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.

Gender effects of acute malathion or zinc exposure on the antioxidant response of rat hippocampus and cerebral cortex

Gender is one of the most important factors in mammalian development and response to exogenous agents. Although there is increasing evidence that health effects of toxic xenobiotics differ in prevalence or are manifested differently in male and female, the molecular mechanisms related to these events remain unclear. In order to investigate the possible influence of gender, male and female Wistar rats from the same litter were exposed to zinc chloride (5 mg/kg, i.p.) or malathion (250 mg/kg, i.p.) 24 hr prior to the analyses of biochemical parameters related to the cholinergic and glutathione-antioxidant systems in cerebral cortex and hippocampus. After treatments, acetylcholinesterase (AChE) activity was reduced in the hippocampus and cerebral cortex of male and female rats treated with malathion, but the effect was more pronounced in the male group. Glutathione reductase (GR) and γ-glutamyl-transpeptidase activities were reduced in the hippocampus of males and females and a gender-specific effect of malathion was seen for glutathione S-transferase (GST), which was decreased only in male hippocampus and cortex, and for male cortical GR. Zinc chloride treatment decreased AChE activity in male and female cerebral cortex, with no obvious effect in the hippocampus. Male-specific antioxidant-related enzyme activity reductions were seen after zinc treatment for cortical GR, GST, glutathione peroxidase and glucose-6-phosphate dehydrogenase; and hippocampal GR. These results clearly demonstrate a greater detrimental effect on antioxidant-related enzyme activities in male hippocampus and cerebral cortex when rats were acutely exposed to malathion and zinc, demonstrating that the research on gender-related differences in health effects caused by xenobiotic and/or essential elements requires further attention.

Modification of the relationship between urinary 8-OHdG and hippuric acid concentration by GSTM1, GSTT1, and ALDH2 genotypes

Urinary hippuric acid (HA) has been widely used as a biological marker of occupational exposure to toluene, although it is no longer valid for low levels of toluene exposure. Toluene exposure is known to induce oxidative DNA damage and the metabolism is affected by genetic polymorphisms of some metabolizing enzymes. Therefore, genetic polymorphisms of these metabolizing enzymes must be considered in the evaluation of oxidative stress caused by toluene exposure. We evaluated the relationship between urinary 8-hydroxydeoxyguanosine (8-OHdG), a marker of oxidative DNA damage, and urinary HA in individuals without occupational exposure to toluene and characterized the possible roles of GSTM1, GSTT1, and aldehyde dehydrogenase 2 (ALDH2) genotypes in the relationships between these markers. In this study, we enrolled 92 healthy Koreans. Urinary HA and 8-OHdG levels were measured and the correlations between them were statistically tested according to the GSTM1, GSTT1, and ALDH2 genotypes. HA did not significantly correlate with urinary 8-OHdG in overall subjects. However, the correlation between them showed a statistical significance in individuals with GSTM1-null, GSTT1-null, and ALDH2 *2/*2 genotypes (r = 0.766, p < 0.01). This study shows that the relationship between urinary HA and 8-OHdG concentration is modified by genetic polymorphisms of some metabolizing enzymes such as GSTM1, GSTT1, and ALDH2.