A Quantitative Ecological Risk Assessment of the Toxicological Risks from<i>Exxon Valdez</i>Subsurface Oil Residues to Sea Otters at Northern Knight Island, Prince William Sound, Alaska

Harwell, Mark A.; Gentile, John H.; Johnson, C. B.; Garshelis, David L.; Parker, Keith R.

doi:10.1080/10807039.2010.501230

Cited by 23 publications

(67 citation statements)

References 64 publications

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“…They concluded that infaunal foraging by sea otters in western Prince William Sound (PWS; Alaska), the distribution of sea otter pits in the intertidal zone, and the presence of SSOR in the vicinity of foraging areas demonstrate a potential pathway for sea otters to be exposed to the polycyclic aro matic hydrocarbons (PAHs) in SSOR. We reached the same conclusion in Harwell et al (2010a).…”

Section: Introductionsupporting

confidence: 73%

“…Their calculations resulted in a frequency of sea otters encountering SSOR of 10 times per year (range 2 to 24, n = 15) for females and 4 times per year (range listed both as 2 to 4 and 2 to 5, n = 4) for males. By comparison, the estimates of Harwell et al (2010a;their Table 2) were about 2 to 7 times per year, depending on the sea otter class (7 classes of sea otters were distinguished based on age and gender); consequently, the Bodkin et al (2012) estimates of the frequency of sea otter encounters with SSOR comport with our previously published estimates.…”

Section: Introductionmentioning

confidence: 51%

“…the 99.9998% quantile). We concluded therefore that there was no plausible risk to any individual sea otter at NKI from 'Exxon Valdez' oil residues (Harwell et al 2010a). When we now use the version of the model that allows assignment of a specific rate of SSOR encounters, the rates estimated by Bodkin et al (2012) result in even lower risks than projected by our base model.…”

Section: Risks To Sea Ottersmentioning

confidence: 99%

“…We have already followed these steps to assess this specific pathway (Harwell et al 2010a(Harwell et al , 2012) using an individual-based model (see DeAngelis & Gross 1992, Munns et al 2007) that we developed to quantify all plausible routes of PAH exposures of sea otters at NKI. The model is stochastic, capturing measured environmental variability for the parameters affecting exposures.…”

Section: Risks To Sea Ottersmentioning

confidence: 99%

“…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 . Thus, our extensive experience in designing and conducting ecological risk assessments informs us that there is a great deal more to understanding risk than implied by Bodkin et al (2012).…”

Section: Introductionmentioning

confidence: 99%

See 4 more Smart Citations

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

Harwell¹,

Gentile²

2013

Mar. Ecol. Prog. Ser.

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Bodkin et al. (2012; Mar Ecol Prog Ser 447:273−287) assessed the frequency at which sea otters Enhydra lutris might encounter subsurface oil residues from the 'Exxon Valdez' oil spill. They concluded that a pathway exists for exposures of sea otters to residual oil in the intertidal zone, and imply that this pathway has delayed recovery of sea otters. We agree that the potential exposure pathway exists, and the Bodkin et al. (2012) estimates of the frequency of encountering subsurface oil residues (4 to 10 times per year) comport with our previously published studies (2 to 7 times per year). However, we disagree that this pathway constitutes a significant risk to sea otters. We discuss results from our quantitative ecological risk assessment using an individualbased model that specifically simulated this pathway of exposures to a population of 500 000 sea otters. This conservative model predicted that assimilated doses of polycyclic aromatic hydrocarbons in subsurface oil residues to the 1-in-1000 th most-exposed sea otters would be 1 to 2 orders of magnitude below the chronic effects thresholds that we established using USEPA data and methodology. When we artificially increased the rate of encountering subsurface oil residues, it required 4 to 10 encounters per day to reach effects levels. We conclude that the subsurface oil residues from the oil spill could not plausibly be responsible for any individual-or populationlevel effect on the sea otters at northern Knight Island.

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Section: Introductionsupporting

confidence: 73%

Section: Introductionmentioning

confidence: 51%

Section: Risks To Sea Ottersmentioning

confidence: 99%

Section: Risks To Sea Ottersmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 3 more Smart Citations

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

Harwell¹,

Gentile²

2013

Mar. Ecol. Prog. Ser.

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Exposure of sea otters and harlequin ducks in Prince William Sound, Alaska, USA, to shoreline oil residues 20 years after the Exxon Valdez oil spill

Neff¹,

Page

Boehm

2011

Enviro Toxic and Chemistry

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We assessed whether sea otters and harlequin ducks in an area of western Prince William Sound, Alaska, USA (PWS), oiled by the 1989 Exxon Valdez oil spill (EVOS), are exposed to polycyclic aromatic hydrocarbons (PAH) from oil residues 20 years after the spill. Spilled oil has persisted in PWS for two decades as surface oil residues (SOR) and subsurface oil residues (SSOR) on the shore. The rare SOR are located primarily on the upper shore as inert, nonhazardous asphaltic deposits, and SSOR are confined to widely scattered locations as small patches under a boulder/cobble veneer, primarily on the middle and upper shore, in forms and locations that preclude physical contact by wildlife and diminish bioavailability. Sea otters and harlequin ducks consume benthic invertebrates that they collect by diving to the bottom in the intertidal and subtidal zones. Sea otters also dig intertidal and subtidal pits in search of clams. The three plausible exposure pathways are through the water, in oil-contaminated prey, or by direct contact with SSOR during foraging. Concentrations of PAH in near-shore water off oiled shores in 2002 to 2005 were at background levels (<0.05 ng/L). Median concentrations of PAH in five intertidal prey species on oiled shores in 2002 to 2008 range from 4.0 to 34 ng/g dry weight, indistinguishable from background concentrations. Subsurface oil residues are restricted to locations on the shore and substrate types, where large clams do not occur and where sea otters do not dig foraging pits. Therefore, that sea otters and harlequin ducks continue to be exposed to environmentally significant amounts of PAH from EVOS 20 years after the spill is not plausible.

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Quantifying population‐level risks using an individual‐based model: Sea otters, Harlequin Ducks, and the Exxon Valdez oil spill

Harwell¹,

Gentile

Parker

2012

Integr Envir Assess & Manag

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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. Integr Environ Assess Manag 2012; 8: 503–522. © 2012 SETAC

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A Quantitative Ecological Risk Assessment of the Toxicological Risks fromExxon ValdezSubsurface Oil Residues to Sea Otters at Northern Knight Island, Prince William Sound, Alaska

Cited by 23 publications

References 64 publications

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

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

Exposure of sea otters and harlequin ducks in Prince William Sound, Alaska, USA, to shoreline oil residues 20 years after the Exxon Valdez oil spill

Quantifying population‐level risks using an individual‐based model: Sea otters, Harlequin Ducks, and the Exxon Valdez oil spill

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