The Effects of Toluene Plus Noise on Hearing Thresholds: An Evaluation Based on Repeated Measurements in the German Printing Industry

Abstract

Objectives: The ototoxicity of occupational exposure to toluene plus noise was investigated in a longitudinal study in rotogravure printing and existing findings in the literature were evaluated. Material and Methods: The study comprised four repeated examinations during 5 years and started with 333 male workers. Lifetime weighted average exposures (LWAE) to toluene and noise were determined from individual work histories and historic recordings; recent individual exposures were measured 10 times during the study (toluene, active sampling; noise, stationary measurements). Auditory thresholds were measured with pure tone audiometry at 0. 125, 0.25, 0.5, 0.75, 1, 2, 3, 4, 6, 8, 12 kHz. Results: Mean LWAE exposures to toluene and noise were 45±17 ppm plus 82±7 dB(A) for high toluene exposed and 10±7 ppm plus 82±4 dB(A) for low toluene exposed subjects, mean current exposures were 26±20 ppm plus 81±4 dB(A) and 3±3 ppm plus 82±4 dB(A). Mean exposure duration was 21.3±6.5 years for long exposed and 5.9±2.2 years for short exposed subjects. Repeated measurement analyses of variance did not reveal effects of toluene intensity, exposure duration and interactions between toluene intensity and noise intensity. Noise intensity [79±3 dB(A) vs. 84±1 dB(A)] was significant for auditory thresholds. A case concept utilising developments of individual auditory thresholds did not reveal significant toluene effects. Logistic models including age, exposure duration, toluene in ambient air, current noise and either hippuric acid or ortho-cresol (o-cresol) found only age to be significant for elevated OR of high frequency hearing loss. Conclusions: Due to missing toluene effects, it was concluded that the threshold level for developing hearing loss as a result of occupational exposure to toluene plus noise might be above the current limit of 50 ppm toluene.

Chemical exposure and hearing loss

“…Several clinical and epidemiological studies confirmed an association between exposure to solvents (styrene, toluene, xylenes, solvent mixtures, and jet fuels) in the workplace and increased prevalence of hearing loss, as well as poor hearing thresholds beyond the traditional 4 kHz noise-related audiometric notch. [83][84][85][86][87][88][89][90][91][92] For an extensive review of human studies, see Johnson and Morata 93 (available online at https:// gupea.ub.gu.se/handle/2077/23240).…”

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

“…Three studies attributed OHL found among individuals of co-exposure groups to the likely action of noise 25,38,41 . This conclusion can be questioned by observing limitations among the studies, which may have affected the quality of the analyses: absence of a control group with isolated exposure to noise 25,41 ; healthy worker effect (sole permanence at the workplace of workers with no impairment or health complaints) and inadequate case definition 25 ; or even differences between the exposure levels of agents (solvents within the allowed limit and noise considerably above the limit) 38 .…”

“…Possible biases are cited in these studies, such as inexistence of control groups, healthy worker effect 25 and inadequate definition of "case" 25,26 , which may have influenced the absence of risk of OHL in exposures at levels below recommendation.…”

“…Four studies evaluated the ototoxic effects of exposure to toluene through PTA: three in printing and rotogravure plants 9,16,25 and one in an adhesive material factory 26 . Only one study evaluated the possible impairment of the central auditory pathway, through observation of peri-stimulatory fatigue of cranial nerve VIII, recorded by immitanciometry (decay decline).…”

Richtwerte für Toluol und gesundheitliche Bewertung von C7-C8-Alkylbenzolen in der Innenraumluft

“…den ototoxischen Effekt von Lärm verstärkt [80]. Andere Studien mit großen Kohorten zeigen, dass bis 172 mg/m³ keine ototoxischen Effekte auftreten [56,81,82]. Die Ototoxizität von Toluol wird durch tierexperimentelle Daten unterstützt [83,84].…”