[Possible outer hair cells hazards from occupational exposure to very low frequency electric and magnetic fields: a pilot study].

Objective: Our purpose was to investigate occupational high-strength very low frequency electric and magnetic fields (VLF EMFs) and assess changes of function of the inner ear.

Method: The people exposed to high-strength VLF EMFs were divided into three groups: long- term exposure group ( > 5 years), short-term exposure group (< 5 years) and the control group. The field intensity indicator and noise analyzer were employed for the examination of the electromagnetic energy intensity and noise value at the working sites. Self-administered questionnaire was adopted. Universal hearing screening by pure tone audiometry (PTA) and distortion product otoacoustic emission (DPOAE) were done. The subjects who failed the screening tests were confirmed with auditory brainstem response (ABR) test.

Result: The frequency of the electromagnetic field was 20 kHz, the average electric power density in job locations was 21-38 kV/m, which was higher than national standard (< 5 kV/m). Average noise-level in job locations was 52-65 dBHL, which was within the standard. Questionnaire presented that VLF EMFs might increase the incidence of headache, insomnia and tinnitus in long-term exposure. The incidence of abnormal DPOAE was higher in the subjects of the long-term exposure group than the short-term exposure group and the control group (P < 0.01). At 676, 933, 3616, 5130, 7253 Hz, the DPOAE amplitudes of the long term exposure group workers were significantly lower than the short-term exposure group and the control group. There was no obvious difference of the incidence of abnormal DPOAE between the short-term exposure group and the control group. The result of ABR with those subjects with abnormal DPOAE were no significant abnormalities.

Conclusion: The average electric power density in job locations was significant worse than health standards. The changes of DPOAE indicated that the exposure to high-strength VLF EMFs had a subtle, discreet and localized impairing effect on outer hair cells. Effective intervention measures should be taken.