Mercury Exposure in a Residential Community -- Florida, 1994

Residential exposure to elemental mercury typically involves small amounts (e.g., the approximately 0.3 mL in a thermometer). During August 1994, five children residing in a neighborhood in Palm Beach County, Florida, found 5 pints of elemental mercury in an abandoned van. During the ensuing 25 days, the children shared and played with the mercury outdoors, inside homes, and at local schools. On August 25, 1994, a parent notified local police and fire authorities that her children had brought mercury into the home. On the same day, 50 homes were immediately vacated and an assessment of environmental and health impacts was initiated by the State of Florida Department of Environmental Protection, the Health and Rehabilitative Services of the Palm Beach County Public Health Unit, and the U.S. Environmental Protection Agency. This report summarizes the investigation of this incident.

Door-to-door interviews of the entire neighborhood (n=363) were conducted, and a decontamination facility was established at the civic center. Based on information collected during the initial survey, residential structures and several classrooms at the local high school were tested for the presence of mercury. Ambient air samples (i.e., adult breathing zone grab samples collected approximately 5 feet above the floor) were collected in affected structures during the 6 days following the report of children handling mercury. In addition, during August 25-29, initial blood and urine samples were collected from potentially exposed persons and analyzed for mercury levels.

A total of 58 residential structures were monitored for indoor mercury vapor concentrations; unsafe indoor air levels of mercury (greater than 15 ug/m3) were detected in 17, prompting the immediate evacuation of 86 persons. Several classrooms at the local high school were determined to be contaminated. This school was closed for 4 days until clearance air sampling indicated that the mercury level was less than or equal to 10 ug/m3. This level of mercury was considered safe for students and teachers rotating among the rooms for 50-minute classes. Pregnant women and young children were excluded from entering classrooms until mercury levels decreased to less than or equal to 0.3 ug/m3.

A total of 477 persons identified by the survey as potentially exposed were evaluated at the emergency department of the local hospital or the health department clinic for mercury poisoning by testing both blood and urine specimens for total inorganic mercury levels. Elevated blood and/or urine mercury levels were detected in 54 persons: blood levels ranged from 1.1 ug/dL to 5.5 ug/dL (normal: less than 1 ug/dL) and urine levels ranged from 21 ug/L to 66 ug/L (normal: less than 20 ug/L). Ambient air samples ranged from 6.5 ug/m3 to 300 ug/m3. Although these 54 persons were asymptomatic, concentrations of mercury detected in their blood and urine were consistent with the levels of mercury detected in their homes.

Homes and classrooms were decontaminated by spreading powdered sulfur absorbent on the floors and vacuuming surfaces with high efficiency particulate- arresting (HEPA) filters. Contaminated items (e.g., carpeting, padding, linoleum, clothing, bedding, vacuum cleaners, furniture, and washing machines) were removed and taken to a hazardous waste facility, and some homes required ventilation for periods up to 3 months. Because of the potential for residential exposure of many children and childbearing-aged women, an air mercury concentration of less than or equal to 0.3 ug/m3 was established as a threshold at which families would be permitted to return to their homes. Ambient air samples were collected 24 inches above the ground (i.e., a child's breathing zone), under normal living conditions for at least 8 hours.

By December 1, 1994, all displaced families had been permitted to return to their homes, and urine mercury levels of all exposed persons decreased. However, the Palm Beach County Health Department continues to monitor persons with persistently elevated urine mercury levels. This incident is under criminal investigation, and information regarding the source of the mercury has not been released. Reported by: JM Malecki, MD, Health and Rehabilitative Svcs/Palm Beach County Public Health Unit, R Hopkins, MD, State Epidemiologist, State of Florida Dept of Environmental Protection. U.S. Environmental Protection Agency. Air Pollution and Respiratory Health Br, National Center for Environmental Health, CDC.

Editorial Note

Editorial Note: Most poisonings associated with exposure to elemental mercury occur in occupational settings, and reports of nonoccupational elemental mercury vapor poisonings are rare, especially in community-based settings (1,2). The exposures described in this report primarily affected homes and schools.

Inorganic mercury is a heavy, silver-white metal that is liquid at room temperature. The vapor pressure of mercury is high compared with other metals, creating the continual hazard of airborne exposure to mercury vapor, which is odorless and colorless. Mercury is absorbed into the blood following inhalation and is then transported to the brain and other areas of the nervous system and to all other tissues. Most elemental mercury is excreted unchanged in feces.

The development of clinical manifestations as the result of inhalation of mercury vapor is related to several factors, including the concentration of vaporized mercury, length of exposure, and individual susceptibility (2,3). Acute exposure to elemental mercury produces symptoms of metallic taste, burning, irritation, salivation, vomiting, diarrhea, upper gastrointestinal tract edema, abdominal pain, and hemorrhage (4). Symptoms of high levels of exposure usually begin abruptly and include fever, chills, malaise, nausea, coughing, shortness of breath, chest pain and tightness; the clinical course may progress to pulmonary edema and death (5). In comparison, chronic inorganic mercury poisoning can result in intention tremor, memory loss, insomnia, depression, irritability, excessive shyness, emotional instability, delirium, and acrodynia and may result in a neurologic syndrome known as "mad hatter syndrome" (2-5).

The risks associated with mercury exposure are especially increased for children because mercury vapor is dense and settles (2) and because children may be active on the floor or playing in dirt. In addition, because of lipid solubility, mercury crosses the placenta and is excreted in breast milk and, therefore, is a potential health hazard for unborn children and breastfeeding infants (6,7).

Elemental mercury is still widely used in industry for the manufacture of thermometers, barometers, vacuum pumps, and electrical components and may be present in household products such as cleaning solutions and adhesives (2,5). Small amounts of mercury, such as from a broken thermometer, can be cleaned up by spraying the mercury gently with hairspray or dusting with an absorbent such as powdered sulfur and sweeping up the mercury and absorbent with a wisk broom. After cleaning the spill, the broom should be securely bagged and discarded (8). Any person who discovers a large quantity of mercury should immediately contact the local poison-control center or health department.

The residential exposure described in this report was unprecedented in terms of the amount of mercury involved and the extent of contamination. The rapid and coordinated response to this incident minimized the risk for and assured the health of the exposed residents.

References

1. CDC. Elemental mercury vapor poisoning--North Carolina, 1988. MMWR 1989;38:770-2,777.

2. CDC. Elemental mercury poisoning in a household--Ohio, 1989. MMWR 1990;39:424-5.

3. Knight, AL. Mercury and its compounds. In: Zenz C, ed. Occupation medicine: principles and practices. 2nd ed. Chicago: Year Book Medical Publishers, 1988:590-6.

4. Rumack B, Peterson R. Clinical toxicology. In: Doull J, Klassen C, Amdu M, eds. Toxicology: the basic science of poisons. 2nd ed. New York: Macmillan Publishing Co., Inc., 1980:690-1.

5. Taueg C, Sanfilippo DJ, Rowens B, Szejda J, Hesse JL. Acute and chronic poisoning from residential exposures to elemental mercury--Michigan, 198

6. Sikorski R, Juszkiewicz T, Paszkowski T, Szprengier-Juskiewicz T. Women in dental surgeries: reproductive hazards in occupational exposure to metallic mercury. Archives Occupational Environmental Health 1987;59:551-7.

7. Thorp JM, Boyette DD, Watson WL, Cefalo RC. Elemental mercury exposure in early pregnancy. Obstet Gynecol 1992;79:874-6.

8. Micromedics, Inc. Poisindex {Software}. Denver: Micromedics, Inc., 1995 (Vol 85).

   
   

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