Noise health effects
Noise health effects, the collection of health consequences of elevated
sound levels, constitute one of the most widespread
public health threats in
industrialized countries. Current conditions expose tens of millions of people to sound levels capable of causing
hearing loss[Senate Public Works Committee, Noise Pollution and Abatement Act of 1972, S. Rep. No. 1160, 92nd Cong. 2nd session], but also are known to induce
tinnitus,
hypertension,
vasoconstriction and other
cardiovascular impacts [
1].
Roadway noise is the main source of
environmental noise exposure.
Aerodynamic noise created at
freeway speeds is particularly intense. Vasoconstriction can also be contributory to
erectile dysfunction[Richard Milsten and Julian Slowinski, The sexual male, W.W. Norton Company, New York, London (1999) ISBN 0-396-04740-7]. Beyond these effects, elevated noise levels create stress, increase workplace accident rates, and stimulate aggression and other anti-social behaviors
[Karl D. Kryter, The Handbook of Hearing and the Effects of Noise : Physiology, Psychology and Public Health,Academic Press, Nov 18, 1994 ISBN 0124274552]. The most important sources of sound levels that create the above effects are motor vehicle and aircraft noise, with industrial worker noise exposure also being notable. Secondary exposures may arise from loud audio media especially if practiced as a lifestyle such as prolonged
digital audio player use.
The
pinna (visible portion of the human
ear) combined with the
middle ear amplifies
sound levels by a factor of 20 when sound reaches the
inner ear.Approximately ten percent of the population in industrialized societies have significant
hearing loss, and millions more are steadily progressing to that outcome. The major source of hearing loss is exposure to elevated sound levels. Once it was thought that only extremely high sound levels create hearing loss; however, more careful investigations showed that cumulative exposure to relatively moderate levels, such as 70
dB(A), can lead to the irreversible loss of hearing. Another myth of noise effects is the overstated role of
presbycusis, or loss of hearing associated with aging. It has been demonstrated that the most important factor of hearing degradation is not aging alone, but rather the cumulative long-term exposure to environmental and occupational noise that create the harm
[Rosenhall, Ulf; Pedersen, Kai; Svanborg, Alvar Presbycusis and Noise-Induced Hearing Loss, Ear & Hearing, 11(4):257-263, August 1990]. In the Rosenhall study,
age cohort populations were tracked, with the result that noise-exposed persons had much greater hearing loss than their
age cohorts who were relatively unexposed to noise. In fact, it has been shown that people in non-industrialized countries do not experience the same progressive hearing loss
[S. Rosen and P. Olin, Hearing Loss and Coronary Heart Disease, Archives of Otollaryngology, 82:236 (1965)].
The mechanism of
hearing loss arises from
trauma to
stereocilia of the
cochlea, the principal fluid filled structure of the
inner ear. The
pinna (visible portion of the ear) combined with the
middle ear amplifies
sound pressure levels by a factor of twenty, so that extremely high sound pressure levels arrive in the cochlea, even from moderate atmospheric sound
stimuli. The cilial damage is known to be cumulative and can be irreversible
[Schneider M.E., Belyantseva I.A., Azevedo R.B., Kachar B,. Rapid renewal of auditory hair bundles Nature. 22 Aug 2002. 418(6900): 837-838.]. The most recent research indicates that high noise levels create elevated levels of
reactive oxygen species in the inner ear
[Henderson, Donald; Bielefeld, Eric C.; Harris, Kelly Carney; Hu, Bo Hua, The Role of Oxidative Stress in Noise-Induced Hearing Loss, Ear & Hearing. 27(1):1-19, February 2006], which interfere with the regenerative process for cochlear cilia repair. This research shows why high noise levels have differing effects over a given population, and lead to a possible preventative strategy of adequate
antioxidant intake.
In 1972 the U.S.
EPA told Congress that at least 34 million people were exposed to sound levels on a daily basis that are likely to lead to significant hearing loss
[Senate Public Works Committee, Noise Pollution and Abatement Act of 1972, S. Rep. No. 1160, 92nd Cong. 2nd session]. The worldwide implication for industrialized countries would place this exposed population in the hundreds of millions.
There are important cardiovascular consequences from elevated sound levels, principally because the elevated
adrenaline levels trigger a narrowing of the blood vessels (
vasoconstriction). Sound levels, again of fairly typical roadway noise exposure, are known to constrict arterial blood flow and lead to
elevated blood pressure; in this case, it appears that a certain fraction of the population is more susceptible to vasoconstriction. (Independently, high noise levels are known to produce
medical stress reactions, another risk associative with
cardiovascular disease.) Noise induced medical stress is significant for two reasons. First, it is often prolonged exposure for eight to 16 hours per day, leading to elevated
blood pressure for much of the day. Second, unlike emotional stress, it has a very clear effect on the blood pressure, whereas this is not always the case with emotional stress. These effects may also be compounded by other environmental vasoconstrictors such as
over-illumination or
light pollution.
Other proven effects of high noise levels are increased frequency of
headaches,
fatigue,
stomach ulcers and
headrush[Noise: A Health Problem United States Environmental Protection Agency, Office of Noise Abatement and Control, Washington, DC 20460, August, 1978 ]. The same U.S. EPA study establishes links between high noise levels and
fetal development. This body of research suggests a correlation between low birth weight babies (using the
World Health Organization definition of 5.5 pounds) and high sound levels, and also correlations in abnormally high rates of
birth defects, where expectant mothers are exposed to elevated sound levels, e.g. typical
airport environs. Specific birth abnormalities included
harelip,
cleft palate, and defects in the
spine. According to Lester W. Sontag of The
Fels Research Institute (as presented in the same EPA study): "There is ample evidence that environment has a role in shaping the physique, behavior and function of animals, including man, from
conception and not merely from
birth. The
fetus is capable of perceiving sounds and responding to them by motor activity and cardiac rate change." Noise exposure is deemed to be particularly pernicious when it occurs between 15 and 60 days after conception, when major internal
organs and the
central nervous system are formed. Later developmental effects occur as vasoconstriction in the mother reduces blood flow, and hence
oxygen and nutrition to the fetus. Low birth weights and noise were also associated with lower levels of certain
hormones in the mother, these hormones being thought to affect fetal growth and to be a good indicator of
protein production. The difference between the hormone levels of pregnant mothers in noisy versus quiet areas increased as birth approached.
Earlier researchers often grouped the non-physiological impacts of noise as "annoyance". As research unfolded, it became clear that there are a host of
psychological and
behavioral effects result from elevated sound levels, including:
sleep disturbance,
reading development in children,
stress,
mental health (including disengagement and increases in aggressive behavior). These effects are statistical but measurable changes in a population of individuals compared to a control group of persons in a quiet environment. Obviously, other negative environmental factors are likely to be present in high noise areas such as higher air pollution levels and possibly
poverty-induced
nutrition deficits; however, the overwhelming weight of dozens of independent studies identify
noise pollution to be responsible for significant increases in the psychological effects studied above.
Measurements of noise annoyance typically rely on
weighting filters, which consider sound frequencies annoying only to the degree that they are audible, on average, to a human ear at a particular decibel volume. Common methods include the older dBA weighting filter used widely in the U.S., which underestimates the impact of frequences around 6000 Hz and at very low frequencies, and the newer
ITU-R 468 noise weighting filter, which is used more widely. It is important to note that these filters do not necessarily reflect the occurrence of adverse health effects from noise, which may not depend on its audibility to the ear, nor do they take into account the propensity of low-frequency noises to penetrate into buildings or to carry over long distances.
Annoyance effects of noise vary greatly by demographics and by the perception of how useful the entity is that originates the noise. For example, aircraft mechanics who live near an airport are less likely to be complainants, since their livelihood is based upon airport operations. Annoyance is also influenced by whether the noise source is visible, whether it has pure tones or hammer effects and whether the recipient believes the noise can be controlled. In any case, the onset
[H.M.E. Miedema and H. Vos, Exposure response relationships for transportation noise, Journal of the Acoustical Society of America, 105, 3336-44] of noise complaints can be as low as 40 dB(A)
[Stanley A Gelfand, Essentials of Audiology, Theime Medical Publishers, New York, N.Y. (2001) ISBN 1588900177]. Whether the noise occurs at night is another critical variable for annoyance phenomena. Most commonly, concerted actions of the public appear at approximately 65dBA regarding roadway, aircraft or industrial noise in the environment. Closely associated with annoyance are
sleep disturbance and speech interference phenomena. The threshold for sleep interference is 45 dB(A) or lower
[F Fahy and J Walker, Fundamentals of Noise and Vibration, Spon Press, UK (2001)]. The onset of
speech interference is about 63dBA, or roughly the sound level of speech in a normal tone between two people separated by one meter.
When young children are exposed to speech interference levels of noise on a regular basis, there is a likelihood of developing speech or reading difficulties, because the auditory processing functions are compromised. In particular the writing learning impairment known as
dysgraphia is commonly associated with environmental
stressors in the classroom.
Effects of environmental noise upon aggression, mental health, anxiety, withdrawal and other psychological factors have been studied by numerous researchers. For example J.M.. Field
[J.M. Field, Effect of personal and situational variables upon noise annoyance in residential areas, Journal of the Acoustical Society of America, 93: 2753-2763 (1993)] examines a variety of these outcomes and finds significant influence of moderate level environmental noise upon human behavior and mood. There are also strong associative impacts when other stressors are present such as
over-illumination and presence of certain drugs.
Main article: Noise regulation
Environmental noise regulations usually specify a maximum outdoor level of 60 to 65
dB(A), while occupational safety organisations recommend that the maximum exposure to noise is 40 hours per week at 85 to 90 dB(A). For every additional 3 dB(A), the maximum exposure time is reduced by a factor 2, e.g. 20 hours per week at 88 dB(A). Sometimes, a factor of two per additional 5 dB(A) is used. However, these occupational regulations are acknowledged by the health literature as inadequate to protect against
hearing loss and other health effects discussed above.
*
Aircraft noise*
Hearing impairment*
Noise pollution*
Noise regulation*
Synaesthesia*
Tinnitus*
Relation of Noise and light in synaesthesia
