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Community Exposure to Toluene Diisocyanate from a Polyurethane Foam Manufacturing Plant -- North Carolina, 1997

In August 1996, residents of a community in Randolph County, North Carolina, contacted the Agency for Toxic Substances and Disease Registry (ATSDR) because of health concerns about possible exposure to chemical emissions from a polyurethane manufacturing plant. ATSDR and the North Carolina Department of Environment, Health, and Natural Resources (NCDEHNR) conducted ambient air monitoring to characterize air contamination near the plant. ATSDR and Randolph County health officials also conducted biologic monitoring to determine whether residents were being exposed to toluene diisocyanate (TDI) emitted from the plant. This report summarizes the results of these investigations, which indicate that residents were being exposed to TDI in ambient air surrounding the plant.

The facility produced polyurethane foam by reacting a polyether resin with TDI and water. Emissions from the manufacturing process were directed to exhaust stacks, which vented them to ambient air. Foam production occurred in batches, resulting in episodic releases of emissions. The facility had produced polyurethane foam for approximately 20 years; during the previous 5 years, foam was produced by a quick-cure process that used greater amounts of TDI.

Since January 1996, NCDEHNR conducted investigations of the facility including air sampling, interviews with residents, risk assessment of ambient air and emissions data, and reviews of medical records. Using a direct monitoring filter-tape instrument, ATSDR detected TDI in ambient air in a residential area near the facility. Concentrations of TDI as high as 29 parts per billion (ppb) were detected at a monitoring station approximately 100 feet outside the facility's fence line. The presence of TDI was confirmed by an alternative method in which diisocyanates were captured on glycerol-impregnated filters, chemically derivatized, and analyzed using high performance liquid chromatography. Air monitoring conducted by ATSDR and NCDEHNR also detected methylene chloride and other volatile organic compounds in ambient air. These findings prompted ATSDR to issue a public health advisory on October 20, 1997.

To determine whether residents were being exposed to TDI emissions from the plant, ATSDR, in cooperation with the Randolph County Health Department (RCHD), initiated a biologic exposure investigation. RCHD mailed flyers to residents to inform them of the investigation. Persons who lived within 1/4 mile of the facility were particularly encouraged to participate. Blood samples were collected from 113 residents and were sent to the University of Cincinnati Diagnostic Allergy Laboratory for analysis. The blood serum specimens were analyzed by an enzyme-linked immunosorbent assay (ELISA) for Immunoglobulin G (IgG) and Immunoglobulin E (IgE) antibodies to TDI, hexamethylene diisocyanate, and diphenylmethane diisocyanate. Samples were classified as positive if they exceeded three standard deviations above the mean value of seven negative control samples and a serum albumin blank.

Of the 113 participants who were tested, 10 (9%) had antibodies to one or more of the diisocyanates, nine had IgG antibodies to TDI, and one had IgE antibodies to TDI. Four participants had antibodies that reacted with more than one diisocyanate.

Persons with positive antibody tests were interviewed to identify possible sources of exposure to diisocyanates. One of the 10 persons with a positive test reported having occupational exposure to TDI or other diisocyanates. In addition, two persons reported using polyurethane varnishes, a possible source of diisocyanates, in their homes. None of the other seven persons reported exposure to known sources of diisocyanates. The presence of TDI antibodies in these persons could have resulted from exposure to TDI in residential ambient air near the facility.

Some residents who lived near the facility reported health effects that they attributed to emissions from the plant. Therefore, persons with positive tests for diisocyanate antibodies and persons with symptoms of respiratory disease were encouraged to seek additional clinical evaluation. NCDEHNR arranged for residents to receive further clinical evaluation by Duke University Medical Center.

Because of public health concerns about the public health impact of chemical emissions from the plant, the state health director issued an Order to Abate a Public Health Nuisance on September 3, 1997. Polyurethane foam production at the plant has not resumed since the order was issued.

Reported by: D Darcey, MD, H Lipscomb, PhD, Duke Univ Medical Center, Durham; L Cherry, MSEH, North Carolina Dept of Environment, Health, and Natural Resources; M Cooper, MPH, Randolph County Health Dept; W Pate, MSPH, CG Smith, MD, North Carolina Dept of Health and Human Svcs. Div of Health Education and Promotion, and Div of Health Assessment and Consultation, Agency for Toxic Substances and Disease Registry.

Editorial Note

Editorial Note: Occupational exposure to TDI and other diisocyanates can cause irritation of the eyes, upper and lower respiratory tract, and skin. In some workers, exposure to TDI results in sensitization, defined as hyperresponsiveness to TDI at concentrations substantially below those that affect most persons. Approximately 5%-10% of workers exposed to diisocyanates develop occupational asthma (1). The exposure level of TDI that causes sensitization is not well characterized, but can occur at levels below the Occupational Safety and Health Administration short-term exposure level of 20 ppb (2).

From 10% to 30% of symptomatic workers develop IgE antibodies to diisocyanates (1). In a study of workers exposed to diisocyanates in the workplace, IgE antibodies to diisocyanates were detected in 13.6% of symptomatic workers and in 8.4% of all workers (3). Symptomatic workers experienced bronchial asthma, chronic bronchitis, rhinitis, or conjunctivitis. In a representative subgroup of this same population, IgG antibodies were more prevalent, being detected in 24% of symptomatic workers and 17% of asymptomatic workers. Antibodies have not been detected in workers in the absence of diisocyanate exposure (4,5).

Several participants in this investigation had positive antibody reactions to more than one diisocyanate. Such cross-reactivity of diisocyanate antibodies has been observed (3,5). In one study, approximately 60% of positive serum cross-reacted with one or more diisocyanates (3).

In the investigation described in this report, antibodies to TDI were used as a biomarker of exposure because they can be detected even in the absence of recent exposure. As demonstrated by this investigation, air and biologic monitoring can be useful in assessing human exposure to diisocyanates in the environment.

References

  1. Bernstein JA. Overview of diisocyanate occupational asthma. Toxicology 1996;111:181-9.

  2. American Conference of Governmental Industrial Hygienists. Documentation of the threshold limit values and biological exposure indices. 5th ed. Cincinnati, Ohio: American Conference of Governmental Industrial Hygienists, 1986.

  3. Bauer X, Marek W, Ammon J, et al. Respiratory and other hazards of isocyanates. Int Arch Occup Environ Health 1994;66:141-52.

  4. Selden AI, Bellin L, Wass U. Isocyanate exposure and hypersensitivity pneumonitis -- report of a probable case and prevalence of specific immunoglobulin G antibodies among exposed individuals. Scand J Work Environ Health 1989;15:234-7.

  5. Keskinen H, Tupasela O, Tikkainen U, Nordman H. Experiences of specific IgE in asthma due to diisocyanates. Clinical Allergy 1988;18:597-604.




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