Ecological Significance of Residual Exposures and Effects from the Exxon Valdez Oil Spill

Harwell Gentile & Associates, LC, Hammock, Florida 32137, USA.
Integrated Environmental Assessment and Management (Impact Factor: 1.38). 07/2009; 2(3):204-46. DOI: 10.1002/ieam.5630020303
Source: PubMed


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 Multiple-lines-of-evidence analyses indicate that residual PAHs from EVOS no longer represent an ecologically significant exposure risk to PWS.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.

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Available from: Mark A Harwell, Feb 26, 2014
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    • "For instance, about 30,000 dead birds (>90 species) were found in the oil spilled areas during the months after the EVOS (Piatt et al., 1990). Crude oil also has harmful effect on living organisms due to its chemical constituents that is a complex mixture of thousands of chemicals with various known mechanisms including aryl hydrocarbon receptor (AhR) associated toxicity (Harwell and Gentile, 2006). For example, VOCs and PAHs are well known major toxic components of crude oil (Page et al., 2002). "
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    ABSTRACT: The Hebei Spirit oil spill (HSOS) in December 7, 2007 spilled approximately 10,900 tons of crude oil in about 10 km off the Taean coasts in South Korea. We first summarize and overview, in the present study, the current status of environmental and ecological effects of the HSOS focusing on i) pollution status for surrounding environment (water, sediment, and porewater), ii) biological effects on living organisms, iii) potential toxic effects in vitro and in vivo, and finally iv) human health risk. In particular, ecological impacts followed by the recoveries of coastal ecosystem are intensively addressed. Water quality seemed to be rapidly recovered considering the background levels of oil pollution indices, while oil impacted sediments experienced fairly long history of contamination. Meanwhile, the benthic epifauna mapping in the worst impacted area of Taean indicated that the coastal organisms are fairly recovered after five years of the HSOS. However, it should be noted that residual oils are still found in some inner part of small bays and mud dominant regions in Taean area which would cause the potential toxic effects on coastal organisms. Finally, the current understandings and limitations of such effects from the HSOS are further discussed highlighting, i) long-term effects of residual oils, ii) identification of certain toxic chemicals in residual oils, iii) weathering characteristics of spilled oils, iv) possible effects from the unknown hydrocarbons in oils, and v) recovery of community level responses to the HSOS.
    Ocean & Coastal Management 02/2014; DOI:10.1016/j.ocecoaman.2014.01.006 · 1.75 Impact Factor
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    • "Further, to prove the effects of DDT on animal health and breeding, the research required long-term generational data for affected populations (Ottoboni et al. 1977) but this resulted in strong societal attitude changes and government action. Effects of oil spills on long-lived mammals also required long-term data (Harwell and Gentile 2006) that can then be used to inform governments and trigger measures to develop safer oil and gas exploration, extraction, and shipping methods (Eicken et al. 2011). "
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    ABSTRACT: Long-term data are critically important to science, management, and policy formation. Here we describe a number of data collections from arctic Canada that monitor vertebrate population trends of freshwater and marine fish, marine birds, marine and terrestrial mammals. These time series data cover the last ca. 30 years and capture a period from the onset of global changes affecting the Arctic up to recent years with a rapid increase in temperature. While many of these data collections were initiated through a variety of government and university programs, they also include a surge in polar research launched with the recent International Polar Year (2007–2008). We estimated the long-term vertebrate index from our data that summarizes various taxa abundance trends within a global context and observed a continuous decline of about 30 % in population abundance since the 1990s. Though most data collections are biased towards few taxa, we conduct time-series analyses to show that the potential value of long-term data emerges as individual monitoring sites can be spread across space and time scales. Despite covering a handful of populations, the different time series data covered a large spectrum of dynamics, cyclic to non-cyclic, including coherence with the North Atlantic Oscillation, lag effects, and density dependence. We describe a synthesis framework to integrate ecological time-series research and thereby derive additional benefits to management, science, and policy. Future requirements include: (1) continuation of current observation systems; (2) expansion of current monitoring sites to include additional trophic links and taxonomic indicators; (3) expansion beyond the existing program to include greater spatial coverage into less-sampled ecosystems and key representative locations; and (4) integration of circumpolar observations and comprehensive analyses. Development of a circumpolar observation system is necessary for innovative science, large-scale adaptive management, and policy revision essential to respond to rapid global change.
    Climatic Change 11/2012; 115(1):235-258. DOI:10.1007/s10584-012-0476-7 · 3.43 Impact Factor
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    • "Presently the sole risk to PWS biota is the potential exposure to residual EVOS-derived PAHs, located either in the SSOR deposits or in the background levels of potentially bioavailable PAHs in EVOS-oiled areas. Using the Gentile and Harwell (1998) criteria for assessing ecological significance (see also Harwell et al. 1994), Harwell and Gentile (2006) evaluated a suite of approximately 2 dozen VECs that characterize the PWS ecosystem, concluding that by that point in time recovery had essentially occurred for almost all of the VECs; similar conclusions were presented in Integral Consulting (2006), with a few exceptions . However, the Exxon Valdez Oil Spill Trustees (EVOSTC 2010) continued to report several endpoints as not recovered, including characterizing sea otters and Harlequin Ducks as ''recovering'' but not yet recovered species. "
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    ABSTRACT: Ecological risk assessments need to advance beyond evaluating risks to individuals that are largely based on toxicity studies conducted on a few species under laboratory conditions, to assessing population-level risks to the environment, including considerations of variability and uncertainty. Two individual-based models (IBMs), recently developed to assess current risks to sea otters and seaducks in Prince William Sound more than 2 decades after the Exxon Valdez oil spill (EVOS), are used to explore population-level risks. In each case, the models had previously shown that there were essentially no remaining risks to individuals from polycyclic aromatic hydrocarbons (PAHs) derived from the EVOS. New sensitivity analyses are reported here in which hypothetical environmental exposures to PAHs were heuristically increased until assimilated doses reached toxicity reference values (TRVs) derived at the no-observed-adverse-effects and lowest-observed-adverse-effects levels (NOAEL and LOAEL, respectively). For the sea otters, this was accomplished by artificially increasing the number of sea otter pits that would intersect remaining patches of subsurface oil residues by orders of magnitude over actual estimated rates. Similarly, in the seaduck assessment, the PAH concentrations in the constituents of diet, sediments, and seawater were increased in proportion to their relative contributions to the assimilated doses by orders of magnitude over measured environmental concentrations, to reach the NOAEL and LOAEL thresholds. The stochastic IBMs simulated millions of individuals. From these outputs, frequency distributions were derived of assimilated doses for populations of 500,000 sea otters or seaducks in each of 7 or 8 classes, respectively. Doses to several selected quantiles were analyzed, ranging from the 1-in-1000th most-exposed individuals (99.9% quantile) to the median-exposed individuals (50% quantile). The resulting families of quantile curves provide the basis for characterizing the environmental thresholds below which no population-level effects could be detected and above which population-level effects would be expected to become manifest. This approach provides risk managers an enhanced understanding of the risks to populations under various conditions and assumptions, whether under hypothetically increased exposure regimes, as demonstrated here, or in situations in which actual exposures are near toxic effects levels. This study shows that individual-based models are especially amenable and appropriate for conducting population-level risk assessments, and that they can readily be used to answer questions about the risks to individuals and populations across a variety of exposure conditions.
    Integrated Environmental Assessment and Management 07/2012; 8(3):503-22. DOI:10.1002/ieam.1277 · 1.38 Impact Factor
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