Flame retardants are compounds added to manufactured materials, such as plastics and textiles, and surface finishes and coatings that inhibit, suppress, or delay the production of flames to prevent the spread of fire. They may be mixed with the base material (additive flame retardants) or chemically bonded to it (reactive flame retardants). Mineral flame retardants are typically additive while organohalogen and organophosphorus compounds can be either reactive or additive.
The annual consumption of flame retardants amounts to[when?] over 1.5 million tonnes per year, which is the equivalent of a sales volume of approx. 1.9 billion euro (US$2.4 billion). As of 2008[update] the United States, Europe and Asia consumed 1.8 million tonnes, valuing US$4.20-4.25 billion. According to Ceresana, the market for flame retardants is increasing due to rising safety standards worldwide and the increased use of flame retardants. It is expected that the global flame retardant market will generate US$5.8 billion. As of 2010[update], Asia-Pacific was the largest market for flame retardants, accounting for approximately 41% of global demand, followed by North America, and Western Europe.
- 1 Classes
- 2 Retardation mechanisms
- 3 Use and effectiveness
- 4 Environmental prevalence
- 4.1 Health concerns
- 4.2 Mechanisms of toxicity
- 4.3 Routes of exposure
- 4.4 Chemical and tobacco industry conspiracy
- 4.5 Disposal
- 4.6 Sudden infant death syndrome
- 5 See also
- 6 References
- 7 External links
Flame retardants can be separated into several different classes:
- Minerals such as aluminium hydroxide (ATH), magnesium hydroxide (MDH), huntite and hydromagnesite, various hydrates, red phosphorus, and boron compounds, mostly borates.
- Organohalogen compounds. This class includes organochlorines such as chlorendic acid derivatives and chlorinated paraffins; organobromines such as decabromodiphenyl ether (decaBDE), decabromodiphenyl ethane (a replacement for decaBDE), polymeric brominated compounds such as brominated polystyrenes, brominated carbonate oligomers (BCOs), brominated epoxy oligomers (BEOs), tetrabromophthalic anyhydride, tetrabromobisphenol A (TBBPA) and hexabromocyclododecane (HBCD). Most but not all halogenated flame retardants are used in conjunction with a synergist to enhance their efficiency. Antimony trioxide is widely used but other forms of antimony such as the pentoxide and sodium antimonate are also used.
- Organophosphorus compounds. This class includes organophosphates such as triphenyl phosphate (TPP), resorcinol bis(diphenylphosphate) (RDP), bisphenol A diphenyl phosphate (BADP), and tricresyl phosphate (TCP); phosphonates such as dimethyl methylphosphonate (DMMP); and phosphinates such as aluminum diethyl phosphinate. In one important class of flame retardants, compounds contain both phosphorus and a halogen. Such compounds include tris(2,3-dibromopropyl) phosphate (brominated tris) and chlorinated organophosphates such as tris(1,3-dichloro-2-propyl)phosphate (chlorinated tris or TDCPP) and tetrekis(2-chlorethyl)dichloroisopentyldiphosphate (V6).
The basic mechanisms of flame retardancy vary depending on the specific flame retardant and the substrate. Additive and reactive flame-retardant chemicals can both function in the vapor (gaseous) or condensed (solid) phase.
Some compounds break down endothermically when subjected to high temperatures. Magnesium and aluminium hydroxides are an example, together with various carbonates and hydrates such as mixtures of huntite and hydromagnesite. The reaction removes heat from the substrate, thereby cooling the material. The use of hydroxides and hydrates is limited by their relatively low decomposition temperature, which limits the maximum processing temperature of the polymers (typically used in polyolefins for wire and cable applications).
Thermal shielding (solid phase)
A way to stop spreading of the flame over the material is to create a thermal insulation barrier between the burning and unburned parts. Intumescent additives are often employed; their role is to turn the polymer into a char, which separates the flame from the material and slows the heat transfer to the unburned fuel. Non-halogenated organophosphate flame retardants typically act through this mechanism by generating a polymeric layer of phosphoric acid.
Dilution of gas phase
Inert gases (most often carbon dioxide and water) produced by thermal degradation of some materials act as diluents of the combustible gases, lowering their partial pressures and the partial pressure of oxygen, and slowing the reaction rate.
Gas phase radical quenching
Chlorinated and brominated materials undergo thermal degradation and release hydrogen chloride and hydrogen bromide or if used in the presence of a synergist like antimony trioxide antimony halides. These react with the highly reactive H· and OH· radicals in the flame, resulting in an inactive molecule and a Cl· or Br· radical. The halogen radical is much less reactive compared to H· or OH·, and therefore has much lower potential to propagate the radical oxidation reactions of combustion.
Use and effectiveness
Fire safety standards
Flame retardants are typically added to consumer products to meet flammability standards for furniture, textiles, electronics, and insulation.
In 1975, California began implementing Technical Bulletin 117 (TB 117), which requires that materials such as polyurethane foam used to fill furniture be able to withstand a small open flame, equivalent to a candle, for at least 12 seconds. In polyurethane foam, furniture manufacturers typically meet TB 117 with additive halogenated organic flame retardants. Although no other U.S. states have a similar standard, because California has such a large market many manufacturers meet TB 117 in products that they distribute across the United States. The proliferation of flame retardants, and especially halogenated organic flame retardants, in furniture across the United States is strongly linked to TB 117.
In response to concerns about the health impacts of flame retardants in upholstered furniture, in February 2013 California proposed modifying TB 117 to require that fabric covering upholstered furniture meet a smolder test and to eliminate the foam flammability standards. This change could substantially reduce flame retardant use in new furniture.
However, these questions of eliminating emissions into the environment from flame retardants may perhaps be solved by using a new classification of highly efficient flame retardants, which do not contain halogen compounds, and which can also be keyed permanently into the chemical structure of the foams used in the furniture and bedding industries. This new technology is based on newly developed "Green Chemistry" with the final foam containing about one third by weight of natural oils. Use of this technology in the production of California TB 117 foams, would allow continued protection for the consumer against open flame ingition whilst providing the newly recognized and newly needed protection, against chemical emissions into home and office environments.
In Europe, flame retardant standards for furnishings vary, and are their most stringent in the UK and Ireland.
The effectiveness of flame retardant chemicals at reducing the flammability of consumer products in house fires is disputed. Advocates for the flame retardant industry, such as the American Chemistry Council’s North American Flame Retardant Alliance, cite a study from the National Bureau of Standards indicating that a room filled with flame-retarded products (a polyurethane foam-padded chair and several other objects, including cabinetry and electronics) offered a 15-fold greater time window for occupants to escape the room than a similar room free of flame retardants. However, critics of this position, including the lead study author, argue that the levels of flame retardant used in the 1988 study, while found commercially, are much higher than the levels required by TB 117 and used broadly in the United States in upholstered furniture.
Several studies in the 1980s tested ignition in whole pieces of furniture with different upholstery and filling types, including different flame retardant formulations. In particular, they looked at maximum heat release and time to maximum heat release, two key indicators of fire danger. These studies found that the type of fabric covering had a large influence on ease of ignition, that cotton fillings were much less flammable than polyurethane foam fillings, and that an interliner material substantially reduced the ease of ignition. They also found that although some flame retardant formulations decreased the ease of ignition, the most basic formulation that met TB 117 had very little effect. In one of the studies, foam fillings that met TB 117 had equivalent ignition times as the same foam fillings without flame retardants. A report from the Proceedings of the Polyurethane Foam Association also showed no benefit in open-flame and cigarette tests with foam cushions treated with flame retardants to meet TB 117.
In 2009, the U.S. National Oceanic and Atmospheric Administration (NOAA) released a report on polybrominated diphenyl ethers (PBDEs) and found that, in contrast to earlier reports, they were found throughout the U.S. coastal zone. This nationwide survey found that New York’s Hudson Raritan Estuary had the highest overall concentrations of PBDEs, both in sediments and shellfish. Individual sites with the highest PBDE measurements were found in shellfish taken from Anaheim Bay, California, and four sites in the Hudson Raritan Estuary. Watersheds that include the Southern California Bight, Puget Sound, the central and eastern Gulf of Mexico off the Tampa-St. Petersburg, Fla. coast, and Lake Michigan waters near Chicago and Gary, Ind. also were found to have high PBDE concentrations.
The earliest flame retardants, polychlorinated biphenyls (PCBs) were banned in the U.S. in 1977 when it was discovered that they are toxic. Industries shifted to using brominated flame retardants instead, but these are now receiving closer scrutiny. The EU has banned several types of polybrominated diphenyl ethers (PBDEs) as of 2008, 10 years after Sweden discovered that they were accumulating in breast milk. As of December 2009, negotiations between EPA and the two U.S. producers of DecaBDE (a flame retardant that has been used in electronics, wire and cable insulation, textiles, automobiles and airplanes, and other applications), Albemarle Corporation and Chemtura Corporation, and the largest U.S. importer, ICL Industrial Products, Inc., resulted in commitments by these companies to phase out decaBDE for most uses in the United States by December 31, 2012, and to end all uses by the end of 2013. The state of California has listed the flame retardant chemical chlorinated Tris (tris(1,3-dichloro-2-propyl) phosphate or TDCPP) as a chemical known to cause cancer. In December 2012, the California nonprofit Center for Environmental Health filed notices of intent to sue several leading retailers and producers of baby products for violating California law for failing to label products containing this cancer-causing flame retardant. While the demand for brominated and chlorinated flame retardants in North America and Western Europe is declining, it is rising in all other regions.
Nearly all Americans tested have trace levels of flame retardants in their body. Recent research links some of this exposure to dust on television sets, which may have been generated from the heating of the flame retardants in the TV. Careless disposal of TVs and other appliances such as microwaves or old computers may greatly increase the amount of environmental contamination. A recent study conducted by Harley et al. 2010 on pregnant women, living in a low-income, predominantly Mexican-immigrant community in California showed a significant decrease in fecundity associated with PBDE exposure in women.
Another study conducted by Chevrier et al. 2010 measured the concentration of 10 PBDE congeners, free thyroxine (T4), total T4, and thyroid-stimulating hormone (TSH) in 270 pregnant women around the 27th week of gestation. Associations between PBDEs and free and total T4 were found to be statistically insignificant. However, authors did find a significant association amongst exposure to PBDEs and lower TSH during pregnancy, which may have implications for maternal health and fetal development.
A prospective, longitudinal cohort study initiated after 11 September 2001, including 329 mothers who delivered in one of three hospitals in lower Manhattan, New York, was conducted by Herbstman et al. 2010. Authors of this study analyzed 210 cord blood specimens for selected PBDE congeners and assessed neurodevelopmental effects in the children at 12–48 and 72 months of age. Results showed that children who had higher cord blood concentrations of polybrominated diphenyl ethers (PBDEs) scored lower on tests of mental and motor development at 1–4 and 6 years of age. This was the first study to report any such associations in humans.
A similar study was conducted by Roze et al. 2009 in Netherlands on 62 mothers and children to estimate associations between 12 Organohalogen compounds (OHCs), including polychlorinated biphenyls (PCBs) and brominated diphenyl ether (PBDE) flame retardants, measured in maternal serum during the 35th week of pregnancy and motor performance (coordination, fine motor skills), cognition (intelligence, visual perception, visuomotor integration, inhibitory control, verbal memory, and attention), and behavior scores at 5–6 years of age. Authors demonstrated for the first time that transplacental transfer of polybrominated flame retardants was associated with the development of children at school age.
Another interesting study was conducted by Rose et al. 2010 to measure circulating PBDE levels in 100 children between 2 to 5 years of age from California. The PBDE levels according to this study, in 2- to 5-year-old California children was 10 to 1,000 fold higher than European children, 5 times higher than other U.S. children and 2 to 10 times higher than U.S. adults. They also found that diet, indoor environment, and social factors influenced children’s body burden levels. Eating poultry and pork contributed to elevated body burdens for nearly all types of flame retardants. Study also found that lower maternal education was independently and significantly associated with higher levels of most flame retardant congeners in the children.
San Antonio Statement on Brominated and Chlorinated Flame Retardants 2010: A group of 145 prominent scientists from 22 countries signed the first-ever consensus statement documenting health hazards from flame retardant chemicals found at high levels in home furniture, electronics, insulation, and other products. This statement documents that, with limited fire safety benefit, these flame retardants can cause serious health issues, and, as types of flame retardants are banned, the alternatives should be proven safe before being used. The group also wants to change widespread policies that require use of flame retardants.
A number of recent studies suggest that dietary intake is one of the main routes to human exposure to PBDEs. In recent years, PBDEs have become widespread environmental pollutants, while body burden in the general population has been increasing. The results do show notable coincidences between the China, Europe, Japan, and United States such as dairy products, fish, and seafood being a cause of human exposure to PBDEs due to the environmental pollutant.
A February 2012 study genetically engineered female mice to have mutations in the x-chromosome MECP2 gene, linked to Rett syndrome, a disorder in humans similar to autism. After exposure to BDE-47 (a PDBE) their offspring, who were also exposed, had lower birth weights and survivability and showed sociability and learning deficits.
A January 2013 study of mice showed brain damage from BDP-49, via inhibiting of the mitochondrial ATP production process necessary for brain cells to get energy. Toxicity was at very low levels. The study offers a possible pathway by which PDBEs lead to autism.
- Cleaning - PBDEs in indoor dust is one of the primary sources of people's exposure. Reduce your exposure to indoor dust. Use a damp cloth to dust indoor living and working areas. Avoid stirring the dust into the air. Use a vacuum with a HEPA filter. Open windows and doors while you clean. Wash hands after dusting and cleaning.
- Foam products - New foam items that you purchase today are unlikely to contain PBDEs. However, mattresses, mattress pads, couches, easy chairs, foam pillows, carpet padding, and other foam products purchased before 2005 likely contain PBDEs. Replace older foam products that have ripped covers or foam that is misshapen or breaking down. If you can't replace the item, try to keep the covers intact. When removing old carpet foam, keep the work area sealed from other areas of the house, avoid breathing in the dust, and use a HEPA-filter vacuum for cleanup.
- Electronics - Deca-BDE has been used in electronics for years but is now being phased out of most electronics. When purchasing electronics, request products that contain no Deca-BDE or other bromine-containing fire retardants.
- Foods - PBDEs can concentrate in the fat of poultry, red meat, fish and other fatty meats. See how to reduce the fat when preparing and cooking fish (these tips can be applied to other meats). Wash hands before preparing and eating food.
- Disposal and recycling - PBDEs will continue to pollute the environment unless flame retardant products are disposed of properly. To keep PBDEs out of the environment, dispose of foam containing products and electronics such as TVs and computers at your nearest hazardous waste collection site.
Mechanisms of toxicity
Many halogenated flame retardants with aromatic rings, including most brominated flame retardants, are likely thyroid hormone disruptors. The thyroid hormones triiodothyronine (T3) and thyroxine (T4) carry iodine atoms, another halogen, and are structurally similar to many aromatic halogenated flame retardants, including PCBs, TBBPA, and PBDEs. Such flame retardants therefore appear to compete for binding sites in the thyroid system, interfering with normal function of thyroid transport proteins (such as transthyretin) in vitro  and thyroid hormone receptors. A 2009 in vivo animal study conducted by the US Environmental Protection Agency (EPA) demonstrated that deiodination, active transport, sulfation, and glucuronidation may be involved in disruption of thyroid homeostasis after perinatal exposure to PBDEs during critical developmental time points in utero and shortly after birth. Disruption of deiodinase as reported in the Szabo et al., 2009 in vivo study was supported in a follow-up in vitro study. The adverse effects on hepatic mechanism of thyroid hormone disruption during development have been shown to persist into adulthood. The EPA noted that PBDEs are particularly toxic to the developing brains of animals. Peer-reviewed studies have shown that even a single dose administered to mice during development of the brain can cause permanent changes in behavior, including hyperactivity.
Based on in vitro laboratory studies, several flame retardants, including PBDEs, TBBPA, and BADP, likely also mimic other hormones, including estrogens, progesterone, and androgens. Bisphenol A compounds with lower degrees of bromination seem to exhibit greater estrogenicity. Some halogenated flame retardants, including the less-brominated PBDEs, can be direct neurotoxicants in in vitro cell culture studies: By altering calcium homeostasis and signalling in neurons, as well as neurotransmitter release and uptake at synapses, they interfere with normal neurotransmission. Mitochondria may be particularly vulnerable to PBDE toxicity due to their influence on oxidative stress and calcium activity in mitochondria. Exposure to PBDEs can also alter neural cell differentiation and migration during development.
Many flame retardants degrade into compounds that are also toxic, and in some cases the degradation products may be the primary toxic agent:
- Halogenated compounds with aromatic rings can degrade into dioxins and dioxin-like compounds, particularly when heated, such as during production, a fire, recycling, or exposure to sun. Chlorinated dioxins are among the highly toxic compounds listed by the Stockholm Convention on Persistent Organic Pollutants.
- Polybrominated diphenyl ethers with higher numbers of bromine atoms, such as decaBDE, are less toxic than PBDEs with lower numbers of bromine atoms, such as pentaBDE. However, as the higher-order PBDEs degrade biotically or abiotically, bromine atoms are removed, resulting in more toxic PBDE congeners.
- When some halogenated flame retardants such as PBDEs are metabolized, they form hydroxylated metabolites that can be more toxic than the parent compound. These hydroxylated metabolites, for example, may compete more strongly to bind with transthyretin or other components of the thyroid system, can be more potent estrogen mimics than the parent compound, and can more strongly affect neurotransmitter receptor activity.
- Bisphenol-A diphenyl phosphate (BADP) and tetrabromobisphenol A (TBBPA) likely degrade to bisphenol A (BPA), an endocrine disruptor of concern.
Routes of exposure
People can be exposed to flame retardants through several routes, including diet; consumer products in the home, vehicle, or workplace; occupation; or environmental contamination near their home or workplace. Residents in North America tend to have substantially higher body levels of flame retardants than people who live in many other developed areas, and around the world human body levels of flame retardants have increased over the last 30 years.
Exposure to PBDEs has been studied the most widely. As PBDEs have been phased out of use due to health concerns, organophosphorus flame retardants, including halogenated organophosphate flame retardants, have frequently been used to replace them. In some studies, indoor air concentrations of phosphorus flame retardants has been found to be greater than indoor air concentrations of PBDEs.
Exposure in the general population
The body burden of PBDEs in Americans correlates well with the level of PBDEs measured in swabs of their hands, likely picked up from dust. Dust exposure may occur in the home, car, or workplace. Levels of PBDEs can be as much as 20 times higher in vehicle dust as in household dust, and heating of the vehicle interior on hot summer days can break down flame retardants into more toxic degradation products. However, blood serum levels of PBDEs appear to correlate most highly with levels found in dust in the home. Perhaps 20% to 40% of adult U.S. exposure to PBDEs is through food intake, with the remaining exposure largely due to dust inhalation or ingestion.
Infants and toddlers are particularly exposed to halogenated flame retardants found in breast milk and dust. Because many halogenated flame retardants are fat-soluble, they accumulate in fatty areas such as breast tissue and are mobilized into breast milk, delivering high levels of flame retardants to breast-feeding infants. And, as consumer products age, small particles of material become dust particles in the air and land on surfaces around the home, including the floor. Young children crawling and playing on the floor frequently bring their hands to their mouths, ingesting about twice as much house dust as adults per day in the United States. Young children in the United States tend to carry higher levels of flame retardants per unit body weight than do adults.
Some occupations expose workers to higher levels of halogenated flame retardants and their degradation products. A small study of U.S. foam recyclers and carpet installers, who handle padding often made from recycled polyurethane foam, showed elevated levels of flame retardants in their tissues. Workers in electronics recycling plants around the world also have elevated body levels of flame retardants relative to the general population. Environmental controls can substantially reduce this exposure, whereas workers in areas with little oversight can take in very high levels of flame retardants. Electronics recyclers in Guiyu, China, have some of the highest human body levels of PBDEs in the world. Workers making products that contain flame retardants (such as vehicles, electronics, and baby products) may be similarly exposed. U.S. firefighters can have elevated levels of PBDEs and high levels of brominated furans, toxic degradation products of brominated flame retardants.
Flame retardants manufactured for use in consumer products have been released into environments around the world. Communities near electronics factories and disposal facilities, especially areas with little environmental oversight or control, develop high levels of flame retardants in air, soil, water, vegetation, and people.
Chemical and tobacco industry conspiracy
A Chicago Tribune investigative series has alleged that the chemical and tobacco industries mounted a campaign to increase the amount of flame retardants in homes while avoiding the need to manufacture a fire safe cigarette. In response to the investigative series, US Senators Durbin and Frank Lautenberg have called for legislation to regulate flame retardants that pose a risk to human health.
When products with flame retardants reach the end of their usable life, they are typically recycled, incinerated, or landfilled.
Recycling can contaminate workers and communities near recycling plants, as well as new materials, with halogenated flame retardants and their breakdown products. Electronic waste, vehicles, and other products are often melted to recycle their metal components, and such heating can generate toxic dioxins and furans. Brominated flame retardants may also change the physical properties of plastics, resulting in inferior performance in recycled products and in “downcycling” of the materials. It appears that plastics with brominated flame retardants are mingling with flame-retardant-free plastics in the recycling stream and such downcycling is taking place.
Poor-quality incineration similarly generates and releases high quantities of toxic degradation products. Controlled incineration of materials with halogenated flame retardants, while costly, substantially reduces release of toxic byproducts.
Many products containing halogenated flame retardants are sent to landfills. Additive, as opposed to reactive, flame retardants are not chemically bonded to the base material and leach out more easily. Brominated flame retardants, including PBDEs, have been observed leaching out of landfills in industrial countries, including Canada and South Africa. Some landfill designs allow for leachate capture, which would need to be treated. These designs also degrade with time.
Sudden infant death syndrome
UK scientist Barry Richardson claimed in 1989 that a fungus in bedding broke down the antimony, phosphorus, and arsenic flame retardants in infant bedding to form toxic gases. This research was taken up by New Zealand scientist Jim Sprott, who published a book on the topic, and eventually aired on The Cook Report in 1994. A 1998 UK government-sponsored study called the Limerick Report found that toxic gases were not created. Based on the Limerick report, position papers publicized by US SIDS organizations say there is not enough evidence to support the toxic gas theory, and that parents should continue to put their babies to sleep on vinyl-covered crib mattresses. However, Sprott maintains that his findings were not refuted.
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