Combined effects of paired solvents on the rat's auditory system

Audition and exhibition to toluene - a contribution for the theme

INTRODUCTION

 With the technological advances and the changes in the productive processes, the workers are displayed the different physical and chemical agents in its labor environment. The toluene is solvent an organic gift in glues, inks, oils, amongst others.

OBJECTIVE

 To compare solvent the literary findings that evidence that diligent displayed simultaneously the noise and they have greater probability to develop an auditory loss of peripheral origin.

METHOD

 Revision of literature regarding the occupational auditory loss in displayed workers the noise and toluene.

RESULTS

 The isolated exposition to the toluene also can unchain an alteration of the auditory thresholds. These audiometric findings, for ototoxicity the exposition to the toluene, present similar audiograms to the one for exposition to the noise, what it becomes difficult to differentiate a audiometric result of agreed exposition - noise and toluene - and exposition only to the noise.

CONCLUSION

 The majority of the studies was projected to generate hypotheses and would have to be considered as preliminary steps of an additional research. Until today the agents in the environment of work and its effect they have been studied in isolated way and the limits of tolerance of these, do not consider the agreed expositions. Considering that the workers are displayed the multiples agent and that the auditory loss is irreversible, the implemented tests must be more complete and all the workers must be part of the program of auditory prevention exactly displayed the low doses of the recommended limit of exposition.

Organic solvents and hearing loss: The challenge for audiology

Organic solvents have been reported to adversely affect human health, including hearing health. Animal models have demonstrated that solvents may induce auditory damage, especially to the outer hair cells. Research on workers exposed to solvents has suggested that these chemicals may also induce auditory damage through effects on the central auditory pathways. Studies conducted with both animals and humans demonstrate that the hearing frequencies affected by solvent exposure are different to those affected by noise, and that solvents may interact synergistically with noise. The present article aims to review the contemporary literature of solvent-induced hearing loss, and consider the implications of solvent-induced auditory damage for clinical audiologists. Possible audiological tests that may be used when auditory damage due to solvent exposure is suspected are discussed.

Effects of Concurrent Noise and Jet Fuel Exposure on Hearing Loss

We sought to examine the effects of occupational exposure to jet fuel on hearing in military workers.

METHODS

Noise-exposed subjects, with or without jet fuel exposure, underwent hearing tests. Work histories, recreational exposures, protective equipment, medical histories, alcohol, smoking, and demographics were collected by questionnaire. Jet fuel, solvent, and noise exposure data were collected from records. Fuel exposure estimates were less than 34% of the OSHA Threshold Limit Values.

RESULTS

Subjects with 3 years of jet fuel exposure had a 70% increase in adjusted odds of hearing loss (OR = 1.7; 95% CI = 1.14-2.53) and the odds increased to 2.41 (95% CI = 1.04-5.57) for 12 years of noise and fuel exposure.

CONCLUSIONS

These findings suggest that jet fuel has a toxic affect on the auditory system.

Volatile organic compounds inhibit human and rat neuronal nicotinic acetylcholine receptors expressed in Xenopus oocytes

The relative sensitivity of rats and humans to volatile organic compounds (VOCs) such as toluene (TOL) and perchloroethylene (PERC) is unknown and adds to uncertainty in assessing risks for human exposures to VOCs. Recent studies have suggested that ion channels, including nicotinic acetylcholine receptors (nAChRs), are targets of TOL effects. However, studies comparing TOL effects on human and rat ligand-gated ion channels have not been conducted. To examine potential toxicodynamic differences between these species, the sensitivity of human and rat nAChRs to TOL was assessed. Since PERC has similar effects, in vivo, to TOL, effects of PERC on nAChR function were also examined. Two-electrode voltage-clamp techniques were utilized to measure acetylcholine-induced currents in neuronal nAChRs (alpha4beta2, alpha3beta2, and alpha7) expressed in Xenopus oocytes. PERC (0.065 mM) inhibited alpha7 nAChR currents by 60.1 +/- 4.0% (human, n = 7) and 40 +/- 3.5% (rat, n = 5), and inhibited alpha4beta2 nAChR currents by 42.0 +/- 5.2% (human, n = 6) and 52.2 +/- 5.5% (rat, n = 8). Likewise, alpha3beta2 nAChRs were significantly inhibited by 62.2 +/- 3.8% (human, n = 7) and 62.4 +/- 4.3% (rat, n = 8) in the presence of 0.065 mM PERC. TOL also inhibited both rat and human alpha7, alpha4beta2, and alpha3beta2 nAChRs. Statistical analysis indicated that although there was not a species (human vs. rat) difference with PERC (0.0015-0.065 mM) or TOL (0.03-0.9 mM) inhibition of alpha7, alpha4beta2, or alpha3beta2 nAChRs, all receptor types were more sensitive to PERC than TOL. These results demonstrate that human and rat nACh receptors represent a sensitive target for VOCs. This toxicodynamic information will help decrease the uncertainty associated with animal to human extrapolations in the risk assessment of VOCs.

Hexachlorobenzene, a dioxin-like compound, disrupts auditory function in rat

Hexachlorobenzene (HCB) is a dioxin-like compound widely distributed in the environment. In this study, we investigated the effects of HCB on the cochlea. Conscious free-moving rats were given HCB per os daily for 4 weeks at doses of 0.16, 4 or 16 mg/kg in olive oil, whereas the control group received olive oil only. The effects of HCB were evaluated at various time intervals, by measuring auditory nerve acoustic thresholds and plasma thyroid hormone concentration by radioimmunoassay. Histological evaluation involved surface preparation and scanning electron microscopy observations of cochlear hair cells. At a dose of 0.16 mg/kg, HCB induced no loss of acoustic sensitivity, whereas at 4 mg/kg, it induced cochlear sensitivity deficits at the mid-frequencies (2-16 kHz) with complete recovery once treatment was stopped. At a dose of 16 mg/kg, permanent threshold shifts were observed at all frequencies tested (from 1 to 32 kHz). Morphological studies showed no cochlear hair cell loss or alteration of stereocilia. HCB treatment reduced circulating thyroxine concentrations. Thyroidectomy had no effect on cochlear sensitivity in control animals. Thus, HCB is a potent oto-toxicant, and its ototoxicity may be independent of its thyroidal effects.

Chemical mixtures and health effects at Superfund sites

Between 1991 and 1993, EPA's Office of Research and Development conducted a small health effects research program dedicated to the problem of chemical mixtures at Superfund sites. This paper summarizes key findings from the program. The studies covered a wide range of endpoints, several chemical classes, and mixture complexities ranging from two to five chemicals. Additivity and antagonism were far more common than synergy. Departures from additivity seemed to be on the order of a factor of two or less, an observation that may provide some bounds for concern.

Evaluation of organic solvent ototoxicity by the upper limit of hearing

To clarify the effects of organic solvents on hearing, we measured the upper limit of hearing in 93 male workers exposed to organic solvents in 7 factories that produced plastic buttons or baths. Medical examinations, environmental monitoring (i.e., concentration in breathing-zone air), and biological monitoring (i.e., concentration in urine) of the organic solvents were also done. Although the organic solvent concentrations in the environmental monitoring were lower than the occupational exposure limit, the upper limit of hearing was reduced in workers who were exposed for 5 y or more. This reduction was dose-dependent and was related to styrene concentrations in breathing-zone air and mandelic acid concentrations in urine. Even individuals who had normal medical examinations showed a reduced upper limit of hearing. The upper limit of hearing may serve as an early detection indicator of health effects in workers constantly exposed to styrene.