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Comment on “Unlike PAHs from Exxon Valdez Crude Oil, PAHs from Gulf of Alaska Coals are not Readily Bioavailable” Deepthike et al. (1), inappropriately and without technical foundation, extrapolate the results of a laboratory study to the environment of Prince William Sound (PWS), Alaska, and the Exxon Valdez oil spill (EVOS). Because of flaws in the selection of test materials and the incomplete inclusion of published literature on the bioavailability of polycyclic aromatic hydrocarbons (PAHs) in PWS, the results have no environmental relevance. The title and the authors’ conclusions imply new information about the bioavailability of EVOS PAHs in PWS compared to the bioavailability of PAH from sources in the eastern Gulf of Alaska (GOA). This is not the case because the study design (1) assessed PAH bioavailability from fresh cargo crude oil when they should have studied PAH bioavailability from the small pockets of extensively weathered subsurface oil (SSO) residues buried on some PWS shorelines and (2) assessed PAH bioavailability from terrestrial coal seams in the eastern GOA, ∼200 km to the east of PWS, when they should have studied PAH bioavailability from organic particles in PWS subtidal sediments, which are mostly kerogens from petroleum source rocks east of PWS s not coal (2, 4). By not testing seafloor sediments, the authors ignored the known effects of physical and biologic processes in the benthic sedimentary environment on the bioavailability of PAH in organic particles (5, 6) (2, 3). The authors’ conclusions about the relative bioavailability of PAH from coal and unweathered crude oil are already well-documented in the published literature. The low bioavailability of sequestered PAH in coal matrices is also wellknown (5). Testing raw coal samples for bioavailable PAH does not tell us anything that we do not already know, nor does testing for the bioavailability of PAH by direct application of a crude oil sample to a test subject. In spite of this, the authors’ key conclusion is that “EVCO represents the primary known source of bioavailable PAHs in the region” (1). This conclusion is not supported by any of the data on the Exxon Valdez cargo crude oil or coal samples presented in this paper and is contrary the large body of work on PAH sources in the region published over the last 15 years (2, 4, 7). One of the environmental issues relating to the many PAH sources in PWS was the source of and bioavailability of petrogenic background hydrocarbons in subtidal sediments that are carried into PWS from eastern GOA, as indicated in Deepthike et al. refs 4-7, and well-summarized by Peters et al. (4). These sediments originate from eroding petroliferous source rocks, including coals. To be relevant to their stated conclusion, Deepthike et al. should have tested the bioavailability of the organic fraction of PWS and eastern GOA benthic sediments, not terrestrial coal-bed samples, which are already well-characterized by Short et al. (2). Moreover, this bioavailability testing has already been done by others. In a comprehensive study of biochemical responses to PAH exposure, Huggett et al. (8), cited in Deepthike et al. ref 8, reported, for the same study region, elevated levels of CYP1A induction in fish exposed to the seafloor and suspended sediments relative to fish caught further to the east, consistent with chronic PAH exposure. Those indicators of PAH exposure continued westward into PWS (8). This finding is ignored by Deepthike et al., who claim that the Huggett study (8) considered the PWS background PAHs responsible for 2210
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observed biochemical responses. Huggett et al. (8), as well as earlier NOAA data cited in ref 8, actually say that there are bioavailable PAHs present in the benthic and suspended sediments in the eastern GOA, offshore of and subject to inputs of eroding organic-rich sediments from coal and oil seep areas. The failure of Deepthike et al. to test the PAH bioavailability of the organic fraction in marine and riverine sediments, rather than upland coal beds, is inconsistent with the published work of one of the authors (2) that showed that “Coaly material accounted for only 1.1-6.1% of the total PAH burden of these (GOA) sediments” (2). Therefore, from a mass balance perspective, PAHs from pure coal, whether bioavailable or not, are irrelevant to the question of bioavailable PAH sources in PWS and eastern GOA. To compare coal to Alaska North Slope crude oils is also questionable because the issue of bioavailability of spill remnants in PWS is now considered moot (9). In fact, a Deepthike et al. author recently reached this conclusion: “Based on the TPAH [Total PAH] trends diminishing to consistently low values, it appears that the final traces of EVOS residues have either stabilized or reached levels that no longer appear in the LTEMP [Long Term Environmental Monitoring Program] mussel samples (10).” This finding is also consistent with the work of others (11-13). The statement in ref 1 that “Long-term biological damage attributed to lingering oil is inferred from spill-related spatial and temporal patterns in biochemical responses, characteristic of polycyclic aromatic hydrocarbons...” is both misleading and wrong. References 1-3 cited in ref 1 rely upon data collected between 1989 and 1998 and are not relevant as evidence of “lingering effects” in 2009. The authors provide no references to support this claim of current injury. Moreover, the recent use of CYP1A (“biochemical response”) measurements in PWS sea otters to show PAH exposure has been shown to have been based on defective methodology (14). In fact, there is no scientifically credible evidence of current exposure to PAH from spill remnants in Prince William Sound (15). Deepthike et al. present a limited set of data to detect PAH bioavailability from laboratory exposure to crude oil and whole coal samples and extrapolate, without foundation or data, from the laboratory to the field. They provide no information about the bioavailability of sequestered SSO residues that currently exist at a scattered handful of wellknown locations in PWS or the relative importance of the many well-documented PAH sources in PWS, even though this paper claims to do so. Therefore, the conclusions of this paper concerning PAH sources in PWS are wrong.
Acknowledgments In the past, the authors have received support for related projects from ExxonMobil.
Literature Cited (1) Deepthike, H. U.; Tecon, R.; Vankooten, G.; Van der Meer, J. R.; Harms, H.; Wells, M.; Short, J. Unlike PAHs from Exxon Valdez crude oil, PAHs from Gulf of Alaska coals are not readily bioavailable. Environ. Sci. Technol. 2009, 43, 5864–5870. (2) Short, J. W.; Kolak, J. J.; Payne, J. R.; Van Kooten, G. K. An evaluation of petrogenic hydrocarbons in northern Gulf of Alaska continental shelf sediments: The role of coastal oil seep inputs. Org. Geochem. 2007, 38, 643–670. (3) Boehm, P. D.; Page, D. S.; Brown, J. S.; Neff, J. M.; Bragg, J. R.; Atlas, R. M. Distribution and weathering of crude oil residues on shorelines 18 years after the Exxon Valdez spill. Environ. Sci. Technol. 2008, 42, 9210–9216. 10.1021/es903508h
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Published on Web 02/12/2010
(4) Peters, K. E.; Walter, C. C.; Moldowan, J. M. The Biomarker Guide, 2nd ed.; Cambridge University Press: Cambridge, U.K., 2007; Vol. I, pp 305-312. (5) Ahrens, M. J.; Morrisey, D. J. Biological effects of unburnt coal in the marine environment. Oceanogr. Mar. Biol. 2005, 43, 69–122. (6) Voparil, I. M.; Mayer, L. M. Dissolution of sedimentary polycyclic aromatic hydrocarbons into the lugworm’s (Arenicola marina) digestive fluids. Environ. Sci. Technol. 2000, 34, 1221–1228. (7) Page, D. S.; Brown, J. S.; Boehm, P. D.; Bence, A. E.; Neff, J. M. A hierarchical approach measures the aerial extent and concentration levels of PAH-contaminated shoreline sediments at historic industrial sites in Prince William Sound, Alaska. Mar. Pollut. Bull. 2006, 52, 367–379. (8) Huggett, R. J.; Stegeman, J. J.; Page, D. S.; Parker, K. R.; Brown, J. S. Biomarkers in fish from Prince William Sound and the Gulf of Alaska: 1999-2000. Environ. Sci. Technol. 2003, 37, 4043–4051. (9) Brahic, C. Is the Exxon Valdez oil spill finally cleaned up? New Scientist , 2008; p 6. (10) Payne, J. R.; Driskell, W. B.; Short, J. W.; Larsen, M. W. Longterm monitoring for oil in the Exxon Valdez spill region. Mar. Pollut. Bull. 2008, 56, 2067–2081. (11) Huggett, R. J.; Neff, J. M.; Stegeman, J. J.; Woodin, B.; Parker, K. R.; Brown, J. S. Biomarkers of PAH exposure in an intertidal fish species from Prince William Sound, Alaska: 2004-2005. Environ. Sci. Technol. 2006, 40, 6513–6517. (12) Carls, M. G.; Harris, P. M.; Rice, S. D. Restoration of oiled mussel beds in Prince William Sound, Alaska. Mar. Environ. Res. 2004, 57, 359–376.
(13) Neff, J. M.; Brown, J. S.; Boehm, P. D.; Bence, A. E.; Parker, K. R.; Page, D. S. Bioavailability of PAH from buried shoreline oil residues 13 years after the Exxon Valdez oil spill: A multispecies assessment. Environ. Toxicol. Chem. 2006, 25, 947–961. (14) Hook, S. E.; Cobb, M. E.; Oris, J. T.; Anderson, J. W. Gene sequences for cytochrome P450 1A1 and 1A2: The need for biomarker development in sea otters (Enhydra lutris). Comp. Biochem. Physiol., Part B: Biochem. Mol. Biol. 2008, 151, 336– 348. (15) Harwell, M. A.; Gentile, J. H. Ecological significance of residual exposures and effects from the Exxon Valdez oil spill. Integ. Environ. Assess. Manage. 2006, 2, 204–246.
David S. Page Chemistry Department, Bowdoin College, Brunswick, Maine 04011
Paul D. Boehm Exponent, Inc., Maynard, Massachusetts 01754
Jerry M. Neff Neff & Associates, Duxbury, Massachusetts 02332 ES903508H
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