Noise Pollution
Every year since 1973, the U.S. Department of Housing and Urban Development has conducted a survey to find out what city residents dislike about their environment. And every year the same factor has been named most objectionable. It is not crime, pollution, or congestion; it is noise--something that affects every one of us every day.
We have known for a long time that prolonged exposure to noises, such as loud music or the roar of machinery, can result in hearing loss. Evidence now suggests that noise-related stress also causes a wide range of psychological and physiological problems ranging from irritability to heart disease. An increasing number of people are affected by noise in their environment. By age forty, nearly everyone in America has suffered hearing deterioration in the higher frequencies. An estimated ten percent of Americans (24 million people) suffer serious hearing loss, and the lives of another 80 million people are significantly disrupted by noise.
What is noise? There are many definitions, some technical and some philosophical. What is music to your ears might be noise to someone else. Simply defined, noise pollution is any unwanted sound or any sound that interferes with hearing, causes stress, or disrupts our lives. Sound is measured either in dynes, watts, or decibels. Note that decibels (db) are logarithmic; that is, a 10 db increase represents a doubling of sound energy.
Noises come from many sources. Traffic is generally the most omnipresent noise in the city. Cars, trucks, and buses create a roar that permeates nearly everywhere. Around airports, jets thunder overhead, stopping conversation, rattling dishes, some times even cracking walls. Jackhammers rattle in the streets; sirens pierce the air; motorcycles, lawn-mowers, snowblowers, and chain saws create an infernal din; and music from radios, TVs, and loudspeakers fills the air everywhere.
We detect sound by means of a set of sensory cells in the inner ear. These cells have tiny projections (called microvilli and kinocilia) on their surface. As sound waves pass through the fluid-filled chamber within which these cells are suspended, the microvilli rub against a flexible membrane lying on top of them. Bending of fibers inside the microvilli sets off a mechanico-chemical process that results in a nerve signal being sent through the auditory nerve to the brain where the signal is analyzed and interpreted.
The sensitivity and discrimination of our hearing is remark able. Normally, humans can hear sounds from about 16 cycles per second (hz) to 20,000 hz. A young child whose hearing has not yet been damaged by excess noise can hear the whine of a mosquito's wings at the window when less than one quadrillionth of a watt per cm2 is reaching the eardrum.
The sensory cell's microvilli are flexible and resilient, but only up to a point. They can bend and then spring back up, but they die if they are smashed down too hard or too often. Prolonged exposure to sounds above about 90 decibels can flatten some of the microvilli permanently and their function will be lost. By age thirty, most Americans have lost 5 db of sensitivity and cannot hear anything above 16,000 Hertz (Hz); by age sixty-five, the sensitivity reduction is 40 db for most people, and all sounds above 8,000 Hz are lost. By contrast, in the Sudan, where the environment is very quiet, even seventy-year-olds have no significant hearing loss.
Extremely loud sounds—above 130 db, the level of a loud rock band or music heard through earphones at a high setting—actually can rip out the sensory microvilli, causing aberrant nerve signals that the brain interprets as a high-pitched whine or whistle. Many people experience ringing ears after exposure to very loud noises. Coffee, aspirin, certain antibiotics, and fever also can cause ringing sensations, but they usually are temporary.
A persistent ringing is called tinnitus. It has been estimated that 94 percent of the people in the United States suffer some degree of tinnitus. For most people, the ringing is noticeable only in a very quiet environment, and we rarely are in a place that is quiet enough to hear it. About 35 out of 1,000 people have tinnitus severely enough to interfere with their lives. Sometimes the ringing becomes so loud that it is unendurable, like shrieking brakes on a subway train. Unfortunately, there is not yet a treatment for this distressing disorder. One of the first charges to the Environmental Protection Agency (EPA) when it was founded in 1970 was to study noise pollution and to recommend ways to reduce the noise in our environment. Standards have since been promulgated for noise reduction in automobiles, trucks, buses, motorcycles, mopeds, refrigeration units, power lawn-mowers, construction equipment, and airplanes. The EPA is considering ordering that warnings be placed on power tools, radios, chain saws, and other household equipment. The Occupational Safety and Health Administration (OSHA) also has set standards for noise in the workplace that have considerably reduced noise-related hearing losses.
Noise is still all around us, however. In many cases, the most dangerous noise is that to which we voluntarily subject ourselves. Perhaps if people understood the dangers of noise and the permanence of hearing loss, we would have a quieter environment.
Resources
Books
Chatwal, G. R., ed. Environmental Noise Pollution and Its Control. Columbia: South Asia Books, 1989.
Energy and Environment 1990: Transportation-Induced Noise and Air Pollution. Washington, DC: Transportation Research Board, 1990.
OECD Staff. Fighting Noise in the Nineteen Nineties. Washington, DC: Organization for Economic Cooperation and Development, 1991.
Periodicals
Bronzaft, A. "Noise Annoys." E Magazine 4 (March-April 1993): 16–20. O'Brien, B. "Quest for Quiet." Sierra 77 (July-August 1992): 41–2.
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