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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.

These San Francisco Bay harbor seals are contaminated with some of the world’s highest levels of perfluorinated chemicals.
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…

Jane Kay