Combined effects of ototoxic solvents and noise on hearing in automobile plant workers in Iran

Simultaneous Exposure to Noise and Toluene Induces Oxidative and Inflammatory Damage in the Heart of Wistar Rats: Therapeutic Potential of Olea europaea L. Leaf Extract

Workers in occupational settings often face simultaneous exposure to multiple risk factors, including noise and chemicals. This study aimed to investigate the effects of combined exposure to noise and toluene on the cardiac health of rats, with a focus on assessing the potential mitigating effects of Olea europaea L. (OLE) leaf extract (40 mg/kg/day). The evaluation involved scrutinizing biochemical and hematological markers, quantifying oxidative stress levels, determining proinflammatory cytokines in the serum, and conducting an in silico Docking studies. Forty-two male Wistar rats were divided into eight groups-(n = 6/group):-Control-group-(C),-OLE-group-(Rats administered OLE), NT-group (rats co-exposed to noise and toluene), NT-4 group-(rats co-exposed to noise and toluene four weeks after the exposure period), NT + OLE1-group (rats co-exposed to noise and toluene treated with OLE for one week), NT + OLE2-group-(rats co-exposed to noise and toluene treated with OLE for two weeks), NT + OLE3-group-(rats co-exposed to noise and toluene treated with OLE for three weeks), and NT + OLE4-group (rats co-exposed to noise and toluene treated with OLE for four weeks). The results revealed that combined exposure to noise and toluene led to oxidative damage and increased serum levels of proinflammatory cytokines. However, OLE treatment attenuated these effects by reducing lipid peroxidation and enhancing catalase and superoxide dismutase activities. Additionally, OLE treatment significantly decreased proinflammatory cytokine levels compared to the noise and toluene co-exposed group. The study highlighted the potential of OLE to attenuate the adverse effects of combined exposure to noise and toluene, attributed to its anti-inflammatory and antioxidant properties.

Olea europaea L. leaf extract mitigates oxidative and histological damage in rat heart tissue exposed to combined noise and toluene: An experimental study

In many occupational settings, workers are frequently exposed to toluene and noise. However, the individual and combined effects of these exposures on the cardiovascular system have not been fully elucidated. Therefore, this study aimed to investigate the impact of simultaneous exposure to toluene and noise on the rat heart, while also evaluating the potential preventive effect of olive leaf extract (OLE). Forty-eight male Wistar rats were randomly assigned to eight groups (n = 6/group): control group (C), control group that received OLE (C + OLE), group exposed to noise (N), group exposed to noise and receiving OLE (N + OLE), group exposed to toluene (T), group exposed to toluene and receiving OLE (T + OLE), group co-exposed to noise and toluene (NT), and group co-exposed to noise and toluene and receiving OLE (NT + OLE). The rats in this study were subjected to simultaneous exposure to toluene and noise for a duration of six weeks, within a custom-built plexiglass chamber. Toluene was administered at a concentration of 300 ppm, while the noise level was set to 85 dB(A). The exposure chamber was equipped with a generation system, an exposure system, and a monitoring system, ensuring precise and accurate exposure conditions. After the six-week period, heart and blood samples were collected from the rats for subsequent analysis. Plasma levels of cholesterol (CHOL), triglycerides (TG), lactate dehydrogenase (LDH), and creatine kinase (CK) were measured, and histopathological investigation was conducted using HE staining. Additionally, superoxide dismutase (SOD) and catalase (CAT) activities, as well as malondialdehyde (MDA) levels in heart tissue were measured. Our results showed that simultaneous exposure to noise and toluene altered CHOL, TG, LDH, and CK levels, and also caused an increase in lipid peroxidation levels and superoxide dismutase activity, along with a decrease in catalase activity in the heart. A significant alteration in the myocardium was also observed. However, treatment with OLE was found to modulate these oxidative and histological changes, ultimately correcting the deleterious effects induced by the combined exposure to noise and toluene. Therefore, our study suggests that OLE could be a potential preventive measure for individuals exposed to toluene and noise in industrial settings.

The Combined Effect of Noise and Solvent Exposure on Hearing Loss in the Tire Factory Workers

Noise and organic solvents are common in many industries and both of them affect hearing. In this study, we estimated the concurrent effect of them on hearing by evaluating the existence of notch in audiograms of workers. The number of 540 persons were enrolled in this study after eliminating workers who had the exclusion criteria. We divided them into 4 groups based on their exposure status; no exposure, exposure to noise, exposure to solvent, exposure to both of them. The presence of notch in left, right, or both ears were assessed through Coles model. The rates of notch presence in both ears in the groups of noise and organic solvents exposure, noise exposure only, solvents exposure only were 11.72, 4.49, 1.86 times higher than the control group and sole solvent exposure didn't affect hearing significantly. The same pattern was seen for notch presence in left or right ear and the solvent-noise exposure group had the highest rate of notch presence. This study aims to show the synergic effect of noise and organic solvents exposure on hearing loss. Hence, we recommend implementing a hearing protection program and a higher frequency of audiological assessments in the industries involved with concurrent exposure to noise and organic solvents.

Exposure to lead, mercury, styrene, and toluene and hearing impairment: evaluation of dose-response relationships, regulations, and controls

The risk of hearing loss from exposure to ototoxic chemicals is not reflected in occupational exposure limits and most jurisdictions. The aims of this research were to investigate dose-response relationships between exposure to lead, mercury, toluene, and styrene and hearing impairment based on current epidemiological evidence, conduct cross-jurisdictional comparisons, and investigate control measures for exposure to ototoxic chemicals. Ovid Medline and Ovid Embase databases were used to find relevant publications. A total of 86 epidemiological studies met the eligibility criteria for final evaluation. When significant associations between exposure and outcome were identified, exposure levels were evaluated to determine whether No Observed Adverse Effect Level (NOAEL) and Lowest Observed Adverse Effect Level (LOAEL) could be identified. Cross-jurisdictional comparisons included the U.K., U.S., Canada, and Australia occupational health and safety legislations. The majority of lead (75%), styrene (74%), and toluene (77%) studies showed significantly increased risks of hearing loss from exposure to these substances, although numerous studies on toluene (70%) and styrene (16%) compared auditory function between "solvent mixture" or "noise and solvent mixture" exposed groups and controls and not necessarily on groups exposed to a single agent. Based on five studies, blood lead ranges of 1-1.99 μg/dL to 2.148-2.822 μg/dL were identified as NOAELs while blood lead levels of 2 μg/dL up to 2.823-26.507 μg/dL were identified as LOAELs for hearing loss. Except for general duty clauses, the U.S., Canadian, and Australian jurisdictions have set no enforceable regulations specific to ototoxic chemical exposures. A biological exposure index of 2 μg/dL is recommended for prevention of hearing impairment from lead exposure. Based on Safe Work Australia, noise exposure limits may be reduced to 80 dB(A) for 8 hr. Other recommendations include performing audiometric testing and controlling exposure through all routes of entry.

Prevalence of hearing loss among noise-exposed workers within the services sector, 2006-2015

OBJECTIVE

The purpose of this study is to estimate the prevalence of hearing loss among noise-exposed U.S. workers within the Services sector.

METHODS

Audiograms for 1.9 million workers (158,436 within Services) from 2006 to 2015 were examined. Prevalence and adjusted risk for hearing loss as compared with a reference industry were estimated for the Services sector/sub-sectors, and all industries combined.

RESULTS

The prevalence of hearing loss within Services was 17 compared to 16% for all industries combined. However, many sub-sectors greatly exceeded the overall prevalence (10-33% higher) and/or had adjusted risks significantly higher than the reference industry. Workers in Administration of Urban Planning and Community and Rural Development had the highest prevalence (50%), and workers in Solid Waste Combustors and Incinerators had more than double the risk, the highest of any sub-sector. Some sub-sectors traditionally viewed as 'low-risk' also had high prevalences and risks.

CONCLUSIONS

Large numbers of workers within Services have an elevated risk of hearing loss and need immediate hearing conservation efforts. Additional research and surveillance are needed for sub-sectors for which there is low awareness of hearing hazards or a lack of hearing data.

The combined effects of occupational exposure to noise and other risk factors - a systematic review

PURPOSE

Noise-induced health effects exacerbate by many other risk factors. This systematic review aims at shedding light on the combined effects of co-exposure to occupational noise and other factors.

MATERIAL AND METHODS

A literature search in Web of Science, Scopus, PubMed, Science Direct, and Google Scholar, with appropriate keywords on combined effects of occupational noise, and co-exposure to noise and other factors, revealed 7928 articles which were screened by two researchers. A total of 775 articles were reviewed in full text. We found 149 articles that were relevant and had sufficient quality for analysis.

RESULTS

We identified 16 risk factors that exacerbate occupational noise-induced health effects. These factors were classified into four groups: chemical (carbon monoxide (CO), solvents, heavy metals, and other chemicals), physical (lighting, heat, vibration, and cold), personal (age, gender, genetics, smoking, medication, contextual diseases) and occupational (workload and shift work). Hearing loss, hypertension, reduced performance, and cardiovascular strains, are the most important risk factors combined effects due to concurrent exposure to noise and other risk factors.

CONCLUSION

Evidences of combined effects of solvents, vibration, heavy metals, CO, smoking, chemicals, aging, heat, and shiftwork were respectively stronger than for other factors. Most of the studies have investigated only the combined effects of risk factors on hearing, and the evidence for non-auditory effects is still limited, and more studies are warranted. Therefore, in the Hearing Conservation Programs, besides noise, aggravating factors of noise effects should also be taken into account.

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.

Association between self-reported hearing impairment and diabetes: a Brazilian population-based study: Association between self-reported hearing impairment and diabetes in adults

BACKGROUND

Some studies have already explored the relationship between diabetes and hearing loss; however, this relationship has still not been well established, especially due to methodological limitations related to lack of control for confounders. The aim of this study was to analyze the association between self-reported hearing impairment and diabetes among adults in Brazil, controlling for sociodemographic and occupational exposure to ototoxic agents.

METHODS

This is a cross-sectional study based on data collected by the National Health Survey of 2013 in Brazil. A total of 60,202 individuals aged≥18 years were interviewed. Crude and adjusted prevalence ratios were calculated using the Poisson regression model with robust estimation of the variance. All analyzes were performed considering the appropriated weights imposed by the complex sample design.

RESULTS

Hearing loss prevalence was 2.56% (95%CI: 2.34-2.79). It was higher in males, older age groups, white and individuals with lower levels of schooling. Diabetes was positively and significantly associated with hearing loss in the crude analysis (PRcrude = 2.92; 95%CI: 2.75-3.11) and also in the analysis adjusted for gender, age, skin color, schooling, smoking, alcohol consumption and occupational exposure (PRadj = 1.46; 95%CI: 1.32-1.61).

CONCLUSIONS

The present results suggest that individuals with diabetes have higher prevalence of hearing impairment. There is the need of longitudinal studies to investigate if diabetes is a risk factor to hearing impairment.

Could fibrinogen and hsCRP be useful for assessing personal risk in workers exposed to a mixture of ultrafine particles and organic solvents?

Purpose: Our study focuses on elucidating if two common inflammatory biomarkers, easily performed in any laboratory - high-sensitivity C-reactive protein (hsCRP), as well as fibrinogen - could be used to assess the personal health risk of workers exposed to a complex occupational exposure to ultrafine particles (UFP) and a mixture of organic solvents. Methods: To assess the inflammatory response on the body, laboratory determinations were performed by testing the serum levels of hsCRP and fibrinogen, in exposed and unexposed groups. Results: There are no statistically significant differences for hsCRPs (p-0.25), medians were similar in groups. The mean values of fibrinogen in the three groups were: in the workers group (1st group): 346.2 mg/dl, in the office staff group (2nd group): 328.7 mg/dl, and in the control group (3rd group): 284.8 mg/dl, with significant differences between 1st group vs 3rd group and between 2nd group vs 3rd group (p-0.002). UFP levels differ between the groups, as follows: 1st group were exposed to the highest levels, ranging from 48349 to 3404000 part/cm3; 2nd group, ranging from 17371 to 40595 part/cm3; and 3rd group, ranging from 213 to 16255 part/cm3. Conclusions: Our study demonstrates that fibrinogen is a useful inflammatory biomarker for exposure to a mixture of UFP and organic solvents. On the other hand, hsCRP is not a useful inflammatory biomarker in occupational exposure to UFP and organic solvents. Further studies are needed to demonstrate the extent to which fibrinogen is more or less influenced by organic solvents or UFP alone.

Sensorineural Hearing Impairment and Subclinical Atherosclerosis in Rheumatoid Arthritis Patients Without Traditional Cardiovascular Risk Factors

Objectives

This study aims to evaluate the association of hearing impairment with carotid intima-media thickness and subclinical atherosclerosis in rheumatoid arthritis (RA) patients.

Patients and methods

A total of 41 RA patients (2 males, 39 females; mean age 46.5±10.2 years; range 20 to 63 years) with no known traditional cardiovascular risk factors were included. Routine clinical and laboratory assessments for RA patients were performed. Pure tone air (250-8000 Hz) and bone conduction (250-6000 Hz) thresholds were obtained, tympanograms and impedance audiometry were conducted. Sensorineural hearing impairment was defined if the average thresholds were ≥25 decibels. Carotid intima-media thickness was assessed and classified with a cut-off point of 0.6 mm.

Results

Thirteen patients (31.7%) had normal audition, while 28 (68.3%) had hearing impairment. Of these, 22 had bilateral sensorineural hearing impairment. Four patients had conductive hearing impairment (right in three patients and left in one patient). Patients with sensorineural hearing impairment had increased carotid intima-media thickness in the media segment of carotid common artery compared to patients with normal hearing (right ear p=0.007; left ear p=0.075). Thickening of the carotid intima-media thickness was associated with sensorineural hearing impairment in RA patients.

Conclusion

Rheumatoid arthritis patients should be evaluated by carotid intima-media thickness as a possible contributing factor of hearing impairment in patients without cardiovascular risk factors.

Perda auditiva associada à exposição ocupacional a solventes orgânicos: uma revisão sistemática

Resumo Introdução: evidências apontam produtos químicos como agentes potencialmente otoneurotóxicos, todavia, ainda não há consenso quanto às associações entre as características das exposições e a ototoxicidade das diversas substâncias químicas presentes em ambientes laborais. Objetivo: revisar a literatura científica disponível, a fim de identificar estudos que apontem evidências de associação, ou não associação, entre dano auditivo e a exposição a solventes orgânicos. Método: revisão sistemática da literatura a partir da consulta a bases de dados eletrônicas, considerando artigos originais, publicados de janeiro de 1987 a fevereiro de 2013. Resultados: trinta e um estudos foram incluídos na revisão sistemática. Discussão: os estudos confirmaram a exposição a determinados solventes como fator de risco para perda auditiva de origem ocupacional, sobretudo na presença do ruído. Foram utilizados métodos variados de avaliação e classificação do desfecho coclear e/ou central, que contribuíram para a compreensão da extensão da perda auditiva induzida quimicamente, bem como com a identificação dos grupos populacionais susceptíveis. Contudo, dados sobre procedimentos diagnósticos adequados, níveis seguros e efeito dose-resposta da exposição química ainda não foram totalmente elucidados.

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.

Combined effects of exposure to occupational noise and mixed organic solvents on blood pressure in car manufacturing company workers

BACKGROUND

Recent studies suggest that occupational exposures such as noise and organic solvents may affect blood pressure. The aim of this study was to investigate interaction of noise and mixed organic solvents on blood pressure.

METHODS

Four hundred seventy-one workers of a car manufacturing plant were divided into four groups: group one or G1 workers exposed to noise and mixed organic solvents in the permitted limit or control group, G3 exposed to noise only, G2 exposed to solvents only, and G4 workers exposed to noise and mixed organic solvents at higher than the permitted limit or co-exposure group. Biological interaction of two variables on hypertension was calculated using the synergistic index.

RESULTS

The workers of co-exposure group (G4), noise only group (G3), and solvents only group (G2) had significantly higher mean values of SBP and DBP than workers of control group (G1) or office workers (P < 0.05). Also logistic regression analysis showed a significant association between hypertension and exposure to noise and mixture of organic solvents. Odds ratio for hypertension in the co-exposure group and the noise only and solvents only exposed groups was 14.22, 9.43, and 4.38, respectively, compared to control group. In this study, the estimated synergism index was 1.11.

CONCLUSIONS

Our results indicate that exposure to noise or a mixture of organic solvents may be associated with the prevalence of hypertension in car manufacturing company workers and co-exposure to noise and a mixture of solvents has an additive effect in this regard. Therefore appropriate preventive programs in these workers recommended.

Ototoxic Substances at the Workplace: a Brief Update

Ototoxic chemicals can impair the sense of hearing and balance. Lately, efforts have been intensified to compile evidence-based lists of workplace agents with ototoxic properties. This article gives a rough overview of the latest relevant publications, which confirm that toluene, styrene, and lead should receive particular attention as ototoxic substances at the workplace. Moreover, there is sufficient evidence that occupational exposure to trichloroethylene, mercury, carbon monoxide, and carbon disulfide can affect the ear. Based on the existing information, industrial hygienists should make sure that occupational health professionals and the workforce are made aware of the risks posed by ototoxic substances; support their replacement or new technical measures to reduce exposure; make these substances a part of regular screening, develop tools that can early diagnose chemically induced hearing impairment, and investigate further into the ototoxic properties of these substances. Further research should focus on quantifying the combined effects of ototoxic substances and noise.

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.