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Oil and natural gas burn cleaner than coal but are heavy polluters, too. Oil and gas are preferred fuels because coal is so polluting, and because it is less useful for many kinds of engines. But these fuels, too, cause a great deal of pollution. Burning gasoline in automobiles produces air pollution and smog. The effect of smog on vegetation and human health are well documented. In addition, oil used in cars, trucks, and airplanes sometimes spills and soaks into soil. Leaking oil and leaking underground gasoline tanks have caused pollution problems and expensive lawsuits; although it now seems that natural soil bacteria are capable of decomposing most oil.
Refineries, also, pollute. What comes out of the ground from a typical oil well is a thick substance that is a mixture of many chemicals from very heavy tars to very light gasoline and natural gas. A refinery is basically a gigantic chemistry set that separates this “crude oil” into its components and can also convert one form of the crude oil into more useful form, usually converting the heavier chemicals to lighter ones. Refineries have accidental spills and slow leaks of gasoline and other products from storage tanks and pipes. Over years of operation, large amount of liquid hydrocarbons may be released, polluting soil and groundwater below the site.
The pollution continues during delivery. A famous example happened on March 24, 1988, when the supertanker Exxon Valdez, carrying 1.2 million barrels of crude oil, ran aground on Bligh Reef in Prince William Sound, Alaska, and broke open. The ship was full of Alaskan crude oil that had been delivered to it through the Trans-Alaska Pipeline, which itself is a controversial way of transporting oil. The oil poured out of ruptured tanks of the tanker at about 20, 000 barrels per hour, spilling a total of about 250,000 barrels (11million gallons) into the sound. An even bigger spill was avoided when the remainder of oil was off-loaded onto another vessel.
The spill killed thousands of fish, birds, and mammals – 13 % of the sound’s harbor seals, 28% of the sea otters, and 645,000 seabirds died. Within three days, winds began spreading the huge oil slick so widely that there was no hope of containing it. Of the 11 million gallons of spilled oil, about 20% evaporated and 50% was deposited on the shoreline. Only 14% was collected by skimming and other waste recovery. The Exxon Valdez spill showed that the technology for dealing with oil spills was inadequate. The spill disrupted the lives of the people who live and work in the vicinity of Prince William Sound. Even after more than $3 billion was sent to clean up, few people were satisfied with the results.
Long-term effects of large oil spills are probably not devastating. There is no evidence that the Ocean’s ecosystems are seriously threatened by oil spills. Nevertheless, the effect can last several decades. Toxic levels of oil have been identified in salt marshes 20 years after a spill.
The Exxon Valdez spill led to the Oil Pollution Act of 1990 and new technology. More modern tankers are being built with double hulls designed to prevent or limit the release of oil in case of collision or grounding. We now also have new techniques to collect oil at sea, using floating barriers and skimmers (oil is lighter than water and so floats on water), but even the best methods are difficult to use in high winds and rough seas. Oil on beaches may be collected by spreading absorbent material, such as straw, waiting for the oil to soak in, and then collecting and disposing the oily straw.
From E. A. Keller, D.B. Botkin. Essential Environmental Science. John Wieley & Sons, Inc., 2007.
Pay attention to the following words:
leak spill
leakage spillage
Unintentional or unauthorized releases of chemicals, gases, or oil are leaks, leakages, spills, or spillages.
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