Noise pollution, operationally defined as 'unwanted sound', has become an environmental contaminant of massive proportions. Noise causes annoyance, frustration, impediment of learning and general stress. Of all present-day sources of noise, the noise from surface transportation - above all that from road vehicles - is the most diffused and difficult to control. Aircraft and industrial noise, and noisy neighbours and their pets are other common sources of noise aggravation.
According to the OECD, prolonged exposure to noise louder than 70dB can increase symptoms of hypertension and provoke aggression. Noise can interfere with mental activities requiring attention, memory and the ability to deal with complex analytical problems. Adaptation strategies (tune out/ignore noise) and the efforts needed to maintain performance have been associated with high levels of stress hormones and blood pressure. There is emerging evidence of an association between hypertension and ischaemic heart diseases and high levels of noise. Children chronically exposed to loud noise (e.g. in the proximity of airports) show impaired acquisition of reading skills, attention and problem-solving ability.
Noise generated by human activity is also endangering fish and oceanic mammals, such as seals and whales, who rely on sonic pulses in the water to navigate and communicate. It destroys the hair cells of the auditory organs of some fish, can burst blood vessels, damages fish eggs and reduces the growth rate of fry.
Major differences exist between noise and other forms of pollution. Noise is everywhere; it is not as easy to control as the sources of water and air pollution. Although certain effects of noise accumulate in the organism, if noise pollution were to cease there would be no noise residual in the environment, as there would be in the case of water and air pollutants. Unlike air and water pollution, the effects of noise are felt only close to the source. An essential awareness of noise and motivation to reduce the problem are not present: people are more likely to complain and demand political action about air or water pollution than about noise. Finally, noise is not likely to have genetic effects, while some forms of air and water pollution, such as radioactive pollution, can.
Men and women appear to react differently to a loud startling noise. Women, it seems, can be frightened by a sound more easily than men, and in response, show an increased tolerance to pain. This suggests that women have a lower threshold to experience noise as stressful.
Studies in several countries have pointed to increased rates of heart disease, high blood pressure and learning disabilities in areas where sound levels exceed 60 decibels (dB), notably in cities where traffic noise is high.
Excessive noise costs the USA $4 billion dollars a year in compensation payments, accidents, inefficiency, and absenteeism. Noise depreciation of real estate values mounts into the billions, particularly in the vicinity of major airports.
The number of noise complaints (per million people) to Environmental Health Officers from all sources in England and Wales rose by 16 per cent between 1994/5 and 1995/6. In 1995/6 complaints about noise from domestic premises accounted for over two thirds of all complaints about noise. Complaints about noise from this source increased by almost 400 per cent between 1983/84 and 1995/96. Amplified music was ranked as the most common source of complaint about neighbourhood noise by almost two-thirds of local authorities responding to a survey on noise.