Mercury exposure in a residential community - Florida, 1994

Morbidity and Mortality Weekly Report, June 16, 1995

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 (> 15 [micro]g/[m.sup.3]) 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 [micro]g/[m.sup.3]. 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 [micro]g/[m.sup.3].

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 [micro]g/dL to 5.5 [micro]g/dL (normal: <1 [micro]g/dL) and urine levels ranged from 21 [micro]g/L to 66 [micro]g/L (normal: <20 [micro]g/L). Ambient air samples ranged from 6.5 [micro]g/[m.sup.3] to 300 [micro]g/[m.sup.3]. 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 [micro]g/[m.sup.3] 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.

TABLE 1. Summary -- cases of specified notifiable diseases, United

States, cumulative, week ending June 10, 1995 (23rd Week)

                                                 Cum. 1995
Anthrax                                               -
Brucellosis                                          33
Cholera                                               7
Congenital rubella syndrome                           3
Diphtheria                                            1
Haemophilus influenzae(*)                           577
Hansen Disease                                       60
Plague                                                2
Poliomyelitis, Paralytic                              -
                                                 Cum. 1995
Psittacosis                                          27
Rabies, human                                         1
Rocky Mountain Spotted Fever                         84
Syphilis, congenital, age < 1 year([dagger])          -
Tetanus                                    10
Toxic shock syndrome                                 93
Trichinosis                                          20
Typhoid fever                                       131