Oil Biodegradation and Bioremediation: A Tale of the Two Worst Spills in U.S. History

Oil biodegradation and bioremediation: A tale of the two worst spills in U. S. history. Ronald M. Atlas, University of Louisville, Louisville KY 40292 Terry C. Hazen, Lawrence Berkeley National Laboratory, Berkeley, CA 94720 Biography Ronald Atlas is Professor of Biology at the University of Louisville. He has over 40 years experience studying the role of microorganisms in oil biodegradation and helped pioneer the field of bioremediation. He has worked extensively on the bioremediation the Exxon Valdez spill. Terry Hazen is DOE BER distinguished scientist in the Earth Sciences Division at Lawrence Berkeley National Laboratory. He has studied oil, chlorinated solvent, and metal and radionuclide bioremediation for more then 30 years. He has been extensively studying the microbial degradation of the BP Deepwater Horizon Spill in the Gulf of Mexico. Abstract The devastating environmental impacts of the Exxon Valdez spill in 1989 and its media notoriety made it a frequent comparison to the BP Deepwater Horizon spill in the popular press in 2010, even though the nature of the two spills and the environments impacted were vastly different. Fortunately, unlike higher organisms that are adversely impacted by oil spills, microorganisms are able to consume petroleum hydrocarbons. These oil degrading indigenous microorganisms played a significant role in reducing the overall environmental impact of both the Exxon Valdez and BP Deepwater Horizon (MC252) oil spills. Introduction to Biodegradation of Petroleum Hydrocarbons Petroleum hydrocarbons in crude oils, such as those released into marine ecosystems by the Exxon Valdez and BP Deepwater Horizon spills, are natural products derived from aquatic algae laid down between 180 and 85 million years ago. Crude oils, composed mostly of diverse aliphatic and aromatic hydrocarbons, regularly escape into the environment from underground reservoirs. Because petroleum hydrocarbons occur naturally in all marine environments there has been time for numerous diverse microorganisms to evolve the capability of utilizing hydrocarbons as sources of carbon and energy for growth. Oil-degrading microorganisms are ubiquitous, but may only be a small proportion of the pre-spill microbial community. Bacteria, archaea, and fungi each have hundreds of species that can degrade petroleum. Most petroleum hydrocarbons are biodegradable under aerobic conditions; though a few compounds found in crude oils, e.g. resins, hopanes, polar molecules, and asphaltenes, have practically imperceptible biodegradation rates. Lighter crudes, such as the oil released from the BP Deepwater Horizon spill, contain a higher proportion of simpler lower molecular weight hydrocarbons that are more readily biodegraded than heavy crudes, such as the oil released from the Exxon Valdez. The polycyclic aromatic hydrocarbons (PAH) are a minor constituent of crude oils; however, they are among the most toxic to plants and animals. Bacteria can convert PAHs completely to biomass, CO 2 , and H 2 O, but they usually require the initial insertion of O 2 via dioxygenase enzymes. Anaerobic degradation of petroleum hydrocarbons can also occur albeit at a much slower rates. Petroleum hydrocarbons can be biodegraded at temperatures below freezing to more than 80°C. Microorganisms require elements other than carbon for