The study of health outcomes in the printing industry: hearing and balance impairments associated to combined exposure to noise and ototoxic volatile organic compounds

Introduction: Exposure to noise and volatile organic compounds (VOCs) is of concern in the printing industry. The changing regulatory and technological environment requires ongoing research to identify reductions in risk, but to also identify new hazards if they exist. This thesis reports on the assessment of noise and VOC exposures in the printing industry in Kuwait. It also reports on hearing and balance function among these workers and the relationship between that and the noise and ototoxic VOC exposures. Recruitment: The study population consisted of all workers at three printeries who had worked there for at least 12 months and could read and speak either Arabic or English. Methods: Workers were sampled for a full shift using personal noise dosimeters. Using the evacuated canister methodology, 72 VOCs were targeted. Chemical analysis was performed using the gas chromatography technique with a flame ionization (GC-FID) detector. Pure tone audiometry (PTA) was used to evaluate hearing function post otoscopic and tympanometric exams. For balance assessments, both functional reach and timed up and go (TUG) tests were performed. Statistical Analysis: Multivariable linear and logistic regression modelling was used to estimate the effect on hearing thresholds, functional reach, TUG time and self-reported dizziness of noise and ototoxic VOC exposures, while controlling for other relevant factors, such as age. Backwards stepwise methods used to exclude variables that were not significant ate 5% level. Results: Noise exposures of 75 dB(A) on average were found among computer-to-plate (CTP) workers and were rarely exposed to noise levels greater than 85 dB(A). However, noise exposure in excess of 85 dB(A) was still common among offset printing workers. Indeed, all web-fed offset workers had exposures greater than 85 dB(A) and spent more than half the shift experiencing noise levels greater than 85 dB(A). Alcohols and aromatics were the most prevalent VOCs in the study. Unexpected levels of chlorofluorocarbons (CFCs) were found, even those banned under the Montréal Protocol (MP) such as CFC-114, which was correlated with levels of vinyl chloride, a known carcinogen. Ototoxic VOCs were present in all printeries, consisting mostly of toluene, ethylbenzene and to a lesser extent m/p-xylene. Multivariable modelling revealed that toluene exposure was significantly and positively associated with hearing thresholds at frequencies 1-4 kHz. There was a significant interaction between toluene and diabetes, meaning that the effect of toluene was exacerbated in workers with diabetes, at 2-4 kHz. A significant effect of noise exposure was only found when interacted with age. For a worker with diabetes, a 100 ppb toluene exposure (0.5% of the occupational exposure limit (OEL)) was associated with a 41.1 dB (95%CI 12-71 dB) increase in hearing threshold at 4 kHz. For a worker without diabetes that increase would be 15.3 dB (95%CI 3-28 dB). A noticeable notch occurred at 4 kHz with toluene exposure. Results for ethylbenzene and m/p-xylene were similar but not as strong at frequencies other than 4 kHz. Toluene had a significant negative effect on functional reach, once height and gender were accounted for. Noise exposure did not have a significant effect of functional reach. For an average height male worker, the functional reach would be on average 26 cm (95%CI 23-30) with 100 ppb toluene exposure, and without exposure his functional reach would be on average 6 cm (95%CI 1-10) more. Toluene had a significant positive effect on TUG time, as did percent of shift at noise levels above 85 dB(A) and worker activity. An active worker experiencing 0% of an 8 hour shift above 85 dB(A) the TUG time would be on 9 secs (95%CI 8-10) with 100 ppb toluene exposure, and without toluene exposure, their TUG time would be on average 2 secs (95%CI 0.6-3) more. The model including ethylbenzene exposure was similar. No effect of VOC or noise exposure on dizziness was significant. Conclusion: VOC exposures in the study printeries were lower than that reported in previous literature. This is a positive outcome of ongoing efforts to reduce the use of harmful VOCs, such as benzene, toluene, ethylbenzene and xylene isomers (BTEX). On the other hand, use other VOCs appear to be increasing, such methyl alcohol, low weight aldehydes, CFCs, vinyl chloride. Other VOCs may be released from washing activities, such as chloroform and bromoform. Now that high exposures to the most dangerous VOCs are no longer an issue, VOC exposure research needs to be focused on those VOCS that appear to be replacing them, and other possible sources of VOCS. Noise exposure for workers operating CTP machines was low, another positive finding. However, noise exposure for workers operating offset printing machines, particularly web-fed machines used in newspaper printeries, remains unacceptably high. These exposures were no lower than that reported 20 years ago. Furthermore, workers in high noise environments did report using personal protective equipment to mitigate the risks of hearing loss. Clearly, more needs to be done to educate workers on risks to hearing and the proper fit and use of personal protective equipment. This study found evidence of clinically relevant levels of hearing and balance impairment related to very low levels ototoxic VOC exposure, particularly toluene, and to a lesser extent ethylbenzene and xylene. The damage to hearing was much worse in workers with diabetes. The effects of noise exposure were much less and were related to age.

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