Biodegradation of Exxon Valdez Oil Slowed by Low Concentrations of Oxygen and Nutrients
The combining of low densities of oxygen and nutrients in the lower levels of the beaches of Alaska’s Prince William Sound is slowing down the aerobiotic biodegradation of oil remaining from the 1989 Exxon Valdez spill, according to researchers at Temple University.
Believed to be one of the biggest environmental tragedies in history, the Exxon Valdez spilled more than 11 million gallons of petroleum into Alaska’s Prince William Sound, polluting some 1,300 miles of shoreline, killing thousands of wildlife and gravely affecting Alaska’s fishing industry and economy.
In the first five years after the accident, the oil was disappearing at a rate of about 70 percent and computations demonstrated that the oil would be gone within the next few years. However, about seven or eight years ago it was discovered that the oil had as a matter of fact slipped to a disappearing rate of approximately four percent a year and it is approximated that nearly 20,000 gallons of oil persists in the beaches.
The researchers, lead by Michel Boufadel, director of the Center for Natural Resources Development and Protection in Temple’s College of Engineering, have been studying the cause of the leftover oil for the past three years.
Boufadel said the beaches they analyzed comprised of two levels: an upper layer that is extremely permeable and a lower level that has very low permeability. He said that, on average, water displaced through the upper level up to 1,000-times faster than the lower level, and while both layers are made up of essentially the same materials, the lower layer has become more compacted through the movement of the tides over time.
These circumstances have produced a kind of sheltering consequence on the oil, which often lies just 1-4 inches below the interface of the two layers.
Boufadel said that oxygen and nutrients are needed for the endurance of micro-organisms that eat the oil and aid in aerobic biodegradation of the oil. But without the proper concentrations of the nutrients and oxygen along with the slow movement of water, anaerobic biodegradation is likely taking place, which is usually very slow.
Utilizing groundwater hydraulic studies, the researchers found that the net movement of water through the lower layer of beach was outwards, so it is preventing oxygen from diffusing through the upper layer to where the oil is located.
Boufadel and his team are now researching processes to deliver the much required oxygen and nutrients to the affected regions in an effort to spur aerobic biodegradation of the remaining oil.
See Related Report: US Alaska Oil and Gas Exploration and Production Industry to 2013
