The San Francisco Chronicle published an article featuring research conducted by Meg Sedlak and other RMP scientists, which has found elevated concentrations of PFOS, a persistent fluorine-containing chemical, in San Francisco Bay apex predators. Once the prime ingredient in Scotchgard, PFOS has remained elevated in 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 remains unclear why the seals are accumulating these high concentrations. PFOS is of concern because it is bioaccumulative and toxic, including possible suppression of immune response.