Emerging Issues - Research Goal 4
Improve understanding of occupational hearing loss through surveillance
and investigation of risk factors
In the past decade, basic research in hearing science has witnessed the advent of many significant findings. While genetic linkage of specific syndromes has been recognized for several decades, the identification of genetic markers for hearing loss susceptibility is relatively new. Although noise-induced hearing loss has been believed to be an equal-opportunity disease, genetic testing for susceptibility presents practical and ethical issues for the protection of workers in noisy environments. In the area of mixed exposures, the HLR program has been successful in bringing attention to the effects of ototoxic chemical exposure in combination with noise exposures. The European Union, Department of Defense and ACGIH have recognized the potential hazards, but research in mixed exposures to define the risk must continue before it will be possible to establish safe exposure limits. NIOSH can develop recommended exposure limits and provide technical support to regulatory agencies to establish national policy for mixed exposures which cause hearing loss. There continues to be a need to examine the normative data collected by surveillance activities. Due to its representative sampling, NHANES will prove to be valuable in revisiting the risk assessment that is the basis of the standards for occupational hearing loss and the effects of aging. Finally, basic research in functional hearing assessment such as measuring otoacoustic emissions and wide band reflectance of the middle ear may lead to practical techniques to better identify workers that have suffered noise exposure and are at risk of developing hearing loss. Early identification of risk through impaired auditory function can provide the opportunity for a health professional to intervene before hearing loss becomes a permanent reality.
With the cost of digital computing on an ever downward spiral and the capabilities doubling every 18 months, the prospect of developing an “impulse meter” and “impulse dosimeter” is achievable. These hardware tools will allow researchers to better analyze the workers acoustic environment and lead to development of a damage risk criterion for impulsive noise. For the near future these instruments must be experimental and will include a number of proposed metrics including, for example, kurtosis, AHAAH modeling, and analytic wavelet transform.
Establish ongoing surveillance programs for occupational hearing loss and noise exposure; repeat large epidemiologic survey of industry (e.g., the NIOSH National Occupational Exposure Survey of the 1980’s); and collect industry/job task specific noise exposure data.
One of the deficiencies of hearing loss research is the paucity of accurate noise exposure data for workers in a variety of industries. The last attempts at comprehensive noise surveys for large target industries were conducted in the 1970s. New tools must be developed to obtain surveillance data to determine the appropriate target audience (i.e. identify which jobs are at risk) for HLR program activity.
Establish the effectiveness of prophylactic treatments for noise-exposed workers
Cheap, safe and effective prophylactic compounds should be developed for workers who cannot avoid high level noise exposure. These compounds do not substitute for an effective hearing loss prevention program. These compounds interfere with apoptotic events in the inner ear and maintain hearing function. The U.S. Department of Defense is currently looking at such compounds for high noise operations (e.g. combat infantry, pilots). Whether these compounds would remain safe and effective for the entire 30-40 year career of a manufacturing worker or miner is an important question.
Establish recommended exposure limits for mixed exposures of ototoxic chemicals and noise
With acceptance of chemical ototoxicity by the European Union, Australia/New Zealand, the U.S. Army and the American Council of Government Industrial Hygienists (ACGIH), American regulators need to recognize the importance of protecting workers from solvents and noise. Without solid epidemiologic risk assessments, recommendations for regulatory action cannot proceed. NIOSH will continue to work towards better understanding and quantification of the interaction. NIOSH will also continue to encourage rules and regulations to protect workers who might be exposed to both agents in the workplace.