Effects of exposure to organic solvents and occupational noise on hearing loss and tinnitus in US adults from 1999 to 2004

There is evidence that organic solvents are ototoxic, and studies suggest there is an interaction between organic solvents and noise on ototoxicity. The purpose of this study was 1) to explore the association between organic solvent exposure and hearing loss or tinnitus and 2) to determine if interaction exists between occupational noise and organic solvent exposure on hearing loss or tinnitus. This study used data from the National Health and Nutrition Examination Survey (NHANES) from 1999-2004 to analyze data on hearing outcomes and organic solvent exposure. The following organic solvents were studied: 1) 1,4-dichlorobenzene, 2) benzene, 3) ethylbenzene, 4) styrene, 5) toluene, 6) o-xylene, and 7) m-/p-xylene. Study participants were excluded if they had bilaterally unsymmetrical hearing loss, missing data on covariates, or detectable blood measurements that exceed the calibrated range of assay. The number of study participants included in this study was 2,513, but the sample size varied by analysis as the available data for each organic solvent and outcome varied. Data from the Occupational Information Network (O*NET) was used to approximate occupational noise exposure in study participants based on their job. Logistic regression was used to determine associations between organic solvent exposure and hearing outcomes (i.e., self-reported hearing loss, audiometrically-assessed hearing loss, self-reported tinnitus, high-frequency hearing loss, and low-frequency hearing loss). The age of study participants ranged from 20-59 years. A majority of study participants had an income equal to or over $20,000 (80.5%) and were non-Hispanic white (49.7%), while a minority of study participants had recently used ototoxic medication (4.3%), were smokers (22.4%), were diabetic (5.0%), or were classified as exposed to non-occupational noise (30.0%). After adjusting for covariates, there was no evidence of an association between hearing loss or tinnitus and organic solvent exposure except for three solvents: higher levels of benzene, ethylbenzene and toluene were associated with high-frequency hearing loss (benzene adjusted odds ratio (OR)=1.43, 95% confidence interval (CI) 1.15- 1.78; ethylbenzene adjusted OR=1.24, 95% CI 1.02-1.50; and toluene adjusted OR=1.27, 95% CI 1.06-1.52). Moreover, the effect estimates for high-and low-frequency hearing loss were higher as compared to audiometrically-assessed hearing loss. Additionally, no evidence of interactions between organic solvent exposure and occupational noise on high-frequency hearing loss was observed. In conclusion, this dissertation found, in a large, diverse population with blood measurements of organic solvents, there was no indication of association between organic solvent exposure and self-reported and audiometrically-assessed hearing loss or self-reported tinnitus, but there was evidence of an association between organic solvents and high-frequency hearing loss