The long-term effects of oil spills on wildlife and their habitats are just beginning to be understood. Reduction of these impacts, which for wildlife can range from reproductive failure to developmental abnormalities, may be assisted by the natural breakdown of oils by organisms found in the marine environment. Some recent studies have looked at biodegradation, giving a slightly clearer picture of what these organisms can and can’t do.
Bacteria in the Arctic break down PAHs at same rate as in the North Sea
On the positive side, amidst concerns about oil and gas development and shipping in the Arctic, a study of the biodegradation of naphthalene, the smallest of the polycyclic aromatic hydrocarbons (PAHs), found breakdown rates were the same in the Arctic near the Svalbard Islands and the North Sea off of southwest Norway.
This contradicts previous results but the reason for that is simple. The previous studies used North Sea water at lower temperature to mimic the Arctic. Using waters from each source, the researchers found that the bacteria in the North Sea is not the same as that found in the Arctic, and the Arctic bacteria have evolved to breakdown PAHs at Arctic temperatures.
Napthalene is one, however, of the less toxic PAHs and the researchers very clearly stated that they have only looked at one type of PAH and results may vary with other types. As can be seen in the next study, some PAHs may not be broken down by some bacteria.
At least one type of bacteria in Gulf of Mexico is not able to break down PAHs
A 2014 study focused on how a Colwellia species and a gammaproteobacterium factored into oil breakdown in the sediments around the Deepwater Horizon oil rig blowout showed less positive results, particularly in terms of breaking down PAHs. The research, led by Assistant Professor Olivia Mason of Florida State University, showed that the Colwellia was able to breakdown some dangerous compounds such as polyethylene glycol (a component of Corexit) and toluene (a simple aromatic found in petroleum products).
Colwellia did not, however, have much effect on phenanthrene, a polycyclic aromatic hydrocarbon or PAH. Phenanthrene is one of the eight PAHs on the US Environmental Protection Agency's Priority Chemical list for toxicity. PAHs have been linked to various types of cancer and respiratory problems following inhalation or skin contact. Since these PAHs are not readily broken down by bacteria found in the areas around the well, they may be reintroduced into ocean currents if the sediments where they have been identified is disturbed, whether by natural means such as ocean currents or disturbances (the Gulf experiences many hurricanes) or by further human activity in the area.
Methane-oxidising microbes unable to remove all methane from Deepwater Horizon
In looking at methane oxidation by microbes in the Gulf of Mexico after the Deepwater Horizon well blowout, the news was not as positive. Early research seemed to indicate that microbes had consumed most of the methane released during that spill, however, this longer-term study showed that methane levels remained high for at least nine months after the spill. Oxidation by microbes peaked in May and early June when numbers of microbes increased significantly.
Methane oxidation then dropped rapidly later in June, before all the methane in the area was gone. The researchers suggest that there are physiological and environmental factors that may have reduced the effectiveness of the bacteria. They also emphasise the need for futher research into the capacity of these marine organisms to respond to sudden large quantities of methane.
Microbes can play a role in oil spill cleanup, however it seems that there is great variation in the microbes present in different environments and their capacity to cope with sudden large quantities of oil. Also in question is just how much of the oil, which is a complex product rather than one or two simple constituents,is broken down by the various organisms found in the sea.
Resources
Bagi, A. et al. 2014. Naphthalene biodegradation in temperate and arctic marine microcosms. Biodegradation. 25(1) 111-124. DOI: 10.1007/s10532-013-9644-3
Crespo-Medina M. et al. 2014. The rise and fall of methanotrophy following a deepwater oil well blowout. Nature Geoscience (2014) doi:10.1038/ngeo2156
Mason, O.U. et al.2014. Metagenomics reveals sediment microbial community response to Deepwater Horizon oil spill. The International Society for Microbial Ecology Journal (2014)8:1464-1475