Effect of noise and ototoxicants on developing standard threshold shifts at a U.S. Air Force depot level maintenance facility

Abstract

Noise exposure has traditionally been considered the primary risk factor for hearing loss. However, ototoxicants commonly found in occupational settings could affect hearing loss independently, additively, or synergistically when combined with noise exposures. The purpose of this investigation was to determine the combined effect of metal and solvent ototoxicants, continuous noise, and impulse noise on hearing loss. Noise and ototoxicant exposure and pure-tone audiometry results were analyzed for U.S. Air Force personnel (n = 2,372) at a depot-level aircraft maintenance activity at Tinker Air Force Base, Oklahoma. Eight similar exposure groups based on combinations of ototoxicant and noise exposure were created including: (1) Continuous noise (reference group); (2) Continuous noise + Impulse noise; (3) Metal exposures + Continuous noise; (4) Metal exposures + Continuous noise + Impulse noise; (5) Solvent exposure + Continuous noise; (6) Solvent exposures + Continuous noise + Impulse noise; (7) Metal exposure + Solvent exposures + Continuous noise; and (8) Metal exposure + Solvent exposures + Continuous noise + Impulse noise. Hearing loss was assessed at center octave band frequencies of 500–6,000 Hz and using National Institute for Occupational Safety and Health Standard Threshold Shift (STS) criteria. Hearing changes were significantly worse at 2,000 Hz in the Metal exposure + Solvent exposure + Continuous noise group compared to the Continuous noise only reference group (p = 0.023). The Metal exposure + Solvent exposure + Continuous noise group had a significantly greater relative risk (RR) of 2.44; 95% CI [1.24, 4.83] for developing an STS at 2,000 Hz. While not statistically significant, the Solvent exposure + Continuous noise group had a RR of 2.32; 95%CI [1.00, 5.34] for developing an STS at 1,000 Hz. These results indicate that noise exposure may dominate hearing loss at ≥3,000 Hz while combined effects of concomitant exposure to ototoxic substances and noise are only noticeable at ≤2,000 Hz. These results also suggest combined exposures to ototoxicants and noise presents a greater hearing loss risk than just noise.

Keywords:

• Continuous noise
• hearing loss
• impulse noise
• metal ototoxicant
• solvent ototoxicant

Acknowledgments

We would like to thank USAF School of Aerospace Medicine (USAFSAM) Epidemiology Consult Service Division for providing the PTA results and USAFSAM’s Occupational and Environmental Health Operations Division (OET) DOEHRS Support Office for chemical and noise stressor information. We wish to thank the 72d Medical Group Bioenvironmental Engineering Flight at Tinker Air Force Base, Oklahoma, for their consultation.

Disclaimer

The authors do not have any financial or personal relationships with organizations that could inappropriately influence the work in this study. The views expressed in this article reflect the results of research conducted by the authors and do not necessarily reflect the official policy or position of the Department of the Navy, Department of the Air Force, Department of Defense, nor the United States Government.

Additional information

Funding

Financial support was provided by 711th Human Performance Wing, Research, Studies, Analysis, and Assessments Council (RSAAC) project #18-015. The sponsor did not influence the study design, collection, analysis, or interpretation of the data.