Surveillance of noise-induced hearing loss in Taiwan, ROC: a report of the PRESS-NHL results

Association of socioeconomic position with sensory impairment among Chinese population: a nationally representative cohort and Mendelian randomization study

Aims

To investigate the association between socioeconomic position (SEP) and sensory impairments (SIs).

Methods

We used data from the China Health and Retirement Longitudinal Study (CHARLS) (2015). Logistic regressions estimated the odds ratio for associations of SEP with SIs. In addition, Mendelian randomization (MR) analysis was conducted to assess the causal relationship between them with the inverse variance weighting (IVW) estimator. MR-Egger, simple median, weighted median, maximum likelihood, and robust adjusted profile score were employed for sensitivity analyses.

Results

In the observational survey, we enrolled 19,690 individuals aged 45 and above. SEP was negatively associated with SIs. Adjusted odds of vision impairment were higher for illiterate (1.50; 95%CI: 1.19, 1.91), less than elementary school diploma (1.76; 95%CI: 1.39, 2.25), middle school diploma (1.53; 95%CI: 1.21, 1.93) and lower income (all p < 0.001). The odds of hearing impairment were significantly higher for people with less than a high school diploma than those with a college degree or higher diploma, for agricultural workers than non-agricultural workers, and for people in low-income families (p < 0.01). The MR analysis also showed that occupation was associated with HI (1.04, 95%CI: 1.01, 1.09, p < 0.05) using IVW.

Conclusion

We found that both observational and causal evidence supports the theory that SEP can result in SIs and that timely discovery, targeted management, and education can prevent SIs among middle-aged and older adults.

The assessment of exposure to occupational noise and hearing loss for stoneworkers in taiwan

Introduction

Stoneworkers in Taiwan are exposed to occupational noise and suffer hearing impairment. A complete assessment of exposure and health effects is needed for a better understanding.

Materials and Methods

We accessed nine stone factories, monitored the environmental and personal doses of noise, analyzed the frequency spectra of noise from various machines, and recruited 55 stoneworkers and 25 administrative staff as controls for pure tone audiometry testing.

Results

The means (standard deviations) of 8-h time-weighted averages for environmental and personal monitoring were 85.0 (6.2) and 87.0 (5.5) dB(A), respectively, with seven of nine personal measurements being higher than the respective environmental results. The monitoring data suggest that occupational noise in the stonework environments should be a matter of great concern. Nearly all frequency spectra indicated peak values occurring between 2 and 4 kHz, which were within the bands for early noise-induced hearing loss (NIHL). The mean hearing threshold levels of the study participants were elevated in low and high frequencies (29.2 and 41.2 dB) compared to that of controls (∼25 dB for both bands). Linear regression analysis indicated no significance in the low frequencies (P = 0.207) but statistical significance in the high frequencies (P = 0.002) after adjustment for covariates, suggesting NIHL among the stoneworkers.

Conclusion

Stoneworkers apparently display early signs of NIHL. Noises in the stonework factories with peaks in the high frequencies are harmful to hearing ability. Employers and workers have to comply with the regulation strictly to prevent further hearing damage.

The Effects of Earphone Use and Environmental Lead Exposure on Hearing Loss in the Korean Population: Data Analysis of the Korea National Health and Nutrition Examination Survey (KNHANES), 2010-2013

BACKGROUND

Although previous studies have reported that frequent earphone use and lead exposure are risk factors for hearing loss, most of these studies were limited to small populations or animal experiments. Several studies that presented the joint effect of combined exposure of noise and heavy metal on hearing loss were also mainly conducted on occupational workers exposed to high concentration.

OBJECTIVES

We investigated both the individual and joint effects of earphone use and environmental lead exposure on hearing loss in the Korean general population.

METHODS

We analyzed data from 7,596 Koreans provided by the Korea National Health and Nutrition Examination Survey (KNHANES) during the period 2010-2013. The pure-tone average (PTA) of hearing thresholds at 2, 3, and 4 kHz frequencies was computed, and hearing loss was defined as a PTA ≥ 25 dB in one or both ears.

RESULTS

A dose-response relationship in hearing loss with earphone use time and blood lead level is observed after adjustment for confounding factors. With a 1-hour increase in earphone use time and 1 μg/dL increase in blood lead concentration, the odds of hearing loss increased by 1.19 and 1.43 times, respectively. For hearing loss, the additive and multiplicative effect of earphone use and blood lead level were not statistically significant.

CONCLUSIONS

Earphone use and environmental lead exposure have an individual effect on hearing loss in the general population. However, the estimated joint effect of earphone use and lead exposure was not statistically significant.

Predictive factors of occupational noise-induced hearing loss in Spanish workers: A prospective study

The purpose of our study was to identify the main factors associated with objective noise-induced hearing loss (NIHL), as indicated by abnormal audiometric testing, in Spanish workers exposed to occupational noise in the construction industry. We carried out a prospective study in Tenerife, Spain, using 150 employees exposed to occupational noise and 150 age-matched controls who were not working in noisy environments. The variables analyzed included sociodemographic data, noise-related factors, types of hearing protection, self-report hearing loss, and auditory-related symptoms (e.g., tinnitus, vertigo). Workers with pathological audiograms had significantly longer noise-exposure duration (16.2 ± 11.4 years) relative to those with normal audiograms (10.2 ± 7.0 years; t = 3.99, P < 0.001). The vast majority of those who never used hearing protection measures had audiometric abnormalities (94.1%). Additionally, workers using at least one of the protection devices (earplugs or earmuffs) had significantly more audiometric abnormalities than those using both protection measures simultaneously (Chi square = 16.07; P < 0.001). The logistic regression analysis indicates that the use of hearing protection measures [odds ratio (OR) = 12.30, confidence interval (CI) = 4.36-13.81, P < 0.001], and noise-exposure duration (OR = 1.35, CI = 1.08-1.99, P = 0.040) are significant predictors of NIHL. This regression model correctly predicted 78.2% of individuals with pathological audiograms. The combined use of hearing protection measures, in particular earplugs and earmuffs, associates with a lower rate of audiometric abnormalities in subjects with high occupational noise exposure. The use of hearing protection measures at work and noise-exposure duration are best predictive factors of NIHL. Auditory-related symptoms and self-report hearing loss do not represent good indicators of objective NIHL. Routine monitoring of noise levels and hearing status are of great importance as part of effective hearing conservation programs.

Interventions to increase the reporting of occupational diseases by physicians

BACKGROUND

Under-reporting of occupational diseases is an important issue worldwide. The collection of reliable data is essential for public health officials to plan intervention programmes to prevent occupational diseases. Little is known about the effects of interventions for increasing the reporting of occupational diseases.

OBJECTIVES

To evaluate the effects of interventions aimed at increasing the reporting of occupational diseases by physicians.

SEARCH METHODS

We searched the Cochrane Occupational Safety and Health Group Specialised Register, the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE (PubMed), EMBASE, OSH UPDATE, Database of Abstracts of Reviews of Effects (DARE), OpenSIGLE, and Health Evidence until January 2015.We also checked reference lists of relevant articles and contacted study authors to identify additional published, unpublished, and ongoing studies.

SELECTION CRITERIA

We included randomised controlled trials (RCTs), cluster-RCTs (cRCTs), controlled before-after (CBA) studies, and interrupted time series (ITS) of the effects of increasing the reporting of occupational diseases by physicians. The primary outcome was the reporting of occupational diseases measured as the number of physicians reporting or as the rate of reporting occupational diseases.

DATA COLLECTION AND ANALYSIS

Pairs of authors independently assessed study eligibility and risk of bias and extracted data. We expressed intervention effects as risk ratios or rate ratios. We combined the results of similar studies in a meta-analysis. We assessed the overall quality of evidence for each combination of intervention and outcome using the GRADE approach.

MAIN RESULTS

We included seven RCTs and five CBA studies. Six studies evaluated the effectiveness of educational materials alone, one study evaluated educational meetings, four studies evaluated a combination of the two, and one study evaluated a multifaceted educational campaign for increasing the reporting of occupational diseases by physicians. We judged all the included studies to have a high risk of bias.We did not find any studies evaluating the effectiveness of Internet-based interventions or interventions on procedures or techniques of reporting, or the use of financial incentives. Moreover, we did not find any studies evaluating large-scale interventions like the introduction of new laws, existing or new specific disease registries, newly established occupational health services, or surveillance systems. Educational materialsWe found moderate-quality evidence that the use of educational materials did not considerably increase the number of physicians reporting occupational diseases compared to no intervention (risk ratio of 1.11, 95% confidence interval (CI) 0.74 to 1.67). We also found moderate-quality evidence showing that sending a reminder message of a legal obligation to report increased the number of physicians reporting occupational diseases (risk ratio of 1.32, 95% CI 1.05 to 1.66) when compared to a reminder message about the benefits of reporting.We found low-quality evidence that the use of educational materials did not considerably increase the rate of reporting when compared to no intervention. Educational materials plus meetingsWe found moderate-quality evidence that the use of educational materials combined with meetings did not considerably increase the number of physicians reporting when compared to no intervention (risk ratio of 1.22, 95% CI 0.83 to 1.81).We found low-quality evidence that educational materials plus meetings did not considerably increase the rate of reporting when compared to no intervention (rate ratio of 0.77, 95% CI 0.42 to 1.41). Educational meetingsWe found very low-quality evidence showing that educational meetings increased the number of physicians reporting occupational diseases (risk ratio at baseline: 0.82, 95% CI 0.47 to 1.41 and at follow-up: 1.74, 95% CI 1.11 to 2.74) when compared to no intervention.We found very low-quality evidence that educational meetings did not considerably increase the rate of reporting occupational diseases when compared to no intervention (rate ratio at baseline: 1.57, 95% CI 1.22 to 2.02 and at follow-up: 1.92, 95% CI 1.48 to 2.47). Educational campaignWe found very low-quality evidence showing that the use of an educational campaign increased the number of physicians reporting occupational diseases when compared to no intervention (risk ratio at baseline: 0.53, 95% CI 0.19 to 1.50 and at follow-up: 11.59, 95% CI 5.97 to 22.49).

AUTHORS' CONCLUSIONS

We found 12 studies to include in this review. They provide evidence ranging from very low to moderate quality showing that educational materials, educational meetings, or a combination of the two do not considerably increase the reporting of occupational diseases. The use of a reminder message on the legal obligation to report might provide some positive results. We need high-quality RCTs to corroborate these findings.Future studies should investigate the effects of large-scale interventions like legislation, existing or new disease-specific registries, newly established occupational health services, or surveillance systems. When randomisation or the identification of a control group is impractical, these large-scale interventions should be evaluated using an interrupted time-series design.We also need studies assessing online reporting and interventions aimed at simplifying procedures or techniques of reporting and the use of financial incentives.

Noise-induced hearing loss in small-scale metal industry in Nepal

Background:

There has been no previous research to demonstrate the risk of noise-induced hearing loss in industry in Nepal. Limited research on occupational noise-induced hearing loss has been conducted within small-scale industry worldwide, despite it being a substantial and growing cause of deafness in the developing world.

Method:

The study involved a cross-sectional audiometric assessment, with questionnaire-based examinations of noise and occupational history, and workplace noise level assessment.

Results:

A total of 115 metal workers and 123 hotel workers (control subjects) were recruited. Noise-induced hearing loss prevalence was 30.4 per cent in metal workers and 4.1 per cent in hotel workers, with a significant odds ratio of 10.3. Except for age and time in occupation, none of the demographic factors were significant in predicting outcomes in regression analyses. When adjusted for this finding, and previous noise-exposed occupations, the odds ratio was 13.8. Workplace noise was significantly different between the groups, ranging from 65.3 to 84.7 dBA in metal worker sites, and from 51.4 to 68.6 dBA in the control sites.

Conclusion:

Metal workers appear to have a greater risk of noise-induced hearing loss than controls. Additional research on occupational noise-induced hearing loss in Nepal and small-scale industry globally is needed.

Noise-induced hearing loss in Korean workers: co-exposure to organic solvents and heavy metals in nationwide industries

Background

Noise exposure is a well-known contributor to work-related hearing loss. Recent biological evidence suggests that exposure to ototoxic chemicals such as organic solvents and heavy metals may be additional contributors to hearing loss. However, in industrial settings, it is difficult to determine the risks of hearing loss due to these chemicals in workplaces accompanied by excessive noise exposure. A few studies suggest that the effect of noise may be enhanced by ototoxic chemicals. Therefore, this study investigated whether co-exposure to organic solvents and/or heavy metals in the workplace modifies the risk of noise exposure on hearing loss in a background of excessive noise.

Methods

We examined 30,072 workers nationwide in a wide range of industries from the Korea National Occupational Health Surveillance 2009. Data on industry-based exposure (e.g., occupational noise, heavy metals, and organic solvents) and subject-specific health outcomes (e.g., audiometric examination) were collected. Noise was measured as the daily 8-h time-weighted average level. Air conduction hearing thresholds were measured from 0.5 to 6 kHz, and pure-tone averages (PTA) (i.e., means of 2, 3, and 4 kHz) were computed.

Results

In the multivariate linear model, PTA increment with occupational noise were 1.64-fold and 2.15-fold higher in individuals exposed to heavy metals and organic solvents than in unexposed individuals, respectively.

Conclusion

This study provides nationwide evidence that co-exposure to heavy metals and/or organic solvents may exacerbate the effect of noise exposure on hearing loss in workplaces. These findings suggest that workers in industries dealing with heavy metals or organic solvents are susceptible to such risks.

Determinants of bilateral audiometric notches in noise-induced hearing loss

OBJECTIVES/HYPOTHESIS

To explore the possible determinants of bilateral audiometric notches in noise-induced hearing loss (NIHL).

STUDY DESIGN

Prospectively enrolled cohort with cross-sectional analysis.

METHODS

Male workers (n = 412) with exposure to continuous loud noise (noise exposure level normalized to a nominal 8-hour working day >75 dBA) during work were included in this cohort study. The relationship between the presence of bilateral audiometric notches and age, noise exposure duration, noise exposure level, and shift from the predicted thresholds over different frequencies were determined by regression model analysis, receiver operating characteristic analysis, and area under the curve analysis.

RESULTS

The presence of bilateral audiometric notches was closely associated with the shifts from the predicted thresholds over 1, 2, 3, 4, and 6 kHz. The shift pattern was somewhat different between those who used hearing protection devices and those who did not. The shifts from the predicted thresholds demonstrated a stronger association with bilateral audiometric notches than did age, gender, noise exposure level, or noise exposure duration.

CONCLUSIONS

The bilateral audiometric notches in NIHL could not be determined only on the basis of age, gender, noise exposure level, or noise exposure duration. The importance of other factors associated with bilateral audiometric notches should be recognized. Elucidation of the factors of formation of bilateral audiometric notches would help us to develop a more comprehensive protection strategy to prevent further NIHL.

10-Year prospective study of noise exposure and hearing damage among construction workers

OBJECTIVES

To characterise the effects of noise exposure, including intermittent and peaky exposure, on hearing damage as assessed by standard pure-tone thresholds and otoacoustic emissions, a longitudinal study was conducted on newly hired construction apprentices and controls over a 10-year period.

METHODS

Among the 456 subjects recruited at baseline, 316 had at least two (mean 4.6) examinations and were included in this analysis. Annual examinations included hearing threshold levels (HTLs) for air conducted pure tones and distortion product otoacoustic emission (DPOAE) amplitudes. Task-based occupational noise exposure levels and recreational exposures were estimated. Linear mixed models were fit for HTLs and DPOAEs at 3, 4 and 6 kHz in relation to time since baseline and average noise level since baseline, while controlling for hearing level at baseline and other risk factors.

RESULTS

Estimated L(EQ) noise exposures were 87±3.6 dBA among the construction workers. Linear mixed modelling demonstrated significant exposure-related elevations in HTL of about 2-3 dB over a projected 10-year period at 3, 4 or 6 kHz for a 10 dB increase in exposure. The DPOAE models (using L1=40) predicted about 1 dB decrease in emission amplitude over 10 years for a 10 dB increase in exposure.

CONCLUSIONS

The study provides evidence of noise-induced damage at an average exposure level around the 85 dBA level. The predicted change in HTLs was somewhat higher than would be predicted by standard hearing loss models, after accounting for hearing loss at baseline. Limited evidence for an enhanced effect of high peak component noise was observed, and DPOAEs, although similarly affected, showed no advantage over standard hearing threshold evaluation in detecting effects of noise on the ear and hearing.

Trends in late-life disability in Taiwan, 1989-2007: the roles of education, environment, and technology

This analysis offers the first strong evidence of trends in late-life disability in an emerging economy. For the population of Taiwan aged 65 and older, consistent measures of limitations in seeing, hearing, physical functions, instrumental activities of daily living (IADLs), and activities of daily living (ADLs) were available for three to six survey waves, depending on the outcome, from 1989 to 2007. Limitations in seeing, hearing, and IADLs declined substantially, but trends were mixed for physical functions and flat for ADLs. The remarkable reduction in difficulty telephoning, an IADL, may reflect changes in telecommunications infrastructure and highlights the roles of environment and technology in disability outcomes. Trends for urban residents were more advantageous than those for rural residents for seeing and hearing, but less so for physical functions and IADLs. Were it not for the substantial increase in educational attainment, trends in all outcomes would have been less favourable.

Longitudinal assessment of noise exposure in a cohort of construction workers

OBJECTIVES

To address questions surrounding noise-induced hearing loss (NIHL) from variable noise, we have been evaluating noise exposures and changes in hearing in a prospective cohort of construction workers (representing eight trades) and controls. In this paper, we develop and explore several long-term exposure estimates for cohort members.

METHODS

We followed cohort members between 1999 and 2009 and interviewed them approximately annually to obtain a detailed work history for the previous subject-interval while also collecting tests of hearing sensitivity. Over the same period, we also collected a sample of full-shift average noise measurements and activity information. We used data from these two sources to develop various exposure estimates for each subject for specific subject intervals and for the duration of the study. These estimates included work duration, trade-mean (TM)-equivalent continuous exposure level (L(EQ)), task-based (TB) L(EQ), a hybrid L(EQ) combining TB and subjective information, and an estimate of noise exposure 'peakiness'.

RESULTS

Of the 456 subjects enrolled in the study, 333 had at least 2 interviews and met several inclusion criteria related to hearing sensitivity. Depending on the metric used, between one-third and three-quarters of 1310 measured full-shift noise exposures exceeded permissible and recommended exposure limits. Hybrid and TB exposure estimates demonstrated much greater variability than TM estimates. Work duration and estimates of exposure peakiness showed poor agreement with average exposures, suggesting that these metrics evaluate different aspects of exposure and may have different predictive value for estimating NIHL.

CONCLUSIONS

Construction workers in the cohort had subject-interval and study-average exposures which present a substantial potential risk of NIHL. In a subsequent paper, we will use these estimates to evaluate the exposure-response relationship between noise and NIHL.

Noise-induced hearing loss in Asia

The aim of this manuscript is to summarize the current scenarios encompassing noise exposure in the workplace and the risk of noise-induced hearing loss (NIHL) in Asia. NIHL is the most prevalent and preventable occupational disease in most Asian countries. Sources of noise in these countries include manufacturing and agriculture industries, exploitation of natural resources, and urban traffic. The highest attributable fraction of adult-onset hearing loss resulting from noise exposure in the world comes from Asian countries. NIHL is a serious health problem in Asia, not only because of the number of affected labourers, but also because the majority of Asian countries are still developing economies where access to health services and preventive programmes are limited. Lack of awareness about NIHL among employers, employees, and health care professionals is one of the main barriers for the prevention of NIHL in Asia. In this paper, the sources of noise, NIHL prevalence in different industries, local legislation, and research publications on NIHL from Asia are discussed.

Prevalence and risk factors of noise-induced hearing loss among liquefied petroleum gas (LPG) cylinder infusion workers in Taiwan

We assessed the exposure levels of noise, estimated prevalence, and identify risk factors of noise-induced hearing loss (NIHL) among male workers with a cross-sectional study in a liquefied petroleum gas cylinder infusion factory in Taipei City. Male in-field workers exposed to noise and administrative controls were enrolled in 2006 and 2007. Face-to-face interviews were applied for demographics, employment history, and drinking/smoking habit. We then performed the measurements on noise levels in field and administration area, and hearing thresholds on study subjects with standard apparatus and protocols. Existence of hearing loss > 25 dBHL for the average of 500 Hz, 1 kHz, and 2 kHz was accordingly determined for NIHL. The effects from noise exposure, predisposing characteristics, employment-related factors, and personal habits to NIHL were estimated by univariate and multivariate logistic regressions. A total of 75 subjects were involved in research and 56.8% of in-field workers had NIHL. Between the in-field and administration groups, hearing thresholds on the worse ear showed significant differences at frequencies of 4 k, 6 k, and 8 kHz with aging considered. Adjusted odds ratio for field noise exposure (OR=99.57, 95% CI: 3.53, 2,808.74) and frequent tea or coffee consumption (OR=0.03, 95% CI: 0.01, 0.51) were found significant. Current study addressed NIHL in a specific industry in Taiwan. Further efforts in minimizing its impact are still in need.

The effectiveness of hearing protection among construction workers

Effective hearing conservation programs in the construction industry are rare. Where programs are present, they often rely on workers' use of hearing protection devices (HPDs) rather than on exposure controls to reduce noise exposure levels. Dependence on HPDs for protection from high noise is problematic, as the protection provided by the HPD depends on both the HPD's attenuation level and the time the HPD is used. This article presents an analysis of data on noise exposure and hearing protection among construction workers drawn from several large datasets covering nine construction trades. A unique combination of 1-min dosimetry noise exposure levels and simultaneous self-reported use of HPDs was evaluated, as were occupational and nonoccupational HPD use data collected by questionnaire as part of a longitudinal study of noise exposure and hearing loss among apprentices. Direct measurements of HPD attenuation were also made on workers at their work site. The workers assessed in this study were found to use hearing protection less than one-quarter of the time that they were exposed above 85 dBA. Workers who reported always using HPDs in high noise on questionnaires were found to wear them only one-third of the time their exposures exceeded 85 dBA. Workers' self-reported use of HPDs during most noisy nonoccupational activities was also found to be low. Direct attenuation measurements found that workers were able to achieve more than 50% of the rated attenuation of their HPD on average, but that the variability in achieved attenuation was large. When the measured HPD attenuation levels and use time data were combined, the effective protection afforded by HPDs was less than 3 dB, a negligible amount given the high exposure levels associated with construction work. However, there was substantial variation in effective protection among the different trades assessed. These results demonstrate the need for better hearing conservation programs and expanded noise control efforts in the construction industry.

Hearing loss among workers at an oil refinery in Taiwan

In this study, the authors determined the characteristics of noise-induced hearing loss (NIHL) and its association with hearing-loss-related symptoms (HLRSs) among workers at an oil refinery in Taiwan. Workers from the refinery (N = 384) who had chronic noise exposure (range = 73 to 89 dBa; mean = 81.2, standard deviation = 5.4 dBa) were enrolled in the study. Workers chronically exposed to noise levels that were less than 85 dBa experienced slight hearing loss at high frequencies [(3k + 4k + 6k)/3]. Workers with > or = 1 HLRSs had increased hearing loss at low frequencies [(0.5k + 1k + 2k)/3] and high frequencies (odds ratios = 7.2 and 3.7, respectively). An increased hearing threshold shift for high frequencies (3k, 4k, and 6k Hz) was found in workers who had chronic noise exposure for more than 15 yr. These findings indicate that self-reported HLRSs provide valuable early warning signs of NIHL.

Relationship between blood lead concentrations and learning achievement among primary school children in Taiwan

Over the past 20 years lead has been proven to exert an influence on the intelligence of children. Especially for children exposed to environmental lead, average blood lead was often lower than the officially recognized intoxication level. Because Kaohsiung is an industrial area in Taiwan and lead exposure is an important environmental issue, we attempted to ascertain the extent to which environmental lead influences the achievement of primary school children. We randomly selected 934 children from 32 primary schools in 11 districts of Kaohsiung City. Blood lead levels of the children were checked, and they were administered a questionnaire about their family information. Scores of several courses were used in this study on the relationship between a child's blood lead and his or her academic performance (Ranking with his or her classmates), including Chinese (reading and writing short Chinese articles), Mathematics, History and Society, and Natural Science. Multiple regression models were done with adjustments for the confounding effects of their parents' socioeconomic levels. The mean (SD) of 934 blood lead level was 5.50 (1.86) microg/dL. Spearman's coefficient showed that class rankings in Chinese, Mathematics, Natural Science, and History and Society were all strongly associated with blood lead levels (P<0.01). The multiple regression models revealed that blood lead level exerts a stronger influence on children's language ability (Chinese) than on their ability to calculate (Mathematics). Our results suggest that environmental lead exposure adversely affects a child's academic achievement, making a direct link between exposure to lead and academic attainment.

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 independent and synergistic effects of lead and noise on auditory function, the authors conducted a cross-sectional study in two lead-battery manufacturing factories. Lead and noise were the two most common sources of occupational exposures in the factories. Blood lead level, ambient lead concentration, noise exposure level, and hearing thresholds of 339 lead-battery workers-including clerical and managerial staffs-were measured. The authors obtained demographics and working histories via an interview-based structured questionnaire. A total of 220 lead-battery workers were exposed to high levels of lead and noise; their average blood lead concentration was 56.9 microg/dl, and their average noise exposure level was 86.0 dBALeq. Multivariate analysis, in which possible risk factors of hearing ability were considered, demonstrated a significant correlation between a high, long-term lead exposure index (defined by duration of employment and ambient lead concentration) and decreased hearing ability. In contrast, such a correlation between short-term lead exposure (defined by blood lead level) and hearing ability was not significant. Furthermore, neither noise exposure level alone nor the interaction between noise exposure level and short- or long-term lead exposure was correlated significantly with hearing ability. The present study raises an important, but typically ignored, issue: lead exposure might precipitate 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 exposure.