Ecological significance of residual exposures and effects from theExxon Valdezoil spill

Abstract

An ecological significance framework is used to assess the ecological condition of Prince William Sound (PWS), Alaska, USA, in order to address the current management question: 17 y following the Exxon Valdez oil spill (EVOS), are there any remaining and continuing ecologically significant exposures or effects on the PWS ecosystem caused by EVOS? We examined the extensive scientific literature funded by the Exxon Valdez Trustees or by ExxonMobil to assess exposures and effects from EVOS. Criteria to assess ecological significance include whether a change in a valued ecosystem component (VEC) is sufficient to affect the structure, function, and/or health of the system and whether such a change exceeds natural variability. The EVOS occurred on 24 March 1989, releasing over 250,000 barrels of crude oil into PWS. Because PWS is highly dynamic, the residual oil was largely eliminated in the first few years, and now only widely dispersed, highly weathered, or isolated small pockets of residual contamination remain. Many other sources of polycyclic aromatic hydrocarbons (PAHs) exist in PWS from past or present human activities or natural oil seeps. Multiple-lines-of-evidence analyses indicate that residual PAHs from EVOS no longer represent an ecologically significant exposure risk to PWS. To assess the ecological significance of any residual effects from EVOS, we examined the literature on more than 20 VECs, including primary producers, filter feeders, fish and bird primary consumers, fish and bird top predators, a bird scavenger, mammalian primary consumers and top predators, biotic communities, ecosystem-level properties of trophodynamics and biogeochemical processes, and landscape-level properties of habitat mosaic and wilderness quality. None of these has any ecologically significant effects that are detectable at present, with the exception of 1 pod of orcas and possibly 1 subpopulation of sea otters; however, in both those cases, PWS-wide populations appear to have fully recovered. Many other stressors continue to affect PWS adversely, including climate and oceanographic variability, increased tourism and shipping, invasive species, the 1964 earthquake, and overexploitation of marine resources, with associated cascading effects on populations of PWS fish and predators. We conclude that the PWS ecosystem has now effectively recovered from EVOS.

Cytochrome P4501A biomarker indication of oil exposure in harlequin ducks up to 20 years after the Exxon Valdez oil spill

“…Some authors have questioned the source of CYP1A-inducing compounds in Prince William Sound [30], recognizing that there may be multiple CYP1A-inducing compounds from multiple sources within a given area [6]. Several authors [30][31][32][33] have argued that non-Exxon Valdez sources of PAHs are more abundant and more likely to induce CYP1A responses than residual Exxon Valdez oil.…”

“…Several authors [30][31][32][33] have argued that non-Exxon Valdez sources of PAHs are more abundant and more likely to induce CYP1A responses than residual Exxon Valdez oil. However, the spatial correspondence between elevated CYP1A induction and history of contamination during the Exxon Valdez oil spill strongly suggests causation.…”

Quantifying long-term risks to sea otters from the 1989 ‘Exxon Valdez’ oil spill: Comment on Bodkin et al. (2012)

“…CERN 1999, Norton et al 2003, Cormier & Suter 2008. We first applied it to the 'Exxon Valdez' oil spill by assessing the ecological significance of remaining risks more than 15 yr after the spill (Harwell & Gentile 2006) following the methodology and criteria that we also developed for USEPA (Gentile & Harwell 1998). We qualitatively assessed the oil spill risks compared with the other major anthropogenic and natural stressors impinging on the PWS-Gulf of Alaska ecosystem (Harwell et al 2010b), we quantified the ecotoxicological risks to sea otters from remaining oil residues (Harwell et al 2010a(Harwell et al , 2012, and we used the ecological risk framework to assess ecological recovery of the PWS ecosystem .…”

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

“…Some authors have questioned whether oil spilled during the Exxon Valdez event can be assumed to be the primary source of CYP1A inducing compounds in oiled areas of Prince William Sound (Harwell and Gentile, 2006), recognizing that there may be multiple CYP1A-inducing compounds from multiple sources within a given area (Lee and Anderson, 2005). However, studies indicate that PAHs in the areas where elevated CYP1A was observed in vertebrates are predominately from the Exxon Valdez (Short et al, 2004), supporting the inference that Exxon Valdez oil was the inducing agent.…”