Oil dispersants reshape Arctic sea-ice microbes but do not markedly accelerate oil breakdown

A recent study by researchers from Estonia and Norway has found that oil dispersants have altered microbial communities in Arctic sea ice but have not noticeably increased the rate of oil breakdown. As climate change has made the Arctic less icy, shipping traffic and oil spill risks have risen. However, these changes may impact the effectiveness of current oil spill response measures.

Sea ice presents a difficult environment for microbes, as they live in narrow brine channels, endure subzero temperatures, high salinity, oxidative stress, and limited access to oil compounds. Nevertheless, a variety of bacterial species manage to thrive there, capable of degrading petroleum compounds for metabolic processes. Oil-degrading bacteria obtain carbon from oil and require nitrogen and phosphorus for growth, though these elements are scarce in North Atlantic waters.

Oil dispersants, which break oil into smaller droplets, have been proposed as a means to counteract oil spills at sea. By dispersing the oil more quickly in the water column, they reduce the direct impact on marine life and make it easier for microbes to break it down. In a three-month study, researchers analyzed how microbial communities behaved in sea ice containing dispersed crude oil or only the dispersant.

They observed a shift in dominance towards cold-adapted bacterial genera like Oleispira, Bermanella, and Pseudoalteromonas. While some of these bacteria possess genes linked to alkane degradation, others have traits for cold survival and other environmental stresses. Genome analysis revealed that certain bacteria can produce enzymes to break down dispersant components, including surface-active agents used for oil dispersion.

Many of these bacteria have also developed adaptations to cope with cold and other stresses. Although dispersants increased the proportion of oil-degrading bacteria, the oil did not degrade any faster. The altered microbial community composition and genetic potential were attributed to the low abundance of microbes in sea ice, which meant the dominant microbes were those adapted to extreme ice conditions.

The study's authors caution that the use of dispersants in sea ice should be approached with caution, as it does not guarantee faster oil dissipation. The findings were published in the journal FEMS Microbes.