Field study to explore possible effects of styrene on auditory function in exposed workers

OBJECTIVES: We conducted this study to examine, whether occupational styrene exposures are associated with reduced hearing ability. METHODS: The auditory function was investigated by pure tone audiometry and registration of transitory evoked otoacoustic emissions (TEOAE) in 32 workers of a fibre-reinforced plastic boat building factory. Sixteen subjects were laminators (mean age: 41 yr (SD: 8)) and therefore regularly exposed to styrene with mean duration of exposure to styrene of 7.5 yr (SD 5.0). The tests were applied to a reference group of 16 workers (mean age: 39 yr (SD: 8)) who were not directly exposed to styrene but had a similar noise exposure. RESULTS: A few and isolated correlations between the parameters of hearing acuity and exposure indices, such as current internal styrene exposures (sum of MA and PGA) and duration of styrene exposure, were statistically significant, but no consistent association was found. CONCLUSION: The results of this study do not support the assumption of an ototoxic effect of chronic styrene exposure in workers.     

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.     

Evaluation of combined effect of organic solvents and noise by the upper limit of hearing

To clarify the combined effects of organic solvents and noise on hearing, the upper limit of hearing was measured in 48 male workers exposed to organic solvents and/or noise in a factory producing plastic buttons. Measuring the organic solvent concentrations in working environments and breathing zone air, and the noise level in workplaces were also done. The readings suggested that most exposures to organic solvents and/or noise were within the occupational exposure limits. The prevalence rate of the upper limit of hearing below 75th percentile curve was higher in workers exposed to organic solvents and noise than expected (25 percent) and the other groups, whereas it was about 25 percent in the noise and control groups. The results suggest that the probable combined effects of organic solvents and noise on hearing should be considered even when the exposures are within the occupational exposure limits.     

高水平苯乙烯接触加重噪声对听力影响的研究

目的 探讨高水平苯乙烯接触和噪声协同作用对职业人群纯音听力结果的影响。
方法 选择某运动器材企业同时接触高水平苯乙烯和噪声的114名生产工人为观察组,单纯接触噪声的97名工人为对照组。分析研究对象不同苯乙烯接触水平下的听力检查结果。
结果 观察组空气中苯乙烯的时间加权平均浓度为（402.81±52.25）mg/m3,合格率为16.67%;对照组的空气中苯乙烯的时间加权平均浓度为未检出。观察组噪声接触水平的8 h等效声级均值为（87.1±1.1）dB（A）,对照组噪声接触水平的8 h等效声级均值为（86.7±1.0）dB（A）,两组接触水平差异无统计学意义（P>0.05）。观察组的听力损失检出率为19.2%,对照组的听力结果异常率为8.2%;观察组和对照组的高频平均听阈分别为（28.3±9.0）dB、（25.0±2.7）dB,观察组的高频听力损失检出率高于对照组,而且随着苯乙烯接触浓度（< 213 mg/m3、213~426 mg/m3、>426 mg/m3）递增,高频听力损失检出率分别为6.5%、25.0%、47.6%。
结论 高浓度的苯乙烯增加听力损伤的风险,可能与噪声具有一定的协同作用,影响职业人群的听力神经系统。应把同时接触噪声和高水平苯乙烯的接触人群列为重点健康监护对象,实施以无毒或低毒物质替代苯乙烯和减少噪声接触时间等多种防治措施,保护工人听力系统的健康。
     

Relationship between styrene exposure and hearing loss: review of human studies

Styrene is an aromatic solvent belonging to the alkylbenzene family. Occupational exposure to styrene occurs mainly in the manufacturing of fiberglass-reinforced polyester products, e.g. reinforced plastics and composites. Since 1988, nine studies have been published on the relationship between occupational exposure to styrene and hearing loss. All studies were the cross-sectional epidemiological studies or clinical studies from occupational health clinics. A total of more than 1000 workers exposed to styrene, both with and without concurrent noise exposure, were examined using different outcome measures for hearing loss. Exposure assessment was usually based on styrene measurements in the breathing zone during several hours of one working day. Some of the studies employed also the biological monitoring of styrene exposure based on determination of its urinary metabolites. The current exposures to styrene varied between 2 and 35 ppm. In some studies, lifetime exposure was calculated using company records and questionnaire data. The current exposure to noise was estimated by noise dosimetry or standard noise measurements. Lifetime noise exposure was assessed using questionnaire data and occupational noise estimates. In many studies, noise-exposed groups were used as controls together with the unexposed workers. Of the nine studies, seven show some effects on the auditory system that were associated with styrene-alone exposure. These effects are examined using different outcome measures such as pure tone audiometry, high frequency hearing loss, and central hearing tests. In some studies, an increased risk for hearing loss was associated with exposure estimates.     

Effect of combined occupational exposure to noise and organic solvents on hearing

Noise exposure has been commonly regarded as the main hazard of occupational hearing loss. Recent studies indicate that several chemicals, including organic solvents have ototoxic effects. This study aimed at evaluating the hearing of workers exposed to both noise and a mixture of organic solvents at concentrations anticipated as safe. The study comprised three groups. The first one included 70 workers exposed to noise only, the second group consisted of 93 workers exposed to organic solvents and noise, and the control group included 59 individuals exposed to neither noise nor organic solvents. The three groups were matched for age, socioeconomic status, and smoking habit. The results of this study revealed that there was no statistically significant difference between the two exposed groups as regards the duration of exposure. There was a highly statistically significant difference between the two exposed groups as regards the different types of hearing loss (conductive deafness, sensory neural hearing loss, and mixed type) compared with the control one. Our study reported that sensory neural hearing loss occurred earlier in subjects with combined exposure to noise and solvents at a mean duration of exposure (16.38?±?9.44 years) compared to (24.53?±?9.59 years) the subjects with sole exposure to noise. The difference between the two groups was statistically significant regarding this type of hearing impairment (p < 0.05). There was a positive significant correlation between hearing impairment and duration of exposure in the two exposed groups. As regards the results of the environmental monitoring, both noise exposure levels (dB) and levels of different organic solvents measured (mg/m(3)) in different work departments were less than the levels recommended by Egyptian Environmental Law No. 4 for 1994. It is recommended that in the case of combined exposure, noise and solvent levels should be lowered than the permissible limits recommended for either alone.     

Hearing status among aircraft maintenance personnel in a commercial airline company

The aim was to study subjective and objective hearing loss in a population of aircraft maintenance workers and identify predictors. A total of 327 aircraft maintenance personnel answered a self-administered work environment questionnaire (response rate 76%) and underwent audiometric test. The mean values for the hearing threshold at 3, 4, and 6 kHz for the ear with the most hearing loss were compared with a Swedish population database of persons not occupationally exposed to noise. Equivalent noise exposure during a working day was measured. Relationships between subjective and objective hearing loss and possible predictors (age, years of employment, self-reported exposure to solvents, blood pressure, and psycho-social factors) were analyzed by multiple logistic regression. At younger ages (<40 years), aircraft maintenance workers had higher hearing thresholds (1-3 dB) compared to the reference group, but such a difference was not found in older employees. Relationships were found between age and objective hearing loss, and between exposure to solvents and reported subjective hearing loss. Equivalent noise exposure during working days were 70-91 dB(A) with a maximal noise level of 119 dB(A). Aircraft maintenance workers are exposed to equivalent noise levels above the Swedish occupational standard, including some very high peak exposures. Younger employees have a higher age-matched hearing threshold level compared with a reference group. Thus, there is a need for further preventive measures.     

镉与职业噪声联合暴露对听力的损害

目的探讨镉与噪声联合暴露对作业人员听力的影响。方法利用现况调查的方法,选择某冶炼厂精馏车间63名作业人员为镉与噪声联合接触组（联合组）,某齿轮厂机加工车间57名作业人员为噪声接触组（噪声组）,同一冶炼厂不接触有害因素的行政后勤人员53名为对照组,对3组人员工作场所噪声和镉及其化合物进行检测,对3组人员进行尿镉测定和0.5～6 kHz 6个频段的纯音气导测试,并进行问卷调查。结果各组工作场所噪声强度均未超标,联合组工作场所镉及其化合物浓度超标率为27.8%,联合组尿镉超标率为23.81%,联合组听力损失总检出率为36.7%,明显高于噪声组和对照组,差异有统计学意义（P〈0.01）。各组不同频段听阈均值比较,联合组0.5、1、2、3、4、6 kHz听阈值分别为（23.29±2.79）、（19.63±3.12）、（18.96±3.72）、（24.00±11.79）、（28.58±17.53）、（32.58±19.65）dB（A）,均高于噪声组和对照组,差异有统计学意义（P〈0.01）。结论镉与噪声职业暴露对听力损失存在协同作用。     

Audiological findings in workers exposed to styrene alone or in concert with noise

Audiological testing, interviews and exposure measurements were used to collect data on the health effects of styrene exposures in 313 workers from fiberglass and metal-product manufacturing plants and a mail terminal. The audiological test battery included pure-tone audiometry, distortion product otoacoustic emissions (DPOAE), psychoacoustic modulation transfer function, interrupted speech, speech recognition in noise and cortical response audiometry (CRA). Workers exposed to noise and styrene had significantly poorer pure-tone thresholds in the high-frequency range (3 to 8 kHz) than the controls, noise-exposed workers and those listed in a Swedish age-specific database. Even though abnormalities were noted on DPOAE and CRA testing, the interrupted speech and speech recognition in noise tests were the more sensitive tests for styrene effects. Further research is needed on the underlying mechanisms to understand the effects of styrene and on audiological test batteries to detect changes in populations exposed to solvents.     

Audiometric findings in workers exposed to low levels of styrene and noise

Audiometry and exposure measurements were conducted on workers from fiberglass and metal products manufacturing plants and a mail distribution terminal (N = 313). Workers exposed to noise and styrene had significantly worse pure-tone thresholds at 2, 3, 4, and 6 kHz when compared with noise-exposed or nonexposed workers. Age, noise exposure, and urinary mandelic acid (a biologic marker for styrene) were the variables that met the significance level criterion in the multiple logistic regression. The odds ratios for hearing loss were 1.19 for each increment of 1 year of age (95% confidence interval [CI], 1.11-1.28), 1.18 for every decibel >85 dB(A) of noise exposure (95% CI, 1.01-1.34), and 2.44 for each millimole of mandelic acid per gram of creatinine in urine (95% CI, 1.01-5.89). Our findings suggest that exposure to styrene even below recommended values had a toxic effect on the auditory system.     

Effects of coexposure to noise and mixture of organic solvents on hearing in dockyard workers

Questionnaire and audiometric data of 701 dockyard workers (517 noise and organic solvent mixture-exposed and 184 noise-only-exposed) were referred to 205 control subjects not exposed to either noise or solvents. The odds ratio (OR) of hearing loss was significantly increased by approximately 3 times in the noise-only group and by almost 5 times in the noise and solvent group. A moderate effect of solvent ototoxicity, in addition to noise, was observed on hearing threshold at a frequency 8 kHz. ORs for hearing loss were 1.12 for each increment of 1 year of age, 1.07 for every decibel of lifetime noise exposure (dB-A), and 1.004 for each increment of the index of lifetime exposure to solvents. The results suggest an additive damaging effect of coexposure to noise and organic solvents to the auditory organ.     

The ototoxicity of styrene: a review of occupational investigations

Objectives: The objective of this study was to review critically a number of occupational investigations of the exposure and effect relation between inhaled styrene vapour and hearing loss. There is concern that workers’ hearing may be impaired by exposure to styrene, as used in industries making plastics and fibreglass-reinforced products. Methods: Seven occupational studies, each dealing with the ototoxicity of styrene, were examined. Factors assessed included the experimental design and number of subjects within exposure groups, measurement of the styrene-in-air concentration, confirmation of the styrene exposure by blood or urine analysis, determination of the hearing threshold levels for the exposure and control groups, and measurement of any occupational noise in the subjects’ workplaces. Consideration was also given to statistical relations between high-frequency hearing loss and lifetime exposure indices for styrene and noise. Results: The results are equivocal. Four investigations failed to find any effect of styrene on hearing thresholds. In contrast, other investigations claimed to have demonstrated styrene-induced hearing loss in industrial populations, with synergism between styrene and noise. However, these reports exhibited shortcomings of experimental design and data analysis. Conclusions: Considering the body of evidence as a whole, hearing deficits due to occupational exposure to styrene at low concentrations have not been demonstrated by scientifically reliable argument. There is some suggestion of an association between styrene exposure, occupational noise, and hearing dysfunction. Further studies in humans are necessary to clarify this question.     

甲苯与职业性噪声接触对听力损失的联合作用

目的 探讨甲苯与噪声联合接触对听力损失的影响。 方法 选择珠海市两家企业中同时接触甲苯和噪声人员78例为混合接触组,单纯接触噪声人员75例为噪声接触组,不接触职业病危害因素的办公室和后勤人员90例为对照组,进行现场甲苯浓度和噪声强度检测,对三组研究对象进行纯音测听检查,并对结果进行统计学分析。 结果 接触组各作业点甲苯浓度、噪声强度均超过国家职业接触限值。混合接触组与噪声接触组在高频段(3.0 kHz、4.0 kHz、6.0 kHz)听阈值差异有统计学意义(P均<0.05)。混合接触组与对照组比较,各频段听力差异均有统计学意义(P均<0.05)。混合接触组、噪声接触组的语频听力异常检出率(25.6%、22.7%)均高于对照组(2.2%),差异均有统计学意义(P<0.05/3);混合接触组的高频听力异常检出率(51.3%)均大于噪声组(24.0%)和对照组(7.8%),差异有统计学意义(P<0.05/3)。工龄≥ 5年者,混合接触组与噪声接触组听力损害发生率差异有统计学意义(P<0.05)。 结论 甲苯与噪声联合接触对听力损害有协同作用,应充分考虑联合接触因素的职业安全防护。     

东莞市集装箱制造企业噪声对工人听力及血压心电图的影响

目的探讨噪声对集装箱制造工人听力和血压、心电图的影响。方法2010-2011年选取东莞市某外资集装箱制造企业接触噪声作业的1025名工人,分为噪声组487人,混合噪声组538人,对照组选取该企业不接触噪声的办公室和后勤人员222名,进行血压,心电图和纯音听力测试检查,对其数据进行统计分析。结果①血压异常率噪声组和混合噪声组分别与对照组比较,差异均无统计学意义（P〉0．05）。②心室高电压噪声组和混合噪声组分别与对照组比较,差异均有统计学意义（P〈0．05）。③纯音听力测试异常率噪声组和混合噪声组分别与对照组比较,差异均有统计学意义（P〈0．05）。结论噪声对集装箱作业工人听力、心血管系统具有一定的损害。集装箱制造业工人流动性大,接噪工龄相对较短,有关部门应加强其职业健康监护工作的监管,同时采取措施降低作业环境噪声,保护工人健康。     

Somatosensory evoked potentials in workers exposed to toluene and styrene.

Somatosensory evoked potentials (SEPs) were used to evaluate possible subclinical impairment of the nervous system due to occupational exposure to toluene and styrene. A group of 36 rotogravure printers with severe exposure to toluene, 20 workers with severe exposure to styrene in a glass laminate manufacturing plant, and a comparison group of healthy subjects were studied. The severity of exposure was documented by measurements of toluene and styrene concentrations in breathing zone air, by hippuric acid concentration in urine in the group exposed to toluene, and by urinary mandelic acid concentration in the group exposed to styrene. Somatosensory evoked potentials were measured by stimulation of the median nerve at the wrist and the tibial nerve at the ankle. Peripheral conduction velocities (CVs) in both extremities and central conduction time (CCT) after tibial nerve stimulation were significantly decreased in both exposed groups. Significantly prolonged latencies of peripheral and cortical SEPs to median nerve stimulation as well as cortical SEPs to tibial nerve stimulation were found in workers exposed to styrene. Some abnormalities in SEPs at peripheral or spinal and cortical levels were found in eight workers exposed to toluene and six workers exposed to styrene. Of these, in three workers exposed to toluene and two to styrene increased CCT and delayed latencies of cortical responses at normal conduction values in the periphery were found. A trend for increased frequency of abnormal SEPs with duration of exposure to toluene and styrene and alcohol abuse was found. Abnormalities in SEPs in the exposed groups are most probably of multifactorial origin. Central SEP abnormalities in both exposed groups could indicate early signs of subclinical dysfunction at spinal and cortical levels and could be due to toluene or styrene exposure probably potentiated by alcohol consumption in the group exposed to toluene.     

Noise exposure and hearing loss among sand and gravel miners

The objectives of this study were to describe workplace noise exposures, risk factors for hearing loss, and hearing levels among sand and gravel miners, and to determine whether full shift noise exposures resulted in changes in hearing thresholds from baseline values. Sand and gravel miners (n = 317) were interviewed regarding medical history, leisure-time and occupational noise exposure, other occupational exposures, and use of hearing protection. Audiometric tests were performed both before the work shift (following a 12-hour noise-free interval) and immediately following the work shift. Full shift noise dosimetry was conducted. Miners' noise exposures exceeded the Recommended Exposure Limit (REL) of the National Institute for Occupational Safety and Health (NIOSH) for 69% of workers, and exceeded the Mine Safety and Health Administration's action level for enrollment in a hearing conservation program for 41% of workers. Significantly higher noise exposures occurred among employees of small companies, among workers with a job classification of truck driver, among males, and among black workers. Hearing protection usage was low, with 48% of subjects reporting that they never used hearing protection. Hearing impairment, as defined by NIOSH, was present among 37% of 275 subjects with valid audiograms. Black male workers and white male workers had higher hearing thresholds than males from a comparison North Carolina population unexposed to industrial noise. Small but statistically significant changes in hearing thresholds occurred following full shift noise exposure among subjects who had good hearing sensitivity at baseline. In a logistic regression model, age and history of a past noisy job were significant predictors of hearing impairment. Overall, sand and gravel workers have excessive noise exposures and significant hearing loss, and demonstrate inadequate use of hearing protection. Well-designed hearing conservation programs, with reduction of noise exposure, are clearly needed.     

Combined effects of noise and mixed solvents exposure on the hearing function among workers in the aviation industry

This study aims to evaluate the effect of occupational exposure to noise and organic solvents on hearing loss in the aviation industry. The study population comprised 542 male workers, who worked in avionics jobs in Kimhae, Korea, who kept records of work environment evaluations and medical examinations. The Cumulative Exposure Index (CEI) was constructed to assess the lifetime cumulative exposure of the workers, and pure tone audiometry (PTA) data of the workers from their biannual medical surveillance was used to assess hearing loss. The prevalence of hearing loss found in the group exposed to noise and mixed solvents simultaneously (54.9%) was higher than those in the other groups (6.0% in the unexposed, 17.1% in the noise-only, and 27.8 % in the exposed to only a solvents mixture). The relative risks, adjusted for age, were estimated to be 4.3 (95 % CI 1.7-10.8) for the noise-only group, 8.1 (95% CI 2.0-32.5) for the noise and solvents group, and 2.6 (95 % CI 0.6-10.3) for the solvents-mixture group. These suggest that chronic exposure to mixed solvents had a toxic effect on the auditory system. This raises the issue of whether hearing conservation regulations should be applied to all workers exposed to solvents.     

Hearing loss associated with smoking and occupational noise exposure in a Japanese metal working company

The effects of smoking on hearing loss within the context of atherosclerosis was assessed, and the statistical interaction of occupational noise evaluated. A cross-sectional study was conducted in 397 Japanese males working at a metal factory, aged 21–66 years, in a periodical health checkup. The following information was obtained: two smoking indices of smoking status and Brinkman index, occupational noise exposures and atherosclerotic risk factors (body mass index, blood pressure, serum cholesterol, hemoglobin A1c, atherosclerosis index). Hearing acuity was measured at 4 kHz using a pure-tone audiometer in a quiet room. Among the total subjects, 55 (13.9%) were identified as having hearing loss at 4 kHz, and 151 (38.0%) were currently exposed to occupational noise. When adjusted for age and occupational noise exposure, odds ratios (95% confidence intervals) of hearing loss were 3.16 (1.04, 9.62) for past smokers and 3.39 (1.05, 11.01) for heavy smokers (Brinkman index >750 cigarettes per day × number of years), compared with never-smokers. Statistical interaction of occupational noise exposure was insignificant with the association between smoking and hearing loss. When including atherosclerotic risk factors in a multiple model, there were no significant associations between hearing loss and either smoking or any other factors (i.e., occupational noise and atherosclerotic factors). Smoking was found to be associated with hearing loss beyond occupational noise exposure, and this association seemed to be masked by atherosclerotic factors, suggesting that the direction of the atherosclerotic effect on the relationship might need to be explored between smoking and hearing impairment.     

南京市噪声作业人员听力损失情况及其影响因素分析

目的 分析南京市噪声岗位作业人员职业健康体检的纯音听力测试(pure tone audiometry,PTA)结果,以期对职业性噪声聋的防治提供科学依据。方法 以2020年1月1日至10月31日在南京市职业病防治院进行职业健康体检并进行PTA的6 614名噪声作业人员为研究对象,询问一般情况、职业史和病史,进行体格检查、PTA、实验室检查等。双耳各频阈值比较采用t检验,双耳各频异常检出率比较采用χ²检验,采用二元Logistic回归分析噪声性听力损失(noise-induced hearing loss,NIHL)的危险因素。结果 6 614名噪声作业人员中,听阈测试异常1 779例,占26.90%。NIHL有678例,占10.25%。不同性别、合并有害因素、吸烟、饮酒的噪声作业人员NIHL检出率差异均有统计学意义(均P<0.01),NIHL检出率随着年龄、接噪工龄增加而增加(均P<0.01),而血压正常组和血压异常组检出率差异无统计学意义(P>0.05)。二元Logistic回归分析结果显示,男性(OR=2.305)、年龄≥31岁(OR=2.1...     

Retention of styrene following controlled exposure to constant and fluctuating air concentrations

An experiment was designed to determine whether the respiratory retention of sytrene vapor, as estimated from measurements of end-exhaled air, was the same during periods of both constant and fluctuating exposure. Six human subjects were exposed to styrene inside an experimental chamber. A computer-controlled system was used to generate time-varying air concentrations of styrene over 4–5 h in both multistep sequences of constant exposure (four subjects exposed to 15–99 ppm. of styrene in 100-min steps) and fluctuating patterns representative of occupational exposures (two subjects exposed to mean concentrations of styrene of 50 ppm). In the latter case, lognormally distributed exposures, which fit one of two first-order autoregressive models, were generated at intervals of 2.5 min. It was found that the concentration of styrene in end-exhaled air was reduced by about half if the subject inhaled one to three breaths of clean air prior to sampling. This suggests that significant amounts of styrene were desorbed from the lining of the lungs during the initial exhalation. The retention of styrene vapor during constant exposures was 0.935 and was independent of the level. During each of the two sets of fluctuating exposure the retention of sytrene was also constant and was independent of both the variance and the autocorrelation coefficient. However, the retention of styrene during fluctuating exposure (estimates ranged from 0.957 to 0.973) was significantly higher than that observed during the constant exposures. It is speculated that the difference in retention between the constant and the fluctuating exposure regimens is related to non-steady-state behavior of styrene in the richly perfused tissues, as suggested by Opdam and Smolders (1986) regarding tetrachloroethylene exposure.