Cytochrome P4501A biomarker indication of the timeline of chronic exposure of Barrow's goldeneyes to residual Exxon Valdez oil

► Barrow's goldeneye are sea ducks that winter on the Pacific coast of North America. ► They occur in areas contaminated by the 1989 Exxon Valdez oil spill. ► CYP1A biomarker of oil exposure declined substantially from 1996-1997 to 2005 and 2009. ► Return to near background levels took nearly 2 decades. ► Exposure following large spills can persistent in some species for long periods.