Oil still musseling into food chain.

The more volatile - and generally toxic - constituents of crude oil tend to evaporate out of petroleum quickly. As oil continues to "weather," it turns progressively tarrier, eventually becoming biologically inert. Surprisingly, some of the Exxon Valdez oil appears to have escaped weathering by hiding out beneath mussel beds, reports Charles H. Peterson of the University of North Carolina at Chapel Hill. More important, he reports, oil "is leaking into those mussels."

The effective protection afforded by these bivalve communities suggests that this unweathered oil is "likely to persist for a long time," he says, permitting the shellfish to accumulate high concentrations of hydrocarbons. The mussels themselves do not appear to be suffering, he notes, but their contamination may prove toxic to humans and others. Indeed, he speculates, this contamination may explain why some key mussel consumers-such as otters, harlequin ducks, and certain shore birdscontinue to suffer unabated oil-related reproductive difficulties despite low concentrations of petroleum in their water and on their home beaches.