Hearing loss among workers exposed to moderate concentrations of solvents.

OBJECTIVES: It is known that some industrial organic solvents are ototoxic. This study was aimed at evaluating the hearing effects of a mixture of organic solvents alone or in combination with noise on employees in paint and lacquer enterprises. The concentration of solvents was below the occupational exposure limits (OEL) for most of the subjects. METHODS: Altogether 517 subjects were divided into the following three groups: persons with no risk due to noise or organic solvent exposure at the workplace, workers exposed to organic solvents only, and workers exposed to both organic solvents and noise. RESULTS: The relative risk (RR) of hearing loss in the solvent-only exposure group was significantly increased (RR 4.4 and RR 2.8 for noise exposure of < 80 dB-A and < 85 dB-A, respectively) in a wide range of frequencies (2-8 kHz). No additional risk in the solvent + noise exposure group was found (RR 2.8). Hearing thresholds were significantly poorer in a wide range of frequencies (1-8 kHz) for both groups exposed to solvents, when compared with the reference group. The mean hearing thresholds at frequencies of 2-4 kHz were poorer for workers exposed to solvents + noise than for the solvent-only group; this finding suggests an additional effect for noise. However, there was no correlation between hearing loss and the extent of solvent exposure. CONCLUSIONS: The results indicate that occupational organic solvent exposure at moderate concentrations increases the risk of hearing loss, and the ototoxic effects should be considered when the health effects of exposed workers are monitored.     

Audiometric pattern in a group of workers with one ear conductive deafness exposed to continuous noise

BACKGROUND: It is common to find workers in developing countries having residual ear problems from childhood affections. When exposed to continuous noise in industry, they might exhibit different patterns of audiometric findings. The aim of this study was to examine the good ear in a group of workers exposed to continuous noise in textile industry with a perforated drum in the other ear from childhood otitis media. METHODS: a 1:2 case control design involving a group of 36 cases and 2 matched groups, same age and duration of exposure was performed. A relevant questionnaire was used and each worker was subjected to an audiometric test. RESULTS: significantly worse hearing threshold levels at the 250 Hz and the 4 kHz frequencies were obtained for the good ears of cases compared to controls. Subjective complaints were also commoner. A different pattern of hearing loss was found adding to the auditory risk of the involved workers.     

High-frequency (10-18 kHz) hearing thresholds: reliability, and effects of age and occupational noise exposure.

The objective was to investigate the reliability and effects of age and noise on high-frequency hearing thresholds. A cross-sectional study was used involving 187 exposed and 52 non-industrial noise-exposed subjects selected randomly from noise-exposed and non-industrial noise-exposed subjects, respectively. Each subject was tested with both conventional-frequency (0.25-8 kHz) and high-frequency (10-18 kHz) audiometry. Test-retest results showed that high-frequency audiometry (HFA) was as reliable as the conventional procedure. Although the inter-subject variation was large, the intra-subject variation was small, indicating that HFA can be used more reliably than the conventional procedure to monitor individual cases over time. Both the hearing threshold at high frequencies and the upper frequency limit deteriorated as a function of age and frequency. The exposed subjects had significantly higher hearing thresholds than the non-exposed subjects at all the high frequencies tested, the difference between the two groups being greatest at 14 kHz. Multivariate analysis indicated that age was the primary predictor and noise exposure the secondary predictor of hearing thresholds in a high frequency range (10-18 kHz). In contrast, multivariate analysis indicated the reverse order-noise exposure as the primary predictor, then age-for a conventional frequency range (0.25-8 kHz). The results of this study suggest that HFA might be used as an early indicator for noise-induced hearing loss and acoustic trauma rather than audiometry at a conventional frequency (4 kHz), particularly for younger groups.     

Occupational noise exposure and hearing loss of workers in two plants in eastern Saudi Arabia.

OBJECTIVE: To determine the prevalence of hearing loss associated with occupational noise exposure and other risk factors. DESIGN: A cross-sectional study involving 269 exposed and 99 non-exposed subjects (non-industrial noise exposed subjects) randomly selected. Current noise exposure was estimated using both sound level meter and noise-dosimeter. Past noise exposure was estimated by interview questionnaire. Otoscopic examination and conventional frequency (0.25-8 kHz) audiometry were used to assess the hearing loss in each subject. RESULTS: 75% (202 subjects) from the exposed group were exposed to a daily Leq above the permissible level of 85 dB(A) and most (61%) of these did not and had never used any form of hearing protection. Hearing loss was found to be bilateral and symmetrical in both groups. Bivariate analysis showed a significant hearing loss in the exposed vs non-exposed subjects with a characteristic dip at 4 kHz. Thirty eight percent of exposed subjects had hearing impairment, which was an 8-fold higher rate than that found for non-exposed subjects. Multivariate analysis indicated exposure to noise was the primary, and age the secondary predictor of hearing loss. Odds of hearing impairment were lower for a small sub-group of exposed workers using hearing protection (N=19) in which logistic regression analysis showed the probability of workers adopting hearing protective devices increased with noise exposure, education, and awareness of noise control. Hearing loss was also greater amongst those who used headphones to listen to recorded cassettes. CONCLUSION: Gross occupational exposure to noise has been demonstrated to cause hearing loss and the authors believe that occupational hearing loss in Saudi Arabia is a widespread problem. Strategies of noise assessment and control are introduced which may help improve the work environment.     

Hearing thresholds in an auto assembly plant: prospects for hearing conservation in an Nigerian factory

Summary The hearing of 165 auto assembly workers exposed to noise levels of between 94 and 108 dB was assessed by means of air and bone conductance audiograms obtained during peak and low production periods to determine acute shifts in hearing. Compared to non-industrially exposed and non-production subgroups, the exposed subjects had significantly (P < 0.001) elevated thresholds at both peak and low production periods. There was an acute and significant (P < 0.001) drop in the hearing thresholds of the exposed subjects during low production period. This was especially true of cross-sections of the exposed subjects and of a cohort specifically sampled at both high and low production periods. Hearing thresholds for the exposed subjects increased with both age and duration of employment and were significantly correlated with duration of employment (P < 0.05). Of all the confounders (age, duration of employment, residential density) assessed by stepwise multiple regression analysis, duration of employment was the only significant contributor to the threshold shift. There was no conductive deafness among the study subjects. There was no consistent association between blood pressure and either hearing threshold or noise level. The results indicate good prospects for hearing conservation for Nigeria workers if hearing protection and noise abatement programs, currently not mandated by statutes, can be instituted.     

Hearing loss in workers exposed to toluene and noise

In this study we investigated the risk of hearing loss among workers exposed to both toluene and noise. We recruited 58 workers at an adhesive materials manufacturing plant who were exposured to both toluene and noise [78.6-87.1 A-weighted decibels; dB(A)], 58 workers exposed to noise only [83.5-90.1 dB(A)], and 58 administrative clerks [67.9-72.6 dB(A)] at the same company. We interviewed participants to obtain sociodemographic and employment information and performed physical examinations, including pure-tone audiometry tests between 0.5 and 6 kHz. A contracted laboratory certified by the Council of Labor in Taiwan conducted on-site toluene and noise exposure measurements. The prevalence of hearing loss of >or=25 dB in the toluene plus noise group (86.2%) was much greater than that in the noise-only group (44.8%) and the administrative clerks (5.0%) (p<0.001). The prevalence rates were 67.2, 32.8, and 8.3% (p<0.001), respectively, when 0.5 kHz was excluded from the estimation. Multivariate logistic regression analysis showed that the toluene plus noise group had an estimated risk for hearing loss>or=25 dB, 10.9 times higher than that of the noise-only group. The risk ratio dropped to 5.8 when 0.5 kHz was excluded from the risk estimation. Hearing impairment was greater for the pure-tone frequency of 1 kHz than for that of 2 kHz. However, the mean hearing threshold was the poorest for 6 kHz, and the least effect was observed for 2 kHz. Our results suggest that toluene exacerbates hearing loss in a noisy environment, with the main impact on the lower frequencies.     

Ototoxic effects of occupational exposure to styrene and co-exposure to styrene and noise

Ototoxicity of styrene and the synergistic action of styrene and noise have been shown in rats. The respective data in humans are scarce and equivocal. This study evaluated the effects of occupational exposure to styrene and combined exposures to styrene and noise on hearing. The study group, comprised of 290-yacht yard and plastic factory workers, was exposed to a mixture of organic solvents, having styrene as its main compound. The reference group, totaling 223 subjects, included (1) white-collar workers, exposed neither to solvents nor noise and (2) metal factory workers, exposed exclusively to noise. All subjects were assessed by means of a detailed questionnaire and underwent otorhinolaryngological and audiometric examinations. Multiple logistic regression analysis revealed almost a 4-fold (or 3.9; 95% CI = 2.4-6.2) increase in the odds of developing hearing loss related to styrene exposure. The factors adjusted for were: age, gender, current occupational exposure to noise, and exposure to noise in the past. In cases of the combined exposures to styrene and noise, the odds ratios were two to three times higher than the respective values for styrene-only and noise-only exposed subjects. The mean hearing thresholds--adjusted for age, gender, and exposure to noise--were significantly higher in the solvent-exposed group than in the unexposed reference group at all frequencies tested. A positive linear relationship existed between an averaged working life exposure to styrene concentration and a hearing threshold at the frequencies of 6 and 8 kHz. This study provides the epidemiological evidence that occupational exposure to styrene is related to an increased risk of hearing loss. Combined exposures to noise and styrene seem to be more ototoxic than exposure to noise alone.     

The Nord-Trøndelag Norway Audiometric Survey 1996-98: unscreened thresholds and prevalence of hearing impairment for adults > 20 years

As supplement to a general health screening examination (HUNT-II), we conducted a puretone audiometry study in 1996-98 on adults (>20 years) in 17 of 23 municipalities in Nord-Tr?ndelag, Norway, including questionnaires on occupational and leisure noise exposure, medical history, and symptoms of hearing impairment. The study aims to contribute to updated normative hearing thresholds for age and gender, while evaluating the effects of noise exposure, medical history, and familial or genetic influences on hearing. This paper presents the unscreened hearing threshold data and prevalence of hearing impairment for different age groups and by gender. Valid audiometric data were collected from 62% (n=50,723) of 82,141 unscreened invited subjects (age-range 20-101 years, mean=50.2 years, SD=17.0 years). Two ambulant audiometric teams each conducted 5 parallel self-administered, pure-tone hearing threshold examinations with the standard test frequencies 0.25-0.5-1-2-3-4-6-8 kHz (manual procedure when needed). Tracking audiometers were used in dismountable booths with in-booth noise levels well within ISO criteria, except being at the criterion around 200 Hz. The data were electronically transferred to a personal computer. Test-retest correlations for 99 randomly drawn subjects examined twice were high. The mean thresholds recorded were some dB elevated from "audiometric zero" even for age group 20-24 years. As also found in other studies, this might indicate too restrictive audiometric reference thresholds. Males had slightly better hearing < or =0.5 kHz for all age groups. Mean thresholds were poorer in males > or = 30 years from > or =2 kHz, with maximal gender differences of approximately 20 dB at 3-4 kHz for subjects aged 55-74 years. Weighted prevalence data averaged over 0.5-1-2-4 kHz showed hearing impairment >25 dB hearing threshold level of 18.8% (better ear) and 27.2% (worse ear) for the total population--for males 22.2% and 32.0%, for females 15.9% and 23.0%, respectively. Mean hearing loss > or =10 dB at 6 kHz registered for both genders even in age groups 20-24 years may be partly due to calibration artefacts, but might possibly also reflect noise-related socio-acusis.     

High-frequency hearing risk of operators of industrial ultrasonic devices

Summary Sound and ultrasound emitted by industrial ultrasonic (Uls) devices exceed the known proposed hygienic limits, especially for frequencies 10–20 kHz. The consequence of this may be a negative influence of this energy on the auditory function in the high-frequency hearing range. To determine the hearing risk to Uls operators, an adequate method for testing the hearing threshold from 10-20 kHz has been developed. In order to get reference values, 189 non-exposed persons were tested. On this basis, the hearing thresholds of 55 operators for frequencies 500–20,000 Hz were evaluated. In addition to threshold elevations in the range 10–20 kHz, a decreasing number of subjects responding to stimuli at the highest audible frequencies was observed. The threshold shift at 10–20 kHz of subjects exposed to sound and ultrasound emitted by Uls-devices depends upon the physical parameters of the sound spectrum, time on the job and daily exposure time. No abnormalities were found in the hearing range 500–8000 Hz.     

The accuracy of self-reported high noise exposure level and hearing loss in a working population in Eastern Saudi Arabia

Objective: To determine the accuracy of questions in identifying subjects occupationally exposed to high noise level and those with hearing loss using noise dosimeter and pure-tone air conduction audiometry as the gold standards.Design: A cross-sectional study involving 259 noise-exposed workers selected randomly from two factories in Eastern Saudi Arabia. Personal noise exposure was determined using a noise dosimeter. The hearing impairment for each subject was assessed using otoscopic examination and audiometry. Each subject completed a comprehensive questionnaire including questions about noise exposure and hearing loss.Results: Eighty five percent of the total workers reported exposure to high noise level, compared to 76% found to be exposed to a high noise level defined as more than 85dB (A) as determined by noise dosimeter. The prevalence of audiometric hearing loss (threshold average of 25dB HL or more in any ear) was 32.4% for the low frequency average (0.5, 1 and 2kHz), 47.9% for the all frequency average (0.5, 1, 2. 4 and 8kHz) and 65.6% for the high frequency average (4 and 8kHz). However, the percentage of the subjects who reported hearing loss ranged between 3.9% and 85.3% depending on the question used as indicator of hearing loss.The question “Do you consider the noise level where you are working now high?” was the most sensitive in correctly identifying subjects exposed to a noise level of more than 85dB (A) (sensitivity=93.4%) and subjects with hearing loss (sensitivity>86%) compared with other questions evaluated. However, it overestimated the prevalence rate determined by audiometryConclusion: We conclude that in industries where facilities for an objective assessment of noise exposure and hearing loss are not available, questions addressing noise exposure and hearing loss might be a useful alternative means for screening subjects exposed to high noise level and those with hearing loss for the purpose of designing and implementing hearing conservation program.     

Combined effects of hand-arm vibration and noise on temporary threshold shifts of hearing in healthy subjects

 Object: To investigate whether hand-arm vibration and noise have a combined effect on temporary threshold shift (TTS) of hearing among healthy subjects. Method and design: Nineteen healthy subjects with an average age of 25.7 (SD 7.7) years were exposed to vibration (30 m/s², 60 Hz), noise [90 dB(A)] and both, respectively. The subject’s right hand was placed on the plate of a vibrator and the right ear exposed to noise via headphones. Subjects were exposed to vibration and/or noise for 3 min and after a 1-min pause the exposure was repeated five times. Hearing thresholds at 1, 4 and 6 kHz were measured during the time periods before, between (during pauses) and after exposure. Results: Exposure to vibration alone caused almost no hearing threshold changes at every frequency tested. But exposure to noise or a combination of vibration and noise caused a significant increase in TTSs at 4 and 6 kHz. Moreover, exposure to a combination of vibration and noise caused significantly higher TTSs than exposure to noise at 4 and 6 kHz. Conclusion: The present results demonstrate the combined effects of hand-arm vibration and noise on hearing: simultaneous exposure to hand-arm vibration and noise can enhance the TTS of hearing more than noise exposure, though hand-arm vibration alone may hardly affect TTS. Received: 14 May 1996/Accepted: 20 September 1996     

Effect of long-term,low-level noise exposure on hearing thresholds,DPOAE and suppression of DPOAE in rats

Loss of adaptability rather than loss of sensitivity may be one of the initial signs of auditory impairment following exposure to noise. One way to examine the adaptability of hearing in experimental investigation is to measure the magnitude of the suppression, exerted by the medial olivocochlear efferent system, on the ipsilateral otoacoustic emissions in response to contralateral sound stimulation. Thus, in order to test the hypothesis it was decided to measure hearing thresholds (HT), the cubic DPOAE and suppression of cubic DPOAE by contralateral wide band noise in rats exposed to long-term, low level noise (90 days of 90 dBlin 4-20 kHz wide band noise 4 hours/day, 5 days/week). Measurements of HT were performed by assessment of the ABR, elicited by tone-pips from the same probe assembly used in the measurements of DPOAE. The suppression of the cubic distortion product (CDP) was determined in ketamine/xylazine anaesthesia, allowing a stable response for a minimum of 20 min. Of the frequencies tested, the rats exposed to noise had an increase in HT at 12.8 kHz only (6.8 dB, P<0.05), while a reduction on the CDP was evident with f2 going from 9.2 kHz to the upper limit at 17.4 kHz. Further, the rats exposed to noise had little suppression of the CDP at low levels of contralateral noise (CN), but no difference from the control animals was seen as the CN noise level was increased. The measurement of DPOAE suppression did not reveal any effects of the low level noise exposure that was not paralleled also by shifts in hearing thresholds. The most sensitive assessment of the auditory changes in the study was the measurements of DPOAE, and further elaboration on the bandwidth and frequency distribution of the CN is necessary, before auditory changes in the high frequency range can be probably assessed.     

听力筛查未通过的新生儿听力损失的高危因素研究

目的:分析听力筛查未通过的新生儿听力损失的高危因素。方法:对43 568例新生儿出生后3～5天用耳声发射仪进行初筛,初筛未通过者在出生后42天内进行复筛,复筛未通过者在出生后3月内用脑干听觉诱发电位仪、声导抗、诊断型耳声发射进行听力障碍的诊断。结果:43 568例新生儿复筛未通过者802例,进行初次诊断者660例,占全部听力筛查儿的1.51%,其中256人出现不同程度的听力损失(含分泌性中耳炎导致的传导性听力损失),重度聋在听力筛查儿中的发生率为1.45‰。分泌性中耳炎发生率在听力损失组与听力正常组差异有统计学意义(χ2检验,P<0.01)。1∶1配对的病例对照多因素分析显示听力损失家族史是听力损失的独立危险因素。结论:听力筛查未通过的新生儿中,约一半听力损失伴有分泌性中耳炎,听力损失家族史是新生儿听力损失高危因素,应加强妇幼保健宣传教育,针对迟发性听力损失,应重视随访。     

Industrial noise and presbyacusia in the determination of hearing damage: studies in chemical industry workers]

An audiometric investigation was carried out on 710 workers of a chemical plant in order to ascertain the role of industrial noise and presbysocio-acusia in causing hearing loss. The workers underwent an audiometric test both aerial and via bone, in a sound-proof chamber, after a 16-hour rest from noise. The subjects also answered a questionnaire on nonoccupational noise exposure and previous hearing and dysmetabolic disorders. Noise exposure was assessed on the basis of a cumulative exposure index obtained for each subject by multiplying the mean daily exposure level by seniority in the job. The results showed that in workers not exposed to high noise levels, industrial noise and presbysocio-acusia induce, via a direct mechanism, either separately or together, only slight damage to social hearing frequencies, i.e., those of normal conversation. At frequencies of 4 and 6 kHz, however, presbysocio-acusia seems to play a more important role than industrial noise in causing hearing loss. The practical implications arising from this study concern the frequencies that should be used for a medicolegal assessment of industrial noise induced hearing loss and the the threshold for these frequencies above which assessment of hearing loss should begin. As regards the first point, the results obtained in this study suggest the use of medicolegal methods based on normal conversation frequencies since presbysocio-acusia should not in any case be taken from these frequencies as it affects them only marginally. As regards the second point, the results show that assessment of hearing loss should begin when the hearing threshold at the above frequencies exceeds 25 dB. The study also showed that in epidemiological investigations on subjects exposed to industrial noise, the cumulative exposure index is better correlated with the rise in hearing threshold at the various frequencies than with seniority.     

噪声作业工人的畸变产物耳声发射观察

目的观察畸变产物耳声发射（DPOAE）在早期发现噪声性听力损失方面的应用价值。方法对54例非噪声作业工人（对照组）和96例纯音听阈正常的噪声作业工人（噪声组）进行纯音测听和DPOAE测试，比较两组的纯音听阈、DPOAE幅值和引出率。结果①噪声组和对照组各频率纯音听闻比较，差异无显著性（P〉0．05）；②噪声组的DPOAE幅值在3kHz、4kHz、6kHz处明显下降，与对照组比较有统计学意义（P〈0．01）；③噪声组在3kHz、4kHz和6kHz三个频率处的DPOAE引出率明显降低，与对照组比较，差异有显著性（P〈0．05，P〈0．01）：结论DPOAE能早期发现噪声性听力损失。     

Evaluation of individual susceptibility to noise-induced hearing loss in textile workers in China

The authors applied noise exposure and audiometry information collected on 156 Chinese textile workers to develop a method of identifying individuals susceptible to noise-induced hearing loss. They estimated noise-induced hearing threshold shift (NIHTS) by averaging the adjusted hearing thresholds at 3, 4, and 6 kHz of both ears, and they fitted a quadratic model to describe the dose-response relationship between cumulative noise exposure and NIHTS. The residual between the actual NIHTS and the model-predicted NIHTS indicated susceptibility. A comparison of the 20% of the subjects with the greatest residuals (those who were susceptible to hearing loss) with the 20% of the subjects with the smallest residuals (those who were resistant to hearing loss) revealed that the former had poorer hearing, although the noise exposures were similar. The identified susceptible individuals also had the poorest hearing thresholds within each subgroup of homogenous noise exposures. With their model-based procedure, the authors were able to identify individuals susceptible to noise-induced hearing loss from subjects with heterogeneous noise exposures.     

我国噪声暴露劳动者高频听力损失检出率的Meta分析

目的运用Meta分析评估我国噪声暴露劳动者高频听力损失检出率及其时间和地区分布,为我国职业人群噪声聋的防治提供科学依据。方法于2020年2至4月,检索中国知识资源总库(中国知网,CNKI)、维普中文科技期刊数据库(VIP)、PubMed等数据库的各地重点职业病监测和职业健康风险评估项目中噪声暴露劳动者听力检测人数和双耳高频平均听阈≥40 dB人数,检索时间段设置为建库以来至2020年2月28日,使用R 3.6.2软件计算合并噪声暴露劳动者高频听力损失检出率。结果共纳入28篇文献、34份数据,进行听力检测的噪声暴露劳动者1 259 571人;研究时间涉及2015-2018年,地区覆盖全国16个省(市、自治区)。全国噪声暴露劳动者高频听力损失检出率为9.45%(96%CI:7.64%~11.64%);按照时间进行亚组分析,2018年高频听力损失检出率(10.54%)最高,其次为2017年(10.17%)和2016年(9.21%),2015年(7.88%)最低。按照地区进行亚组分析,中部地区高频听力损失检出率(12.23%)最高,东部地区(10.21%)次之,西部地区(7.91%)和东北部地区(5.21%)最低。结论我国噪声暴露劳动者高频听力损失检出率较高,应加强噪声暴露劳动者听力保护,防止噪声聋的发生。