The Interactive Effects of Crude Oil and Corexit 9500 on Their Biodegradation in Arctic Seawater

Abstract

The risk of petroleum spills coupled with the potential application of chemical dispersants as a spill response strategy necessitates further understanding of the fate of oil and dispersants and their interactive effects during biodegradation. Using Arctic seawater mesocosms amended with either crude oil, Corexit 9500, or both together, we quantified the chemical losses of crude oil and Corexit 9500 and identified microbial taxa implicated in their biodegradation based on shifts in the microbial community structure over a 30-day time course. Chemical analyses included total petroleum hydrocarbons (TPH), n-alkanes, branched alkanes, and polycyclic aromatic hydrocarbons (PAHs) for oil loss and the surfactant components dioctyl sodium sulfosuccinate (DOSS), Span 80, Tween 80, Tween 85, and the DOSS metabolite ethylhexyl sulfosuccinate (EHSS) for Corexit loss. Changes to the microbial communities and identification of key taxa were determined by 16S rRNA gene amplicon sequencing. The nonionic surfactants of Corexit 9500 (Span 80, Tweens 80+85) biodegraded rapidly, dropping to below the limits of detection within 5 days and prior to any detectable initiation of oil biodegradation. This resulted in no observable suppression of petroleum biodegradation in the presence of Corexit compared to that of oil alone. In contrast, biodegradation of DOSS was delayed in the presence of oil, based on the prolonged presence of DOSS concentrations and accumulation of the degradation intermediate EHSS that did not occur in the absence of oil. Microbial analyses revealed that oil and Corexit enriched different overall microbial communities, with the presence of both resulting in a community composition that shifted from one more similar to that of Corexit-only, then shifting to reflect the oil-only community over time, in parallel with the degradation of predominantly Corexit and then oil components. Some microbial taxa (Oleispira, Pseudofulvibacter, Roseobacter) responded to either oil or Corexit, suggesting that some organisms may be capable of utilizing both substrates. Together, these findings reveal interactive effects of crude oil and Corexit 9500 on chemical losses and microbial communities as they biodegrade, providing further insight into their fate when co-present in the environment. Importance Chemical dispersants such as Corexit 9500 are commonly used in oil spill response and are currently under consideration for use in the Arctic, where their fate and effects have not been well studied. This research was performed to determine the interactive effects of the co-presence of crude oil and Corexit 9500 on the degradation of components from each mixture and the associated microbial community structure over time in Arctic seawater. These findings will help yield a better understanding on the biodegradability of dispersant components applied to an oil spill, the temporal microbial community response to dispersed oil, and the fundamental microbial ecology of organic contaminant biodegradation processes in the Arctic marine environment.

Metatranscriptomic shifts suggest shared biodegradation pathways for Corexit 9500 components and crude oil in Arctic seawater

“…Recent incubation studies have also demonstrated an upregulation of β-oxidation gene transcripts in treatments that contained Corexit compared to oil-only treatments and unamended controls (Doyle et al, 2020;Peña-Montenegro et al, 2020).Based on the significant enrichment of fadE, fadA, and fadB genes at the 5-day time point, increased β-oxidation of chemical compounds was likely occurring in the presence of Corexit and oil + Corexit relative to oil-only or the control. This agrees with previously reported chemical loss data from this experiment, which showed that the majority of Corexit surfactant loss occurred within 5 days and the majority of oil loss within 10 days (Figure 3; Gofstein et al, 2020). When examining the constituents of Corexit 9500 compared to crude oil, their chemical structures, which contain multiple ester groups, (Figure 5A) have functional groups that may lead to their being more labile than the alkanes present in crude oil due to fewer steps being required to prepare esters to undergo β-oxidation (Figure 5B).…”

“…The taxa previously reported to proliferate in response to oil and/or Corexit in this incubation study (Gofstein et al, 2020) were associated with enriched gene transcripts for several key metabolic and biogeochemical processes relevant to contaminant degradation including fatty acid degradation, nitrogen cycling, and sulphur cycling (Table 1). Based on the taxonomic affiliations of the metabolic transcripts, different populations became metabolically active in response to oil and/or Corexit (Figure 4).…”

“…Samples used for this study were obtained from a previously performed mesocosm experiment as described in Gofstein et al, 2020. Mesocosms containing 800 ml of seawater collected from the Chukchi Sea were treated with either 50 ppm Alaska North Slope crude oil, 5 ppm Corexit 9500, both (1:20 dispersant-to-oil ratio), or neither (unamended control) and incubated on stir plates at 4 C on a 19-h day/5-h night light cycle for 30 days. Mesocosms for all treatment and time point combinations were prepared in triplicate (n = 3).…”

A Multifaceted Approach to Advance Oil Spill Modeling and Physical Oceanographic Research at the United States Bureau of Ocean Energy Management

“…Their results showed a quick initial removal of hydrocarbons by volatilization, but microbial biodegradation of crude oil was low, especially at the lower temperature. McFarlin et al (2018) [157] and Gofstein et al (2020) [154] quantified biodegradation and abiotic losses of ANS crude oil and Corexit 9500 in Arctic seawater mesocosms. They identified microorganisms potentially involved in biodegradation of these substrates using tools based on gene analysis.…”

Deep marine oil spills : Oil-particles-dispersants interaction and impact on oil biodegradation

“…Toxicity experiments performed on a closely related species indicated that oil had little effect on coral's health but that oil and dispersant mixtures were particularly toxic to corals (DeLeo et al, 2016;Goodbody-Gringley et al, 2013;Negri et al, 2018). The long-term persistence of elevated DOSS concentrations on beaches and in the deep sea demonstrates that at least some of the components of dispersants are persistent in the environment (Gofstein et al, 2020;Gray et al, 2014;Mascarelli, 2011).…”