Commentary on the regulatory implications of noise-induced cochlear neuropathy

Abstract

Objective: A discussion on whether recent research on noise-induced cochlear neuropathy in rodents justifies changes in current regulation of occupational noise exposure. Design: Informal literature review and commentary, relying on literature found in the authors’ files. No formal literature search was performed. Study sample: Published literature on temporary threshold shift (TTS) and cochlear pathology, in humans and experimental animals, as well as the regulations of the US Occupational Safety and Health Administration (OSHA). Results: Humans are less susceptible to TTS, and probably to cochlear neuropathy, than rodents. After correcting for inter-species audiometric differences (but not for differences in susceptibility), exposures that caused cochlear neuropathy in rodents already exceed OSHA limits. Those exposures also caused “pathological TTS” (requiring more than 24 h to recover), which does not appear to occur with human broadband noise exposure permissible under OSHA. Conclusion: It would be premature to conclude that noise exposures permissible under OSHA can cause cochlear neuropathy in humans.

Key Words:

• Noise-induced
• neuropathy
• occupational safety and health administration
• temporary threshold shift
• species
• regulation
• permissible exposure limit

Acknowledgements

An earlier version of this paper, with the same title, was presented at the annual meeting of the National Hearing Conservation Association on 20 February 2016, in San Diego, California. This work received no funding or other support other than administrative support from the authors’ universities. The authors thank John H. Mills and M. Charles Liberman for their helpful suggestions regarding a previous draft of this paper.

Declaration of interest

Dr Dobie has consulted for hearing conservation programs, for government agencies and non-profit organizations concerned with occupational noise regulation, and for both plaintiffs and defendants in litigation related to noise-induced hearing loss. He receives royalties from sales of Medical-Legal Evaluation of Hearing Loss (3rd edition, 2015, Plural Publishing). Dr Humes reports no declarations of interest.

Notes

Notes

1. Time‐weighted average (TWA): the sound level (dBA) that, if constant over an 8 h exposure, is presumed to be equally hazardous as the exposure in question. The OHSA PEL uses a 5 dB exchange rate: a 5 dB increase in level is considered to increase hazard as much as a doubling of duration. For example, 90 dBA for 8 h is considered to pose the same hazard as 95 dBA for 4 h. For the literature reviewed in this commentary, we estimated TWA using two calculators available online at www.esion.com: A‐WEIGHT, which converts octave band levels to dBA, and EXPOSURE, which converts dBA and duration to TWA.