Quantitative Assessment of Current Risks to Harlequin Ducks in Prince William Sound, Alaska, from the Exxon Valdez Oil Spill

ABSTRACT

Harlequin Ducks (Histrionicus histrionicus) were adversely affected by the Exxon Valdez oil spill (EVOS) in Prince William Sound (PWS), Alaska, and some have suggested effects continue two decades later. We present an ecological risk assessment evaluating quantitatively whether PWS seaducks continue to be at-risk from polycyclic aromatic hydrocarbons (PAHs) in residual Exxon Valdez oil. Potential pathways for PAH exposures are identified for initially oiled and never-oiled reference sites. Some potential pathways are implausible (e.g., a seaduck excavating subsurface oil residues), whereas other pathways warrant quantification. We used data on PAH concentrations in PWS prey species, sediments, and seawater collected during 2001–2008 to develop a stochastic individual-based model projecting assimilated doses to seaducks. We simulated exposures to 500,000 individuals in each of eight age/gender classes, capturing the variability within a population of seaducks living in PWS. Doses to the maximum-exposed individuals are ∼400–4,000 times lower than chronic toxicity reference values established using USEPA protocols for sea- ducks. These exposures are so low that no individual-level effects are plausible, even within a simulated population that is orders-of-magnitude larger than exists in PWS. We conclude that toxicological risks to PWS seaducks from residual Exxon Valdez oil two decades later are essentially non-existent.

Key Words:

• seaducks
• Exxon Valdez oil spill
• ecological risk assessment
• PAHs
• Prince William Sound
• ecotoxicology
• individual-based models

ACKNOWLEDGMENTS

The authors acknowledge the participants in the workshops that were convened to develop the pathways conceptual model and the data for the parameterization of the quantitative toxicological risk assessment model, specifically: Drs. Paul Boehm, John Brown, Susan Kane Driscoll, David Garshelis, Ray Highsmith, Rick Johnson, and David Page. We also thank these scientists for their comments and suggestions on earlier drafts of the article. Additionally, Dr. Highsmith provided very useful insights and unpublished information on the fat innkeeper in Prince William Sound. Dr. Ken Cummins provided very useful insights on measurements of energy density in tissues of prey species relevant to the risk assessment. We particularly appreciate the careful reviews and suggestions of three peer reviewers on the pre-submission draft of the article—Drs. Ken Dickson, David Weinstein, and Terry Young, and the formal peer reviewers selected by the editors of Human and Ecological Risk Assessment—Drs. Donald DeAngelis, Jean-Pierre Savard, and Christopher Teaf. Finally, we acknowledge the financial support provided by ExxonMobil Corporation for the time needed to prepare this article.

The opinions and conclusions expressed herein are strictly those of the authors and do not necessarily represent the opinions of ExxonMobil.