title: The Relationship between Occupational Exposure to Lead and Hearing Loss in a Cross-Sectional Survey of Iranian Workers.
abstract: OBJECTIVE
  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).
  
  
  CONCLUSIONS
  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.
authors.affiliation: Forensic and Toxicology Department, Iran University of Medical Sciences , Tehran , Iran.
authors.forename: Masoumeh
authors.initials: M
authors.lastname: Ghiasvand
authors.affiliation: Occupational Medicine Department, Iran University of Medical Sciences , Tehran , Iran.
authors.forename: Saber
authors.initials: S
authors.lastname: Mohammadi
authors.affiliation: Division of Medical Toxicology, Department of Emergency Medicine, UT Southwestern Medical Center , Dallas, TX , USA.
authors.forename: Brett
authors.initials: B
authors.lastname: Roth
authors.affiliation: Medical School, Iran University of Medical Sciences , Tehran , Iran.
authors.forename: Mostafa
authors.initials: M
authors.lastname: Ranjbar
keywords: blood lead level; hearing loss; lead ototoxicity; pure tone audiometry