In a shallow arm of the bay, where Pacific tides cause hardly a ripple, hundreds of harbor seals lounge, mate and bear young. With placid expressions on bewhiskered faces and bulky bodies reclining on shorelines, the seals belie a disturbing burden they carry.
Living on the edge of a metropolitan hub, these seals are under scrutiny by scientists. There’s a mystery afoot in San Francisco Bay: A manmade chemical, pulled from production 12 years ago, is still turning up at high levels in the seals.
Once the prime ingredient in Scotchgard, a chemical known as PFOS has remained elevated in these harbor seals even though it has declined in sea birds that share their fish diet.
San Francisco Bay’s harbor seals have some of the highest PFOS levels in the world, and the chemical isn’t following the pattern of slow decline of other persistent pollutants.
“It’s a real conundrum. What are the sources of these compounds? How are they getting into the food web? ” said Margaret Sedlak, a program manager at the San Francisco Estuary Institute, which tracks chemicals in the bay.
PFOS, perfluorooctanesulfonic acid, is toxic, mobile and virtually indestructible. And it accumulates in the tissues of people and wildlife around the world, including whales, polar bears, sea turtles, bald eagles and pelicans.
The chemical’s persistence in the bay’s seals foreshadows potential effects for generations to come. And because the seals are top predators that feed on fish, they take up many contaminants and serve as barometers of the health of other marine life along the West Coast…