June 18, 2009
Got ear plugs? You may want to sport them on the subway, researchers say
The U.S. mass transit system, the largest in the world, provides affordable and efficient transportation to more than 33 million riders each weekday. The system is generally considered one of the safest modes of travel. But recent public health studies have identified several sources of environmental hazards associated with mass transit, including excessive noise, a large and growing problem in urban settings.
Now, a team of researchers from the University of Washington and Columbia University have found that Metropolitan Transit Authority (MTA) subways had the highest average noise levels of all mass transit in New York City, with levels high enough to potentially increase the risk of noise- induced hearing loss.
Researchers studied the risk of excessive exposure to noise related to mass transit ridership, conducting an extensive set of noise measurements of New York City mass transit systems. The findings are available online today in the American Journal of Public Health and will be published in the August 2009 issue.
“Transit-related noise levels are high enough to potentially present a risk of noise-induced hearing loss to some frequent transit riders,” said Richard Neitzel, lead author and research scientist at the University of Washington Department of Environmental and Occupational Health Sciences. “This risk could increase substantially when we account for riders’ other noise exposures from work and recreational activities.”
Noise induced hearing loss, a permanent, irreversible health problem, is estimated to affect more than 30 million people worldwide, and as many as 10 million in the U.S. alone.
Using sensitive noise-measuring instruments called dosimeters, Neitzel and co-authors, including Robyn Gershon, an environmental and occupational health scientist and faculty member at the Columbia University Mailman School of Public Health, measured noise levels at platforms and stations, as well as inside vehicles on New York City subways, buses, ferries, commuter railways and the Roosevelt Island tramway.
The research team found that, on average, MTA subways had the highest average noise levels, at 80.4 decibels (dBA). The lowest average level measured, 75.2 dBA, was obtained from Metro-North trains. The highest individual measurements in the study were found on an MTA subway platform (102.1dBA) and at a bus stop (101.6 dBA).
In contrast, the noise level of a whisper is 30 dBA, normal conversation is 60 to 70 dBA, a chainsaw is 100 dBA, and gunfire is 140 dBA.
Of all mass transit, subways had the highest noise levels, with roughly half of the maximum levels exceeding 90 dBA. “At some of the highest noise levels we obtained (102.1 dBA on the subway platforms), as little as two minutes of exposure per day would be expected to cause hearing loss in some people with frequent ridership,” Gershon said.
The U.S. Environmental Protection Agency and the World Health Organization recommend daily exposures of no more than 70 dBA for a 24-hour average. Noises that register below 70 dBA generally have no impact on hearing health and don’t cause people to exceed the daily recommendations.
“For many people, unless the noise is also considered to be a nuisance, such as noisy neighbors late at night, exposure to most loud noise levels is often not perceived as potentially hazardous, and precautions are rarely taken,” Gershon said. People do not necessarily pay attention, for example, to excessive noise while attending concerts, riding motorcycles or even listening to MP3 players at high volume for extended periods, she added.
Scientists said that noise control efforts, including increased transit infrastructure maintenance and the use of quieter equipment should be a priority. What’s more, the use of personal protection is helpful. Music headphones and earbuds generally do little to reduce noise exposures, and often increase exposures, as users turn up the volume of MP3 players to drown out surrounding noise.
But a variety of earplugs and earmuffs are commercially available, most of which would be sufficient to reduce transit noise exposures to below the recommended limits. “A loss of just 10 decibels in your hearing acuity can damage your ability to hear other people talking,” Neitzel said. “Therefore, protection — and, even better, avoidance of high noise exposure when possible – is the best way to preserve your hearing.”
The research team is following up this study with a large, community–based study of noise exposures from multiple sources to develop even more accurate predictions of noise-induced hearing loss in urban populations.
The study “Noise Levels Associated with New York City’s Mass Transit Systems” was funded by the National Institute of Environmental Health Sciences. Co-authors include Columbia University’s Marina Zeltser, Allison Canton, and Dr. Muhammad Akram.
About the University of Washington Department of Environmental and Occupational Health Sciences, School of Public Health
http://depts.washington.edu/envhlth/
Researchers in the Department of Environmental and Occupational Health Sciences study how environmental factors, such as noise pollution, can harm human health and how to identify, prevent and control these effects. The Department is part of the School of Public Health, which was founded in 1970 and is one of 40 accredited schools of public health in the nation and the only one in the Northwest.
About the Mailman School of Public Health
contact: Stephanie Berger, 212-305-4372 (office)
sb2247@columbia.edu
The only accredited school of public health in New York City and among the first in the nation, Columbia University Mailman School of Public Health pursues an agenda of research, education, and service to address the critical and complex public health issues affecting millions of people locally and globally. The Mailman School is the recipient of some of the largest government and private grants in Columbia University’s history. Its more than 1000 graduate students pursue master’s and doctoral degrees, and the School’s 300 multi-disciplinary faculty members work in more than 100 countries around the world, addressing such issues as infectious and chronic diseases, health promotion and disease prevention, environmental health, maternal and child health, health over the life course, health policy, and public health preparedness.
