Some stain repellents becoming less common in harbor seals.

Ahrens, L, U Siebert and R Ebinghaus. 2009. Temporal trends of polyfluoroalkyl compounds in harbor seals (Phoca vitulina) from the German Bight, 1999–2008. Chemosphere doi:10.1016/j.chemosphere.2009.03.053.

Researchers report a shift in the types and amounts of stain-repelling chemicals found in harbor seals living near populated regions in the North Sea. Levels of one of the most studied types in this family of chemicals showed declines during the study's ten-year span.

These findings add to a growing number of studies showing that environmental concentrations of some of the most widely used perfluorinated compounds (PFCs) are declining, possibly because of replacement by less long-lived chemicals.

The animals carry a mixed bag of the pollutants that the scientists say have fluctuated in levels during the last ten years. The up-and-down trends varied, depending on which chemicals were measured. While some types showed declines, others remain unchanged or had increased in the marine mammals.

This suggests there is still room to improve pollution control and that further reductions in production and use should be considered, the study's authors conclude.

Perfluorinated compounds (PFCs) have been widely used for the past five decades as water and grease repellents in food packaging, carpeting, furniture, clothing and other consumer products. Because of their popularity and persistence in the environment, they are found at high concentrations near where they are used and even in remote environments, such as the Arctic.

Growing concern around their use motivated a recent ban on some of the PFCs. As a result, levels of certain PFCs are decreasing in seabird eggs and ringed seals in the Arctic regions.

The question remained whether similar declines were occurring in mammals closer to the source of these contaminants, urban areas. To find out, this recent study analyzed liver tissue collected from harbor seals living in the German Bight – a bay in the North Sea – in 1988, 1996 and 1999-2008 (n= 1 to 10 per year).

The seals had 5 to 50 times higher levels of PFCs than ringed seals from the Arctic and harbor seals from other parts of Europe, the study reports. Despite this, concentrations of several PFCs decreased between 58 to 80 percent in the seals between 1999 and 2008.

Perfluorooctane sulfonate, knicknamed PFOS, was the most common compound measured. It accounted for up to 94 percent of the measured PFCs. Even so, its concentrations decreased by 49 percent between 1999 and 2008.

Young seals (less than seven months old) had higher concentrations of some of the PFCs than older seals. But again, the trends depended on which chemical was measured. The variable levels could result from the transfer of chemicals from their mothers during development and nursing or by the types of fish eaten.