Paul D. Boehm

Polycyclic aromatic hydrocarbon levels in mussels from prince william sound, ALASKA, USA, document the return to baseline conditions

Bioavailable hydrocarbons in the Exxon Valdez oil spill zone in Prince William Sound (PWS; AK, USA) shorelines were at or near background levels in 2002, as indicated by low concentrations of polycyclic aromatic hydrocarbons (PAHs) in mussels (Mytilus trossulus) collected from sites throughout PWS. Total PAH (TPAH) minus parent naphthalene concentrations in mussels collected in 1998 to 2002 from sites oiled in 1989 were at or near reference-site values. Both oiled and reference sites included locations associated with past human and industrial activity (HA). Inclusion of the unoiled HA sites in the range of reference sites that define prespill conditions is consistent with federal regulations. For the period from 1998 to 2002, the geometric mean of TPAH concentrations for 218 mussel samples collected from 72 sites, including four HA sites that had been heavily oiled in 1989, is 54 ng/g dry weight (range, 2-1,190 ng/g). The maximum mussel TPAH concentrations are equivalent to a weathered-oil exposure dose to intertidal foragers that is one to three orders of magnitude less than the doses shown to cause sublethal effects in surrogate species. The geometric mean of TPAH concentrations for mussel samples from 28 locations not oiled in 1989 and unaffected by human use (NHA sites) is 28 ng/g (range, 3-355 ng/g), whereas the geometric mean of TPAH concentrations for mussel samples from 14 locations not oiled in 1989 and affected by human use (HA sites) is 106 ng/g (range, 2-12,056 ng/g). The range of data for the unoiled HA and NHA sites defines the background of bioavailable PAHs to mussels on western PWS shorelines that would have prevailed if the oil spill had not occurred. The low PAH concentrations in mussels from sites known to have subsurface oil residues demonstrates the low bioavailability of these spill remnants and, thus, are a low additional risk to foraging wildlife. The present study shows continuous exposure from four- to six-ring PAHs originating at HA sites in western PWS. At low concentrations, these PAHs are known to cause adverse biological effects. However, in the context of PWS, oiled and HA sites represent a small percentage (approximately 0.1-0.2%) of the total PWS shoreline.

Bioavailability of polycyclic aromatic hydrocarbons from buried shoreline oil residues thirteen years after the Exxon Valdez oil spill: A multispecies assessment

Seven taxa of intertidal plants and animals were sampled at 17 shoreline sites in Prince William Sound ([PWS]; AK, USA), that were heavily oiled in 1989 by the Exxon Valdez oil spill (EVOS) to determine if polycyclic aromatic hydrocarbons (PAH) from buried oil in intertidal sediments are sufficiently bioavailable to intertidal prey organisms that they might pose a health risk to populations of birds and wildlife that forage on the shore. Buried residues of EVOS oil are present in upper and middle intertidal sediments at 16 sites. Lower intertidal (0 m) sediments contain little oil. Much of the PAH in lower intertidal sediments are from combustion sources. Mean tissue total PAH (TPAH) concentrations in intertidal clams, mussels, and worms from oiled sites range from 24 to 36 ng/g (parts per billion) dry weight; sea lettuce, whelks, hermit crabs, and intertidal fish contain lower concentrations. Concentrations of TPAH are similar or slightly lower in biota from unoiled reference sites. The low EVOS PAH concentrations detected in intertidal biota at oiled shoreline sites indicate that the PAH from EVOS oil buried in intertidal sediments at these sites have a low bioavailability to intertidal plants and animals. Individual sea otters or shorebirds that consumed a diet of intertidal clams and mussels exclusively from the 17 oiled shores in 2002 were at low risk of significant health problems. The low concentrations of EVOS PAH found in some intertidal organisms at some oiled shoreline sites in PWS do not represent a health risk to populations of marine birds and mammals that forage in the intertidal zone.

Exposure Elements in Oil Spill Risk and Natural Resource Damage Assessments: A Review

ABSTRACT The use of the ecological risk assessment (ERA) framework for assessing effects of oil spills is applicable to the injury assessment component of natural resource damage assessment (NRDA). Central to the ERA process is the assessment of exposure, the critical component linking the release of oil to the assessment of effects. Exposure of biological receptors to the toxic fractions of spilled oil, usually considered the polycyclic aromatic hydrocarbons (PAH), requires carefully designed and implemented assessment studies, which are periodically refocused on various environmental pathways and the various biological receptors of concern over the life history of an oil spill from initial release to recovery. As important is the detailed assessment of the exposure regime in the absence of a spill (i.e., the baseline or background exposure). A release of petroleum may not, in itself, equate to an effect on a natural resource. The presence of residual petroleum hydrocarbons does not imply either availability to living organisms or injury to a biological resource. Precise and accurate chemical concentration and compositional data for 2–6 ringed PAHs and alkylated homologues are the key toxicologically important chemical components that are central to the exposure assessment. These principles are illustrated in several oil spill case studies.

Advances in forensic techniques for petroleum hydrocarbons: The Exxon Valdez experience

Exxon Valdez oil spill (EVOS) in Prince William Sound (PWS), Alaska, is the most extensively studied spill in history. In the years immediately following the spill and continuing today, PWS and the adjacent Gulf of Alaska (GOA) has proven to be natural laboratories for the development and testing of new chemical forensic techniques for oil spill impact studies. Methods were developed for the quantification of both total mass loss and the chemical changes that occur in various fractions of shoreline oils as they weather. They confirmed that the inert asphaltenes and resin fractions make up an increasing fraction of the bulk oil as it weathers. Furthermore, they showed that all of the PAHs, including the 3- and 4-ring PAHs, are removed as weathering progresses, a feature of EVC not previously recognized. Multiple hydrocarbon inputs at oil spill sites are well documented, and an objective forensic approach should consider the possibility of other hydrocarbon sources; both anthropogenic and natural may exist. The application of advanced fingerprinting and geochemical forensic methods to chemistry data for intertidal and subtidal sediment samples identified and quantitatively resolved a number of hydrocarbon sources that contribute to the PWS marine environment: petrogenic hydrocarbons, pyrogenic hydrocarbons, and biogenic hydrocarbons.

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.

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.

Forensic Assessment of Refined Tar-Based Sealers as a Source of Polycyclic Aromatic Hydrocarbons (PAHs) in Urban Sediments

Atmospheric deposition of particles and their subsequent transport by stormwater are a major source of polycyclic aromatic hydrocarbons (PAHs) in urban sediments. Recently, the results of forensic analysis have been used to promote a hypothesis that refined tar-based pavement sealers (RT-sealers) are another significant source. To evaluate this hypothesis, a suite of forensic methods was applied to a wider range of PAH data for this study. Sediments PAH profiles are no more similar to RT-sealers than they are to a number of other environmental inputs. While RT-sealers were not eliminated as a potential source in some locations, forensic methods did not differentiate their contribution from other sources of PAHs, indicating RT-sealers are not a unique or readily quantifiable source of PAHs to the urban environment.

Are sea otters being exposed to subsurface intertidal oil residues from the Exxon Valdez oil spill

Twenty years after the Exxon Valdez oil spill, scattered patches of subsurface oil residues (SSOR) can still be found in intertidal sediments at a small number of shoreline locations in Prince William Sound, Alaska. Some scientists hypothesize that sea otters continue to be exposed to SSOR by direct contact when otters dig pits in search of clams. This hypothesis is examined through site-specific examinations where SSOR and otter-dug pits co-occur. Surveys documented the exact sediment characteristics and locations on the shore at the only three subdivisions where both SSOR and otter pits were found after 2000. Shoreline characteristics and tidal heights where SSOR have persisted are not suitable habitat for sea otters to dig pits during foraging. There is clear separation between areas containing SSOR and otter foraging pits. The evidence allows us to reject the hypothesis that sea otters encounter and are being exposed by direct contact to SSOR.

Aromatic Hydrocarbon Concentrations in Seawater: Deepwater Horizon Oil Spill

ABSTRACT When oil is spilled or discharged into the marine environment, the chemistry and chemical concentrations of oil constituents in seawater become the target of intensive investigation as these ephemeral data are crucial to toxicity and injury assessments. The preliminary results from more than 6000 offshore water samples (>3 miles from shore) from the Deepwater Horizon (MC252) oil spill are discussed. Total Polycyclic Aromatic Hydrocarbon (TPAH) concentrations in whole, unfractionated water samples were found at concentrations ranging from not detected (ND) to 146,000 μg/L (parts per billion), with a geometric mean of 0.007 ppb. Eighty-five (85) percent of all samples were at TPAH concentrations of <0.1 ppb, essentially at or near background levels. Total Petroleum Hydrocarbons (TPH) ranged from ND to 6130 mg/L (parts per million), with a geometric mean = 1.09 ppb. Concentrations of TPAH attenuated rapidly with distance from the release point (the wellhead) and were seen to reach <1.0 ppb within 15...

Congener-based analysis of the weathering of PCB Aroclor 1242 in paper mill sludge.

Aroclor 1242 contains a high percentage of lightly chlorinated congeners, which makes it susceptible to congener profile alterations as a result of physical-chemical environmental weathering by water washing, evaporation, and volatilization. The analysis of the variability of congener profiles in paper sludge samples using PCA, mixing models, and correlation (R(2)) analysis, provided an integrated description of the behavior of Aroclor 1242 after its release in the environment. The results showed that the total PCB concentration decreased as the sample experienced weathering, with the congener profile of Aroclor 1242 shifting towards resembling heavier Aroclors as lighter congeners were lost. Mixing model analysis confirmed that a sample containing weathered Aroclor 1242 could easily be misidentified by laboratories as containing a mix of heavier Aroclors. The R(2) analysis showed that the profile of the congeners within a homologue group remained the same after weathering. This analysis showed that congeners that belong to the same level of chlorination behave similarly in such a manner that retains their overall profile when exposed to physical weathering.

Use of Receptor Models to Evaluate Sources of PAHs in Sediments

Receptor models are mathematical procedures for resolving one or more of these parameters in a mixed chemical system: (1) the number of sources, (2) their chemical characteristics, and (3) the relative contribution of each source in environmental samples. These models are being used increasingly to evaluate sources of polycyclic aromatic hydrocarbons (PAHs) in sediments. As with any mathematical model, understanding the underlying assumptions is critical in interpreting the output. Three assumptions that raise particular challenges when applying receptor models to evaluate multiple sources of pyrogenic PAHs are (1) identification of all important sources, (2) stability of source profiles, and (3) linear independence of each profile. Variability within source types, and similarities among the PAH profiles of different sources, create uncertainties that must be considered when evaluating the results of receptor models. Various procedures for evaluating uncertainties have been applied in the literature, but validation and standardization of such methods are often lacking. Using a case study, this article demonstrates how a more detailed evaluation of model output can produce conclusions that differ from those initially published. While not eliminating uncertainty, we recommend a multiple-lines-of-evidence approach that includes both mixing and unmixing receptor models, along with other environmental forensic techniques.