Cessation of oil exposure in harlequin ducks after the Exxon Valdez oil spill: Cytochrome P4501A biomarker evidence

Daniel Esler, Brenda E. Ballachey, Lizabeth Bowen, A. Keith Miles, Rian D. Dickson, John D. Henderson

The authors quantified hepatic hydrocarbon-inducible cytochrome P4501A (CYP1A) expression, as ethoxyresorufin-O-deethylase (EROD) activity, in wintering harlequin ducks (Histrionicus histrionicus) captured in Prince William Sound, Alaska, during 2011, 2013, and 2014 (22 to 25 years following the 1989 Exxon Valdez oil spill). EROD activity was compared between birds from areas oiled by the spill and those from nearby unoiled areas. This work replicated studies conducted from 1998 to 2009 that demonstrated harlequin ducks using areas that were oiled in 1989 had elevated EROD activity, indicative of oil exposure, up to 2 decades post-spill. In the present study, the authors found that average EROD activity during March 2011 was significantly higher in wintering harlequin ducks captured in oiled areas relative to unoiled areas, which the authors interpret to indicate that harlequin ducks continued to be exposed to residual Exxon Valdez oil up to 22 years after the original spill. However, the 2011 results also indicated reductions in exposure relative to previous years. Average EROD activity in birds from oiled areas was approximately 2 times that in birds from unoiled areas in 2011, compared to observations from 2005 to 2009 in which EROD activity was 3 to 5 times higher in oiled areas. The authors also found that average EROD activity during March 2013 and March 2014 was not elevated in wintering harlequin ducks from oiled areas. The authors interpret these findings to indicate that exposure of harlequin ducks to residual Exxon Valdez oil abated within 24 years after the original spill. This work finalizes a timeline of exposure, extending over 2 decades, for a bird species thought to be particularly vulnerable to oil contamination in marine environments. This article is protected by copyright. All rights reserved.