Environ. Sci. Technol. 2010, 44, 2212–2213
Response to Comment on “Unlike PAHs from Exxon Valdez Crude Oil, PAHs from Gulf of Alaska Coals are not Readily Bioavailable” We thank Page et al. (1)for this opportunity to address their concerns regarding our recent article entitled “Unlike PAHs from Exxon Valdez Crude Oil, PAHs from Gulf of Alaska Coals are not Readily Bioavailable” (2). Page et al. (1)criticize our article as inappropriately extrapolating our results to present field conditions in Prince William Sound (PWS), Alaska, having a study design so flawed that our results are environmentally irrelevant, not having presented new information, and implying that impacts on biota from the 1989 Exxon Valdez oil spill are ongoing. The crux of our reply is that their comments do not address what our paper is about. Our primary objective was to introduce a powerful new method for evaluating PAH bioavailability. The unsolved questions noted in Peters et al. (3) regarding the presence of bioavailable PAH in the Gulf of Alaska (GOA) motivated our choice for an environmentally relevant application. We clearly stated that our goal was to conduct a carefully controlled end-member study and not to revisit previous studies. Application aside, over 50% of our paper’s introduction discussed bioavailability, confusions in its definition (and versus other terms in use), and the use of genetically engineered bioreporters to access a more relevant metric. Sea otters, though not mentioned in our paper, are specifically addressed in Page et al.’s (1)comments, but bioreporters are not mentioneds not once. As Page et al. (1)do not address much of the content of our paper, their comments incorrectly contextualize selected comments from it. The multiple positive peer reviews that this paper had prior to publication demonstrate that Page et al.’s misinterpretation of our paper is not representative of the majority consensus view of experts in the field. With regard to specifics of Page et al.’s (1)concerns, the fundamental environmental issue from the 1989 Exxon Valdez oil spill is impact. Biota not adapted to a contaminated environment might be especially sensitive to PAH exposure from such an anthropogenic insult, unless a natural source is implicated. The plausible natural sources of PAH in GOA sediments include oil seeps, coals, and hydrocarbon-rich shales and other source rocks (4). Unfortunately, attempts to quantitatively estimate contributions from all these sources are compromised by the inaccessibility of likely (i.e., therefore unknown/unverified) source end-members, many of which lay beneath glaciers. Hence, the accuracy of mixture models that have been used is unknown because model completeness (incorporation of all important source end-members) is indeterminate (5). The natural oil seeps east of Prince William Sound are negligibly small and may be dismissed as insignificant (5, 6). Physically separable coal particles are present in marine sediments of the GOA in quantities too small to account for background PAHs in these sediments (5). Microparticulate coal particles cemented to siliciclastic sediments plausibly contribute substantively to the sedimentary burden of GOA sediments, as noted in our introduction (2). Thus GOA coals may be a substantial or even dominant source of nonanthropogenic PAH in GOA sediments. 2212
9
ENVIRONMENTAL SCIENCE & TECHNOLOGY / VOL. 44, NO. 6, 2010
PAH in liquid matrixes (Exxon Valdez oil spilled, GOA seeps) are clearly bioavailable, and our study’s demonstration of dose-dependent bioreporter response to unweathered crude oil served as a positive control. On coal, Page et al. (1)state “testing raw coal samples for bioavailable PAH does not tell us anything that we don’t already know” in contravention of some facts presented in our paper. The Kulthieth Formation coals we tested are unusual because they are strongly oil prone, producing about 20% of their weight as oil on heating (4), in contrast to typical gas prone coals that produce little or no oil (4). We are not aware of any other studies that assess the bioavailability of PAHs in strongly oil-prone or GOA coals. Our paper further addresses Kd variability (and lower than anticipated values) and provides several citations regarding the importance of coal characteristics and diagenetic history in controlling bioavailability. Though these points were not acknowledged by Page et al. (1), their merit was recognized by reviewers. Studying other end-members is desirable but constrained by the difficulty of verifying, locating, and sampling them. Regarding Page et al.’s (1)arguments that cytochrome P450A-1A (CYP 1A) induction in livers and fluorescent aromatic compounds (FAC) of bile in resident fish in the GOA is prima facie evidence of a natural source of bioavailable PAH in the region (7), this evidence is inconclusive. As noted elsewhere (8), these results may reflect the basal activity levels of fish unexposed to contaminants and/or differences arising from different fish stocks, sex/state of sexual maturity, collection methods, research teams, and analytical laboratories. The absence of standard reference materials for environmental analyses of CYP 1A or bile FAC make comparisons across and even within laboratories problematic. Absent establishment of the basal levels of contaminant biomarkers and dependence on biological factors, the results of Huggett et al. (4) are suggestive at best, especially given the considerable evidence indicating the absence of a significant natural source of bioavailable PAH in the GOA east of PWS. Putative confirmation of such a source would require that it demonstrably release PAH and elicit an ambient biological response, using the method we presented or some other sensitive approach. In contrast, the absence of composition changes characteristic of weathering in the PAH and n-alkane signatures of benthic sediments in the GOA argues strongly against bioavailability of natural sources (5) as does the failure of these sediments to release PAHs (9). The findings of scientific studies involving controversial issues have potential to verge to the subjectivesemotional if the popular press is involved. Investigators heavily involved in industry-led oil spill research may develop a stakeholder perspective, if one is not pre-existing. In such circumstances, dispassionate evaluation may be difficult. Lengthy literature exchanges have occurred previously between one or more of our paper’s authors, and one or more of Page et al.’s (1) number, and our paper has also been covered extensively in the popular media. We ask that interested Environmental Science & Technology readers evaluate our paper, with all comments in mind, and formulate their own conclusions.
Literature Cited (1) Page, D. S.; Boehm, P. D.; Neff, J. M. Comment on “Unlike PAHs from Exxon Valdez Crude Oil, PAHs from Gulf of Alaska Coals are not Readily Bioavailable”. Environ. Sci. Technol. 2010; DOI: 10.1021/es903508h. 10.1021/es100176k
2010 American Chemical Society
Published on Web 02/12/2010
(2) 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. (3) Peters, K. E.; Walter, C. C.; Moldowan, J. M. The Biomarker Guide 2nd ed.; Cambridge University Press, Cambridge, U.K., 2005; Vol. I, 305-312. (4) Van Kooten, G. K.; Short, J. W.; Kolak, J. J. Low-maturity Kulthieth Formation coal: A possible source of polycyclic aromatic hydrocarbons in benthic sediments of the northern Gulf of Alaska. J. Environ. Forensics 2002, 3, 227–242. (5) Short, J. W.; Kolak, J. J.; Payne, J. R.; Van Kooten, G. V. An evaluation of petrogenic hydrocarbons in northern Gulf of Alaska continental shelf sediments: The role of coastal seep inputs. Org. Geochem. 2007, 38, 643–670. (6) Short, J. W.; Kvenvolden, K. A.; Carlson, P. R.; Hostettler, F. D.; Rosenbauer, R. J.; Wright, B. A. The natural hydrocarbon background in benthic sediments of Prince William Sound, Alaska: Oil versus coal. Environ. Sci. Technol. 1999, 33, 3442. (7) 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. (8) Springman, K. R.; Short, J. W.; Lindeberg, M. R.; Maselko, J. M.; Kahn, C.; Hodson, P. V.; Rice, S. D. Semipermeable membrane deviceslinksite-specificcontaminantstoeffects:PartIsInduction of CYP1A in rainbow trout from contaminants in Prince William Sound, Alaska. Mar. Environ. Res. 2008, 66, 477–486. (9) Short, J. W.; Springman, K. R.; Lindeberg, M. R.; Holland, L. G.; Larsen, M. L.; Sloan, C. A.; Khan, C.; Hodson, P. V.; Rice, S. D. Semipermeable membrane devices link site-specific contaminants to effects: Part IIsA comparison of lingering Exxon Valdez oil with other potential sources of CYP1A inducers in Prince William Sound, Alaska. Mar. Environ. Res. 2008, 66, 487498.
Halambage Upul Deepthike Department of Chemistry, Tennessee Technological University, Cookeville, TN 38505
Robin Tecon Department of Microbial Ecology, Netherlands Institute of Ecology, Heteren, The Netherlands
Gerald K. Van Kooten Department of Geography, Geology, and Environmental Studies, Calvin College, Grand Rapids, Michigan 49546
Jan Roelof van der Meer Department of Fundamental Biology, University of Lausanne, Lausanne CH 1015, Switzerland
Hauke Harms and Mona Wells Department of Environmental Microbiology, UFZ, Helmholtz Centre for Environmental Research, Permoserstraβe 15, Leipzig 04318, Germany
Jeffrey Short Oceania, 175 S. Franklin St, Juneau, Alaska 99801 ES100176K
VOL. 44, NO. 6, 2010 / ENVIRONMENTAL SCIENCE & TECHNOLOGY
9
2213
