, very typical runoff and wastewater discharges, as opposed to some locations that have a lot of chemical manufacturing and other kinds of heavy industry,” she said. “So, we might anticipate that this is a pretty strong urban signal that will be seen elsewhere as well.”
They found that 83% of their fish samples exceeded the concentration level considered dangerous if consumed more than once per day in eight-ounce servings.
Alarmingly, 100% of samples of striped bass and white croaker – two very popular dinner table items among anglers – exceeded Massachusetts’ one-meal-daily threshold, and about half for both species exceeded the once-weekly limit.
Past studies have found decreasing PFOS concentrations in tissue samples from double-crested cormorants and harbor seals in San Francisco Bay. Though the trend was not observed in sport fish, Sutton’s team attributed the pattern to national regulations phasing out PFOS use over the past two decades in various products, including firefighting foams and many household uses.
However, replacement compounds being adopted by industrial users may not be much safer.
“We call these regrettable substitutes,” Sutton said.
Other PFAS are also still used in making items like paint, furniture, cookware, cosmetic products and food packaging.
In their paper, Sutton and her colleagues called for further studies of PFAS exposure and risks, with research and regulations ideally designed to cover all PFAS rather than individual members of the chemical family.
“If you can’t use any PFAS …, then whether we know how to measure it or don’t know how to measure it, it shouldn’t be in that product,” she said.
This story was produced by Estuary News Group.
