Effects of lead and noise exposures on hearing ability

Lead and noise, via different mechanisms, may damage hearing ability, and, in some cases, cause severe and irreversible damage. To explore possible in dependent and synergistic effects of lead and noise on auditory function, t he authors conducted a cross-sectional study in two lead-battery manufactur ing factories. Lead and noise were the two most common sources of occupatio nal exposures in the factories. Blood lead level, ambient lead concentratio n, noise exposure level, and hearing thresholds of 339 lead-battery workers -including clerical and managerial staffs-were measured. The authors obtain ed demographics and working histories via an interview-based structured que stionnaire. A total of 220 lead-battery workers were exposed to high levels of lead and noise; their average blood lead concentration was 56.9 mu g/dl , and their average noise exposure level was 86.0 dBALeq. Multivariate anal ysis, in which possible risk factors of hearing ability were considered, de monstrated a significant correlation between a high, long-term lead exposur e index (defined by duration of employment and ambient lead concentration) and decreased hearing ability. In contrast, such a correlation between shor t-term lead exposure (defined by blood lead level) and hearing ability was not significant. Furthermore, neither noise exposure level alone nor the in teraction between noise exposure level and short- or long-term lead exposur e was correlated significantly with hearing ability. The present study rais es an important, but typically ignored, issue: lead exposure might precipit ate a more severe auditory than noise-exposure effect. The preservation of workers' hearing ability requires that preventive measures be taken against noise exposure, which is as essential as measures taken against lead expos ure.