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Study examines impacts of noise and chemical exposure on hearing health

Research audiologist Dr. Rozela Melgoza, DoD Hearing Center of Excellence, completes a study participant's acoustic immittance test to evaluate their middle ear function. Immittance audiometry is one of several tests completed by participants during the Noise Outcomes in Servicemembers Epidemiology (NOISE) study's comprehensive audiologic evaluation. (DoD HCE photo) Research audiologist Dr. Rozela Melgoza, DoD Hearing Center of Excellence, completes a study participant's acoustic immittance test to evaluate their middle ear function. Immittance audiometry is one of several tests completed by participants during the Noise Outcomes in Servicemembers Epidemiology (NOISE) study's comprehensive audiologic evaluation. (DoD HCE photo)

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Scientists are studying the possible long-term effects of exposure to high levels of noise and certain chemicals on the auditory functioning among active-duty Service members and Veterans.

Called the Noise Outcomes in Servicemembers Epidemiology, or NOISE study, one objective of the project is to clarify the correlation between hearing injury and exposure to non-pharmaceutical chemical agents used in military operations. These can include solvents like toluene, xylene, styrene, and hydrocarbon blends found in jet fuel, as well as metals and asphyxiants in welding fumes and vehicle exhaust.

According to the Occupational Safety and Health Administration, exposure to certain chemicals, called ototoxicants, can cause hearing loss or balance problems. The risk of hearing loss may be magnified when workers are exposed to these chemicals while working around elevated noise levels.

A first-of-its-kind in the Department of Defense, the NOISE study is a collaboration between the Department of Veterans Affairs (VA), National Center for Rehabilitative Auditory Research (NCRAR) in Portland, Oregon, and the DoD Hearing Center of Excellence (HCE) at Joint Base San Antonio, Texas. Researchers are collecting data on service members during their active duty time and into their post-military lives.

“The long-term intent is to collect data from subjects for 20-plus years to observe changes in their hearing and tinnitus and associate those changes with numerous different variables,” said Dr. James Henry, NOISE study principal investigator with the VA’s NCRAR.

In addition to undergoing comprehensive audiologic assessments for the study, participants fill out extensive questionnaires about their medical history and military exposures. Participants are also completing an analysis called the Lifetime Exposure to Noise and Solvents Questionnaire (LENS-Q), which documents their military occupational, non-military occupational, and recreational exposures to both noise and chemicals.

When analyzing the data, researchers will evaluate the prevalence of chemical exposures across demographic categories and examine the relationship, if any, between those exposures and injury risk. They will also identify factors related to any identified effects of chemical exposures on auditory injuries, including any possible significant differences between individuals with higher versus lower noise exposures, as determined by objective and subjective hearing and tinnitus problems.

Henry said researchers are in the early stages of looking at the data, and to date have enrolled more than 600 participants, including Veterans through NCRAR in Portland and active-duty service members in the San Antonio area. He added that the team will soon provide a full analysis of the data collected so far from the participants.

Additional research into the long-term effects of noise and chemical exposure is anticipated, with the plan to conduct hearing tests to measure future audiometric outcomes in the NOISE study participants.

“A study of this magnitude will give us more definitive information about the hearing health of our service members, which can then be used to develop future hearing loss prevention programs, hearing protection devices and other protective equipment to safeguard service members,” said Dr. Carlos Esquivel, NOISE study principal investigator for the HCE.

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