Skip directly to search Skip directly to A to Z list Skip directly to site content





The Juncos Landfill is an inactive 20-acre municipal landfill that operated from 1957-1977. In addition to municipal wastes that were disposed in the landfill, a large volume of whole and broken thermometers containing mercury were dumped in the landfill. After the landfill closed in 1981, houses were built along the northern edge of the landfill. The backyards of some residences extend onto filled-in portions of the landfill, and many residents reported finding landfill debris near the surface on their property.

In December 1982, the U.S. Environmental Protection Agency listed the Juncos Landfill on the National Priorities List. Sampling conducted in 1983 and 1984 revealed the presence of mercury in on-site soil and air and in off-site leachate, fish, and house dust. In 1984, the Centers for Disease Control evaluated the site and recommended that indoor air mercury levels be measured in homes next to the landfill [1].

In 1993, the Agency for Toxic Substances and Disease Registry prepared a Site Review and Update for the site [2]. Based on the available data, ATSDR concluded that the site did not pose an ongoing public health hazard. Nevertheless, residents of the community have continued to express concern over possible exposures to hazardous substances from the landfill. They have reported finding pieces of mercury-containing thermometers on their property. In addition, there are anecdotal reports that children brought elemental mercury they found in the landfill into their homes.

To address these concerns, ATSDR conducted an Exposure Investigation in the homes on Acacia Street along the northern edge of the landfill. ATSDR staff tested air inside the homes for elemental mercury. In addition, ATSDR staff collected urine samples from the residents, and the samples were tested for mercury.


Target population

On November 30, 1999, staff from ATSDR, the U.S. Environmental Protection Agency, and the Commonwealth of Puerto Rico Environmental Quality Board met with the residents of the affected community. ATSDR staff explained the purpose of the Exposure Investigation and invited the residents to participate.

There are 24 homes located along the edge of the landfill, but three of the homes have been vacated. ATSDR invited all current residents and residents who had lived there within the past two months to participate.

Residents of 21 homes volunteered for testing.

Informed Consent

Prior to testing, an adult occupant of each house gave ATSDR written, informed consent to conduct indoor air sampling in their home. In addition, each adult, and the parent or guardian of each child, was required to sign an informed consent for urine mercury testing. The consent forms were in Spanish, the native language of the residents.

Environmental Sampling

On December 1, staff from ATSDR and the Commonwealth of Puerto Rico Environmental Quality Board ATSDR visited the homes. ATSDR staff monitored for mercury vapor in indoor air in each room in the house using a Jerome Mercury Meter. All of the houses except one were built on concrete slabs; one house had a crawl space beneath it. Readings were taken in each room at floor level, particularly near floor-wall junctions and above cracks in the floor where mercury could gain entry into the house. The detection limit of the Jerome instrument was 0.001 mg mercury/cubic meter of air.

A Jerome Meter can give a false positive reading if certain chemicals are present in air at high concentrations. Therefore, if the Jerome Meter gave a positive reading, a confirmatory air sample was collected using a Hopcalite adsorbent tube and a personal air pump with a flow rate of 1 liter per minute. The adsorbent tube was sent to DataChem Laboratories in Denver, Colorado, for mercury analyses using NIOSH method 6009.

Biological Sampling

During the visits to the houses to test indoor air, ATSDR staff distributed acid-washed plastic cups to the residents to collect urine samples. The residents were instructed to collect a first morning void urine sample and to store it in their refrigerator until ATSDR staff collected it the next day.

After retrieving the urine samples, ATSDR staff transferred a 10 ml aliquot to a sample tube. Three drops of concentrated nitric acid were added to each tube as a preservative. The tubes were packaged and shipped by express mail to Pacific Toxicology in Woodland Hills, California, for analyses. The urine specimens were analyzed for total mercury, creatinine, and specific gravity. The analytical detection limit of the mercury assay was 5 µg/liter of urine.


Environmental Sampling

Mercury was not detected in indoor air in any of the houses with one exception. In the bathroom of one house, the Jerome Meter registered positive readings. The positive reading was suspect since the bathroom had recently been cleaned, and a chlorine smell was noticeable. Therefore, a confirmatory 4-hour air sample was collected on a Hopcalite adsorbent tube and sent to the laboratory for analysis. No mercury was detected in the sample (< 1.3 x 10-4 mg/m3) when it was analyzed using NIOSH method 6009.

Biological Sampling

Mercury is a naturally occurring element. Increased concentrations in the environment can result from emissions from incinerators and the use of mercury-containing paints and fungicides. On an individual basis, the release of mercury from dental amalgams and the consumption of mercury-contaminated fish (mostly as methyl mercury) can be significant sources of mercury. In people with no unusual exposures to mercury, the normal background concentration of mercury in urine is about 4-5 µg/liter [3], and the 95 percentile is about 20 µg/liter [4].

In the Juncos Exposure Investigation, ATSDR tested urine samples from 64 residents for total mercury. No mercury was detected (detection limit of 5 µg/L) in 62 of the samples. In two of the samples, the mercury concentrations were 7.2 and 10.3 µg/L, or 3.2 and 1.9 µg/gram creatinine, respectively. All of these mercury concentrations are within the normal background range. Therefore, there is no evidence for unusual mercury exposure in any of the residents.

After chronic exposure to mercury, its half-life in urine has been estimated to be 55 days [5]. Therefore, if any of the residents had experienced significant mercury exposure in the past month or two, a elevated mercury level in the urine would be expected. No such elevations were detected.


  1. No mercury was detected during indoor air monitoring in 21 homes.

  2. Urine samples from 64 residents were tested for total mercury. The mercury concentrations in all samples were within the normal background range.

  3. There is no evidence that residents living adjacent to the Juncos Landfill are currently being exposed to elemental mercury.


Kenneth Orloff, Ph.D.
Senior Toxicologist

Robert Johnson, M.D.
Medical Officer

Greg Zarus
Atmospheric Scientist


  1. Center for Environmental Health, Centers for Disease Control; Juncos Landfill, Superfund Site; April 24, 1984.

  2. Agency for Toxic Substances and Disease Registry; Site Review and Update - Juncos Landfill NPL Site; September 30, 1993.

  3. Agency for Toxic Substances and Disease Registry; Toxicological Profile for Mercury (Update); page 312, March 1999.

  4. National Center for Environmental Health; Division of Environmental Health Laboratory Services; Atlanta, Georgia.

  5. Gerd Sallsten, Lars Barregard, and Andrejs Schultz; Clearance half life of mercury in urine after the cessation of long term occupational exposure: influence of a chelating agent (DMPS) on excretion of mercury in urine; Occup Environ Med 51(5) 337-342 (1994).

Table of Contents The U.S. Government's Official Web PortalDepartment of Health and Human Services
Agency for Toxic Substances and Disease Registry, 4770 Buford Hwy NE, Atlanta, GA 30341
Contact CDC: 800-232-4636 / TTY: 888-232-6348

A-Z Index

  1. A
  2. B
  3. C
  4. D
  5. E
  6. F
  7. G
  8. H
  9. I
  10. J
  11. K
  12. L
  13. M
  14. N
  15. O
  16. P
  17. Q
  18. R
  19. S
  20. T
  21. U
  22. V
  23. W
  24. X
  25. Y
  26. Z
  27. #