Potentiation of Noise-Induced Hearing Loss by Low Concentrations of Hydrogen Cyanide in Rats

Details

• Personal Author:
  Chen GD ; Fechter LD ; Johnson, Douglas L.
• Description:
  Noise-induced hearing loss is the most prevalent occupational injury in the United States despite the adoption of clear permissible exposure limits and protocols for hearing conservation. This study identifies low-level chemical asphyxiant exposure as a risk factor capable of potentiating noise-induced hearing loss. Rats were exposed to 10, 30, and 50 ppm hydrogen cyanide (HCN) alone for 3.5 h (n = 28) or in combination with 2 h octave band noise exposure (100 dB(lin); n = 28). Additional groups received noise exposure alone (n = 16) and no treatment other than placement in an inhalation chamber with clean air and quiet (n = 16). Pure tone compound action potential (CAP) thresholds were determined 4 weeks following the exposure in order to assess pure tone auditory sensitivity and permanent threshold impairment. Cochleae from an additional 13 subjects were processed for light microscopy to permit assessment of hair cell loss. The results demonstrate that the noise exposure alone impaired CAP threshold by about 10 dB, averaged between 12-40 kHz, and produced a 5% loss of outer hair cells at the base of the cochlea, but no inner hair cell loss. The combined exposure to noise and HCN caused a cyanide dose-dependent CAP threshold impairment that exceeds the noise exposure alone. This effect reached statistical significance at a HCN level of 30 ppm. Combined exposure also produced more outer hair cell loss than noise alone. HCN alone did not cause significant hearing loss or hair cell loss. A risk assessment analysis was conducted for the auditory threshold data using benchmark dose software published by the U. S. EPA (BMDS version 1.3). A continuous model showed that the data could be described by a linear function. For a benchmark response corresponding to a 5 dB increase in auditory threshold above the effect of noise alone, the lower bound on the 95% confidence interval for the benchmark dose was 9 ppm. The benchmark dose that impaired auditory threshold 10% above the effect of noise alone had a lower bound of 2 ppm. The lower bound to the HCN dose that produced a 1 SD elevation in noise-induced hearing loss was 16 ppm. These exposure levels provide a range of concentrations below to slightly above the short-term exposure limit for HCN. However, if these levels are adjusted for an 8 h time-weighted average (TWA), the resulting levels are below the permissible exposure level (PEL) for HCN. [Description provided by NIOSH]
• Subjects:
  Hearing Hearing Loss, Noise-Induced Noise Noise, Occupational Occupational Health Safety Solvents
• Keywords:
  Audiological Testing Audiometry Auditory Discrimination Auditory Feedback Author Keywords: Hydrogen Cyanide Complex Exposures Hearing Protection Noise Noise-induced Hearing Loss Noise Induced Hearing Loss Organic Solvents Ototoxicity Potentiation Rats Synergistic Effects

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• ISSN:
  1096-6080
• Document Type:
  Text
• Funding:
  Grant
• Genre:
  Journal Article
• Place as Subject:
  Oklahoma ; OSHA Region 6
• CIO:
  National Institute for Occupational Safety and Health (NIOSH)
• Topic:
  Workplace Safety & Health
• Location:
  North America
• Pages in Document:
  131-138
• Volume:
  66
• Issue:
  1
• NIOSHTIC Number:
  nn:20029504
• Citation:
  Toxicol Sci 2002 Mar; 66(1):131-138
• Contact Point Address:
  Laurence D. Fechter, Oklahoma Center for Toxicology, College of Pharmacy, The University of Oklahoma Health Sciences Center, 1110 North Stonewall Street, Room 329, Oklahoma City, Oklahoma 73117
• Email:
  fechter@ouhsc.edu
• CAS Registry Number:
  Carbon monoxide (CAS RN 630-08-0) ; Cyanide (CAS RN 57-12-5)
• Federal Fiscal Year:
  2002
• NORA Priority Area:
  Disease and Injury: Hearing Loss
• Performing Organization:
  University of Oklahoma, Health Sciences Center, Oklahoma Center for Toxicology, Oklahoma City, Oklahoma
• Peer Reviewed:
  True
• Start Date:
  19970901
• Source Full Name:
  Toxicological Sciences
• End Date:
  20000831
• Collection(s):
  National Institute for Occupational Safety and Health
• Main Document Checksum:
  urn:sha-512:f5b3449b1795254aeb7fd0730e66883d0023e47dd60fa034b990c0a8dbf3ddd497e4b041bfe5cd0560302988ebebc0f8ccbc1e769b880fc13c716dab2b95d9a3
• Download URL:
  https://stacks.cdc.gov/view/cdc/190462/cdc_190462_DS1.pdf
• File Type:
  [PDF - 139.23 KB ]