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.     

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.     

Evaluation of organic solvent ototoxicity by the upper limit of hearing.

To clarify the effects of organic solvents on hearing, we measured the upper limit of hearing in 93 male workers exposed to organic solvents in 7 factories that produced plastic buttons or baths. Medical examinations, environmental monitoring (i.e., concentration in breathing-zone air), and biological monitoring (i.e., concentration in urine) of the organic solvents were also done. Although the organic solvent concentrations in the environmental monitoring were lower than the occupational exposure limit, the upper limit of hearing was reduced in workers who were exposed for 5 y or more. This reduction was dose-dependent and was related to styrene concentrations in breathing-zone air and mandelic acid concentrations in urine. Even individuals who had normal medical examinations showed a reduced upper limit of hearing. The upper limit of hearing may serve as an early detection indicator of health effects in workers constantly exposed to styrene.     

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.     

Evaluation of noise-induced hearing loss by reference to the upper limit of hearing

We have defined the upper limit of hearing as the maximum audible frequency measured with fixed intensity and changing frequency. We have previously established the standard upper limit ageing curves from the normal age variation in the upper limit of hearing. In the present study, we sought to clarify the effects of occupational noise on the upper limit of hearing. We measured the upper limit of hearing in 239 healthy male workers (478 ears) exposed to intensive occupational noise. Their age variation in the upper limit of hearing was compared with the standard upper limit ageing curves in males. There were statistically significant deteriorations. Even if the ears that had normal hearing levels (35 dB or less) were selected, deterioration in the upper limit of hearing was noticeable. The upper limit of hearing may serve as clinically useful information on the hearing impairment that precedes noticeable hearing impairment in conventional audiometry for workers exposed to intensive occupational noise.     

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。     

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.     

NoiseChem: An European Commission research project on the effects of exposure to noise and industrial chemicals on hearing and balance

Exposure to multiple physical and chemical agents is common in occupational environments but workplace hazards and occupational safety criteria for combined exposures is lacking. NoiseChem is an European Commission research project examining the effects of exposure to noise and chemicals on hearing and balance. Partners in Sweden, Finland, France, Denmark, UK and Poland with expert guidance from partners in USA will examine workers and study the mechanisms of action in animals to determine the levels of risk associated with joint exposure to noise and solvents. This paper briefly outlines the project details.     

NoiseChem: an European Commission research project on the effects of exposure to noise and industrial chemicals on hearing and balance

Exposure to multiple physical and chemical agents is common in occupational environments but workplace hazards and occupational safety criteria for combined exposures are lacking. NoiseChem is an European Commission research project examining the effects of exposure to noise and chemicals on hearing and balance. Partners in Sweden, Finland, France, Denmark, UK and Poland with expert guidance from partners in the USA will examine workers and study the mechanisms of action in animals to determine the levels of risk associated with joint exposure to noise and solvents. This paper briefly outlines the project details.     

Exposure to organic solvent mixture and hearing loss: literature overview

The chemical sector is the third largest industry in Europe. There is increasing evidence from epidemiological and clinical studies that occupational exposures to organic solvents may have detrimental effect on hearing. Most of the literature data concern one of the three following types of exposure to industrial solvents: mixed solvent exposure (the most common type); styrene-only exposure; and toluene-only exposure. This paper overviews the effects of industrial exposure to a mixture of organic solvents on hearing, with special regard to the dose-response relationship. Although the existing data make it difficult to derive a correlation between solvent concentration and hearing outcome, the current occupational exposure limits for solvents seem to be inadequate with respect to the effect that solvents may have on the auditory system.     

Contributions of non-occupational activities to total noise exposure of construction workers

This paper describes how exposures received during routine and episodic non-occupational activities contribute to total noise exposure in a group of occupationally exposed workers. Two-hundred and sixty-six construction apprentices enrolled in a longitudinal hearing loss study and completed questionnaires at 1 yr of follow-up to determine their episodic activities (e.g. concert attendance, power tool use, firearms exposure). Noise exposure levels for these episodic exposures were determined from the published literature. Routine activities were assessed using activity cards filled out over 530 subject-days, along with noise dosimetry measurements made over 124 subject-days of measurement. Equivalent Leq exposure levels were then calculated for specific activities. These activity-specific Leq values were combined into estimated individual annual Leq exposure levels for the 6760 nominal annual non-occupational hours in a year (LAeq6760h), which were then transformed into equivalent levels for a 2000 h exposure period (LA2000hn) for comparison with occupational noise exposure risk criteria. The mean non-occupational LAeq6760h exposure values for the cohort ranged from 56 to 87 dBA (equivalent LA2000hn 62-93 dBA). At the mid range of the routine and episodic activity exposure level distribution, the mean LAeq6760h was 73 dBA (LA2000hn 78 dBA). Nineteen percent of the LA2000hn non-occupational exposures exceeded 85 dBA, the generally recommended occupational limit for a 2000 h workyear, at the mid-range of exposure levels. Due to a lack of available data, firearms use could not be incorporated into the total noise exposure estimates. However, firearms users reported more exposure to other noisy non-occupational activities and had statistically significantly higher estimated exposure levels even without including their firearms exposure than did non-shooters. When compared with the high levels of occupational noise found in construction, non-occupational noise exposures generally present little additional exposure for most workers. However, they may contribute significantly to overall exposure in the subset of workers who frequently participate in selected noisy activities.     

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.     

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.     

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。     

Solvent-induced hearing loss: mechanisms and prevention strategy

While noise exposure is the most significant contributor to occupational hearing loss, evidence gained over the last 10 years, has pointed to organic solvents as additional contributors to occupational hearing disorders. Despite the implications of this finding, no significant measure has been undertaken to limit exposure to occupational solvents, or to occupational solvents and noise, within the European community. Guidelines for improving hearing protection of people exposed to solvents, or to solvents and noise, are addressed in the present article. Recently, it has been shown that the lowest-observed-adverse-effect level (LOAEL) of styrene was 300 ppm in active (working wheel) rats, and that the same amount of styrene-induced hearing loss (SIHL) can be obtained with styrene concentration difference of 200 ppm between active and sedentary (inactive) rats. Supported by a reasonable safety factor (SF) of 10, the authors proposed to decrease the French threshold limit value of styrene from 50 to 30 ppm (RfD=LOAEL/SF) to ensure a higher level of protection for human hearing. It is widely acknowledged that outer hair cells in the organ of Corti can be considered as the first target tissue of solvents, while little is known about the action of aromatic solvents on the auditory efferent system. In a recent experiment using both the cochlear microphonic and compound action potentials, the authors have shown that toluene can inhibit the action of the middle ear reflex by modifying the cholinergic receptors. It is likely that toluene affects the cholinergic receptors at the brainstem level. By its anticholinergic-like effect, toluene could allow higher acoustic energy penetration into the cochlea exposed to both noise and solvent. Based on this phenomenon, the authors recommend the use of hearing protection for the lower exposure action value: Lex,8h=80 dB(A) in noisy environments polluted by solvents.     

Occupational exposures to noise resulting from the workplace use of personal media players at a manufacturing facility

This study examined the contribution of noise exposures from personal media player (PMP) use in the workplace to overall employee noise exposures at a Colorado manufacturing facility. A total of 24 workers' PMP and background noise exposures were measured. Twelve PMP users worked in high-background-noise exposure (HBNE) areas, and 12 worked in low-background-noise exposure (LBNE) areas. The self-selected PMP listening level of each worker was measured using an ear simulator, and the background noise of each employee workstation was measured using a sound level meter. Workers' self-reported PMP duration of use, PMP listening exposure levels, and background noise levels were used to estimate the daily occupational noise exposures. Measured background noise levels averaged 81 dBA for HBNE workers and 59 dBA for LBNE workers. Measured, free-field equivalent listening exposure levels were significantly greater for HBNE workers (85 dBA) compared with LBNE workers (75 dBA) (p = 0.0006). Estimated mean daily noise exposures for both groups were below the ACGIH threshold limit value for noise of 85 dBA8-hr time weighted average (TWA), specifically 84 dBA TWA for HBNE workers and 72 dBA TWA for LBNE workers. Three of 12 (25%) HBNE workers had estimated exposures greater than 85 dBA TWA when only background noise was considered, yet when PMP use was also considered, 6 of 12 (50%) had estimated exposures greater than 85 dBA TWA, suggesting that PMP use doubled the number of overexposed workers. None of the LBNE workers had estimated exposures greater than 85 dBA TWA. The contribution of PMP use to overall noise exposures was substantially less among HBNE workers than LBNE workers due to the disproportionate selection of noise-attenuating headsets among HBNE workers compared with LBNE workers. It is recommended that the facility management either restrict workplace PMP use among HBNE workers or require output-limiting technology to prevent occupational noise-induced hearing loss.     

噪声与高温、硫化氢联合作用对听力损伤影响的研究

目的通过对某石化厂单纯接触噪声及接触噪声同时伴有高温、硫化氢混杂因素工人的听力测试结果进行分析,了解噪声与其他危害因素联合作用对工人听力的影响,为噪声性听力损失的防治工作提供参考。方法根据某石化厂2007年242例接触噪声及相关有害因素的工人听力检查结果,按工作中接触的职业危害因素差异分成3组:单纯噪声组,噪声合并高温组,噪声合并硫化氢组。测定计算每组各工人的语频和高频听力损失值,对各组的听力损失值进行统计分析。结果3组工人均不同程度地出现噪声性听力损伤。三组工人的听力损失程度存在区别(P0.05),尤其在语言频率的损失上表现明显。噪声合并硫化氢组工人在语言频率的听力损伤程度最严重,噪声合并高温组的工人次之,单纯噪声组工人在语言频率的听力损伤程度最小。结论噪声联合高温或硫化氢作用的听损率和损失程度均较单纯性噪声高,提示噪声联合高温、硫化氢作用于人耳存在联合加强作用。应对噪声作业场所环境温度和硫化氢浓度加以控制,以减少噪声与其他有害因素联合作用对工人听力的影响。     

某鞋厂347例接触混合有机溶剂作业工人肝脏B超检查结果分析

目的 探讨长期低浓度接触混合有机溶剂对制鞋作业工人肝脏的影响。 方法 对生产车间使用甲苯、苯、二氯乙烷、正己烷等混合有机溶剂的某鞋业工厂347名工人(接触组)和工厂无毒物接触史后勤人员321人(对照组)进行肝脏B超检查,比较两组检查结果。 结果 生产车间使用的有机溶剂的时间加权平均浓度均未超过职业接触限值。接触组弥漫性肝回声音改变、肝大的检出率均高于对照组,上述指标在两组间比较,差异均有统计学意义(χ2=27.8、12.5,P<0.05)。将两组各分成6个工龄段,弥漫性肝回声改变的检出率在工龄大于等于2年(4个工龄段)的两组员工间比较,差异均有统计学意义(χ2=8.9、10.2、10.2、10.5,P<0.05),两组的异常检出率均随着工龄的增加而升高。 结论 较长时间接触混合有机溶剂对作业工人肝脏可能存在慢性损害,应注意预防。     

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.     

Evaluation of occupational environment in two textile plants in Northern India with specific reference to noise

Occupational Noise exposure has been linked with a range of negative health effects by various researchers. The resulting injury of occupational hearing loss is also a well recognized and global problem. To protect workers from hearing damage due to noise exposure and other related health effects, a vast store of knowledge has been accumulated till date about its nature, etiology and time course. There is still ignorance, amongst majority of people working in industries in developing and third world countries including India about ill effects of exposure to high values of noise. The study being reported here has been carried out in two textile plants located in Northern Indian state of Punjab. Equivalent sound pressure level L(eq) has been measured in various sections of these plants with the help of a Class-I type digital sound level meter. The noise spectrum has been evaluated with the help of 1/3 octave filter set. A cross sectional study involving 112 workers exposed to different levels of occupational noise has been conducted. The results of the study establish the fact that noise level in certain sections of the plants i.e Loom Shed, Spinning, Ring Frame, TFO Area is more than the acceptable limit of 90 dBA for 8 h exposure stipulated by OSHA. The noise level in other sections like carding, blow room, combing etc., although is less than 90 dB(A), but is quite higher than limits used for assessment of noise for community response. Octave band analysis of the noise shows the presence of high sound level in 4,000 Hz frequency range, which can be a major reason for causing occupational hearing loss. The results of the interview questionnaire which included a number of parameters reveal the following; (i) only 29% workers are aware about the effects of noise on health (ii) 28% workers are using ear protectors (iii) the satisfaction with the working environment is related to noise level, as workers exposed to comparatively less noise level report better satisfaction (iv) 70% of the workers reported that high noise level causes speech interference (v) 42% workers report the noise to be annoying. The study thus demonstrates the presence of gross occupational noise exposure in both the plants and the author believes that occupational noise exposure and the related effects in India is a widespread problem.