Ewa Zamyslowska-Szmytke

Ototoxic effects of occupational exposure to styrene and co-exposure to styrene and noise.

Learning ObjectivesRecall the reported effects of exposure to styrene and noise on the cochlear hair cells and hearing function in rats.Describe which possible confounding factors were and were not controlled for in this study, and what the results indicate about the respective ototoxic effects on humans of exposure to styrene and noise.Characterize the effects in humans of isolated and combined exposure to styrene and noise. Ototoxicity of styrene and the synergistic action of styrene and noise have been shown in rats. The respective data in humans are scarce and equivocal. This study evaluated the effects of occupational exposure to styrene and combined exposures to styrene and noise on hearing. The study group, comprised of 290-yacht yard and plastic factory workers, was exposed to a mixture of organic solvents, having styrene as its main compound. The reference group, totaling 223 subjects, included (1) white-collar workers, exposed neither to solvents nor noise and (2) metal factory workers, exposed exclusively to noise. All subjects were assessed by means of a detailed questionnaire and underwent otorhinolaryngological and audiometric examinations. Multiple logistic regression analysis revealed almost a 4-fold (or 3.9; 95% CI = 2.4–6.2) increase in the odds of developing hearing loss related to styrene exposure. The factors adjusted for were: age, gender, current occupational exposure to noise, and exposure to noise in the past. In cases of the combined exposures to styrene and noise, the odds ratios were two to three times higher than the respective values for styrene-only and noise-only exposed subjects. The mean hearing thresholds—adjusted for age, gender, and exposure to noise—were significantly higher in the solvent-exposed group than in the unexposed reference group at all frequencies tested. A positive linear relationship existed between an averaged working life exposure to styrene concentration and a hearing threshold at the frequencies of 6 and 8 kHz. This study provides the epidemiological evidence that occupational exposure to styrene is related to an increased risk of hearing loss. Combined exposures to noise and styrene seem to be more ototoxic than exposure to noise alone.

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

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

Exacerbation of noise-induced hearing loss by co-exposure to workplace chemicals

BACKGROUND : Numerous organic solvents applied in industry, like toluene, styrene, xylene and n-hexane have been demonstrated to impair hearing in animals. However, the effects of exposure to a given organic solvent and the interaction of noise and solvents on hearing in humans are still not fully recognized. STUDY DESIGN : The study was aimed to assess the effects of occupational exposure to solvents alone or in combination with noise on hearing in 1117 employees of yacht, ship, plastic, shoe, and paint and lacquer industry. These persons were exposed either to the mixture of organic solvents with xylene as the main component, or predominantly to styrene, or to the mixture of n-hexane and toluene. Detailed questionnaire data and pure-tone audiometry were compared with data of the reference group that included white collar workers, exposed neither to solvents nor noise and metal factory workers exposed to noise only. In all statistics, the confounding factors were recognized as gender, age, exposure to noise, and other variables occurring at a different rate in study and reference group. RESULTS : Odds ratio (OR) of hearing loss related with the particular exposure to chemicals was 2.4 (95%CI 1.59-3.74) in case of solvent mixture, 3.9 (95%CI 2.4-6.2) in case of styrene and 5.3 (95%CI 2.6-10.9) in case of n-hexane and toluene exposure. The odds of developing hearing loss substantially increased in the case of combined exposure to organic solvents and noise as compared to isolated exposure to each of these hazards. The highest OR (over 20-fold) was demonstrated in subgroups of subjects exposed simultaneously to noise and two ototoxic solvents (i.e. styrene and toluene or n-hexane and toluene). The mean hearing thresholds were significantly higher in the solvent-exposed groups than in the reference group. The differences in thresholds were observed at high frequencies in the solvent mixture- and n-hexane + toluene-exposed groups and at all frequencies in the styrene-exposed group. A positive linear relationship existed between exposure to solvents and hearing thresholds at high frequencies. CONCLUSIONS : The results of the study provide the epidemiological evidence that exposure to organic solvents in humans is associated with an increased risk of hearing loss. The simultaneous exposure to organic solvents and noise seems to enhance the hearing deficit if compared with isolated exposures.

A multicenter study on the audiometric findings of styrene-exposed workers

Abstract Objective: The objective of this study was to evaluate hearing loss among workers exposed to styrene, alone or with noise. Design: This cross-sectional study was conducted as part of NoiseChem, a European Commission 5th Framework Programme research project, by occupational health institutes in Finland, Sweden, and Poland. Study sample: Participants’ ages ranged from 18–72 years (n = 1620 workers). Participants exposed to styrene, alone or with noise, were from reinforced fiberglass products manufacturing plants (n = 862). Comparison groups were comprised of workers noise-exposed (n = 400) or controls (n = 358). Current styrene exposures ranged from 0 to 309 mg/m3, while mean current noise levels ranged from 70–84 dB(A). Hearing thresholds of styrene-exposed participants were compared with Annexes A and B from 2. Results: The audiometric thresholds of styrene exposed workers were significantly poorer than those in published standards. Age, gender, and styrene exposure met the significance level criterion in the multiple logistic regression for the binary outcome ‘hearing loss’ (P = 0.0000). Exposure to noise (<85 dBA p = 0.0001; ≥85 dB(A) p = 0.0192) interacted significantly with styrene exposure. Conclusions: Occupational exposure to styrene is a risk factor for hearing loss, and styrene-exposed workers should be included in hearing loss prevention programs. Sumario Objetivo: El objetivo de este estudio fue evaluar la pérdida auditiva en trabajadores expuestos a estireno, aisladamente o con ruido. Diseño: Se realizó este estudio transversal como parte del NoiseChem, Comisión Europea del 5°. Proyecto Marco de investigación, en institutos de salud ocupacional de Finlandia, Suecia y Polonia. Muestra de estudio: La edad de los participantes fue de 18–72 a os (N = 1,620 trabajadores). Los trabajadores (n = 862) estuvieron expuestos a estireno, solo o con ruido, en plantas de fabricación de productos de fibra de vidrio reforzada. Los grupos de comparación fueron trabajadores expuestos a ruido (n = 400) y los de un grupo control (n = 358). Las exposiciones reales a estireno variaron de 0 a 309 mg/m3, mientras que los niveles reales de ruido, variaron de 80–84 dB(A). Se compararon los niveles de audición de los participantes expuestos a estireno con los de los anexos A y B de 2. Resultados: Los umbrales audiométricos de los trabajadores expuestos a estireno, fueron significativamente más pobres que los que se han publicado como estándar. La edad, el género y la exposición a estireno, cubrieron los criterios de niveles de significatividad de la regresíón logística múltiple para los resultados binarios de la “perdida auditiva” (P = 0.0000). La exposición a ruido (<85 dB(A) p = 0.0001; ≥85 dB(A) p = 0.0192) interactu significativamente con la exposición a estireno. Conclusiones: La exposición ocupacional a estireno es un factor de riesgo de pérdida auditiva por lo que los trabajadores expuestos a estireno deben ser incluidos en programas de prevención de pérdidas auditivas.

Correlation between Acoustic Parameters and Voice Handicap Index in Dysphonic Teachers

Objective: The aim of this study was to investigate the relationship between acoustic analysis and biopsychosocial implications of voice problems, evaluated by the Voice Handicap Index (VHI). Materials and Methods: The study comprised 120 female teachers with voice disorders, evaluated by videolaryngostroboscopy. 60.8% of this group were diagnosed as having functional dysphonia and 39.2% had dysphonia with benign vocal fold masses (nodules and polyps). The controls consisted of 30 euphonic women. The correlations between VHI and acoustic analysis were assessed in both groups using the Pearson correlation coefficient and regression analysis. Results: In teachers, the total VHI score was over 5 times as high as in controls (p < 0.001). Moreover, in teachers, significant positive correlations were found between the total VHI score and the frequency perturbation parameters and amplitude perturbation parameters when both statistical methods were used. These acoustic parameters also significantly correlated with the score on the functional and emotional subscales, but rarely with the physical subscale of the VHI. Conclusions: The study revealed a significant relationship between the objective voice measurements and the VHI. The results confirmed that VHI can be a valuable tool for assessing biopsychosocial implications of occupational dysphonia and should be incorporated in multidimensional voice evaluation.

Temporal processing disorder associated with styrene exposure.

Little evidence exists on the possible adverse effects of styrene on the central part of the auditory system. The present investigation aimed to study the possible association between styrene exposure and temporal processing abilities. Fifty-nine styrene-exposed subjects and 50 nonexposed control subjects were tested. Pure-tone audiometry (125–8000 Hz) and 3 temporal processing tests (gaps-in-noise, frequency pattern test and duration pattern test) were carried out. Significant differences between groups were found for most of the audiometric thresholds for both ears. ANCOVA analysis showed that styrene-exposed subjects had significantly poorer performances on the frequency and duration pattern tests than nonexposed subjects, when including hearing level and age as covariates. The results of the present research study suggest an association between styrene exposure and central auditory dysfunction characterized by a temporal processing disorder.

Balance system assessment in workers exposed to organic solvent mixture.

Objective: The aim of this study was to assess the balance and vestibular systems in healthy workers exposed to low concentrations of organic solvent mixtures. Methods: The study groups comprised 60 workers exposed to mixture of organic solvents and 110 reference workers. All subjects performed static posturography and electronystagmography (ENG). Results: In posturography, abnormal reaction time was more frequent and statistically longer in solvent-exposed group. Also, worse results of movement coordination parameters were observed in this group. The ENG square waves and abnormal optokinetic results were more common in exposed group. Mean caloric response was shorter in the exposed group. Negative relationship was found between time of caloric response and cumulative toluene concentration. Conclusions: Balance abnormalities in solvent-exposed workers indicated subclinical damage, mainly of central part of vestibular system and body-movement coordination. It would not be reasonable to exclude the vestibular hyporeactivity.

Vestibular and balance findings in nonsymptomatic workers exposed to styrene and dichloromethane.

Abstract Objective: The aim of our study was to assess the vestibular and balance system in non-symptomatic workers exposed to styrene and dichloromethane at the workplace. Design: Subjects underwent videonystagmography including saccades, smooth pursuit (SP), optokinetic test (OKN), gaze nystagmus assessment, bithermal caloric test, and static posturography. Study sample: Study groups included 74 workers in plastics manufacturing, aged 40 (SD 8) years, exposed to styrene and dichloromethane, and the reference group of 49 non-exposed subjects, aged 36 (SD 10) years. Results: More than 60% of exposed and non-symptomatic workers revealed abnormal results of vestibular tests. Saccadic latency elongation (p = 0.0098), lower gain in SP (p = 0.0037) and OKN (p = 0.0000) were more common in the exposed group, as well as lower reactivity (p = 0.0337) and mean slow phase velocity of caloric nystagmus. Static posturography revealed higher sway velocities in the test with eyes closed, on foam and worse results of three from five limit of stability tests. No relationship between chemicals exposure and vestibular and balance test results was found. Conclusions: In principle, our findings indicate the possibility of high-level deficits in the central part of vestibular system. Lower vestibular reactivity may suggest that bilateral vestibular hypofunction might also be the possible consequence of solvent exposure. Sumario Objetivo: El propósito de nuestro estudio fue evaluar el sistema vestibular de equilibrio en trabajadores no sintomáticos expuestos al estireno y al diclorometano en su lugar de trabajo. Diseño: Los sujetos se sometieron a videonistagmografía, incluyendo sacada, seguimiento continuo (SP), prueba de nistagmo optoquinético (OKN), evaluación de nistagmo de mirada horizontal, Prueba térmica bicalórica y posturografía estática. Muestra del Estudio: Los grupos de estudio incluyeron a 74 trabajadores de una f´brica de plásticos, con edad de 40 años (DE 8), expuestos a estireno y a diclometano, y el grupo de referencia de 49 sujetos no expuestos, con edad de 36 años (DE 10). Resultados: Más del 60% de los trabajadores expuestos y no sintom´ticos reveló resultados anormales en las pruebas vestibulares. La elongación en la latencia sacádica (p = 0.0098), una ganancia baja en la SP (p = 0.0037) y en el OKN (p = 0.0000) fueron más comunes en el grupo expuesto, así como una menor reactividad (p = 0.0337) y una velocidad media de fase lenta del nistagmo calórico. La posturograf a estítica reveló velocidad más altas de balanceo en la prueba con los ojos cerrados, en la plataforma de esponja y peores resultados en tres de las cinco pruebas de límite de estabilidad. No se encontró relación entre la exposición a químicos y las pruebas vestibulares de balance. Conclusiones: En principio, nuestros hallazgos indican la posibilidad de deficiencias de alto nivel en la parte central del sistema vestibular. Una reactividad vestibular baja puede sugerir que la hipofunción vestibular bilateral podría ser una posible consecuencia de la exposición a solventes.

Bedside examination for vestibular screening in occupational medicine

OBJECTIVES The aim of the study was to assess the usefulness of bedside examination for screening of vestibular and balance system for occupational medicine purposes. Study group comprised 165 patients referred to Audiology and Phoniatric Clinic due to vestibular and/or balance problems. Caloric canal paresis of 19% was the cut off value to divide patients into 43 caloric-positive vestibular subjects and 122 caloric-negative patients. The latter group comprised 79 subjects revealing abnormalities of videonystagmographic (VNG) oculomotor tests (central group) and 43 subjects with normal VNG. MATERIAL AND METHODS Vestibular and balance symptoms were collected. Five tests were included to bedside examination: Romberg and Unterberger tests, Head Impulse Test (HIT), Dynamic Visual Acuity (DVA) and gaze nystagmus assessment. RESULTS Vestibular and balance symptoms were reported by 82% of vestibular, 73% of central and 40% of VNG-normal patients. Thirteen out of 18 VNG-normal but symptomatic subjects (73%) had abnormal tests in clinical assessment. The sensitivity of bedside test set for vestibular pathology was 88% as compared to caloric test and 68% for central pathology as compared to VNG oculomotor tests. CONCLUSIONS The combination of 5 bedside tests reveal satisfactory sensitivity to detect vestibular abnormalities. Bedside examination abnormalities are highly correlated with vestibular/balance symptoms, regardless the normal results of VNG. Thus, this method should be recommended for occupational medicine purposes.

Vibration perception thresholds assessed by two different methods in healthy subjects

The values of vibration perception threshold (VPT) should be related to the equipment and methods of measurement that differ between European countries. ISO Standard 13091-1-2001 specifies the general guidelines regarding device facilities and measurement methodology. This study was designed to compare VPTs in healthy subjects by using two different methods of measurement. The first one was a standard technique applied currently in Poland and the second one was based on the principles of the International Standard ISO 13091-1-2001. The study comprised 187 healthy subjects, aged 17–57 years, not occupationally exposed to vibration. Both measurements of VPTs were performed using the same equipment (P-8, EmsonMat). The main differences in methodology between the Polish standard method and the method of ISO included: different mode of stimuli presentation (ascending in standard vs. Bekesy in ISO method), frequency range applied (63–500 Hz vs. 4–125 Hz), probe contact force (larger in Polish method), probe diameter (12 mm vs. 5 mm) and its surface (plane vs. rough). The results obtained found that the mean VPTs differed significantly at the overlapping frequencies depending on the method used, the differences varied from 2.2 to 6.4 dB at frequencies 125 and 250Hz, respectively. The correlation between the thresholds obtained by both methods at these frequencies was moderate (correlation coefficients about 0.6), although statistically significant. In the ISO method, the best VPTs were found at 4 and 125 Hz. There was a poor correlation between the thresholds at the extreme frequencies (i.e. 125 and 4 Hz) and rather high between adjacent frequencies (i.e. 25 and 32 Hz). Age, weight and height were significant covariates in both measurements. The model to calculate the normative values of VPTs adjusted for explanatory factors was set up in this study. It was concluded that different methods of VPT measurement are not comparable. The ISO method seems to supply more information about skin receptors and different kinds of tough sense than the Polish standard method. In order to perform international cohort studies there is a need to establish a unified standardised method of vibrotactile sense assessment.