Noise-induced hearing loss in Korean workers: co-exposure to organic solvents and heavy metals in nationwide industries

Association of sudden sensorineural hearing loss with meteorological factors: a time series study in Hefei, China, and a literature review

Air pollution can cause disease and has become a major global environmental problem. It is currently believed that air pollution may be related to the progression of SSNHL. As a rapidly developing city in recent years, Hefei has serious air pollution. In order to explore the correlation between meteorological variables and SSNHL admissions, we conducted this study. This study investigated the short-term associations between SSNHL patients admitted to the hospital and Hefei climatic variables. The daily data on SSNHL-related hospital admissions and meteorological variables containing mean temperature (T-mean; °C), diurnal temperature range (DTR; °C), atmospheric pressure (AP; Hp), and relative humidity (RH; %), from 2014 to 2021 (2558 days), were collected. A time-series analysis integrating distributed lag non-linear models and generalized linear models was used. PubMed, Embase, Cochrane Library, and Web of Science databases were searched. Literature published up to August 2023 was reviewed to explore the potential impact mechanisms of meteorological factors on SSNHL. The mechanisms were determined in detail, focusing on wind speed, air pressure, temperature, humidity, and air pollutants. Using a median of 50.00% as a baseline, the effect of exceedingly low T-mean in the single-day hysteresis effect model began at a lag of 8 days (RR = 1.032, 95% CI: 1.001 ~ 1.064). High DTR affected the admission rate for SSNHL on lag 0 day. The significance of the effect was the greatest on that day (RR = 1.054, 95% CI: 1.007 ~ 1.104) and then gradually decreased. High and exceedingly high RH affected the admission rate SSNHL on lag 0 day, and these effects lasted for 8 and 7 days, respectively. There were significant associations between all grades of AP and SSNHL. This is the first study to assess the effect of meteorological variables on SSNHL-related admissions in China using a time-series approach. Long-term exposures to high DTR, RH values, low T-mean values, and all AP grades enhance the incidence of SSNHL in residents. Limiting exposure to extremes of ambient temperature and humidity may reduce the number of SSNHL-related hospital visits in the region. It is advisable to maintain a suitable living environment temperature and avoid extreme temperature fluctuations and high humidity. During periods of high air pollution, it is recommended to stay indoors and refrain from outdoor exercise.

Higher exposure to 1,3-butadiene is associated with more severe hearing loss

While volatile organic compounds (VOCs) impair various organs, their influence on hearing loss (HL) has not been extensively researched. We aimed to identify the association between VOCs and HL or high-frequency hearing loss (HFHL). We extracted data on age, sex, pure tone audiometry, hypertension, occupational noise exposure, and creatinine-corrected urine VOC metabolite concentrations from the eighth Korea National Health and Nutrition Survey. Among the VOC metabolites, N-acetyl-S-(benzyl)-L-cysteine (BMA, P = 0.004), N-acetyl-S-(phenyl)-L-cysteine (SPMA, P = 0.027), and N-acetyl-S-(3,4-dihydroxybutyl)-L-cysteine (DHBMA, P < 0.001) showed associations with HL. Additionally, HFHL exhibited significant associations with BMA (P = 0.005), 3- and 4-methylhippuric acid (3, 4 MHA, P = 0.049), mandelic acid (MA, P = 0.015), SPMA (P < 0.001), N-acetyl-S-(3-hydroxypropyl)-L-cysteine (3-HPMA, P < 0.001), and DHBMA (P < 0.001). After controlling other factors, DHBMA were associated with HL (P = 0.021) and HFHL (P = 0.014) and exhibited a linear association with the mean hearing level (β = 0.054, P = 0.024) and high-frequency hearing level (β = 0.045, P = 0.037). Since 1,3-butadiene may act as an ototoxic material, early screening for workers exposed to 1,3-butadiene and reducing exposure to 1,3-butadiene in everyday life may be helpful to prevent further HL.

Risk factors associated with occupational noise-induced hearing loss in the Hispanic community health study/study of Latinos: A cross-sectional epidemiologic investigation

The purpose of this study was to estimate the prevalence of occupational noise exposure and risk factors of occupational noise-induced hearing loss (NIHL) in Hispanic/Latino adults included in the baseline wave of the Hispanic Community Health Study/Study of Latinos collected from 2008 to 2011. Sequential multiple linear regression modeled the relationship between occupational NIHL (defined as a 3-, 4-, 6-kHz pure-tone average [PTA]) and occupation type, self-reported noise exposure, cardiovascular disease (CVD) risk score, and hearing protective device (HPD) use. The final model controlled for sex, age, and recreational noise exposure. Among 12,851 included participants, approximately 40% (n = 5036) reported occupational noise exposure "Sometimes" (up to 50% of the time) or "Frequently" (75-100% of the time). In the final fitted model, longest-held occupation and CVD risk were associated with poorer hearing. Specifically, those in non-skilled, service, skilled, and military/police/other job categories had between 2.07- and 3.29-dB worse PTA than professional/office workers. Additionally, a shift in the CVD risk score category from low to medium was associated with a 2.25- and 8.20-dB worse PTA for medium and high CVD risk, respectively. Age and sex were also significantly associated with poorer hearing, such that men presented with 6.08 dB worse PTA than women, and for every one-year increase in age, PTA increased by 0.62 dB (ps < .001). No interactions were seen between noise*sometimes or frequent exposure to other ototoxic agents and PTA (ps = .33 & .92, respectively). The prevalence of occupational noise exposure was high in this cross-sectional investigation of adults from Hispanic/Latino backgrounds. Findings contribute to the extant literature by demonstrating that risk factors for occupational NIHL in adults from varying Hispanic/Latino backgrounds are consistent with those of other previously studied groups.

Identification and characterisation of PRXamide peptides in the western flower thrips, Frankliniella occidentalis

Insect CAPA-PVK (periviscerokinin) and pyrokinin (PK) neuropeptides belong to the PRX family peptides and are produced from capa and pyrokinin genes. We identified and characterised the two genes from the western flower thrips, Frankliniella occidentalis. The capa gene transcribes three splice variants, capa-a, -b, and -c, encoding two CAPA-PVKs (EVQGLFPFPRVamide; QGLIPFPRVamide) and two PKs (ASWMPSSSPRLamide; DSASFTPRLamide). The pyrokinin mRNA encodes three PKs: DLVTQVLQPGQTGMWFGPRLamide, SEGNLVNFTPRLamide, and ESGEQPEDLEGSMGGAATSRQLRTDSEPTWGFSPRLamide, the most extended pheromone biosynthesis activating neuropeptide (PBAN) ortholog in insects. Multiple potential endoproteolytic cleavage sites were presented in the prepropeptides from the pyrokinin gene, creating ambiguity to predict mature peptides. To solve this difficulty, we used three G protein-coupled receptors (GPCRs) for CAPA-PVK, tryptophan PK (trpPK), and PK peptides, and evaluated the binding affinities of the peptides. The binding activities revealed each subfamily of peptides exclusively bind to their corresponding receptors, and were significant for determining the CAPA-PVK and PK peptides. Our biological method using specific GPCRs would be a valuable tool for determining mature peptides, particularly with multiple and ambiguous cleavage sites in those prepropeptides. Both capa and pyrokinin mRNAs were strongly expressed in the head/thorax, but minimally expressed in the abdomen. The two genes also were clearly expressed during most of the life stages. Whole-mounting immunocytochemistry revealed that neurons contained PRXamide peptides throughout the whole-body: four to six neurosecretory cells in the head, and three and seven pairs of immunostained cells in the thorax and abdomen, respectively. Notably, the unusual PRXamide profiles of Thysanoptera are different from the other insect groups.

Evaluating the potential impact of ototoxicant exposure on worker health

Occupational exposure to ototoxicants, substances that can cause hearing loss alone or exacerbate hearing loss when exposure occurs in combination with noise, is a workplace hazard that is poorly understood. A review of existing research indicates that some solvents and heavy metals may be ototoxic, but few studies have attempted to estimate the impact of ototoxicant exposure on the United States worker population. Researchers examined trends in workplace exposure to ototoxicants among workers in the United States by comparing exposure data collected by the Occupational Safety and Health Administration against worker hearing loss data provided by the Bureau of Labor Statistics (BLS) for 2012-2019. The study found that the noise exposure data was strongly correlated to the hearing loss data using Pearson's correlation (p < .001), confirming that the exposure data collected by OSHA is predictive of the risk of occupational illness as reported by BLS. Chi-square analysis indicates that reported hearing loss was more common among industry subsectors with exposure to ototoxicants than those without exposure to ototoxicants. These findings suggest that workers with coexposure to ototoxicants and noise may be at a higher risk of experiencing hearing loss than those exposed to noise alone, and action should be taken to minimize this risk.

Effect of ambient noise on indoor environments in a health care facility in Oman

Hospital-noise levels can induce physiological responses and affect sleep quality, which could contribute to cardiovascular-related health problems. Till date, high-resolution hospital noise exposure assessment studies have not received much attention in Oman. This study aims at assessing sound pressure levels across hospital wards and intensive care unit (ICU) rooms to determine annoyance and potential health effects based on perception and risk estimates. An indoor exposure assessment using high precision noise sensors was conducted in a female medical ward (FMW), isolated ward (SLW), emergency ward (EMW), and intensive care unit (ICU) in a public hospital in Muscat city, Oman. Self-administered questionnaire was randomly distributed among respondents using both online and field survey approach to ascertain annoyance, health effects, and potential risks associated with exposure. The study found that 24-h noise levels (L_Aeq) ranged from 55.2 to 61.7 dB(A) in the hospital wards and ICU rooms, which exceeded WHO's hospital indoor rooms critical limit of 35 dB(A) by 58-76%. A total of 150 participants took part in the survey. Among the respondents, 53% reported moderate annoyance at the hospital wards, while 56% felt sensitivity to the noise levels. Noise annoyance was reported by the majority of the patients across the various wards and emergency rooms as causing slight annoyance (50%) and intermittent sleep disturbances (49%). The majority (73%) of the medical staff have complained that the current noise levels affect overall work performance (p = 0.004), while 70% of them have further complained of it as a cause of workplace distraction (p = 0.011). Logistic binary regression analysis has revealed that the complaint of noise sensitivity has a positive association with noise levels in VCW (OR: 1.54; 95% CI: 0.92-2.58), and reported loss of concentration by the medical staff also associated with noise levels at the EMW (OR: 1.61; 95% CI: 0.65-4.01). Quantitative risk estimates showed that both the percentages of highly annoyed (HA) persons (16%), and highly sleep-disturbed (HSD) persons (9%) were very high in FMW, while ICU was found to have the lowest risk. However, the greater number of the respondents (87%) believed that there are possibilities of mitigating (p < 0.001) the current noise levels.

Long-term exposure to air pollution and the risk of developing sudden sensorineural hearing loss

Background

The association between exposure to air pollution and sudden sensorineural hearing loss (SSNHL) has not been extensively discussed in the literature. Therefore, we conducted this nationwide study to evaluate the risk of SSNHL in Taiwanese residents with exposure to air pollution.

Methods

We enrolled subjects aged older than 20 years with no history of SSNHL from 1998 to 2010, and followed up until developing SSNHL, withdrawn from the National Health Insurance program, and the end of the database (2011/12/31). The air quality data are managed by Taiwan Environmental Protection Administration. The annual concentrations of PM_2.5, SO₂, CO, NO, and NO₂ from 1998 to 2010 were classified into the three levels according to tertiles. We calculated the annual average of pollutants from baseline until the end of the study, and classified into tertiles. The adjusted hazard ratio (aHR) was estimated by using the multivariate Cox proportional hazard model.

Results

When considered continuous air pollutants concentration, subjects who exposed with higher concentration of CO (aHR = 2.16, 95% CI 1.50–3.11), NO (aHR = 1.02, 95% CI 1.01–1.03), and NO₂ (aHR = 1.02, 95% CI 1.01–1.04) developing significant higher risk of SSNHL. When classified air pollutants concentration into low, moderate and high level by tertiles, and selected low level as reference, patients exposed with moderate (aHR = 1.56, 95% CI 1.20–2.04) or high level (aHR = 1.33, 95% CI 1.01–1.75) of PM_2.5 showed significant higher risk of developing SSNHL.

Conclusion

This study indicated an increased risk of SSNHL in residents with long-term exposure to air pollution. Nevertheless, further experimental, and clinical studies are needed to validate the study findings.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12967-021-03095-8.

Effect of noise and ototoxicants on developing standard threshold shifts at a U.S. Air Force depot level maintenance facility

Noise exposure has traditionally been considered the primary risk factor for hearing loss. However, ototoxicants commonly found in occupational settings could affect hearing loss independently, additively, or synergistically when combined with noise exposures. The purpose of this investigation was to determine the combined effect of metal and solvent ototoxicants, continuous noise, and impulse noise on hearing loss. Noise and ototoxicant exposure and pure-tone audiometry results were analyzed for U.S. Air Force personnel (n = 2,372) at a depot-level aircraft maintenance activity at Tinker Air Force Base, Oklahoma. Eight similar exposure groups based on combinations of ototoxicant and noise exposure were created including: (1) Continuous noise (reference group); (2) Continuous noise + Impulse noise; (3) Metal exposures + Continuous noise; (4) Metal exposures + Continuous noise + Impulse noise; (5) Solvent exposure + Continuous noise; (6) Solvent exposures + Continuous noise + Impulse noise; (7) Metal exposure + Solvent exposures + Continuous noise; and (8) Metal exposure + Solvent exposures + Continuous noise + Impulse noise. Hearing loss was assessed at center octave band frequencies of 500-6,000 Hz and using National Institute for Occupational Safety and Health Standard Threshold Shift (STS) criteria. Hearing changes were significantly worse at 2,000 Hz in the Metal exposure + Solvent exposure + Continuous noise group compared to the Continuous noise only reference group (p = 0.023). The Metal exposure + Solvent exposure + Continuous noise group had a significantly greater relative risk (RR) of 2.44; 95% CI [1.24, 4.83] for developing an STS at 2,000 Hz. While not statistically significant, the Solvent exposure + Continuous noise group had a RR of 2.32; 95%CI [1.00, 5.34] for developing an STS at 1,000 Hz. These results indicate that noise exposure may dominate hearing loss at ≥3,000 Hz while combined effects of concomitant exposure to ototoxic substances and noise are only noticeable at ≤2,000 Hz. These results also suggest combined exposures to ototoxicants and noise presents a greater hearing loss risk than just noise.

Audiometric findings of printing press workers exposed to noise and organic solvents

OBJECTIVE

To determine if exposure to organic solvents and noise is associated with audiometric results among workers from a printing press in Mexico City.

DESIGN

Cross-sectional study.

STUDY SAMPLE

One hundred and seventy-six male workers at a printing press in Mexico City exposed to noise and organic solvents, including xylene, and 103 non-exposed male workers as reference group. Hearing thresholds were assessed with pure-tone audiometry.

RESULTS

Poorer hearing thresholds were observed among printing workers than non-exposed controls, particularly among groups with over 5 years of exposure. Hearing thresholds differences were observed in the frequencies above 500 Hz, especially in 4000 Hz in all exposure groups compared to the reference. Adjusted models for age and previous exposure to noise and organic solvents showed worse hearing thresholds as years of seniority increased -β coefficients (95% CI): ≤5 years: 3.06 dB (0.01, 6.10); >5-10 years: 4.51 dB (1.13, 7.89); >10 years: 4.58 dB (1.20, 7.96). Further analyses showed no interaction between noise and organic solvents on hearing thresholds, considering both current and previous occupational exposures.

CONCLUSION

Exposure to noise levels that were below recommended exposure limits and organic solvents were associated with poorer hearing thresholds than those observed among non-exposed study participants. This suggests that workers exposed to solvents should be included in hearing conservation programmes, even when noise exposures are below 85 dB. If only noise levels were taken into consideration in the risk assessment of this worker population, the risk of hearing effects could have been overlooked.

Environmental exposure to lead and cadmium and hearing loss in Chinese adults: A case-control study

Hearing loss is the second most common nonfatal problem affecting the Chinese population. Historical studies have suggested an association between exposure to heavy metals, such as cadmium and lead, and hearing loss. Few studies have investigated this relationship in the general population in China. We conducted a case-control study with 1008 pairs of participants from a cross-sectional epidemiological survey conducted in Zhejiang Province. A self-designed questionnaire was adopted to collect information on demographics, chronic diseases, lifestyles and environmental noise. Pure-tone averages of hearing thresholds at frequencies of 0.5, 1, 2, and 4 kHz were computed. Blood lead and cadmium levels were analyzed with an atomic absorption spectrometer. After adjusting for all other potential confounding factors, compared with the lowest blood cadmium quartile (0.00-0.53 μg/L), blood cadmium quartile 2 (0.54-0.92 μg/L), quartile 3 (0.93-1.62 μg/L) and quartile 4 (1.63-57.81 μg/L) exhibited significantly elevated risks for hearing loss, with odds ratios of 1.932 (95% CI: 1.356-2.751), 2.036 (95% CI: 1.423-2.914) and 1.495 (95% CI: 1.048-2.133), respectively (P-trend<0.001). However, an association of lead with hearing loss was not found. Young age (less than 60 years), male sex and current smoking were associated with increased blood cadmium concentration. Additionally, a positive association between blood cadmium and lead concentrations was found. Therefore, we conclude that exposure to environmental cadmium may be a risk factor for hearing loss among the general population in China.

Increased Risk of Sensorineural Hearing Loss as a Result of Exposure to Air Pollution

Whether exposure to air pollution is associated with developing sensorineural hearing loss (SHL) remains controversial. Using data from the National Health Insurance Research Database, we recruited a total of 75,767 subjects aged older than 20 years with no history of SHL from 1998 to 2010, and they were followed up until SHL was observed, they withdrew from the National Health Insurance program, or the study ended. The subjects were evenly exposed to low-level, mid-level, and high-level carbon monoxide (CO) and nitrogen dioxide (NO₂). The incidence rate ratio of SHL for patients exposed to high-level CO was 1.24 (95% confidence interval (CI) = 1.14–1.36). The NO₂ pollutants increased the incidence rate ratios of SHL in mid-level NO₂ and high-level NO₂ exposures by 1.10 (95% CI = 1.10–1.32) and 1.36 (95% CI = 1.24–1.49) times, respectively. The adjusted hazard ratio (adj. HR) of SHL in patients exposed to high-level CO was 1.45 (95% CI = 1.31–1.59), relative to that of patients exposed to low-level CO. Compared to patients exposed to low-level NO₂, patients exposed to mid-level NO₂ (adj. HR = 1.40, 95% CI = 1.27–1.54) and high-level NO₂ (adj. HR = 1.63, 95% CI = 1.48–1.81) had a higher risk of developing SHL. The increased risk of SHL following the increased concentrations of air pollutants (CO and NO₂) was statistically significant in this study. In conclusion, the subjects’ exposure to air pollution exhibited a significantly higher risk of developing SHL in Taiwan.

Mechanotransduction Activity Facilitates Hair Cell Toxicity Caused by the Heavy Metal Cadmium

Hair cells are sensitive to many insults including environmental toxins such as heavy metals. We show here that cadmium can consistently kill hair cells of the zebrafish lateral line. Disrupting hair cell mechanotransduction genetically or pharmacologically significantly reduces the amount of hair cell death seen in response to cadmium, suggesting a role for mechanotransduction in this cell death process, possibly as a means for cadmium uptake into the cells. Likewise, when looking at multiple cilia-associated gene mutants that have previously been shown to be resistant to aminoglycoside-induced hair cell death, resistance to cadmium-induced hair cell death is only seen in those with mechanotransduction defects. In contrast to what was seen with mechanotransduction, significant protection was not consistently seen from other ions previously shown to compete for cadmium uptake into cells or tissue including zinc and copper. These results show that functional mechanotransduction activity is playing a significant role in cadmium-induced hair cell death.

Prevalence and determinants of noise-induced hearing loss among workers in the automotive industry in China: A pilot study

Objective

Data on noise‐induced hearing loss (NIHL) in the automotive industry are rare. This pilot study aimed to investigate the prevalence and determinants of NIHL among workers in the automotive industry in China.

Methods

A cross‐sectional survey was conducted with 6557 participants from the automotive industry. The questionnaire survey was administered, and individual noise exposure level (L_Aeq.8h) and hearing loss level were measured.

Results

Of participants, 96.43% were male; the median age was 27.0 years and 28.82% had NIHL defined as adjusted high‐frequency noise‐induced hearing loss (AHFNIHL). Concerning individual noise levels (L_Aeq.8h), 62.53% exceeded 85 dB(A), which were mainly concentrated in various jobs, including metal cutting, surface treatment, stamping, welding, grinding, assembly, plastic molding, and forging. Each typical noise source generated its own unique temporal waveform shape with the type of non‐Gaussian noise. Of workers, 53.15% regularly used hearing protector devices (HPD), and the proportion of regular HPD use increased with L_Aeq.8h. The trend test showed that the prevalence of AHFNIHL in male workers significantly increased with an increase in L_Aeq.8h at <94 dB(A) and cumulative noise exposure (CNE) in each age group (P < 0.05 or P < 0.01). A logistic regression analysis showed that CNE and HPD usage frequency were important factors contributing to AHFNIHL.

Conclusions

CNE and HPD usage frequency were the determinants for NIHL. Much more human surveys are needed to understand the prevalence and determinants of NIHL in the automotive industry in China.

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 of organic solvents and occupational noise on hearing loss and tinnitus among adults in the U.S., 1999-2004

PURPOSE

Exposure to organic solvents and noise may be causal agents in the development of hearing loss and tinnitus. The objectives of the present study were to examine the association of organic solvents with hearing loss and tinnitus and to assess the interaction of organic solvent and occupational noise exposure on hearing loss and tinnitus.

METHODS

A secondary data analysis of data from the National Health and Nutrition Examination Survey and Occupational Information Network (O*NET) among a study population ranging from 1085 to 2471 study participants from 1999 to 2004. Multiple multivariate logistic regression models were used to assess the associations of individual organic solvent exposures as measured by blood biomarkers (1,4-dichlorobenzene, benzene, ethylbenzene, styrene, toluene, o-xylene, and m-/p-xylene) with self-reported hearing loss, audiometrically assessed hearing loss, and self-reported tinnitus. Models were adjusted for age, gender, race/ethnicity, diabetes, non-occupational noise exposure, smoking, and income. Organic solvents found to be statistically significantly associated with the outcome after adjusting for covariates were tested for interaction with occupational noise exposure.

RESULTS

Solvent exposure was not statistically significantly associated with self-reported tinnitus. Benzene (OR 1.43, 95% CI 1.15-1.78), ethylbenzene (OR 1.24, 95% CI 1.02-1.50), and toluene (OR 1.27, 95% CI 1.06-1.52) concentrations were statistically significantly associated with increased adjusted odds of high-frequency hearing loss. No statistically significant interaction was observed between these solvents and occupational noise on high-frequency hearing loss.

CONCLUSIONS

We found no evidence of an association between organic solvents and tinnitus; however, there was evidence of an association between organic solvent exposure and prevalence of high-frequency hearing loss.

Traditional oriental medicine for sensorineural hearing loss: Can ethnopharmacology contribute to potential drug discovery?

ETHNOPHARMACOLOGICAL RELEVANCE

In Traditional Oriental Medicine (TOM), the development of hearing pathologies is related to an inadequate nourishment of the ears by the kidney and other organs involved in regulation of bodily fluids and nutrients. Several herbal species have historically been prescribed for promoting the production of bodily fluids or as antiaging agents to treat deficiencies in hearing.

AIM OF REVIEW

The prevalence of hearing loss has been increasing in the last decade and is projected to grow considerably in the coming years. Recently, several herbal-derived products prescribed in TOM have demonstrated a therapeutic potential for acquired sensorineural hearing loss and tinnitus. Therefore, the aims of this review are to provide a comprehensive overview of the current known efficacy of the herbs used in TOM for preventing different forms of acquired sensorineural hearing loss and tinnitus, and associate the traditional principle with the demonstrated pharmacological mechanisms to establish a solid foundation for directing future research.

METHODS

The present review collected the literature related to herbs used in TOM or related compounds on hearing from Chinese, Korean, and Japanese herbal classics; library catalogs; and scientific databases (PubMed, Scopus, Google Scholar; and Science Direct).

RESULTS

This review shows that approximately 25 herbal species and 40 active compounds prescribed in TOM for hearing loss and tinnitus have shown in vitro or in vivo beneficial effects for acquired sensorineural hearing loss produced by noise, aging, ototoxic drugs or diabetes. The inner ear is highly vulnerable to ischemia and oxidative damage, where several TOM agents have revealed a direct effect on the auditory system by normalizing the blood supply to the cochlea and increasing the antioxidant defense in sensory hair cells. These strategies have shown a positive impact on maintaining the inner ear potential, sustaining the production of endolymph, reducing the accumulation of toxic and inflammatory substances, preventing sensory cell death and preserving sensory transmission. There are still several herbal species with demonstrated therapeutic efficacy whose mechanisms have not been deeply studied and others that have been traditionally used in hearing loss but have not been tested experimentally. In clinical studies, Ginkgo biloba, Panax ginseng, and Astragalus propinquus have demonstrated to improve hearing thresholds in patients with sensorineural hearing loss and alleviated the symptoms of tinnitus. However, some of these clinical studies have been limited by small sample sizes, lack of an adequate control group or contradictory results.

CONCLUSIONS

Current therapeutic strategies have proven that the goal of the traditional oriental medicine principle of increasing bodily fluids is a relevant approach for reducing the development of hearing loss by improving microcirculation in the blood-labyrinth barrier and increasing cochlear blood flow. The potential benefits of TOM agents expand to a multi-target approach on different auditory structures of the inner ear related to increased cochlear blood flow, antioxidant, anti-inflammatory, anti-apoptotic and neuroprotective activities. However, more research is required, given the evidence is very limited in terms of the mechanism of action at the preclinical in vivo level and the scarce number of clinical studies published.

Exposure to noise and ototoxic chemicals in the Australian workforce

OBJECTIVE

To determine the current prevalence of exposure to workplace noise and ototoxic chemicals, including co-exposures.

METHOD

A cross-sectional telephone survey of nearly 5000 Australian workers was conducted using the web-based application, OccIDEAS. Participants were asked about workplace tasks they performed and predefined algorithms automatically assessed worker's likelihood of exposure to 10 known ototoxic chemicals as well as estimated their full shift noise exposure level (L_Aeq,8h) of their most recent working day. Results were extrapolated to represent the Australian working population using a raked weighting technique.

RESULTS

In the Australian workforce, 19.5% of men and 2.8% of women exceeded the recommended full shift noise limit of 85 dBA during their last working day. Men were more likely to be exposed to noise if they were younger, had trade qualifications and did not live in a major city. Men were more likely exposed to workplace ototoxic chemicals (57.3%) than women (25.3%). Over 80% of workers who exceeded the full shift noise limit were also exposed to at least one ototoxic chemical in their workplace.

CONCLUSION

The results demonstrate that exposures to hazardous noise and ototoxic chemicals are widespread in Australian workplaces and co-exposure is common. Occupational exposure occurs predominantly for men and could explain some of the discrepancies in hearing loss prevalence between genders.

Comparison of Pure-Tone Average Methods for Estimation of Hearing Loss Caused by Environmental Exposure to Lead and Cadmium: Does the Pure-Tone Average Method Which Uses Low-Frequency Ranges Underestimate the Actual Hearing Loss Caused by Environmental Lead and Cadmium Exposure?

Previous studies have reported that exposure to lead and cadmium can damage the inner ear receptor, which perceives high-frequency sounds. However, few studies have used the pure-tone average (PTA), including high-frequency ranges, for the estimation of hearing loss caused by lead and cadmium exposure. We estimated hearing loss using the PTA test, in low-frequency, speech frequency, and high-frequency ranges and compared the differences in the results using 3 PTA calculation methods. We analyzed the data of 2,387 participants, between the ages of 19 and 85 years, that were obtained from the Korea National Health and Nutrition Examination Survey (KNHANES) of 2010-2012. A dose-response relationship between hearing loss and heavy metal exposure was observed in the high-frequency method after adjustment for confounding factors. When using the high-frequency PTA, it was found that doubling of the levels of lead and cadmium in the blood was associated with a 1.88- (95% CI 1.11-3.17) and 1.89-fold (95% CI 1.02-3.50) increase in the OR for hearing loss. In the case of the low-frequency and speech frequency PTA, however, there were no significant relationships between hearing loss and the concentrations of lead and cadmium in the blood. The outcomes of the present study suggest that the estimation of hearing loss caused by environmental exposure to lead and cadmium is affected by the frequencies used in the PTA calculation.

Environmental exposure of heavy metal (lead and cadmium) and hearing loss: data from the Korea National Health and Nutrition Examination Survey (KNHANES 2010-2013)

BACKGROUND

Lead and cadmium have been identified as risk factors for hearing loss in animal studies, but large-scale studies targeting the general human population are rare. This study was conducted to investigate the link between heavy metal concentrations in blood and hearing impairment, using a national population-based survey.

METHODS

The study participants comprised 6409 Koreans aged 20 or older, who were included in the Fifth and Sixth Korea National Health and Nutrition Examination Surveys (KNHANES 2010-2013). Hearing impairment was categorized into two types, low- and high-frequency hearing impairment, using pure tone audiometry. Low-frequency hearing impairment was defined as having a binaural average of hearing thresholds for 0.5, 1, and 2 kHz exceeding 25 dB, and high-frequency hearing impairment was defined as having a binaural average of hearing thresholds for 3, 4, and 6 kHz exceeding 25 dB. The blood levels of heavy metals (lead and cadmium) were classified into quartiles. Cross-sectional association between hearing impairment and the level of heavy metals (lead and cadmium) was examined in both sexes. Multivariate logistic regression was used to obtain adjusted odds ratios (ORs) and 95% confidence intervals (CIs).

RESULTS

Among men, the prevalence of low- and high- frequency hearing impairment was 13.9% and 46.7%, respectively, which was higher than the prevalence among women (11.8% and 27.0%, respectively). Regarding lead, the adjusted OR of high-frequency hearing impairment for the highest blood level group versus the lowest group was significant in both men (OR = 1.629, 95% CI = 1.161-2.287) and women (OR = 1.502, 95% CI = 1.027-2.196), after adjusting for age, body mass index, education, smoking, alcohol consumption, exercise, diagnosis of diabetes mellitus, hypertension, and noise exposure (occupational, loud, firearm noises). No links were found between blood lead levels and low-frequency hearing impairment, or between blood cadmium levels and low- or high-frequency hearing impairment in either sex.

CONCLUSIONS

The present study findings suggest that even exposure to low-level lead is a risk factor for high-frequency hearing loss. A prospective epidemiologic study should be conducted to identify the causal relationship between human health and exposure to heavy metals, and efforts to reduce heavy metal exposure in the general population should continue.

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.

Occupational Styrene Exposure on Auditory Function Among Adults: A Systematic Review of Selected Workers

A review study was conducted to examine the adverse effects of styrene, styrene mixtures, or styrene and/or styrene mixtures and noise on the auditory system in humans employed in occupational settings. The search included peer-reviewed articles published in English language involving human volunteers spanning a 25-year period (1990–2015). Studies included peer review journals, case–control studies, and case reports. Animal studies were excluded. An initial search identified 40 studies. After screening for inclusion, 13 studies were retrieved for full journal detail examination and review. As a whole, the results range from no to mild associations between styrene exposure and auditory dysfunction, noting relatively small sample sizes. However, four studies investigating styrene with other organic solvent mixtures and noise suggested combined exposures to both styrene organic solvent mixtures may be more ototoxic than exposure to noise alone. There is little literature examining the effect of styrene on auditory functioning in humans. Nonetheless, findings suggest public health professionals and policy makers should be made aware of the future research needs pertaining to hearing impairment and ototoxicity from styrene. It is recommended that chronic styrene-exposed individuals be routinely evaluated with a comprehensive audiological test battery to detect early signs of auditory dysfunction.

Bioaerosols, Noise, and Ultraviolet Radiation Exposures for Municipal Solid Waste Handlers

Few studies have investigated the occupational hazards of municipal solid waste workers, particularly in developing countries. Resultantly these workers are currently exposed to unknown and unabated occupational hazards that may endanger their health. We determined municipal solid waste workers' work related hazards and associated adverse health endpoints. A multifaceted approach was utilised comprising bioaerosols sampling, occupational noise, thermal conditions measurement, and field based waste compositional analysis. Results from our current study showed highest exposure concentrations for Gram-negative bacteria (6.8 × 103 cfu/m3) and fungi (12.8 × 103 cfu/m3), in the truck cabins. Significant proportions of toxic, infectious, and surgical waste were observed. Conclusively, municipal solid waste workers are exposed to diverse work related risks requiring urgent sound interventions. A framework for assessing occupational risks of these workers must prioritize performance of exposure assessment with regard to the physical, biological, and chemical hazards of the job.

The Effects of Earphone Use and Environmental Lead Exposure on Hearing Loss in the Korean Population: Data Analysis of the Korea National Health and Nutrition Examination Survey (KNHANES), 2010-2013

BACKGROUND

Although previous studies have reported that frequent earphone use and lead exposure are risk factors for hearing loss, most of these studies were limited to small populations or animal experiments. Several studies that presented the joint effect of combined exposure of noise and heavy metal on hearing loss were also mainly conducted on occupational workers exposed to high concentration.

OBJECTIVES

We investigated both the individual and joint effects of earphone use and environmental lead exposure on hearing loss in the Korean general population.

METHODS

We analyzed data from 7,596 Koreans provided by the Korea National Health and Nutrition Examination Survey (KNHANES) during the period 2010-2013. The pure-tone average (PTA) of hearing thresholds at 2, 3, and 4 kHz frequencies was computed, and hearing loss was defined as a PTA ≥ 25 dB in one or both ears.

RESULTS

A dose-response relationship in hearing loss with earphone use time and blood lead level is observed after adjustment for confounding factors. With a 1-hour increase in earphone use time and 1 μg/dL increase in blood lead concentration, the odds of hearing loss increased by 1.19 and 1.43 times, respectively. For hearing loss, the additive and multiplicative effect of earphone use and blood lead level were not statistically significant.

CONCLUSIONS

Earphone use and environmental lead exposure have an individual effect on hearing loss in the general population. However, the estimated joint effect of earphone use and lead exposure was not statistically significant.

PON2 and ATP2B2 gene polymorphisms with noise-induced hearing loss

BACKGROUND

Noise-induced hearing loss (NIHL) is a complex disease induced by a combination of genetic and environmental factors. Paraoxonase2 (PON2) gene involved in the regulation of reactive oxygen species, and affecting the vulnerability of cochlea to NIHL, and ATPase, calcium-transporting, plasma membrane 2 (ATP2B2) gene which encodes plasma membrane calcium-transporting ATPase isoform 2 (PMCA2) are the candidate genes relating to the attack of NIHL. In this study, we investigated whether ATP2B2 and PON2 polymorphisms were associated with NIHL in Chinese of Han nationality population.

METHODS

We performed a case-control study between six single nucleotide polymorphisms (SNPs) (rs1719571, rs3209637 and rs4327369 within ATP2B2, rs12026, rs7785846 and rs12704796 within PON2) and NIHL in 454 subjects. All the SNPs were genotypes, using the TaqMan MGB probe assay. Odds ratios (ORs) were calculated with 95% confidence intervals (95% CIs) with logistic regression analysis to test the level of association for SNPs.

RESULTS

In our study, 221 subjects with hearing loss and 233 subjects without hearing loss were recruited. The frequencies of the CG and CG + GG genotype of rs12026 (PON2) conferred risk factors for NIHL with adjusted OR values of 2.62 (95% CI, 1.69-4.06) and 2.48 (95% CI, 1.63-3.78), respectively. This kind of significance was also found at locus rs7785846, where genotypes CT and CT + TT were the risk types, with adjusted ORs of 2.52 (95% CI, 1.62-3.93) and 2.35 (95% CI, 1.54-3.58), respectively. We performed stratified analysis per noise exposure level, when it came to rs7785846 and rs12026 in the >92 dB(A) noise exposure group, the subjects who carried heterozygote were of significantly (P<0.01) higher susceptibility to NIHL than homozygote carriers. By contrast, no significantly higher risk was found for any rs12704796 genotypes or any genotypes in ATP2B2 (P>0.05), which may suggest that these SNPs did not have significant effects on noise susceptibility across noise exposure.

CONCLUSIONS

Our research suggested that PON2 might play a role in the etiology of NIHL in Chinese of Han nationality population.

Cadmium and nickel in blood of Tunisian population and risk of nasosinusal polyposis disease

Nasosinusal polyposis (NSP) is a chronic inflammatory disease of the nasal mucosa. Although the pathophysiology underlying NSP formation is not fully understood, environmental factors appear to be contributed the development of this disease. A case-control study of Tunisian patients was examined to assess the levels of cadmium (Cd) and nickel (Ni) in blood and reparse the association between the exposure to these metals and the risk of nasosinusal polyposis disease. Mean blood levels of Cd in patients (2.2 ± 12.8 μg/L) were significantly higher than those of controls (0.5 ± 0.7 μg/L). Levels of blood Cd were positively correlated with tobacco smoking and chewing among controls. The Cd and Ni concentrations among control (p = 0.001) and patient (p = 0.018) tobacco consumers (smoking, chewing, and shisha) were significantly higher than those nonconsumers. Additionally, Ni blood levels of patient and control smokers were significantly higher than those of nonsmokers. Cd levels in blood samples of NSP patients occupationally exposed for more than 14 years were eight times higher than that of nonexposed. Drinking water was also found to be incriminated as exposure sources. Among risk factors, shisha consumption, environmental exposure, and occupational exposure presented the most significant association with NSP disease (odds ratio (OR) = 14.1, 10.1, and 1.7, respectively). High levels of blood Cd (OR = 3.5) were strongly associated with NSP disease (p = 0.027). Ni blood levels were shown to be associated with the four stages of polyps in both nasal cavities (right and left) (p < 0.05). This investigation suggested a potential role of toxic metals in the mechanism of NSP disease development. Exposure assessment investigations encompassing a wider population are needed.