Bioremediation of marine oil spills: when and when not--the Exxon Valdez experience.
Bottom Line: Where SSOR does remain, it is for the most part highly weathered, with 82% of 2007 samples indicating depletion of total polycyclic aromatic hydrocarbon (Total PAH) of >70% relative to EVOS oil.This SSOR is sequestered in patchy deposits under boulder/cobble armour, generally in the mid-to-upper intertidal zone.The relatively high nutrient concentrations measured at these sites, the patchy distribution and the weathering state of the SSOR suggest that it is in a form and location where bioremediation likely would be ineffective at increasing the rate of hydrocarbon removal.
Affiliation: University of Louisville, Louisville, KY 40292, USA. email@example.comShow MeSH
Mentions: Even where SSOR remains it is highly weathered. Almost no resolvable alkanes remain in samples collected from 2002 through 2007 (Fig. 5). Most samples also had lost more than 70% of the original PAHs through a combination of biodegradation and other weathering processes. We believe 70% depletion of Total PAH is the approximate threshold above which bioremediation is likely to be ineffective. This threshold is supported by results from the Prestige bioremediation tests (Fig. 4) that showed dramatic reduction in bioremediation effectiveness upon depletion of light alkanes, the almost total depletion of resolvable alkanes in current PWS samples (Fig. 5), and other studies showing lack of biodegradation rate sensitivity to added nitrogen once lighter alkanes and aromatics were depleted (Oudot et al., 1998; Wang et al., 1998; Wrenn et al., 2006). We have computed bioremediation indices for all analysed samples for which Total PAH loss could be quantified. The 70% is meant as a probable threshold, not a specific value above which bioremediation would not work. Figure 6 shows the bioremediation index for all samples collected from 2002 through 2007. If the Total PAH content of a sample was less than 500 ng g−1 sediment, that sample was not included in plots because the Total PAH concentration was approaching natural background levels in PWS and could not be confirmed as EVOS SSOR. However, note that the average percentage of depletion of Total PAH computed for all samples with Total PAH content < 500 ng g−1 sediment was 94%. HOR residues were found that contained Total PAH of less than 500 ng g−1 sediment; however, these comprised 80–95% polars – they looked like ‘oil’ but contained only highly degraded EVOS‐derived residues. As shown in Fig. 6, only about 25% of the total samples from 2002 to 2007 contained SSOR that might respond to bioremediation based on the 70% threshold.
Affiliation: University of Louisville, Louisville, KY 40292, USA. firstname.lastname@example.org