Biodegradation of water-accommodated aromatic oil compounds in Arctic seawater at 0 °C

Oil spills in Arctic marine environments are expected to increase concurrently with the expansion of shipping routes and petroleum exploitation into previously inaccessible ice-dominated regions. Most research on oil biodegradation focusses on the bulk oil, but the fate of the water-accommodated fraction (WAF), mainly composed of toxic aromatic compounds, is largely underexplored. To evaluate the bacterial degradation capacity of such dissolved aromatics in Greenlandic seawater, microcosms consisting of 0 °C seawater polluted with WAF were investigated over a 3-month period. With a half-life (t_1/2) of 26 days, m-xylene was the fastest degraded compound, as measured by gas chromatography - mass spectrometry. Substantial slower degradation was observed for ethylbenzene, naphthalenes, phenanthrene, acenaphthylene, acenaphthene and fluorenes with t_1/2 of 40-105 days. Colwellia, identified by 16S rRNA gene sequencing, was the main potential degrader of m-xylene. This genus occupied up to 47 % of the bacterial community until day 10 in the microcosms. Cycloclasticus and Zhongshania aliphaticivorans, potentially utilizing one-to three-ringed aromatics, replaced Colwellia between day 10 and 96 and occupied up to 6 % and 23 % of the community, respectively. Although most of the WAF can ultimately be eliminated in microcosms, our results suggest that the restoration of an oil-impacted Arctic environment may be slow as most analysed compounds had t_1/2 of over 2-3 months and the detrimental effects of a spill towards the marine ecosystem likely persist during this time.