5. Discussion
Annoyance, leading to sleep disruption and psychological distress, is the impact most frequently linked to wind turbines in peer-reviewed studies. Various causes of annoyance have been presented and debated, including the sound of wind turbines, unique characteristics of wind turbine noise and visual disturbance of the landscape. Characteristics of the individual, such as noise sensitivity, attitudes to wind turbines and financial gain from wind turbines, and characteristics of the environment, such as other sources of noise, are supported as moderating variables. Findings of published studies demonstrate a dose-response relationship between annoyance and wind turbine noise126 but it is noteworthy that the level of noise explains one-third or less of the variance in annoyance in the multivariate analyses done to date. Visual impact and such characteristics of the individual as attitudes toward wind turbines, financial compensation, noise sensitivity and values are also correlated with annoyance. Regardless of the cause, this report accepts that annoyance is real for the residents who experience it.
Wind turbines are not unique in creating noise that is perceived to be hazardous or annoying by a segment of the population. There are many common sources of noise, including motor, rail and air traffic, and noise of machinery, where it has been judged appropriate to limit noise levels. Where noise is loud enough to cause temporary or permanent hearing impairment, there are laws to protect the hearing of those exposed. Health does have a very real role to play in advocating for safe limits to noise and for ensuring that exposure is limited, regardless of the source. In this respect, there are current regulations regarding acceptable levels of noise from wind turbines. Residents living in areas in which these limits are violated are encouraged to report their concerns to the Ministry of the Environment.
Ontario Boards of Health are governed by the Health Protection and Promotion Act, R.S.O., l990 Chapter H.7. Through this legislation, Medical Officers of Health are required to investigate possible health hazards. At present, this review has not revealed that wind turbines present a health hazard as defined within the HPPA and therefore we are not in a position to write an order regarding wind turbines under section 13 of the Act.
In this review, no evidence was found to indicate that the hearing of residents is affected by the sound of wind turbines compliant with the regulations. However, annoyance and associated manifestations of annoyance have been shown in peer-reviewed studies, and well documented in case reports. Like any other source of noise, wind turbines may cause annoyance in a subset of residents living close to them. Like other sources of noise, it is legitimate for those exposed to wind turbine noise to lobby for acceptable limits to noise levels. It is our opinion that the issue of tolerable limits to factors which are part of our way of life but which annoy or disturb members of the population, such as light and noise, are best addressed in the civic and political arenas, rather than by public health. This is a discussion on a societal level which balances advantages and disadvantages of this energy source for the individual and for society at large.
Wind turbines are unique in that they may cause an annoyed response at sound levels lower than other sources of unwanted noise. There are many factors which may contribute to this. Acoustical characteristics of the noise emissions, the height of the sound source and varying meteorological conditions, and the location of wind turbines in quiet rural environments are hypothesized to contribute to this outcome. Risk communication theory says that people will react more strongly to a perceived threat when they feel that it is imposed rather than undertaken voluntarily, when it is man-made rather than natural, when it is new rather than familiar, when they feel little control over the situation, and when the individual feels that he or she is assuming a higher level of risk than the majority who benefit127. Wind turbines are likely to be located in areas with low background sound levels, especially at night, and in places where residents might have chosen to live in a quiet or natural environment. The evidence does suggest that 40 dBA nighttime exposure is the maximum that should be permissible under night time noise regulations, and some consideration should be given to lower maximums in circumstances of very low ambient noise levels.
Although there is a large body of literature on the health effects of wind turbines, there are few studies that use appropriate quasi-experimental designs to adequately address issues of internal and external validity, confounding and bias. There is a need for further, carefully designed studies, and studies which include measured sound levels as well as objective measures of adverse health outcomes.