SYNOPSISNoise loading has a considerable effect on the working conditions of telephone operators. This study comprises noise field and laboratory measurements and field investigation of workers at three departments of the Telephone and Telegraph Communication Services in Sofia.Noise measurements revealed a background noise in the range of 57.4 -70.6 dB A in the International Department, 70.6 -71.7 dB A in the Intercity Department and 68.7 • 70.1 dB A in the Information Department and highest intensities of 63.5, 62.1 and 58.2 dB for frequencies of 0.5, 1 and 2 kHz. The registered noise (L eq ) from the inner telephone receivermicrophone (type Star-set) was in the range of 78.4 -86.6 dB A. Peaks of 90-96 dB A were registered during different working operations ("dialing", "speaking", "fax", "occupied") with duration less than 5s and stochastic appearance during the 15 min measuring periods.A total of 260 female telephone operators (mean age 36.7 ± 8.22 years and mean length of employment 12.7 ± 7.12 years) with similar job activities at the three departments were investigated. No marked decreased hearing sensitivity for 0.5, 1, 2, 4, 6 and 8 kHz was observed. A high percentage of the examinees gave positive answers in different questionnaires regarding subjective symptoms (psychological, neurovegetative, neurological), mental health, depression and anxiety. An elevated urine excretion of catecholamines (11-OCS, adrenalin and noradrenalin) was found during the morning and afternoon working shifts. The intensity of the noise and its annoying effect were subjectively estimated as "high" and "very This paper was presented at the Bulgarian Symposium on Work and Environmental Physiology, Sofia, October 1992.high" by most of the examined telephone operators. In a large percentage of operators in the Intercity Department, the changes of the audiometric, psychological and biochemical examinations were more pronounced.The obtained results indicate that redesign of the work place should be undertaken in order to prevent health effects on the telephone operators.

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Liver changes after separate and combined action of vibration (whole body, 100 Hz, 0.1 mm amplitude) and other factors: noise (white noise 105 dB/A), heat (35 degrees C, humidity 45--55% and air velocity 0.2--0.3 ms-1) and lead (lead acetate, 20 mg/kg) were studied in white rats. The exposure lasted for 2 h daily during 10 days (lead was daily applied per os in a water solution). After the treatment in liver homogenates the activity of SucDH, LDH, and ATP-ase, as well as the quantity of soluble proteins (SP) and -SH gr were determined. In fresh frozen liver slices the activity of SucDH, LDH, and ATP-ase were investigated. Liver samples were studied by light and electro-microscopy. The results show that vibration alone did not produce marked changes, but when the other factors acted simultaneously, more expressed alterations in the liver were found. The most pronounced changes were obtained after vibration and lead effect. The histological, histochemical, and electron-microscopic findings support the biochemical data about certain disturbances in the energy supply and utilization in the liver tissue.

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