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Public Health Status

The Frontera Creek National Priorities List (NPL) site is not a public health hazard based on alack of current exposure to site-related contaminants. Mercury in the soil and air may havecaused slight muscle tremors prior to 1990 for a few individuals at the Technicon facility. It ispossible that methylene chloride in the air, though not site-related, may have caused slightchanges in the liver and kidney or mild reversible decreases in vision and hearing in individualswho both worked and lived in the Frontera Creek area during the period between 1983 - 1985. However, this conclusion about methylene chloride is uncertain because of difficulties inidentifying methylene chloride exposure levels for the Frontera Creek area and in evaluating thetoxicity of methylene chloride.

Extent of Contamination

The environmental sampling of the Frontera Creek NPL site was well-designed for evaluating thehealth impact of the site. The initial air monitoring done in 1989 was not conducted for asufficient period of time to adequately identify probable exposure levels, especially off-site. However, monitoring done in 1993-4 was appropriately conducted.

The environmental data indicates that mercury contamination is restricted to air, surface soil, andsediment from the ditch at the Technicon facility. Mercury concentrations in surface andsubsurface soils, sediment, surface water, ground water, potable water, and biota for the rest ofthe Frontera Creek site area were either below method detection limits or within the backgroundrange for Puerto Rico. Air levels of mercury and methylene chloride both on- and off-site wereabove background. Methylene chloride and methyl isobutyl ketone concentrations in the water ofthat portion of Frontera Creek that passed through the industrial facilities met ATSDR'sguidelines for contaminants of concern. Except for arsenic levels in soils from one samplinglocation at each of two industrial facilities, other chemicals analyzed were either withinbackground ranges or below method detection limits.

Even though the mercury levels in fish were within background levels, the individuals who eatseveral fish meals a week may be exposed to mercury at a level of health concern. Fishermenneed to be informed of the possible health risk from consuming large amounts of fish.

Toxicological Evaluation

The maximum (2.2 µg/m3) and average (0.4 µg/m3) concentrations of mercury in the on-site(industrial area) air could represent a health hazard if those levels are an accurate measurement oftypical concentrations and if exposure continued regularly for a year or more. It is not possible todetermine whether the maximum (0.09 µg/m3) and average (0.07 µg/m3) concentrations ofmercury measured in the off-site air represent a health hazard, because the only availableanalytical method is not very accurate. In addition, air samples taken in 1989 were not taken onenough days and over a sufficient portion of the day to accurately identify typical exposurelevels.

The individuals who worked at or near Squibb and also lived at Ciudad Cristiana during theperiod of 1983 - 1985 were at risk of having noncarcinogenic health effects related to methylenechloride exposure. Those individuals may have had continuous exposure to methylene chloridefor varying periods and air levels. There also may have been periods when there was noexposure. Slight subclinical (i.e., not harmful) changes in the liver and kidney or mild, reversibledecreases in vision and hearing might have occurred. However, this conclusion about methylenechloride is uncertain because of difficulties in identifying methylene chloride exposure levels forthe Frontera Creek area and in evaluating the toxicity of methylene chloride.

Health consequences due to barium, even at the background levels found at Ciudad Cristiana,may have been possible for children at Ciudad Cristiana who ate large amounts of soil (5 gramsor more a day). Neither carcinogenic nor noncarcinogenic effects appear to be possible for any ofthe other exposures.

Health Outcome Data Evaluation

Cancer and developmental effects were identified as biologically plausible health outcomes. Cancer is plausible because there was a carcinogen, methylene chloride, in a completed humanexposure pathway. Methylene chloride was not a site-related contaminant. Cancer incidencewere not evaluated in this public health assessment because the only available data, the city ofHumacao, was for a much greater population, 50,000, than the probable exposed population of1,000. Developmental effects were plausible health outcomes because some women wereexposed to mercury levels (4.0 µg/dl or greater) which could result in delayed motordevelopment and delayed language development in children exposed in the womb. This mercuryexposure was not related to the Frontera Creek NPL site. Appropriate data to evaluate thosekinds of effects were not available.

Self-reported outcomes ranged from rashes, bleeding gums, and headaches to numbness, lupus,and cancer. Most of the individuals reporting health outcomes associated them with exposure tomercury. Many of the reported outcomes/symptoms such as joint and back pain, asthma,cardiovascular disease, diabetes, lupus, and cancer have not been associated with mercuryexposure in the past. While the other reported outcomes have been associated with mercury, atleast some of them have also been linked with several other causes such as methylene chloride,infectious diseases, and stress. Mercury is an unlikely cause for the reported health outcomesbecause of the lack of significant exposure.

The average blood mercury level for the approximately 290 individuals tested while or just afterthey were residents of Ciudad Cristiana are within "normal" limits for a population thatconsumes 5 or more fish meals a week. It is not clear whether the average Ciudad Cristianaresident ate that amount of fish. None of the individual results was above the 20 µg/dl levelwhere health effects appear to begin to be observed.

However, 27 of the 64 (42%) women of child-bearing age in the 290 tested had blood mercurylevels above the 4.0 µg/dl where health effects appear to begin to be observed in their unbornbabies. Children exposed to these levels while in their mother's womb may have walked laterthan the normal maximum of 19 months, or talked later than the normal maximum of 26 months. A study done of Iraqi children indicates that about 25% of the children with maternal bloodmercury levels of 4 - 20 µg/dl would have walked or talked later; the rest with this range ofmaternal blood levels had no adverse health effects. It is not known whether thosedevelopmental delays would be permanent or temporary. At maternal levels of 4 - 20 µg/dl,more severe effects such as mental retardation, deafness, blindness, microcephaly (small brain),and cerebral palsy are not observed.

A major limitation with the blood mercury data reviewed is that the participants wereself-selected which could result in a weighing of the results either to the high or low side. Thedifference of the percentage of results above 5 µg/dl between the Puerto Rico Department ofHealth (PRDH) study (0.6% - 6/993) and this set of results (29.0% - 84/290) indicates that theremay be such a problem.


ATSDR recommends that Puerto Rico review all available data on mercury in Puerto Rican fish and, then, consider advising Puerto Rican fishermen about the possibility of health consequencesfrom eating large amounts of fish.

The Comprehensive Environmental Response, Compensation, and Liability Act of 1980(CERCLA), as amended, requires ATSDR to perform public health actions needed at hazardouswaste sites. To determine if public health actions are needed, ATSDR's Health ActivitiesRecommendation Panel (HARP) has evaluated the data and information developed in theFrontera Creek Public Health Assessment.

HARP determined that the former residents of Ciudad Cristiana and Humacao health careprofessionals should receive additional information on the toxicity of mercury and of other site-related contaminants. The specific type and targets of this education will be identified byATSDR's Divisions of Health Assessment and Consultation, and Health Education.

If additional information becomes available which indicates human exposure to site-relatedcontaminants may be at levels of public health concern, the HARP will reevaluate the need forfollow-up public health actions.

Public Health Action Plan

The purpose of the Public Health Action Plan (PHAP) is to ensure that this public healthassessment not only identifies public health hazards but also provides a plan of action designedto mitigate and prevent adverse human health effects resulting from exposure to hazardoussubstances in the environment.

Two public health action have already been completed. Squibb, with review by EPA, conducted additional air monitoring for methylene chloride in the Frontera Creek area in 1993-4which met ATSDR concerns about the 1989 air monitoring. In the second, ATSDR requestedthat Puerto Rico consider issuing a fish consumption advisory on mercury for those areas ofPuerto Rico where a combination of background mercury levels and high fish consumption ratescould result in a hazard to health. Puerto Rico Department of Health considered ATSDR'srequest, but declined to issue a fish advisory because the fish mercury levels were typical forPuerto Rico.

One public health action was planned, but circumstances have delayed its implementation. Inthis planned public health action, staff from ATSDR's Divisions of Health Education and HealthAssessment and Consultation were going to provide information on mercury and methylenechloride during public availability meetings that were to be held as part of the public commentrelease of the Frontera Creek Public Health Assessment The meetings were cancelled becausethe Ciudad Cristiana ex-residents group withdrew their invitation. ATSDR will mail informationon mercury and methylene chloride directly to the ex-residents.

Public Health Comment

The Frontera Creek Public Health Assessment was available for public review and commentfrom August 12, 1994 through October 12, 1994. The Public Comment Period was announced inthe El Nuevo Diá and San Juan Star, which are island-wide newspapers, the El Oriental, aHumacao-based weekly, and on WALO, a Humacao radio station. Copies of the public healthassessment were made available for review at the home of Jose Sepulveda, the leader of theCiudad Cristiana Ex-Residents Group, the Antonio Roig Public Library in Humacao, theHumacao College Library, and the EPA Caribbean Field Office in Santurce. In addition, thepublic health assessment was sent to eight persons or organizations. Comments were receivedfrom Applied Geotechnical and Environmental Service Corporation (AGES), the environmentalconsultant to Squibb Manufacturing, and the Puerto Rico Department of Health.

A public meeting and a public availability session to discuss the public health assessment withthe Ciudad Cristiana Ex-Residents and take public comments was scheduled for August 20, 1994at Vista Hermosa in Humacao. The Ex-Residents withdrew their invitation on August 19 andthus the public meeting and availability session were not held.

Comments and responses are described in Appendix G which starts on page 99.


John R. Crellin, Ph.D.
Environmental Health Scientist
Health Science Section
Remedial Program Branch (now called the Superfund Site Assessment Branch [SSAB])

Rosalyn Leea
Environmental Engineer
Environmental Science Section
Remedial Program Branch

Mark Rodriguez, M.D., M.P.H.a
Medical Officer
Health Science Section
Remedial Program Branch

ATSDR Regional Representative:

Arthur C. Block
Senior Public Health Advisor
Region II - New York
Regional Program Office

a No longer with ATSDR


  1. ATSDR. Health Assessment for Frontera Creek, Humacao, Puerto Rico. Atlanta, GA: Agency for Toxic Substances and Disease Registry (ATSDR). July 30, 1985.

  2. Agency for Toxic Substances and Disease Registry. Public Health Assessment GuidanceManual. Chelsea, MI: Lewis Publishers. 1992.

  3. U.S. District Court for Puerto Rico. Consent Degree between United States of America andMiles Diagnostics Corporation; Miles, Inc.; Cooper Development Company; and Revlon, Inc. forFrontera Creek NPL site, Humacao, Puerto Rico. Washington, DC: U.S. Department of Justiceand Environmental Protection Agency (EPA). 1992.

  4. Remedial Investigation Report for Frontera Creek Site, Humacao, Puerto Rico (September1990) vol. 1-7; Environmental Service Division, Dynamac Corporation.

  5. Medina JL. Jury finds Commonwealth at fault on Ciudad Cristiana. San Juan Star. San Juan,PR

  6. PRDH and EQB. Acceptance of results of remedial investigation of Frontera Creek NPL site. February 2, 1989.

  7. ATSDR. Health Consultation - Frontera Creek Site, Humacao, Puerto Rico. Atlanta, GA: Agency for Toxic Substances and Disease Registry (ATSDR). June 5, 1992.

  8. Ross K. Feds deem mercury-poisoning tests valid. Cause of tainting may remain mysteryforever. San Juan Star, San Juan, Puerto Rico. January 20, 1993.

  9. Anonymous. Forgotten Faces... Ciudad Cristiana, Puerto Rico is named contaminated site ofthe month. Citizen's Clearinghouse for Hazardous Waste. October 1993. p. 26.

  10. Memorandum to Record: Report on the Frontera Creek NPL Site in Humacao, Puerto Ricoon January 11-15, 1993. From JR Crellin, M Rodriguez, and A Quiñones (ATSDR), March 1,1993.

  11. O'Neill J. Medical help demanded by chemical-waste victims. San Juan Star, San Juan, PR. June 8, 1984.

  12. Weisskopf M. The poisoning of Christian City. Mercury turns Puerto Rican community intoa ghost town. Washington Post, Washington, DC. June 30, 1986.

  13. EPA. 1987-1992 Toxic Chemical Release Inventory (TRI) files on Toxicology Data Network(TOXNET). Bethesda, MD: National Library of Medicine (NLM). November 1994.

  14. EPA. Chemical Releases and Chemical Risks. A Citizen's Guide to Risk Screening. Washington, D.C.: U.S. Environmental Protection Agency (EPA). 1989.

  15. AGES. Proposal for continued long-term monitoring of methylene chloride in air. Bristol-Myers Squibb Manufacturing, Inc. Humacao, Puerto Rico. Valley Forge, PA: AppliedGeotechnical and Environmental Service Corporation (AGES). February 1993.

  16. ATSDR. Toxicological Profile for Mercury - Update. Agency for Toxic Substances andDisease Registry, U.S. Public Health Service. Atlanta, GA. 1992.

  17. AGES. Summary report of ambient air methylene chloride concentrations. SquibbManufacturing, Inc. Humacao, Puerto Rico. Valley Forge, PA: Applied Geotechnical andEnvironmental Service Corp. (AGES). April 1994.

  18. AGES. Discussion and Comment - Frontera Creek Public Health Assessment. AppliedGeotechnical and Environmental Service Corp. (AGES). October 1994

  19. Letter re: Squibb Manufacturing, Inc. Emissions Reduction Report. From: Ortiz-Torres J(Bristol Myers-Squibb). To: Eng K (EPA). March 4, 1993.

  20. ATSDR. Toxicological Profile for Arsenic. Agency for Toxic Substances and DiseaseRegistry, U.S. Public Health Service. Atlanta, GA. 1993.

  21. ATSDR. Draft Toxicological Profile for Barium. Agency for Toxic Substances and DiseaseRegistry, U.S. Public Health Service. Atlanta, GA. 1992.

  22. 22. EPA. Integrated Risk Information System (IRIS) file on Toxicology Data Network(TOXNET). Bethesda, MD: National Library of Medicine (NLM). September 1993.

  23. ATSDR. Toxicological Profile for Methylene Chloride. Agency for Toxic Substances andDisease Registry, U.S. Public Health Service. Atlanta, GA. 1992.

  24. ATSDR. Toxicological Profile for Acetone. Agency for Toxic Substances and DiseaseRegistry, U.S. Public Health Service. Atlanta, GA. 1993.

  25. NTP. Fifth Annual Report on Carcinogens. Summary 1989. Research Triangle Park, NC: National Toxicology Program. 1989.

  26. ATSDR. Case Studies in Environmental Medicine - Mercury Toxicity. Atlanta, GA: Agency for Toxic Substances and Disease Registry (ATSDR). March 1992.

  27. Benenson AS (editor). Control of Communicable Diseases in Man. 15th Edition. Washington, DC: American Public Health Association (APHA). 1990.

  28. Vyner HM. Invisible Trauma. The Psychosocial Effects of the Invisible EnvironmentalContaminants. D.C. Heath, Lexington, MA. 1988.

  29. WHO. Environmental Health Criteria 1. Mercury. Geneva, Switzerland: World HealthOrganization (WHO). 1976.

  30. Clarkson TW. Mercury: major issues in environmental health. Env Hlt Persp 100: 31-38. 1992.

  31. Weiss B. Behavioral toxicology of heavy metals. In (Dreosti IE, Smith RM, eds)Neurobiology of Trace Elements. Volume 2 - Neurotoxicology and Neuropharmacology. Clifton,NJ: Humana Press. 1983.

  32. Cox C, Clarkson TW, Marsh DO, Amin-Zaki L, Tikriti S, and Myers GG. Dose-responseanalysis of infants prenatally exposed to methyl mercury: an application of a single compartmentmodel to single-strand hair analysis. Env Research 49: 318-332. 1989.

  33. WHO. Environmental Health Criteria 101. Methylmercury. Geneva, Switzerland: WorldHealth Organization (WHO). 1990.

  34. Menzer RE. Water and Soil Pollutants. In (Amdur MO, Doull J, and Klaassen CD, eds.)Casarett and Doull's Toxicology. The Basic Science of Poisons. 4th Edition. New York, NY: Pergamon Press. 1991.

  35. NIOSH. Registry of Toxic Effects of Chemical Substances (RTECS) file on Toxicology DataNetwork (TOXNET). Bethesda, MD: National Library of Medicine (NLM). October 1993.

  36. Letter: Ciudad Cristiana. From Phernambucg SG (U.S. Corps of Engineers) to Rivera G(Senator, Commonwealth of Puerto Rico). October 3, 1986.

  37. Dames and Moore. Environmental Site Assessment. Frontera Creek Site, Humacao, PuertoRico, December 1989

  38. QAA. Draft Decision Statements for Reviewing Health Assessments. Atlanta, GA: Agencyfor Toxic Substances and Disease Registry (ATSDR). October 1991.

  39. Barnes DG and Dourson M. Reference dose (RfD): description and use in health riskassessments. Regul Toxicol Pharmacol 8: 471-486. 1988.

  40. Hill RN. Current EPA perspectives on animal selection and extrapolation. In (Roloff MV etal, eds) Human Risk Assessment. The Role of Animal Selection and Extrapolation. London: Taylor and Francis. 1987.

  41. Stallones RA. Epidemiology and Environmental Hazards. In (Gordis L and Libauer CH,eds) Epidemiology and Human Risk Assessment. Oxford: Oxford University Press. 1988.

  42. Paustenbach DJ. A survey of health risk assessment. In (Paustenbach DJ, ed) The RiskAssessment of Environmental Hazards. A Textbook of Case Studies. New York: John Wiley andSons. 1989.

  43. ATSDR. Health Consultation - Review of Biological Samples, Frontera Creek Site, CiudadCristiana. Atlanta, GA: Agency for Toxic Substances and Disease Registry (ATSDR). August18, 1986.

  44. ATSDR. Health Consultation - Review of Biological Mercury Testing of Persons residingnear the Frontera Creek Site in Humacao, Puerto Rico. Atlanta, GA: Agency for ToxicSubstances and Disease Registry (ATSDR). March 18, 1988.

  45. Mercury contamination in Puerto Rico: the Ciudad Cristiana experience. Bol Assoc Med PRico 83: 296-299. July 1991.

  46. Brune D, Nordberg GF, Vesterberg O, Gerhardsson L, and Wester PO. A review of normalconcentrations of mercury in human blood. Sci Total Enviro 100: 235-282. 1991.

  47. Katz SA and Katz RB. Use of hair analysis for evaluating mercury intoxication of the humanbody: a review. J Appl Tox 12: 79-84. 1992.

  48. McKeown-Eyssen GE and Ruedy J. Methyl mercury exposure in northern Quebec. I.neurologic findings in adults. Am J Epidem 118: 461-469.

  49. McKeown-Eyssen GE, Ruedy J, and Neims A. Methyl mercury exposure in northernQuebec. II. neurologic findings in children. Am J Epidem 118: 470-479.

  50. EPA. Record of Decision -- Juncos Landfill, Juncos, Puerto Rico. New York, NY: U.S.Environmental Protection Agency (EPA) Region II. September 24, 1991.

  51. Burger J and Gochfeld M. Fishing a superfund site: dissonance and risk perception ofenvironmental hazards by fishermen in Puerto Rico. Risk Analysis 11: 269-277.

  52. Burger J, Copper K, and Gochfeld M. Exposure Assessment for heavy metal ingestion froma sport fish in Puerto Rico: estimating risk for local fisherman. J Tox Env Hlth 36: 355-365. 1992.

  53. Murphy JM. Santería: An African Religion in America. Boston, MA: Beacon. 1988.

  54. Aronow R, Cubbage C, Wiener R, Johnson B, Hesse J, and Bedford J. Mercury Exposurefrom Interior Latex Paint - Michigan. MMWR 39: 125-126. 1990.

  55. Mortensen ME, Powell S, Sferra TJ, Lautzenheiser R, Sobeih I, Pompili, Long TC, ClarksonTW, and Semple B. Elemental mercury poisoning in a household - Ohio, 1989. MMWR 39: 424-425.

  56. Taueg C, Sanfilippo DJ, Rowens B, Szejda J, and Hesse JL. Acute and chronic poisoningfrom residential exposures to elemental mercury - Michigan, 1989-1990. MMWR 40: 393-395.

  57. Wendroff AP. Domestic mercury pollution. Nature 347: 623. 1990.

  58. Rauch KD. The Spiritual Use of Poisonous Mercury. Washington Post Health. August 13,1991.

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