Organic solvents and hearing loss: The challenge for audiology

The effect of occupational exposure to noise and chemical agents on hearing abilities

Exposure to loud noise or chemical agents may cause hearing disorders such as tinnitus and recruitment, known as an increase in the perception of loudness in addition to hearing loss. Our study aims to evaluate the hearing abilities of hairdressers exposed to noise and chemical agents in the working environment. The study included one hundred hairdressers and one hundred participants who do not work as hairdressers or are nonworkers. The participants' demographic characteristics, working conditions, and auditory complaints were questioned, and each participant completed the Speech, Spatial, and Qualities of Hearing Scale (SSQ). A statistically significant difference was found between the two groups in speech perception, spatial perception, hearing quality, and general SSQ scores. Hairdressers' SSQ scores were significantly lower in all sub-dimensions and general scale scores (p < 0.001). The auditory complaints of the hairdressers and the low SSQ scores indicate that exposure to noise and chemical agents affects the hairdressers' hearing system.

Effect of Determinants of Health on the Hearing Care Framework: An Economic Perspective

Hearing care is expanding accessibility to consumers through new service delivery channels and methods of technology distribution (see Brice et al, this issue). This diversification has the potential to overcome longstanding consumer disparities (e.g., health, socioeconomic, psychological, environmental) in receiving care and provider constraints (e.g., accessibility, geography, direct access) to delivering care that adversely impacts quality of life (e.g., social isolation, depression, anxiety, self-esteem). In this article, the reader is provided with an overview of health outcomes factors (i.e., determinants of health)-in the context of an economic framework (i.e., supply, demand)-and their effect on consumer behavior and provider preferences toward hearing healthcare services. This overview also affords readers with strategic business insights to assess and integrate future hearing care services and technology to consumers in their local markets.

Effects of coexposure to noise and mixture of toluene, ethylbenzene, xylene, and styrene (TEXS) on hearing loss in petrochemical workers of southern China

Many harmful factors existing simultaneously with noise are reported to induce hearing impairment, such as organic solvents. However, the existing hearing safety limits and current risk assessment for hearing loss rely on single noise exposure. It is urgent to clarify the combined effect of noise and other harmful factors on hearing loss. Petrochemical workers are always exposed to noise and organic solvents, mainly benzene, toluene, ethylbenzene, xylene, and styrene (BTEXS), while the combined effect of their coexposure on hearing remains unclear. Herein we conducted a cross-sectional survey, measuring pure-tone audiometry of 1496 petrochemical workers in southern China. Participants exposed to BTEXS were 569, 524, 156, 452, and 177 respectively. Individual cumulative noise exposure (CNE) levels and BTEXS exposure were assessed. The average CNE was 93.27 ± 4.92 dB(A)·years, and the concentrations of BTEXS were far below the occupational exposure limits of China. Logistic regression analyses showed that CNE was consistently positively associated with hearing loss (HL) and high-frequency hearing loss (HFHL) but not related to speech-frequency hearing loss (SFHL). Compared with participants in the lowest quartile of CNE, those in the highest quartile showed an OR of 5.229 (95% CI: 3.179, 8.598) for HFHL. Two-pollutant model analysis indicated that TEXS exposure was positively associated with HL (OR 1.679, 95%CI 1.086, 2.597), SFHL (OR 2.440, 95%CI 1.255, 4.744), and HFHL (OR 1.475, 95%CI 1.077, 2.020). However, no interactions were observed between CNE and TEXS coexposure on hearing loss. In our study, covariates including smoking and drinking status, body mass index (BMI), ear protection and personal protective equipment, and use of earphone/headphone were adjusted. In conclusion, coexposure to noise and low-level TEXS could induce more severe damage on hearing function than exposure to each alone, especially SFHL. Therefore, petrochemical workers simultaneously exposed to noise and TEXS, even at low-level, should be included in hearing protection programs.

Potential Risks to Hearing Functions of Service Members From Exposure to Jet Fuels

Purpose Several military occupations, particularly those within the U.S. Air Force, require working with or around jet fuels. Jet fuels contain components that are known to affect central nervous function, yet effects of these fuels on auditory function, specifically auditory processing of sound, are not well understood at this time. Animal studies have demonstrated that exposure to jet fuels prior to noise exposure can exacerbate the noise exposure's effects, and service members exposed to jet fuels are at risk of noise exposure within their work environments. The purpose of this article was to give a brief synopsis of the evidence on the ototoxic effects due to jet fuel exposure to aid audiologists in their decision making when providing care for populations who are occupationally exposed to fuels or while during military service. Conclusions Exposure to jet fuels impacts central nervous function and, in combination with noise exposure, may have detrimental auditory effects that research has yet to fully explain. Additional longitudinal research is needed to explain the relationships, which have clinical implications for service members and others exposed to jet fuels. In the meantime, audiologists can gain useful information by screening for chemical exposures when obtaining patient case histories. If jet fuel exposure is suspected, the Lifetime Exposure to Noise and Solvents Questionnaire can be used to estimate a noise exposure ranking and identify other potentiating agents such as jet fuel and industrial chemicals. A history of jet fuel exposure should inform the selection of hearing tests in the audiometric evaluation and when devising the treatment plan.

Occupational exposures to hazardous chemicals and agents among healthcare workers in Bhutan

BACKGROUND

Occupational exposures to hazardous chemicals among healthcare workers can result in long-term adverse health outcomes. Research on such exposures from low- and middle-income countries is limited. The aim of this study was to estimate the prevalence of exposures to a range of chemicals used in healthcare settings among Bhutanese healthcare workers.

METHODS

A cross-sectional study was conducted among healthcare workers (n = 370) working in three hospitals in the western region of Bhutan. Demographic and occupational information was collected, and exposures to asthmagens, carcinogens, ototoxic and other agents were assessed using a web-based tool. The prevalence of exposure to these chemicals was calculated and the circumstances resulting in such exposures were examined.

RESULTS

The prevalence of exposure to one or more asthmagen, carcinogen, and ototoxic agent was 98.7%, 28.1%, and 7.6%, respectively; and was 6.2% for anesthetic gases and 2.2% for antineoplastic drugs. The most common exposures were to latex, and cleaning and disinfecting agents in the asthmagens group; formaldehyde in the carcinogens group; and p-xylene among ototoxic agents. The circumstances resulting in exposures were using latex gloves, using bleach and chlorhexidine for cleaning, using formaldehyde as a disinfectant and in the laboratory, and using p-xylene in the laboratory.

CONCLUSIONS

The results indicate that a large proportion of Bhutanese healthcare workers are occupationally exposed to chemicals linked to chronic diseases, with exposure prevalence higher than in high-income countries. The study provides information that can be used to formulate policies and to implement control measures to protect healthcare workers.

Reliability and Validity of an Adapted Questionnaire Assessing Occupational Exposures to Hazardous Chemicals among Health Care Workers in Bhutan

BACKGROUND

Collection of reliable and valid occupational history data is of utmost importance to assess work-related exposures and their health effects. Few standardized questionnaires are available for the collection of occupational history data in low-and-middle income countries.

OBJECTIVE

To adapt and test a validated questionnaire developed in the United States by the National Institute of Safety and Health, in order to assess occupational chemical exposures among health care workers in Bhutan.

METHODS

The questionnaire was first adapted to suit the Bhutanese context with the advice of an expert review committee. 30 health care workers then completed the questionnaire at baseline and 10-14 days later. Test-retest reliability was assessed by calculating Cohen's κ and percentage agreement.

RESULTS

The questionnaire had high test-retest reliability. Cohen's κ ranged from 0.61 to 1.00, and percentage agreement ranged from 86.7% to 100%. Further adaptations included omitting questions on chemicals not available in Bhutan.

CONCLUSION

The adapted questionnaire is appropriate for assessing occupational chemical exposures among health care workers in Bhutan.

The estimated prevalence of exposure to carcinogens, asthmagens, and ototoxic agents among healthcare workers in Australia

BACKGROUND

Healthcare workers are occupationally exposed to various hazardous chemicals and agents that can potentially result in long-term adverse health effects. These exposures have not been comprehensively examined at a population level. The aim of this study was to examine occupational exposures to a wide range of asthmagens, carcinogens, and ototoxic agents among healthcare workers in Australia.

METHODS

Data were collected as part of the Australian Work Exposures Studies, which were computer-assisted telephone surveys conducted in 2011, 2014, and 2016 to assess the prevalence of occupational exposures to carcinogens, asthmagens, and ototoxic agents, respectively, among Australian workers. Using data on healthcare workers, the prevalence of exposures to these agents was calculated and associations of demographic variables and occupation groups with exposure status were examined.

RESULTS

The prevalence of exposure to at least one asthmagen, carcinogen, and ototoxic agent was 92.3%, 50.7%, and 44.6%, respectively. The most common exposures were to (a) cleaning and sterilizing agents in the asthmagen group; (b) shift work in the carcinogen group; and (c) toluene and p-xylene among ototoxic agents. Exposure varied by occupation, with exposure to carcinogens and ototoxic agents highest among personal carers and exposure to carcinogens most likely among nursing professionals and health and welfare support workers.

CONCLUSION

The results demonstrate that a substantial proportion of Australian healthcare workers are occupationally exposed to asthmagens, carcinogens, and ototoxic agents. These exposures are more common among certain occupational groups. The information provided by this study will be useful in prioritizing and implementing control strategies.

Distortion product otoacoustic emission sensitivity to different solvents in a population of industrial painters

Objective: To evaluate the ototoxic effect of the exposure to different organic solvents and noise using distortion product otoacoustic emissions (DPOAEs).Design: The exposure to different solvents was evaluated by measuring, before and at the end of the work-shift, the urinary concentrations of solvent metabolites used as dose biomarkers. The urinary concentrations of DNA and RNA oxidation products were also measured as biomarkers of oxidative damage. The simultaneous exposure to noise was also evaluated. DPOAEs and pure tone audiometry (PTA) were used as outcome variables, and were correlated to the exposure variables using mixed effect linear regression models.Study sample: Seventeen industrial painters exposed to a solvent mixture in a naval industry. A sample size of 15 was estimated from previous studies as sufficient for discriminating small hearing level and DPOAE level differences (5 dB and 2 dB, respectively) at a 95% confidence level.Results: Statistically significant associations were found between the DPOAE level and the urinary dose biomarkers and the oxidative damage biomarkers. DPOAE level and the logarithm of the metabolite concentration showed a significant negative correlation.Conclusions: DPOAE are sensitive biomarkers of exposure to ototoxic substances and can be effectively used for the early detection of hearing dysfunction.

The effects of combined exposure of solvents and noise on auditory function - A systematic review and meta-analysis

BACKGROUND

 Chemical substances can negatively affect the auditory system. Chemical substances alone or combined with high-level noise have recently become a major concern as a cause of occupational hearing loss.

OBJECTIVE

 To assess the combined effect of solvents and noise versus solvents only, or noise only, on the auditory function of workers.

METHOD

 Published articles which included noise and/or solvent exposure or combined effects of solvents and noise, studies conducted on human beings only and the use of audiological tests on participants.

RESULTS

 Thirteen papers were eligible for inclusion. The participants' ages ranged from 18 to 68 years. Results revealed that 24.5% presented with hearing loss as a result of noise exposure only; 18% presented with hearing loss owing to solvent exposure only; and a total of 43.3% presented with hearing loss owing to combined noise and solvent exposure. Furthermore, the prevalence of hearing loss in the noise and solvent group was significantly (p < 0.001) higher than the other groups in 10 out of the 13 studies analysed, with a pooled odds ratio (OR) of 2.754. Of the 178 participants (total of all participants exposed to solvents), a total of 32 participants presented with auditory pathology as a result of exposure to solvents only. There was a significantly higher pooled odds of hearing loss in noise and solvent-exposed group compared to solvent-only group (pooled OR = 2.15, 95% CI: 1.24-3.72, p = 0.006).

CONCLUSION

 The findings revealed significantly higher odds of acquiring hearing loss when workers were exposed to a combination of solvents and noise as opposed to solvents only, motivating for its inclusion into hearing conservation programmes.

Impact of Aging on the Auditory System and Related Cognitive Functions: A Narrative Review

Age-related hearing loss (ARHL), presbycusis, is a chronic health condition that affects approximately one-third of the world's population. The peripheral and central hearing alterations associated with age-related hearing loss have a profound impact on perception of verbal and non-verbal auditory stimuli. The high prevalence of hearing loss in the older adults corresponds to the increased frequency of dementia in this population. Therefore, researchers have focused their attention on age-related central effects that occur independent of the peripheral hearing loss as well as central effects of peripheral hearing loss and its association with cognitive decline and dementia. Here we review the current evidence for the age-related changes of the peripheral and central auditory system and the relationship between hearing loss and pathological cognitive decline and dementia. Furthermore, there is a paucity of evidence on the relationship between ARHL and established biomarkers of Alzheimer's disease, as the most common cause of dementia. Such studies are critical to be able to consider any causal relationship between dementia and ARHL. While this narrative review will examine the pathophysiological alterations in both the peripheral and central auditory system and its clinical implications, the question remains unanswered whether hearing loss causes cognitive impairment or vice versa.

Effects of combined exposure to metals, solvents, and noise on permanent threshold shifts

BACKGROUND

Studies suggest metal and solvent exposure may damage hearing. This study evaluated the association between exposures classified as high for metals, solvents, and noise on permanent threshold shift (PTS) development.

METHODS

A total of 1,546 personnel at an industrial shipyard were divided into five exposure groups based on level of concentration: high noise, high metals/solvents, high metals/noise, high metals/solvents/noise, and a low metals/solvents/noise reference group. Hearing threshold changes were analyzed to identify development of a PTS.

RESULTS

Logistic regression indicated high metals/solvents and high metals/solvent/noise groups had significantly greater odds ratios of 2.4; 95%CI [1.02, 2.85] and 1.7; 95%CI [1.46, 3.94], respectively, compared to a reference group. Both groups were associated with PTSs while controlling for age, gender, and exposure duration.

CONCLUSIONS

Simultaneous exposures classified as high for metals and solvents may damage hearing. Results suggest the need for expanding hearing conservation programs to consider combinations of exposures to metals, solvents, and noise. Am. J. Ind. Med. 60:227-238, 2017. © 2017 Wiley Periodicals, Inc.

Impact of environmental volatile organic compounds on otitis media in children: Correlation between exposure and urinary metabolites

INTRODUCTION

Volatile organic compounds (VOCs) induce inflammatory responses. Tobacco smoke contains numerous VOCs and is a risk factor for otitis media effusion (OME); however, no previous studies have investigated the association between VOCs and OME.

OBJECTIVES

We used urinary metabolites and exposure to environmental risk factors to investigate the association between VOC and polycyclic aromatic hydrocarbon exposure and recurrent OME in children.

METHODS

Children with recurrent OME who visited the Otorhinolaryngology Department of Seoul National University Hospital between November 2014 and June 2015 were prospectively enrolled in the study. Recurrent OME was defined as more than two OME episodes over a 6-month period lasting longer than 2 months. The control group consisted of children without OME in the last year. Demographic information, including age, sex, and previous medical history was obtained, and endoscopic examinations of the tympanic membrane were performed. Urinary concentrations of 1-hydroxypyrene, 2-naphthol, hippuric acid, trans, trans-muconic acid (t,t-MA), mandelic acid, phenyl glyoxylic acid, and methyl hippuric acid were analyzed using high-performance liquid chromatography/tandem mass spectroscopy. Environmental factors assessed included house type, age, renovations, the presence of furniture <6 months old, proximity to a road, and exposure to passive smoking.

RESULTS

We enrolled 11 children with OME and 39 controls. Age and sex did not differ between groups. Exposure to passive smoking was significantly more common in the OME group than in the controls (P < 0.001). Urinary concentrations of t.t.-MA were significantly higher in the OME group (126.33 μg/g cr) than in controls (52.661 μg/g cr; P = 0.003). Other metabolites including 1-hydroxypyrene, 2-naphthol, hippuric acid, mandelic acid, phenyl glyoxylic acid, and methyl hippuric acid did not demonstrated significant relation with the OME.

CONCLUSIONS

Levels of t,t-MA, a biomarker of benzene exposure, were significantly higher in the OME group than in controls. Passive smoking was significantly more common in the OME group. Our findings suggest that high t,t-MA levels which were probably originated from passive smoking and other pollutants could be indicative OME in children.

Background Noise Contributes to Organic Solvent Induced Brain Dysfunction

Occupational exposure to complex blends of organic solvents is believed to alter brain functions among workers. However, work environments that contain organic solvents are also polluted with background noise which raises the issue of whether or not the noise contributed to brain alterations. The purpose of the current study was to determine whether or not repeated exposure to low intensity noise with and without exposure to a complex blend of organic solvents would alter brain activity. Female Fischer344 rats served as subjects in these experiments. Asynchronous volume conductance between the midbrain and cortex was evaluated with a slow vertex recording technique. Subtoxic solvent exposure, by itself, had no statistically significant effects. However, background noise significantly suppressed brain activity and this suppression was exacerbated with solvent exposure. Furthermore, combined exposure produced significantly slow neurotransmission. These abnormal neurophysiologic findings occurred in the absence of hearing loss and detectable damage to sensory cells. The observations from the current experiment raise concern for all occupations where workers are repeatedly exposed to background noise or noise combined with organic solvents. Noise levels and solvent concentrations that are currently considered safe may not actually be safe and existing safety regulations have failed to recognize the neurotoxic potential of combined exposures.

Self-Reported Hearing Difficulties Among Adults With Normal Audiograms: The Beaver Dam Offspring Study

OBJECTIVE

Clinicians encounter patients who report experiencing hearing difficulty (HD) even when audiometric thresholds fall within normal limits. When there is no evidence of audiometric hearing loss, it generates debate over possible biomedical and psychosocial etiologies. It is possible that self-reported HDs relate to variables within and/or outside the scope of audiology. The purpose of this study is to identify how often, on a population basis, people with normal audiometric thresholds self-report HD and to identify factors associated with such HDs.

DESIGN

This was a cross-sectional investigation of participants in the Beaver Dam Offspring Study. HD was defined as a self-reported HD on a four-item scale despite having pure-tone audiometric thresholds within normal limits (<20 dB HL0.5, 1, 2, 3, 4, 6, 8 kHz bilaterally, at each frequency). Distortion product otoacoustic emissions and word-recognition performance in quiet and with competing messages were also analyzed. In addition to hearing assessments, relevant factors such as sociodemographic and lifestyle factors, environmental exposures, medical history, health-related quality of life, and symptoms of neurological disorders were also examined as possible risk factors. The Center for Epidemiological Studies-Depression was used to probe symptoms associated with depression, and the Medical Outcomes Study Short-Form 36 mental score was used to quantify psychological stress and social and role disability due to emotional problems. The Visual Function Questionnaire-25 and contrast sensitivity test were used to query vision difficulties.

RESULTS

Of the 2783 participants, 686 participants had normal audiometric thresholds. An additional grouping variable was created based on the available scores of HD (four self-report questions), which reduced the total dataset to n = 682 (age range, 21-67 years). The percentage of individuals with normal audiometric thresholds who self-reported HD was 12.0% (82 of 682). The prevalence in the entire cohort was therefore 2.9% (82 of 2783). Performance on audiological tests (distortion product otoacoustic emissions and word-recognition tests) did not differ between the group self-reporting HD and the group reporting no HD. A multivariable model controlling for age and sex identified the following risk factors for HD: lower incomes (odds ratio [OR] $50,000+ = 0.55, 95% confidence interval [CI] = 0.30-1.00), noise exposure through loud hobbies (OR = 1.48, 95% CI = 1.15-1.90), or firearms (OR = 2.07, 95% CI = 1.04-4.16). People reporting HD were more likely to have seen a doctor for hearing loss (OR = 12.93, 95% CI = 3.86-43.33) and report symptoms associated with depression (Center for Epidemiological Studies-Depression [OR = 2.39, 95% CI = 1.03-5.54]), vision difficulties (Visual Function Questionnaire-25 [OR = 0.93, 95% CI = 0.89-0.97]), and neuropathy (e.g., numbness, tingling, and loss of sensation [OR = 1.98, 95% CI = 1.14-3.44]).

CONCLUSIONS

The authors used a population approach to identify the prevalence and risk factors associated with self-reported HD among people who perform within normal limits on common clinical tests of auditory function. The percentage of individuals with normal audiometric thresholds who self-reported HD was 12.0%, resulting in an overall prevalence of 2.9%. Auditory and nonauditory risk factors were identified, therefore suggesting that future directions aimed at assessing, preventing, and managing these types of HDs might benefit from information outside the traditional scope of audiology.

Inhalation of Hydrocarbon Jet Fuel Suppress Central Auditory Nervous System Function

More than 800 million L/d of hydrocarbon fuels is used to power cars, boats, and jet airplanes. The weekly consumption of these fuels necessarily puts the public at risk for repeated inhalation exposure. Recent studies showed that exposure to hydrocarbon jet fuel produces lethality in presynaptic sensory cells, leading to hearing loss, especially in the presence of noise. However, the effects of hydrocarbon jet fuel on the central auditory nervous system (CANS) have not received much attention. It is important to investigate the effects of hydrocarbons on the CANS in order to complete current knowledge regarding the ototoxic profile of such exposures. The objective of the current study was to determine whether inhalation exposure to hydrocarbon jet fuel might affect the functions of the CANS. Male Fischer 344 rats were randomly divided into four groups (control, noise, fuel, and fuel + noise). The structural and functional integrity of presynaptic sensory cells was determined in each group. Neurotransmission in both peripheral and central auditory pathways was simultaneously evaluated in order to identify and differentiate between peripheral and central dysfunctions. There were no detectable effects on pre- and postsynaptic peripheral functions. However, the responsiveness of the brain was significantly depressed and neural transmission time was markedly delayed. The development of CANS dysfunctions in the general public and the military due to cumulative exposure to hydrocarbon fuels may represent a significant but currently unrecognized public health issue.

Occupational Hearing Loss among Chinese Municipal Solid Waste Landfill Workers: A Cross-Sectional Study

Background

Occupational hearing loss is an increasingly prevalent occupational condition worldwide, and has been reported to occur in a wide range of workplaces; however, its prevalence among workers from municipal solid waste landfills (MSWLs) remains less clear. This study aimed to investigate the occupational hearing loss among Chinese MSWL workers.

Methods

A cross-sectional study of 247 workers from 4 Chinese MSWLs was conducted. Noise and total volatile organic compounds (TVOCs) levels at worksites were determined. We conducted hearing examinations to determine hearing thresholds. A worker was identified as having hearing loss if the mean threshold at 2000, 3000 and 4000 Hz in either ear was equal to or greater than 25 dB. Prevalence of occupational hearing loss was then evaluated. Using unconditional Logistic regression models, we estimated the odds ratios (ORs) of MSWL work associated with hearing loss.

Results

According to the job title for each worker, the study subjects were divided into 3 groups, including group 1 of 63 workers without MSWL occupational hazards exposure (control group), group 2 of 84 workers with a few or short-period MSWL occupational hazards exposure, and group 3 of 100 workers with continuous MSWL occupational hazards exposure. Both noise and TVOCs levels were significantly higher at worksites for group 3. Significantly poorer hearing thresholds at frequencies of 2000, 3000 and 4000 Hz were found in group 3, compared with that in group 1 and group 2. The overall prevalence rate of hearing loss was 23. 5%, with the highest in group 3 (36.0%). The OR of MSWL work associated with hearing loss was 3.39 (95% confidence interval [CI]: 1.28-8.96).

Conclusion

The results of this study suggest significantly higher prevalence of hearing loss among MSWL workers. Further studies are needed to explore possible exposure-response relationship between MSWL occupational hazards exposure and hearing loss.

Auditory effects of exposure to noise and solvents: a comparative study

Introduction Industry workers are exposed to different environmental risk agents that, when combined, may potentiate risks to hearing. Objective To evaluate the effects of the combined exposure to noise and solvents on hearing in workers. Methods A transversal retrospective cohort study was performed through documentary analysis of an industry. The sample (n = 198) was divided into four groups: the noise group (NG), exposed only to noise; the noise and solvents group (NSG), exposed to noise and solvents; the noise control group and noise and solvents control group (CNS), no exposure. Results The NG showed 16.66% of cases suggestive of bilateral noise-induced hearing loss and NSG showed 5.26%. The NG and NSG had worse thresholds than their respective control groups. Females were less susceptible to noise than males; however, when simultaneously exposed to solvents, hearing was affected in a similar way, resulting in significant differences (p < 0.05). The 40- to 49-year-old age group was significantly worse (p < 0.05) in the auditory thresholds in the NSG compared with the CNS. Conclusion The results observed in this study indicate that simultaneous exposure to noise and solvents can damage the peripheral auditory system.

A study on neurobehavioral performance of workers occupationally exposed to solvent in synthetic resin manufacturing

Background:

One major effect of occupational solvent exposure is central nervous system (CNS) impairment, ranging from depression to encephalopathy with cognitive, behavioral changes. Exposures in industries being varied, classification of health outcomes for different exposures is important.

Objectives:

This study assessed neurobehavioral performance of synthetic resin manufacturing workers exposed to organic solvent, mainly formalin.

Materials and Methods:

This cross-sectional study selected subjects by random selection from all such workers of an Indian city. Questionnaire survey and assessment by a neurobehavioral test battery (NBT) was undertaken.

Results:

Comparison between actual and allied workers observed significant difference in tweezer dexterity, card sorting and backward memory scores. Significant effect of exposure was observed on tweezer dexterity, card sorting, and hand dynamometer scores.

Conclusion:

Changes of neurobehavioral performance might occur following solvent exposure and these changes might have a relationship with the quantum of exposure. Periodic examination of workers with NBT is needed for detection of early neurotoxic effects.

Sound Levels and Risk Perceptions of Music Students During Classes

It is well recognized that professional musicians are at risk of hearing damage due to the exposure to high sound pressure levels during music playing. However, it is important to recognize that the musicians' exposure may start early in the course of their training as students in the classroom and at home. Studies regarding sound exposure of music students and their hearing disorders are scarce and do not take into account important influencing variables. Therefore, this study aimed to describe sound level exposures of music students at different music styles, classes, and according to the instrument played. Further, this investigation attempted to analyze the perceptions of students in relation to exposure to loud music and consequent health risks, as well as to characterize preventive behaviors. The results showed that music students are exposed to high sound levels in the course of their academic activity. This exposure is potentiated by practice outside the school and other external activities. Differences were found between music style, instruments, and classes. Tinnitus, hyperacusis, diplacusis, and sound distortion were reported by the students. However, students were not entirely aware of the health risks related to exposure to high sound pressure levels. These findings reflect the importance of starting intervention in relation to noise risk reduction at an early stage, when musicians are commencing their activity as students.

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.

Bilateral hearing loss after dichloromethane poisoning: a case report

Dichloromethane is a widely used organic solvent. Occupational exposure to dichloromethane is frequent and can result in both acute and chronic toxicity, affecting mostly the central nervous system, directly or through its metabolite, carbon monoxide. The effects of dichloromethane on the peripheral nervous system are debated. Here we report the case of a 37-year-old woman who was accidentally exposed to dichloromethane. In the days following the incident she experienced bilateral hypoacusis. Hearing loss regressed after 25 days treatment with hyperbaric oxygen. This is the first report of sudden hearing loss after acute exposure to dichloromethane, suggesting a possible toxic effect of this solvent on the auditory system.

Review of toluene action: clinical evidence, animal studies and molecular targets

It has long been known that individuals will engage in voluntary inhalation of volatile solvents for their rewarding effects. However, research into the neurobiology of these agents has lagged behind that of more commonly used drugs of abuse such as psychostimulants, alcohol and nicotine. This imbalance has begun to shift in recent years as the serious effects of abused inhalants, especially among children and adolescents, on brain function and behavior have become appreciated and scientifically documented. In this review, we discuss the physicochemical and pharmacological properties of toluene, a representative member of a large class of organic solvents commonly used as inhalants. This is followed by a brief summary of the clinical and pre-clinical evidence showing that toluene and related solvents produce significant effects on brain structures and processes involved in the rewarding aspects of drugs. This is highlighted by tables highlighting toluene's effect on behaviors (reward, motor effects, learning, etc.) and cellular proteins (e.g. voltage and ligand-gated ion channels) closely associated the actions of abused substances. These sections demonstrate not only the significant progress that has been made in understanding the neurobiological basis for solvent abuse but also reveal the challenges that remain in developing a coherent understanding of this often overlooked class of drugs of abuse.

Self-reported hearing performance in workers exposed to solvents

OBJECTIVE: To compare hearing performance relating to the peripheral and central auditory system between solvent-exposed and non-exposed workers. METHODS: Forty-eight workers exposed to a mixture of solvents and 48 non-exposed control subjects of matched age, gender and educational level were selected to participate in the study. The evaluation procedures included: pure-tone audiometry (500 - 8,000 Hz), to investigate the peripheral auditory system; the Random Gap Detection test, to assess the central auditory system; and the Amsterdam Inventory for Auditory Disability and Handicap, to investigate subjects' self-reported hearing performance in daily-life activities. A Student t test and analyses of covariance (ANCOVA) were computed to determine possible significant differences between solvent-exposed and non-exposed subjects for the hearing level, Random Gap Detection test and Amsterdam Inventory for Auditory Disability and Handicap. Pearson correlations among the three measures were also calculated. RESULTS: Solvent-exposed subjects exhibited significantly poorer hearing thresholds for the right ear than non-exposed subjects. Also, solvent-exposed subjects exhibited poorer results for the Random Gap Detection test and self-reported poorer listening performance than non-exposed subjects. Results of the Amsterdam Inventory for Auditory Disability and Handicap were significantly correlated with the binaural average of subject pure-tone thresholds and Random Gap Detection test performance. CONCLUSIONS: Solvent exposure is associated with poorer hearing performance in daily life activities that relate to the function of the peripheral and central auditory system.

Auditory dysfunction associated with solvent exposure

Background

A number of studies have demonstrated that solvents may induce auditory dysfunction. However, there is still little knowledge regarding the main signs and symptoms of solvent-induced hearing loss (SIHL). The aim of this research was to investigate the association between solvent exposure and adverse effects on peripheral and central auditory functioning with a comprehensive audiological test battery.

Methods

Seventy-two solvent-exposed workers and 72 non-exposed workers were selected to participate in the study. The test battery comprised pure-tone audiometry (PTA), transient evoked otoacoustic emissions (TEOAE), Random Gap Detection (RGD) and Hearing-in-Noise test (HINT).

Results

Solvent-exposed subjects presented with poorer mean test results than non-exposed subjects. A bivariate and multivariate linear regression model analysis was performed. One model for each auditory outcome (PTA, TEOAE, RGD and HINT) was independently constructed. For all of the models solvent exposure was significantly associated with the auditory outcome. Age also appeared significantly associated with some auditory outcomes.

Conclusions

This study provides further evidence of the possible adverse effect of solvents on the peripheral and central auditory functioning. A discussion of these effects and the utility of selected hearing tests to assess SIHL is addressed.

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/m3) 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.

Assessment of styrene oxide neurotoxicity using in vitro auditory cortex networks

Styrene oxide (SO) (C8H8O), the major metabolite of styrene (C6H5CH=CH2), is widely used in industrial applications. Styrene and SO are neurotoxic and cause damaging effects on the auditory system. However, little is known about their concentration-dependent electrophysiological and morphological effects. We used spontaneously active auditory cortex networks (ACNs) growing on microelectrode arrays (MEA) to characterize neurotoxic effects of SO. Acute application of 0.1 to 3.0 mM SO showed concentration-dependent inhibition of spike activity with no noticeable morphological changes. The spike rate IC50 (concentration inducing 50% inhibition) was 511 ± 60 μM (n = 10). Subchronic (5 hr) single applications of 0.5 mM SO also showed 50% activity reduction with no overt changes in morphology. The results imply that electrophysiological toxicity precedes cytotoxicity. Five-hour exposures to 2 mM SO revealed neuronal death, irreversible activity loss, and pronounced glial swelling. Paradoxical "protection" by 40 μM bicuculline suggests binding of SO to GABA receptors.

Hearing impairment in F-111 maintenance workers: the study of health outcomes in aircraft maintenance personnel (SHOAMP) general health and medical study

BACKGROUND

We sought to examine hearing loss in a group from the Royal Australian Air Force who undertook fuel tank maintenance on F-111 aircraft, with exposure to formulations containing ototoxins, relative to two different comparison groups.

METHODS

Using pure-tone audiometry, hearing thresholds were assessed in 614 exposed personnel, 513 technical-trade comparisons (different base, same job), and 403 non-technical comparisons (same base, different job). We calculated percentage loss of hearing (PLH) and used regression models to examine whether there was an association between PLH and F-111 fuel tank maintenance, adjusting for possible confounders. In addition, the difference between the observed hearing thresholds and the expected thresholds based on an otologically normal population (ISO-7029-2003) was determined.

RESULTS

The PLH ranged from nil to 96 (median 1.5, quartiles 0.3, 5.5). A logistic regression model showed no statistically significant difference in PLH among the three exposure groups (exposed vs. non-technical controls 1.1: 95% CI 0.7, 2.0 and exposed vs. technical OR 0.9: 95% CI 0.6, 1.3). The model also highlighted a number of other risk factors for PLH including age, tinnitus, smoking, depression, and use of depression medications. However, at all eight frequencies measured, all populations had lower than expected hearing thresholds based on published ISO-7029 medians.

CONCLUSIONS

Although there was no difference in PLH between the three exposure groups, the study did reveal a high degree of hearing loss between the 3 groups and a normal population.

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.

Occupational styrene exposure and hearing loss: a cohort study with repeated measurements

OBJECTIVE

Associations between occupational styrene exposure and impairment of hearing function were investigated, guided by three questions: are there hearing losses concerning high frequency and standard audiometric test? Are there dose-response relationships and measurable thresholds of effects? Are there signs of reversibility of possible effects if the workers are examined during times of improvement from their work?

METHODS

A group of workers from a boat building plant, some of whom were laminators, were examined in subgroups of current low (n = 99, mean mandelic acid MA + phenylglyoxylic acid PGA = 51 mg/g creatinine), medium (n = 118, mean 229 mg/g creat.) and high (n = 31, mean 970 mg/g creat.) exposure to styrene. In addition, subgroups chronically exposed to high-long (n = 17) and low-short (n = 34) styrene levels were analysed. The examinations were carried out during normal work days and during the company holidays. Hearing thresholds and transient evoked otoacoustic emissions (TEOAE) were measured. Statistics included multiple co-variance analyses with repeated measures, linear regressions, and logistic regressions.

RESULTS

The analyses of all participants demonstrated no clear exposure effects. Particularly no sufficient proof of dose-response relationship measured against parameters of current exposure (MA + PGA, styrene/blood) and of chronic exposure (cumulative and average life time exposure resp.) was found. The analyses of groups exposed to high levels show elevated thresholds at frequencies up to 1,500 Hz among the subgroup exposed to high styrene levels (e.g. 40-50 ppm as average) for a longer period of time (e.g. more than 10 years). These participants also demonstrated signs of "improvement" at frequencies above 2,000 Hz during work holidays, when they were not exposed to styrene. A significantly elevated odds ratio for cases of hearing loss (more than 25 dB (A) in one ear, 3,000-6,000 Hz) was found among the group exposed to high levels (above 30 ppm as average) for a longer period of time (more than 10-26 years). The measurements of TEOAE did not exhibit significant results related to exposure.

CONCLUSION

This study found, that chronic and intensive styrene exposure increases the hearing thresholds. At levels of about 30-50 ppm as an average inhaled styrene per work day over a period of about 15 years with higher exposure levels above 50 ppm in the past, an elevated risk for impaired hearing thresholds can be expected. The formerly published results on ototoxic effects below 20 ppm could not be confirmed. With few exceptions (at frequencies of 1,000 and 1,500 Hz) no dose-response relationship between threshold and exposure data was found. Improvements of hearing thresholds during work- and exposure-free period are possible.

Hearing loss among licensed pesticide applicators in the agricultural health study

OBJECTIVE

We evaluated self-reported hearing loss and pesticide exposure in licensed private pesticide applicators enrolled in the Agricultural Health Study in 1993 to 1997 in Iowa and North Carolina.

METHODS

Among 14,229 white male applicators in 1999 to 2003, 4926 reported hearing loss (35%). Logistic regression was performed with adjustment for state, age, and noise, solvents, and metals. We classified pesticides by lifetime days of use.

RESULTS

Compared with no exposure, the odds ratio (95% confidence interval) for the highest quartile of exposure was 1.19 (1.04 to 1.35) for insecticides and 1.17 (1.03 to 1.31) for organophosphate insecticides. Odds of hearing loss were elevated for high pesticide exposure events (1.38, 1.25 to 1.54), pesticide-related doctor visits (1.38, 1.17 to 1.62) or hospitalization (1.81, 1.25 to 2.62), and diagnosed pesticide poisoning (1.75, 1.36 to 2.26).

CONCLUSIONS

Although control for exposure to noise or other neurotoxicants was limited, this study extends previous reports suggesting that organophosphate exposure increases risk of hearing loss.

Selective inhibition of human heteromeric alpha9alpha10 nicotinic acetylcholine receptors at a low agonist concentration by low concentrations of ototoxic organic solvents

Ethylbenzene and para-xylene (p-xylene), but not the chemically closely related organic solvents ortho-xylene (o-xylene) and meta-xylene (m-xylene), are known to cause ototoxicity and irreversible hearing loss, though the underlying mechanisms are still unknown. In this study, effects of ethylbenzene and of p-, o-, and m-xylene on human heteromeric alpha9alpha10 nicotinic acetylcholine receptors (nAChRs) expressed in Xenopus oocytes were investigated using the two-electrode voltage clamp technique. ACh dose-dependently evoked an alpha9alpha10 nAChR-mediated ion current with an EC(50) of 137 microM. When ACh is applied at a low concentration (10 microM), the nAChR-mediated ion current is inhibited by a low concentration (10 microM) of ethylbenzene and p-xylene, but not by the same concentration of the non-ototoxic solvents. At a high solvent concentration (300 microM), all solvents cause inhibition of the ion currents evoked by 10 microM ACh. Ion currents evoked by a near maximum-effective concentration ACh (1mM) are inhibited by the selected organic solvents only at 300 microM. These results demonstrate that low concentrations of the known ototoxic solvents ethylbenzene and p-xylene inhibit alpha9alpha10 nAChR-mediated ion currents, whereas the structurally related, non-ototoxic solvents m-xylene and o-xylene do not, indicating that the alpha9alpha10 nAChR is a potential target for solvent-induced ototoxicity.

Deafness in the developing world: the place of cochlear implantation

INTRODUCTION

This paper attempts to review changes in the lives of hearing-impaired patients within the developing world, brought about by globalisation and development. The paper also explores limitations to improved care and addresses the collective moral responsibility of developed nations.

METHODS

Analysis of literature.

RESULTS

Within developing nations, large populations have emerged with a similar pattern of problems, access to information and aspirations as those living in developed nations. However, marked differences in income have persisted. These trends have resulted in a relative increase in the proportion of the hearing-impaired population in need of cochlear implantation, while at the same time restricting their access to such treatment.

CONCLUSIONS

The emergence of global markets and media and a shared sense of destiny amongst the people of this planet should translate into a concerted, worldwide effort to assist the deaf in developing countries. Much more can be done within existing resources and frameworks to improve the quality of these peoples' lives.

Chemobrain: a translational challenge for neurotoxicology

Neurotoxicity is a frequent accompaniment of cancer chemotherapy, and held by many oncologists to be the major dose-limiting side effect. It appears in many forms, but attracted attention during the past decade primarily because of complaints by patients of impaired cognitive function they have labeled as "chemobrain". Neuropsychological testing confirmed the validity of these complaints and has generated a substantial literature examining different aspects of cognitive impairment in various clinical populations undergoing a variety of treatments. Cognitive impairment is far from the only manifestation of neurotoxicity induced by chemotherapy, however. It alters sensory function and motor function as well. A critical need for patients is a suite of methods that will enable clinicians to trace the onset and progression of neurotoxicity so as to guide and balance decisions about the course of chemotherapy. This commentary describes some of the potential methods and encourages neurotoxicologists to enlist their unique skills in the service of these needs.

Occupationally-acquired noise-induced hearing loss: a senseless workplace hazard

OBJECTIVES

Occupational noise-induced hearing loss (ONIHL) describes an acquired hearing deficiency directly attributable to excessive workplace noise exposure. Data suggest that excessive noise attributes to approximately 37% of all adult causes of hearing loss and remains a significant contributor to employment-related morbidity internationally. Typically insidiously-acquired, often without frank progressive symptomatology, regional medical agencies continue to struggle with this potentially debilitating condition. The aim of the study was to provide a synopsis of the current understanding of ONIHL, its impact on individual workers and the wider international community, and to identify barriers to more uniform adoption of personal hearing protection.

MATERIALS AND METHODS

A review of the contemporary literature was performed using defined keyword searches and OVID, PubMed, and Google Scholar as primary electronic search engines.

RESULTS

A number of published works were identified, describing aspects of the relationship between workplace-related noise exposure and subsequent development of employee hearing impairment, which demonstrate an overwhelming gender imbalance, with up to 97% of affected individuals being male. Industry-specific associations (e.g., mining, manufacturing and heavy construction) were well documented, as were links to toxin-specific exposures, in the recognized development of hearing loss. However, evidence of integration of appraisal of the topically-current area of genetic susceptibility was often lacking. Much discordance still exists among international agencies in the prescriptive regulation and enforcement of "safe" exposure limits.

CONCLUSIONS

Despite a high level of public awareness regarding the importance of hearing preservation and increasingly stringent international occupational health, safety and welfare requirements mandating provision of safer work environments, ONIHL continues to be a significant occupational hazard. ONIHL is permanent and may cause significant disability, for which there currently exists no cure, but is largely overtly-preventable. The impact of ONIHL on the global transition toward dominant communication-rich white-collar employment roles is difficult to quantitate, but is likely to be substantive upon the afflicted individual. In the mainstream setting, exposure-avoidance strategies aimed to reduce the incidence of ONIHL remain the focus of public health and occupational medicine approaches.