Elemental Mercury Vapor Poisoning -- North Carolina, 1988

In July 1988, the Environmental Epidemiology Section, North Carolina Department of Environment, Health, and Natural Resources (DEHNR), investigated chronic mercury poisoning diagnosed in a 3-year-old boy from North Carolina. The patient's clinical manifestations included hypersalivation, myalgia and tremor in the hands, myalgia and weakness in both lower extremities, diaphoresis, irritability, insomnia, and anorexia. Analysis of a random urine sample detected a mercury level of 160 ug/L (normal: less than 25 ug/L). Results of 24-hour urine specimens for mercury collected from both the patient and his parents were: patient, 360 ug/L; mother, 230 ug/L; and father, 145 ug/L.

Although the family reported no known mercury exposures, in April 1988, they had moved into a house whose previous owner had collected elemental mercury. Several containers of mercury reportedly had been spilled in the house during the previous owner's occupancy. As a result of the determination that the house was the probable source of exposure, the family temporarily relocated.

In July 1988, DEHNR conducted an extensive investigation of the house. A mercury vapor analyzer detected a mercury concentration of 20 ug/m3-60 ug/m3 in five rooms and two bathrooms. The average mercury concentration in the patient's bedroom was 55 ug/m3 (range: 30 ug/m3-140 ug/m3). In the vacuum cleaner filter bag, the mercury concentration for air exceeded the range of the analyzer (1000 ug/m3). A dust sample from the vacuum cleaner bag had an elemental mercury concentration of 4400 ppm, and carpet samples had concentrations of 0.8 ppm-638 ppm.

Urine mercury screening was carried out for two children of the previous occupant and for seven persons who had frequently visited them The two children had urine mercury levels of 98 ug/L and 49 ug/L; the seven other persons had levels less than 25 ug/L.

Corrective measures included removal of the carpets, decontamination of the house (i.e., several cleanings of floors, walls, and solid surfaces with a product containing a metallic-mercury-sulphide-converting powder, a chelating compound, and a dispersing agent), and application of a polyurethane coating to all floor surfaces. Subsequent analysis indicated that the mercury concentration was less than 1 ug/m3 throughout the house.

Over a 2-month period, the urine mercury levels of the family decreased to normal. The patient, who had been treated with penicillamine, recovered without neurologic sequelae. In August 1988, the family returned to the house. Because the patient's parents and the children of the previous owner remained asymptomatic, they were not treated. Reported by: EI Blair, MD, Dept of Pediatrics, RE Cross, PhD, Depts of Pathology and Medicine, Univ of North Carolina School of Medicine, Chapel Hill; GM Stave, MD, Duke Occupational Health Svc, Duke Univ Medical Center, Durham; WW Hill Jr, MPH, J Smith, Nash County Health Dept, Nashville; JI Freeman, DVM, DL Newton, MSPH, WJ Pate, WA Williams, JN MacCormack, MD, State Epidemiologist, North Carolina Dept of Environment, Health, and Natural Resources. Div of Environmental Hazards and Health Effects, Center for Environmental Health and Injury Control; Div of Field Svcs, Epidemiology Program Office, CDC.

Editorial Note

Editorial Note: Reported cases of nonoccupational elemental mercury vapor poisoning are relatively rare (1). Acute cases usually result from inhalation of high concentrations of mercury vapor, which is produced when the metal is heated in an enclosed space (1). The North Carolina investigation and other reported cases indicate that chronic elemental mercury vapor poisoning can also occur in the home (2).

In this report, the patient developed many of the symptoms typical of chronic elemental mercury vapor poisoning (3). In addition, the patient's urine mercury concentration was greater than 150 ug/L, the level associated with the earliest neurologic effects in adults (4). The 8-hour time-weighted average air concentration of elemental mercury vapor associated with the earliest neurologic effects in adult workers has been estimated at 50 ug/m3 (4). This concentration was detected throughout the house; higher concentrations were recorded in the patient's bedroom.

The concentrations of elemental mercury found in the vacuum cleaner bag dust sample and the carpet samples indicate that the carpets were heavily contaminated. Vacuuming the mercury-contaminated carpet may have resulted in dispersal of particles and vapor throughout the house. Vaporization probably increased with the spread of the mercury and the onset of warmer weather (5).

The Environmental Protection Agency's suggested ambient air concentration for mercury is less than 1 ug/m3 (6). Although this level exceeds those found in pristine environments (6)--and presumably in uncontaminated homes--it is below the accepted exposure concentrations for occupational settings (7). In addition, a concentration of 1 ug/m3 has been considered an obtainable goal for decontamination in other cases of residential mercury contamination (8).

Elemental mercury should not be stored in residences, particularly those with carpeted surfaces. If spilled, mercury should be removed before it can be dispersed. However, a contaminated carpet or rug should be vacuumed only with a specialized industrial mercury vacuum. A contaminated carpet or rug that cannot be adequately cleaned should be considered a substantial health risk and removed promptly. If necessary, decontamination procedures should be undertaken to reduce the ambient mercury vapor concentration in the house to less than 1 ug/m3.

References

1. Sexton DJ, Powell KE, Liddle J, et al. A nonoccupational outbreak of inorganic mercury vapor poisoning. Arch Environ Health 1978;33:186-91.

2. Moutinho ME, Tompkins AL, Rowland TW, et al. Acute mercury vapor poisoning. Am J Dis Child 1981;135:42-4.

3. Grandjean P. Diseases associated with metals. In: Last JM, ed. Public health and preventive medicine. 12th ed. Connecticut: Appleton-Century-Crofts, 1986:587-615.

4. WHO Study Group. Recommended health-based limits in occupational exposure to heavy metals. Geneva: World Health Organization, 1980. (Technical report series no. 647).

5. Goldwater LJ. The toxicology of inorganic mercury. Ann NY Acad Sci 1957;65:498-503.

6. Environmental Protection Agency. Background information on the development of national emission standards for hazardous air pollutants: asbestos, beryllium, and mercury. Research Triangle Park, North Carolina: US Environmental Protection Agency, 1973; publication no. APTD-1503.

7. Occupational Safety and Health Administration. Air contaminants--permissible exposure limits (title 29, Code of federal regulations, part 1910.1000). Washington, DC: US Department of Labor, Occupational Safety and Health Administration, 1989.

8. Zirschky J, Witherell L. Clean-up of mercury contamination of thermometer workers' homes. Am Ind Hyg Assoc J 1987;37:311-4.

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