Biodegradation of Dispersed Oil in Arctic Seawater at -1°C

Abstract

As offshore oil and gas exploration expands in the Arctic, it is important to expand the scientific understanding of arctic ecology and environmental impact to mitigate operational risks. Understanding the fate of oil in arctic seawater is a key factor for consideration. Here we report the chemical loss due to the biodegradation of Alaska North Slope (ANS) crude oil that would occur in the water column following the successful dispersion of a surface oil slick. Primary biodegradation and mineralization were measured in mesocosms containing Arctic seawater collected from the Chukchi Sea, Alaska, incubated at −1°C. Indigenous microorganisms degraded both fresh and weathered oil, in both the presence and absence of Corexit 9500, with oil losses ranging from 46−61% and up to 11% mineralization over 60 days. When tested alone, 14% of 50 ppm Corexit 9500 was mineralized within 60 days. Our study reveals that microorganisms indigenous to Arctic seawater are capable of performing extensive biodegradation of chemically and physically dispersed oil at an environmentally relevant temperature (−1°C) without any additional nutrients.

Hydrocarbon biodegradation by Arctic sea-ice and sub-ice microbial communities during microcosm experiments, Northwest Passage (Nunavut, Canada)

“…4B). This contrasts with recent experimental results obtained with Arctic seawater bacteria where parent PAHs were degraded before their methylated homologues (McFarlin et al 2014). These compounds are considerably toxic and bioaccumulate more than the non-methyl forms because the addition of a methyl group decreases water solubility (Seo et al 2009).…”

“…This is faster than other recent experimental results, which suggest that the half-life of crude oil would be ca. 60 days in the Chukchi Sea at sub-zero temperatures (McFarlin et al 2014). No bacterial activity was measured during that experiment, but nutrient concentrations were below the detection limit in the Chukchi Sea, suggesting that bacterial growth may have been limited and explaining the comparatively shorter half-life measured in our microcosms.…”

“…5B). Alkanes are major components of crude oil, and are typically utilized as carbon and energy sources by bacteria (Rojo 20 2009), including Arctic populations growing at 4°C (Deppe et al 2005) down to 1°C (Gerdes et al 2005), and as low as -1°C (McFarlin et al 2014). Interestingly, the methylated forms of PAHs were degraded almost as much as the alkanes by the sub-ice seawater bacteria (Fig.…”

“…Nonetheless, coldadapted bacteria that possess hydrocarbon-degrading genes have been found in Arctic soils (Whyte et al 1999;Yergeau et al 2012) and seawater (McFarlin et al 2014). Sea ice is another distinctive Arctic ecosystem, characterized by very cold temperature and high brine content, and yet it harbors abundant and diverse microbial assemblages thriving in several distinct microhabitats (Bowman et al 2012).…”

Biodegradation of dispersed oil in natural seawaters from Western Greenland and a Norwegian fjord

“…Small oil-droplet dispersions generate large surfaces which hydrocarbonoclastic bacteria may attach to, and several studies have shown that the use of oil spill dispersants may stimulate oil biodegradation (Siron et al 1995;Venosa and Holder 2007;Baelum et al 2012;Prince et al 2013;Brakstad et al 2014;McFarlin et al 2014b;Techtmann et al 2017). By encouraging the formation of small oil droplets, dispersants increase the surface-to-volume ratio of the oil and enhance oil biodegradation by creating larger oil surfaces for microbial attachment, but also dissolution of soluble compounds may be increased compared to oil emulsions.…”