Release: September 9, 2001
Contact: Kenneth Satterfield(703) 519-1563[email protected]303-228-8460 (9/7-9/12)
EXPOSURE TO INORGANIC MERCURY AND NOISE MAY LEAD TO AUDITORY PATHWAY DYSFUNCTION
Brazilian medical researchers fear that their nation's increasing use of fluorescent light bulbs to save energy may create a public health hazard.
Denver, CO -- The Brazilian government has recently responded to an energy crisis and risk of blackouts by imposing a general reduction of 20 percent in power consumption. The public has increased taken to the use of fluorescent light bulbs versus conventional high energy consuming lamps. A group of medical researchers from that nation's leading medical schools is now warning that neither the industry nor the population are aware of the health risks involved with improper handling or dropping of fluorescent light bulbs that contain mercury. They believe accidental intoxication with mercury vapors may become a public health concern.
Hearing impairment, balance disorders, ataxia (abnormality of muscle balance or inability to finely coordinate movements), speech disturbance, progressive numbness of the perioral region and inferior members, blurred vision and constriction of visual fields are commonly attributed to chronic organic mercury intoxication (methyl mercury intoxication). The Brazilian team believes that occupational exposure to inorganic mercury may have equally dire consequences. Accordingly, they set out to examine the audiometric and brain stem responses of workers in a fluorescent light bulb manufacturing facility who were exposed to both noise and inorganic mercury. None of them used ear protection.
Their research findings suggest there may be a synergistic effect of noise and inorganic mercury upon the auditory system. The authors of "Effects of Mercury and Noise on the Human Auditory System," are Signe Schuster Grasel, M.D, M¥rcia Akemi Kii, MD, Edigar Rezende De Almeida, MD, Ph.D, Ricardo Ferreira Bento, MD, PhD, Marcilia Medrado De Faria, MD, and Erika Cisi Domingues, MD, all from the University of S¥o Paulo School of Medicine, S¥o Paulo, Brazil. Their findings were presented at the American Academy of Otolaryngology--Head and Neck Surgery Foundation Annual Meeting/OTO EXPO, being held September 9-12, 2001, at the Colorado Convention Center, Denver, CO.
Methodology: This prospective multidisciplinary study consisted of examining 116 ears of 58 subjects exposed to inorganic mercury and noise for more than six months and with neuropsychological symptoms suggestive of chronic mercury intoxication. Age ranged from 28 to 58 with a mean of 42 years. Forty-four (76 percent) were males and 14 (24 percent) females. The control group included 18 unexposed subjects (36 ears) with no hearing complaints, PTA (pure tone audiometry) thresholds less than 25 dB HL (hearing level) at all frequencies and normal ABR (auditory brainstem responses) latencies and waveforms. The mean age was 38 years.
Exposure duration to inorganic mercury and noise was recorded and correlated to audiometric and ABR findings. Three indices of PTA thresholds (low, middle and high frequencies) were evaluated. PTA findings were correlated to four groups of ABR wave patterns (group one: normal; group two: decreased V/I amplitude ratio; group three: prolonged latencies/interpeak latencies; group four: absent waves).
Results: Seventy-four of the 116 ears (63.8 percent) in the study group had normal PTA thresholds at all frequencies, 42 (36.2 percent) had abnormal thresholds at least at one frequency, 36 (31 percent) of them at 4000 Hz.
Eighteen subjects had unilateral threshold shifts involving eleven right and seven left ears. ABR abnormalities were found in 29 (25 percent) ears; 12 (10.3 percent) with decreased V/I amplitude ratio; 14 (12.1 percent) with prolonged latencies and interpeak I-V latencies and 3 (2.6 percent) with absent waves. Nine ears (two right and seven left ears) showed unilateral abnormalities. Ten of 12 ears with decreased V/I amplitude ratio had normal PTA thresholds up to 4000 Hz. Ears with normal ABR patterns or decreased V/I amplitude ratio (groups 1 and 2) had significantly lower PTA threshold levels (PTA2 and PTA3) as compared to groups 3 and 4 (prolonged latencies/interpeak latencies and absent waves).
The prolonged latencies in group 3 revealed a significant latency shift of wave III and V. So the prolonged I-III interpeak interval was responsible for the increased I-V intervals. Exposure duration varied from one and a half to 21 years (mean: 8.9 years) and was not associated with the audiometric and ABR findings. There was no significant difference of age between the groups.
The study found the combined effect of inorganic mercury and noise induced elevated PTA threshold levels in 42 (36.2 percent) ears and ABR abnormalities in 29 (25 percent) ears. A 4000 Hz notch as typically described in cases of noise-induced hearing loss was observed in 36 (31 percent) ears.
Conclusion: Exposure to inorganic mercury and noise induced elevated PTA thresholds and abnormal ABR patterns among the study population. Decreased V/I amplitude ratio, detected in a significant number of ears with normal audiometric thresholds, may be an early event in auditory pathway dysfunction. As public use of fluorescent lighting increases, employers, health staffs at emergency units and public health centers should be trained to recognize symptoms of acute and chronic mercury poisoning and its consequences.
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