In 1973 the National Academy of Sciences Ocean Affairs Board reported that each year 5 to 10 million metric tons of crude oil and its byproducts (fuel oil, kerosene, gasoline, and lubricants) go into the sea.
Sources range from expended ocean transport fuel to the much publicized and controversial oil spills.
Although big spills near populated beach areas receive widespread headlines and arouse considerable public outrage, smaller, confined spills in marshlands and harbors are far more grave and dangerous. In such places the oil cannot disperse, and continued release of oil can cause whole classes of plant or animal life to sicken and die, resulting in permanent changes in the ecosystem.
If the oil is light, gasoline or kerosene, for example, some evaporates, whereas heavier oils tend to break down into small, hard tar balls. In either case, some soluble elements always dissolve in the water, creating an invisible threat to the life in that area. Bacteria in the water may eat some of the oil, but nature cannot rid itself entirely of the huge amounts of oil going into the sea, and we are dependent on technology to help with the job.
One of the best and most widely used methods for containing oil so that it may be mopped up is the use of oil spill booms. A boom acts as a mechanical barrier to obstruct surface water and oil, while allowing subsurface water to pass.
An upper barrier of polyurethane, polyethylene, foam, or compressed air covered with plastic reaches above the water and is supported by a float. Below this tubular float hangs a “skirt” made of plastic, rubber, canvas, or plywood, which blocks the oil. The boom is stabilized by a lead ballast. Two boats may “boom off” an area by towing a spill boom between them at a rate of 1.5 miles per hour, or a boat tows one end while the other end is anchored. The slow speed is necessary to prevent water from slipping under the boom; furthermore, the method is often impractical in open ocean, for waves more than 2 or 3 feet high can cause oil to rush over the top of the boom.
To actually remove oil from the water, a variety of skimmers may be employed. A floating suction head, which is simply an enlargement of the end of a suction hose, can be immersed in thick oil slicks. Powered by a hydraulic pump, the hose draws in oil and water, and the two are then separated by gravity or other means. A floating weir, usually in the form of an inverted cup, 18 to 24 inches in diameter, supported by floats, has a straight edge that separates oil from the surface of the water and, in most cases, another weir inside it to further separate the two. Weirs, obviously, are impractical in strong winds and choppy water.
A drum or disk is another type of skimmer, which operates by rotating in and out of the oil slick. As the drum comes out of the water, coated with oil, it is wiped clean, then re-immersed to pick up more oil.
The most efficient types consist of two counter-rotating drums: one placed near the surface of the water moves rapidly with the water flow, while the other, immersed at a deeper level, moves slowly in the opposite direction. The former is coated with polyethylene, which works well with heavy oils; the latter has a water wetted steel surface, which is more effective on lighter oils.
Oleophilic belts, long belts covered with a material such as polyurethane foam which absorbs oil and repels water, may be set loose in a slick and harvested later by hand, or dragged behind a boat, or mounted on an inclined plane between two rollers. The oleophilic fibers soak up oil, which is then squeezed out and the belt reused. Like other skimmers, the belts do not work well in rough water, which can wash oil off before the belts are removed.
A very good method for cleaning up small, well contained spills and vestiges of large spills involves the use of sorbents, which float in the water and soak up oil by capillary action or cause the oil to adhere to a large surface area.
Inorganic sorbents include vermiculite, perlite, expanded perlite, and volcanic ash, which absorb four to eight times their own weight in oil and can then be recovered with dip nets or pool skimmers. If the wind is not too strong, organic sorbents such as peat moss, straw, milled corncobs, wood cellulose fiber, and milled cottonseed hulls can be spread on the water. In contact with oil these materials become heavy, fibrous mats which must be collected by hand or with sewer vacuuming equipment. Synthetic organic sorbents are also used. Although costly, these materials, which include polyurethane foam, urea formaldehyde foam, polyethylene, and polypropylene, can be reused several times. Since they are persistent in the environment, they must eventually be recovered.
Chemicals, under very strict control of the Environmental Protection Agency (EPA) and similar agencies, are also useful in cleaning up spills. If placed with a spraying device around the perimeter of a spill, chemicals containing a complex alcohol that repel oil can actually move it and concentrate it into a smaller slick.
Other chemicals, such as detergents, disperse oil by breaking it down into small globules that spread out through the water. Dispersants must be thoroughly mixed with the water in order to be effective. If there is sufficient wave action, the chemical may be sprayed from a plane; otherwise, it is discharged by a device dragged behind a boat.
Sinking agents spread by dusting from a plane that cause oil to sink to the bottom to be degraded by biological action are illegal, according to EPA and U.S. Coast Guard regulation, subsequent to the Federal Water Pollution Control Act of 1972. The sinking agents themselves sand, for example, may be innocuous, but heavy oil on the ocean bottom may be harmful to fish and plant life, or the oil may escape and resurface, thus re creating the initial problem. Sometimes oil is burned, and certain chemicals are used to provide wicks or sorbents that insulate oil from water and allow it to burn, though not always successfully.
All these methods are helpful, but none is completely effective, and each has its drawbacks. Oil spill research continues, and one of the most exciting breakthroughs derives from nature itself: the use of petrophilic bacteria, bacteria that eat hydrocarbons.
Since several different species of bacteria are required to consume oil efficiently, Dr. Ananda M. Chakabarty of the General Electric Research and Development Center used genetic engineering to come up with a single strain having the eating capabilities of four different bacteria.
This super strain, the patent for which was recently upheld in a landmark Supreme Court case, consumes oil far more rapidly than any other natural organism. Experiments at the University of Texas have resulted in another remarkable development: several different strains of natural bacteria may be dried and stored indefinitely as a powder, ready to be spread on a spill at a moment’s notice.
Researchers have conducted a test in which the powder was spread on a 10 gallon spill contained by booms; within six hours, not a trace of oil remained.