How chronic exposure to tiny levels of carbon monoxide damages hearing in young ears

FINDINGS: UCLA scientists have discovered how chronic exposure to low levels of carbon monoxide (CO) damages the inner ear of young rats, resulting in permanent hearing loss. At the Ca/OSHA's exposure limit of 0.0025 percent -- or 25 parts per million CO in the air -- the gas creates oxidative stress, a condition that damages the cochlear cells, leading to impairment of the auditory nerves.

CONTEXT: Tobacco smoke, gas heaters, stoves and ovens all emit CO, which can rise to high concentrations in poorly ventilated homes. Infants and children are particularly vulnerable to CO exposure because they spend a great deal of time in the home. No policies exist to regulate CO in the home. Many commercial home monitors sound an alarm only 20 minutes after CO concentrations reaches 70 parts per million -- nearly three times the 25 parts per million limit set by Cal/OSHA.

IMPACT: This is the first time that inhaled CO has been linked to oxidative stress, a known risk factor in many disorders, including Alzheimer's, Parkinson's, multiple sclerosis, Lou Gherig's disease and cardiovascular disease. Tobacco smoke, which contains CO, aggravates many of these diseases. The UCLA findings highlight the need for policy makers to reexamine the regulation of car exhaust, tobacco smoke, smog, and heating and cooking appliances.

AUTHORS: John Edmond, Ph.D., professor of biological chemistry; Ivan Lopez, Ph.D., assistant professor of head and neck surgery; and Douglas Webber, Ph.D., postdoctoral fellow; at the David Geffen School of Medicine at UCLA, are available for interviews.

JOURNAL: The research appears in the June 1 issue of the Journal of Neuroscience Research.

FUNDING: The University of California's Tobacco-related Disease Research Program and the Stein-Oppenheimer Foundation.

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