Is There an Ototraumatic Interaction Between Noise and Solvents?

Ototoxicity of hydrocarbons present in gasoline: a literature review

ABSTRACT Purpose: to investigate the toxicity effects of major hydrocarbons present in gasoline on the auditory system and the related mechanisms of action. Methods: a literature review between 2005 and 2015 was conducted using LILACS, MEDLINE and SciELO, by combining descriptors and their respective terms in Portuguese, English and Spanish. Results: studies performed in humans and animals with hearing impairment, confirmed by morphological tests in rats, the influence of factors such as dose, duration, species and type of stimulus in hearing loss, and ineffective protection of workers by the threshold levels of exposure in the mixture of the compounds, were chosen. Conclusion: toluene is regarded as an ototoxic compound that damages outer hair cells in the middle region of the cochlea, with evidence of interaction with noise. Ethylbenzene and xylenes can be considered potentially ototoxic based on the results of animal studies. No sufficient data were found on benzene to form a conclusion.

The Relationship between Occupational Exposure to Lead and Hearing Loss in a Cross-Sectional Survey of Iranian Workers

OBJECTIVES

Ototoxic effect of exposure to lead has been reported by many researchers. This study was undertaken with a view to investigate the relationship between blood lead level (BLL) and hearing loss in workers in a lead-acid battery manufacturing plant in Tehran, Iran.

METHODS

In a cross-sectional study, 609 male workers were recruited from different locations in the factory. Association between BLL and hearing loss in different frequencies were measured. Relationships were analyzed by logistic regressions. Statistical significance was defined as p-value <0.05.

RESULTS

Six hundred nine male workers with mean age 40 ± 7 years and mean noise exposure level of 80 (75-85) dB were evaluated. BLLs were categorized into four quartiles, and hearing loss in each quartile was compared to the first one. In our regression models, BLL was associated significantly with high frequency hearing loss, adjusted odds ratios for the comparison of the fourth, third, and second quartiles to the first one are respectively: 3.98 (95% CI: 1.63-9.71, p < 0.00), 3.05 (95% CI: 1.28-7.26, p < 0.01), and 2.89 (95% CI: 1.11-7.51, p < 0.03).

CONCLUSION

This study showed a dose-response relationship between BLL and hearing loss, after adjusting for potential confounders (age, body mass index, work duration, smoking, and occupational noise exposure) in logistic regressions. It is concluded that periodic hearing assessment by pure tone audiometry in workers exposed to lead should be recommended. However, additional studies are required to clarify the mechanisms of lead ototoxicity.