Assessment of outer hair cell function and blood antioxidant status of rabbits exposed to noise and metal welding fumes.
OBJECTIVE
To investigate the interaction between welding fumes and noise in causation of hearing impairment.


METHODS
Groups of rabbits (n=6) were exposed to noise, welding fumes or combination of both prior to Distortion Product Otoacoustic-Emissions (DPOAEs) analysis. The function of outer hair cells (OHCs) was examined by DPOAE assessment over a broad range of frequencies. Variations in DPOAE amplitude were compared between control (n=6) and exposed (n=18) groups.


RESULTS
The DPOAEs levels measured at different frequencies (1379-6299 Hz) were found to decrease significantly (P<0.05) in rabbits exposed to 110 dB sound pressure level (SPL) broadband noise (8h/day, 12 days). In rabbits, exposed to carbon-steel welding fumes alone (157 mg/m(3)), the threshold shift was limited to the high frequencies (2759-6299 Hz), whereas, mixed exposure to noise and fumes resulted in reduction of DPOAEs at all the frequencies. Changes in DPOAEs were associated with increased susceptibility of erythrocytes to oxidation (P<0.05). Exposure to noise or fumes alone or simultaneously, suppressed total antioxidant ability of plasma as measured by ferric reducing ability of plasma (FRAP). Noise alone or in combination with fumes resulted in depletion of blood glutathione (GSH). Despite suppression of FRAP in the exposed groups, GSH was found to remain unchanged due to welding fumes suggesting that antioxidants other than GSH are affected by toxicants present in metal welding fumes.


CONCLUSIONS
Exposure to very high levels of welding fumes can increase noise-related effects on OHC function by extending hearing threshold shift to wide band frequencies.
Mirzaee
Ramazan
R
Department of Occupational Hygiene, Faculty of Medical Sciences, Tarbiat Modarres University, Tehran, Iran.
Allameh
Abdolamir
A
Mortazavi
Seyed Bagher
SB
Khavanin
Ali
A
Kazemnejad
Anoshirvan
A
Akbary
Mehdi
M
D000395:Air Pollutants, Occupational / Q000633:toxicity*; D000818:Animals; D000975:Antioxidants / Q000378:metabolism*; D005978:Glutathione / Q000097:blood; D018072:Hair Cells, Auditory, Outer / Q000187:drug effects*; D006317:Hearing Loss, Noise-Induced / Q000209:etiology; D015227:Lipid Peroxidation / Q000187:drug effects; D008297:Male; D009622:Noise / Q000009:adverse effects*; D017084:Otoacoustic Emissions, Spontaneous / Q000187:drug effects*; D010898:Pitch Perception / Q000187:drug effects; D011817:Rabbits; D020711:Threshold Limit Values; D014896:Welding
D000395:Air Pollutants, Occupational; D000975:Antioxidants; D005978:Glutathione