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Introduction

IGNITION of upholstered furniture by small open flames from matches, cigarette lighters, and candles is one of the leading causes of residential-fire deaths in the United States. These fires accounted for about 16% of civilian fire deaths in 1996. On average, each year since 1990, about 90 deaths (primarily of children), 440 injuries, and property losses amounting to 50 million dollars have resulted from fires caused by the ignition of upholstered furniture by small open flames. Certain commercial seating products (such as aircraft and bus seats) are subject to flammability standards and sometimes incorporate FR-treated upholstery cover materials, but there is no federal-government requirement for residential upholstered furniture, and it is generally not treated with FR chemicals. It is estimated that less than 0.2% of all U.S. residential upholstery fabric is treated with flame-retardant (FR) chemicals.

The Consumer Product Safety Act of 1972 created the U.S. Consumer Product Safety Commission (CPSC) as an independent federal regulatory agency whose mission is to protect the public from unreasonable risks of injury and death associated with consumer products. CPSC also administers the Flammable Fabrics Act, under which it regulates flammability hazards and the Federal Hazardous Substances Act (FHSA), which regulates hazardous substances including chemicals. In 1993, the National Association of State Fire Marshals petitioned CPSC to issue a performance-based flammability standard for upholstered furniture to reduce the risk of residential fires. The Commission granted that portion of the petition relating to small open flame ignition risks. The



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Toxicological Risks of Selected Flame-Retardant Chemicals 1 Introduction IGNITION of upholstered furniture by small open flames from matches, cigarette lighters, and candles is one of the leading causes of residential-fire deaths in the United States. These fires accounted for about 16% of civilian fire deaths in 1996. On average, each year since 1990, about 90 deaths (primarily of children), 440 injuries, and property losses amounting to 50 million dollars have resulted from fires caused by the ignition of upholstered furniture by small open flames. Certain commercial seating products (such as aircraft and bus seats) are subject to flammability standards and sometimes incorporate FR-treated upholstery cover materials, but there is no federal-government requirement for residential upholstered furniture, and it is generally not treated with FR chemicals. It is estimated that less than 0.2% of all U.S. residential upholstery fabric is treated with flame-retardant (FR) chemicals. The Consumer Product Safety Act of 1972 created the U.S. Consumer Product Safety Commission (CPSC) as an independent federal regulatory agency whose mission is to protect the public from unreasonable risks of injury and death associated with consumer products. CPSC also administers the Flammable Fabrics Act, under which it regulates flammability hazards and the Federal Hazardous Substances Act (FHSA), which regulates hazardous substances including chemicals. In 1993, the National Association of State Fire Marshals petitioned CPSC to issue a performance-based flammability standard for upholstered furniture to reduce the risk of residential fires. The Commission granted that portion of the petition relating to small open flame ignition risks. The

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Toxicological Risks of Selected Flame-Retardant Chemicals CPSC staff subsequently developed a small open flame performance standard. If such a standard were promulgated, most residential upholstery fabric would likely be treated with FR chemicals. It is estimated that FR chemicals would be applied as formulations to as much as 600 million square yards of upholstery fabrics each year (R.Berkley, American Textile Manufacturers Institute, pers. commun., July 30, 1999). If, over the lifetime of the furniture, the chemicals leach out from the formulations, consumers might be exposed to them and possibly suffer adverse health effects. Because there is a potential for exposure of millions of people to FR chemicals, some have recommended banning the use of FR chemicals until they are shown to be safe. In response to concerns regarding the safety of FR chemicals, Congress, in the fiscal year 1999 appropriations report for CPSC, requested that the National Research Council conduct an independent study of the health risks to consumers posed by exposure to FR chemicals that are likely to be used in residential upholstered furniture to meet a CPSC standard. The National Research Council assigned the project to the Committee on Toxicology (COT) of the Commission on Life Sciences’ Board on Environmental Studies and Toxicology. COT convened the Subcommittee on Flame-Retardant Chemicals, which prepared this report. Subcommittee members were chosen for their recognized expertise in toxicology, pharmacology, epidemiology, chemistry, exposure assessment, risk assessment, andbiostatistics. Appendix A provides brief biographical sketches of subcommittee members. THE CHARGE TO THE SUBCOMMITTEE The charge to the subcommittee was to assess the health risk to consumers and the general population from exposure to 16 FR chemicals that are likely to be applied to fabrics used in residential upholstered furniture. Specifically, the subcommittee was asked to assess the following chemicals or classes:1 (1) hexabromocyclododecane, (2) decabromodiphenyl oxide, (3) alumina trihydrate, (3) (4) magnesium hydroxide, (5) zinc borate, (6) calcium and zinc molybdates, (7) antimony trioxide, (8) antimony pentoxide and sodium antimo- 1   The list was developed by the Flame Retardant Chemicals Association. The subcommittee arbitrarily chose to discuss risk assessments for the FR chemicals in the following order: (1) brominated compounds, (2) metal compounds, (3) phosphorous compounds, and (4) chlorinated paraffins. It should be noted that chemicals discussed first are not necessarily more toxic or used more often as flame retardants.

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Toxicological Risks of Selected Flame-Retardant Chemicals nate, (9) ammonium polyphosphates, (10 phosphonic acid, (3-{[hydroxymethyl]amino}-3-oxopropyl)-dimethyl ester, (11) organic phosphonates, (12) tris (monochloropropyl) phosphate, (13) tris (1,3-dichloropropyl-2) phosphate, (14) aromatic phosphates plasticizers, (15) tetrakis (hydroxymethyl) hydronium salts, and (16) chlorinated paraffins. The subcommittee was also asked to identify data gaps and make recommendations for future research. In addressing its charge, the subcommittee was asked to focus its assessment on the health risks to consumers who might use FR-treated upholstered furniture, including those with an increased susceptibility to FR chemicals. The subcommittee did not consider the toxicity of combustion products of FR materials from fires involving FR-treated upholstered furniture. The subcommittee also did not address ecotoxicological effects, adverse environmental effects of the disposal of household furniture, cost, technology, exposure-standard achievability, or alternative methods. Those issues are beyond the scope of the subcommittee’s charge, expertise, and resources. Similarly, the subcommittee did not compare FR chemicals for efficacy or evaluate the benefits of using FR chemicals in upholstered furniture to reduce fire risk; the latter issue has been the subject of recent reports prepared for the U.K. Department of Trade and Industry. THE SUBCOMMITTEE’S APPROACH TO ITS CHARGE To gather information, the subcommittee commissioned papers on the various FR chemicals and held public meetings at which representatives of CPSC, the U.S. Environmental Protection Agency, Congress, the National Association of State Fire Marshals, and industrial groups made presentations on issues of critical importance to the subcommittee’s task. Some of the speakers provided technical documents on FR chemicals. CPSC staff also provided its toxicity assessments to the NAS. To characterize the human health risks from dermal, oral, and inhalation exposures to each of the 16 FR chemicals, the subcommittee adopted the NRC risk assessment paradigm (NRC 1983, 1994). Data were evaluated relating to key elements of this risk assessment paradigm-hazard identification, dose-response assessment, exposure assessment, and risk characterization. Specifically for each FR chemical, the subcommittee reviewed data on physical and chemical properties, toxicity, and exposure. Several of the 16 chemicals were actually chemical classes rather than single compounds. In some of these cases, one chemical of the class was selected as a surrogate: tetrakis (hydroxymethyl) hydronium chloride for the tetrakis (hydroxymethyl) hydronium salts and their compounds; dimethyl hydrogen phosphite for organic phosphonates; and tri-

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Toxicological Risks of Selected Flame-Retardant Chemicals cresyl phosphate for aromatic phosphate plasticizers. Surrogates were selected on the basis of representativeness of the class, availability of data, and most potent chemical in the class. Conclusions about the class are based on the properties of the surrogate. The risk from other members of the class might be different from the risk from the surrogate. To identify adverse effects associated with an FR, the subcommittee reviewed human and animal data on local and systemic effects, e.g., neurologic, immunologic, reproductive, developmental, and carcinogenic effects. In vitro data were also reviewed to determine the potential for genotoxicity, other toxic effects, and to understand the mechanism of toxic action. Toxicokinetic studies were reviewed to understand the absorption, distribution, metabolism, and excretion of the FRs. Quantitative toxicity assessments were performed to determine the toxic potency for noncancer and cancer effects. The subcommittee used the NOAEL-uncertainty-factor approach to identify reference doses (RfDs) or reference concentrations (RfCs) for noncancer effects. For carcinogens, carcinogenic potency was estimated using the linearized multistage nothreshold model because it provides a conservative risk estimate. Human exposures to FRs in residential furniture were estimated using extremely conservative assumptions and assuming exposure occurs via skin contact, ingestion (especially for infants or children that might suck or chew on fabric), inhalation of particles generated during abrasion of the surface fibers, and inhalation of vapors off-gassing from treated fabric. To characterize health risks from exposure to a non-carcinogenic chemical, a hazard index approach was used. The subcommittee’s approach for estimating risks from exposure to carcinogenic FRs involved estimating an upper limit on lifetime cancer risk. To identify data gaps and make recommendations for future research needs, the subcommittee noted deficiencies in the databases on the FR chemicals and, where appropriate, recommended future research that would reduce uncertainty and increase confidence in the risk assessments. FLAME RETARDANT PROCESSES Some upholstery cover materials fabrics are inherently resistant to small open flames because of their chemical or physical structure. Others are made flame resistant with flame-retardant additives. FR chemicals are incorporated into fibers, applied to the surface of a textile, or applied to the back of a textile in the form of a polymeric coating. Chemical after-treatments for flame retardancy may include surface or topical treatments, use of coatings, and use of

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Toxicological Risks of Selected Flame-Retardant Chemicals functional finishes that become part of the final fiber structure. Appendix B describes the four basic processes typically used on various types of fabric. CALIFORNIA, UNITED KINGDOM, AND EUROPEAN EXPERIENCE California is the only state with mandatory flammability regulations for residential upholstered furniture. A flammability performance standard was developed and is administered by the California Bureau of Home Furnishings and Thermal Insulation. The principal standard, applicable since 1975 to all upholstered furniture sold in the state, is known as Technical Bulletin 117 (TB-117). Technical Bulletin 117 contains a series of flammability performance tests and minimum requirements for both cigarette ignition and small open flame resistance of furniture component materials. Manufacturers generally rely on FR-treated polyurethane foam or other foam filling materials to meet the flame-prevention requirement for fillings. Cover fabrics do not require FR treatment to comply with TB-117. As a consequence of UK furniture-fire regulations, which were introduced in 1988, flame retardants are widely used both in upholstery fabrics and in foams and other fillings for furniture to meet performance requirements. Appendix B provides an overview of the types of application methods and level of FRs presently being used, and available information on durability, degradation, and fate of FRs after treatments of furniture upholstery. Flame retardants are incorporated at the fabric-finishing stage before furniture manufacture, so furniture upholsterers have been occupationally exposed to fabrics containing flame retardants and UK consumers who have purchased new furniture or have lived in rented furnished accommodations have been exposed for over a decade to FR-treated fabrics and foams. Some workers were reported to have experienced dermal sensitization to FR-treated upholstery, but the sensitization was in fact due to fabric finish and fiber factors, not to FRs, and no other adverse effects have been reported. No adverse effects have been reported in the general population exposed to FR-treated furniture or other FR-treated consumer products. Almost all FR chemicals used in Europe were used commercially at the time the European existing-substances regulations were introduced. These chemicals continue to be used without the requirement of formal risk assessments unless they were identified as high-priority substances that specifically needed such an assessment. The latter is the case for a small number of flame retardants that

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Toxicological Risks of Selected Flame-Retardant Chemicals are undergoing formal risk assessment in Europe, including the polybrominated diphenyl ethers and hexabromocyclododecane. ORGANIZATION OF THIS REPORT The remainder of this report is organized into 18 chapters and two appendices. Chapter 2 describes the risk assessment process used by the subcommittee in determining the risk associated with potential exposure to the various FR chemicals. Chapter 3 describes the method the subcommittee used to measure and estimate the intensity, frequency, extent, and duration of human exposure to FR chemicals. Chapters 4–19 provide the subcommittee’s review and assessment of health risks posed by exposure to each of the 16 FR chemicals. Data gaps and research needs are provided at the end of these chapters. REFERENCES NRC (National Research Council). 1983. Risk Assessment in the Federal Government: Managing the Process. Washington, D.C.: National Academy Press. NRC (National Research Council). 1994. Science and Judgment in Risk Assessment. Washington, D.C.: National Academy Press.