[Assessment of the hearing system in workers chronically exposed to carbon disulfide and noise]

Epidemiological studies carried out in the years 1984-1993 revealed carbon disulfide (CS2) to be one of the major chemical occupational hazards. Whereas among physical factors, noise was found to be the most common threat. Industrial workers very often face a combined exposure of two or more factors, like CS2 and noise, responsible for significant biological risk to the human health, although health effects of such an exposure have not as yet been thoroughly recognized and explored. The aim of this study was to assess changes in the hearing system in people exposed to toxic effect of CS2, recognized as characteristic of an overall clinical history of chronic poisoning by this solvent, in cases of concomitant exposure to noise exceeding maximum allowable levels. The study covered 80 workers aged 44-65 years (mean = 44.9 +/- 5.1), employed in a spinning mill of viscose fibre for 20.3 years on average (+/- 5.4 years) with clinically observed chronic CS2 poisoning, and a group of 40 people (mean age = 56.8 years) exposed to CS2 but without subjective or objective symptoms indicating chronic poisoning by the solvent. Both groups of subjects at similar age and with almost the same duration of employment were exposed to CS2 in concentrations changing in time between 10 and 35 mg/m3 (mean concentration = 25.8 mg/m3), and to continuous noise with the level ranging from 88 to 92 dB(A) for six hrs per one shift. The control group was composed of 40 workers (mean age = 52.0 +/- 5.3 years) employed in the cotton industry plant, without contact with CS2 or other chemicals and working in the acoustic environment with similar level of exposure to noise (86-93 dB(A)). Audiological and electronystagmographic examinations revealed bilateral retrocochlear hearing impairment associated with symptoms of the central vestibular syndrome in 97.5 subjects with diagnosed chronic CS2 poisoning. In workers free from clinical symptoms of chronic CS2 poisoning, perceptive hearing impairment of various degrees was found, including retrocochlear in 45% of subjects and cochlear in 32.5%, while in 22.5% of those under study normal hearing was observed. In the control group of subjects exposed to noise without contact with CS2, sensorineural cochlear hearing loss, typical of chronic acoustic trauma without concomitant vestibular disorders, was revealed. The results of the study show that in subjects with diagnosed chronic CS2 poisoning and exposed to noise, hearing impairment and vestibular disorders occur in the form of central changes which suggests a dominating CS2 toxic effect on the hearing system. But in some people exposed to both CS2 and noise, the hearing impairment in localised in cochlea like in acoustic trauma damage. This probably depends on individual susceptibility to harmful effect of these factors.