Polybrominated flame-retardant materials

Striebich RC, Rubey WA, Tirey DA, et al. 1991. High-temperature degradation of polybrominated flame retardant materials. Chemosphere 23(8-10) 1197-1204. 

Polybrominated flame retardants are in extensive use in modem society as additives in many products, e.g. computers, other electronic equipment, furniture, cars, construction materials, sealings, etc. They are lipophilic substances with differing Kow and differing persistence, many of them characterized by very high bioavailability and bioconcentration factors. 

In addition, the concern about e-waste not only focuses on its vast quantity generated daily, but also more on the need to handle the toxic chemicals embedded in it. It is well known that e-waste contains lead, beryllium, mercury, cadmium (Cd), and brominated flame retardants (BFRs) among other chemical materials [3]. Furthermore, highly toxic chemicals such as polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) and polybrominated dibenzo-p-dioxins and dibenzo-furans (PBDD/Fs) can be formed during the recycling process [4]. 

BFRs are one of the last classes of halogenated compounds that are still being produced worldwide and used in high quantities in many applications. In order to meet fire safety regulations, flame retardants (FRs) are applied to combustible materials such as polymers, plastics, wood, paper, and textiles. Approximately 25% of all FRs contain bromine as the active ingredient. More than 80 different aliphatic, cyclo-aliphatic, aromatic, and polymeric compounds are used as BFRs. BFRs, such as polybrominated biphenyls (PBBs), polybrominated diphenyl ethers (PBDEs), hexabromocyclododecane (HBCD), and tetrabromobisphenol A (TBBPA), have been used in different consumer products in large quantities, and consequently they were detected in the environment, biota, and even in human samples [26, 27]. 

Decabromodiphenyl ether (BDE-209) is a major industrial product from the polybrominated diphenyl ethers used as flame retardants derivatives of this product have been detected in the environment. After exposure to the land surface, these contaminants adsorb on soil materials and may reach the atmosphere as particulate matter these particulates are subsequently subject to photolytic reactions. In this context, Ahn et al. (2006) studied photolysis of BDE-209 adsorbed on clay minerals, metal oxides, and sediments, under sunhght and UV dark irradiation. Dark and light control treatments during UV and sunlight irradiation showed no disappearance of BDE-209 during the experiments. Data on half-lives and rate constants of BDE-209 adsorbed on subsurface minerals and sediments, as determined by Ahn et al. (2006) and extracted from the literature, are shown in Table 16.6. 

Polybrominated Diphenyl Ethers. PBDEs are used as additive flame retardants in thermoplastics. Additive flame retardants are physically combined with the polymer material being treated rather than chemically combined (as in reactive flame retardants). This means that there is a possibility that the flame retardant may diffuse out of the treated material to some extent. 

With the demise of PBBs as a viable product, the brominated flame retardant industry turned to polybrominated diphenyl ethers (PBDEs) as a replacement. PBDEs have become a popular product for example, furniture-grade polyurethane foam is now treated with 1-10% by weight of PBDEs to make this material safe for home use [27]. Not surprisingly, the use of PBDEs has increased over the years, and global annual sales are now 70 000 metric tons [27]. 

PBDEs Considered the new PCBs, polybrominated diphenyl ethers are a group of brominated flame retardants used in lots of products, including the foam in couches and mattresses, and plastic TV and computer monitors (Dell and HP, among others, have banned them). One of the reasons PBDEs are so hard to avoid is that they re not bound to the molecules in materials, so toxic residue can escape in the form of dust. Most kinds of PBDEs have been banned in Europe since 2004, and American women carry ten to seventy times as many PBDEs in their breast milk, tissues, and blood as Europeans do. Exposure to PBDEs during fetal development can negatively affect how the brain functions. 

However, especially brominated flame retardants are creating problems when electronic and electrical equipment reach end of life. If landfilled, toxic brominated flame retardants may slowly leach ont into the groundwater, where they persist for several years or they can evolve into the air. If waste materials are burned toxic polybrominated dioxins and furans can be formed [53, 50]. 

Polybrominated biphenyls (PBBs) are inert, stable chemicals used primarily as additive flame retardants to suppress or delay combustion. In their use as flame retardants, PBBs were added to polymer materials, but were not chemically incorporated into the polymer matrix and therefore could migrate out of the polymer matrix with time. Hexabromobiphenyl was used as a Are retardant mainly in thermoplastics in electronic equipment housings. Smaller amounts were used as a Are retardant in coating and lacquers, and in polyurethane foam for auto upholstery. After the voluntary ban of hexabromobiphenyl in the late 1970s, polybrominated diphenyl ethers (PBDEs) and other flame retardants were used as replacements. 

No traces of curing agents were found, further indicating a complete curing reaction. Triphenyl phosphate flame retardant was also found in this analysis. Since devices of this type are predominantly mounted on wooden utility poles, a flame retardant formulation may provide a desirable operating margin in the event of an electrical failure. However, as shown in Figure 10-14, this same insulator was also found to contain polybrominated biphenyls (PBBs), which are banned from manufacture or use in most countries. The analysis of this material protected the electric utility company from potentially inadvertent deployment of a hazardous material. 

Polybrominated diphenyl ethers (PBDEs), mainly used as flame-retardants, have a total of 209 possible congeners. These compounds are being released into the environment more frequently because of their increased use in plastic materials and synthetic fibers. Environmentally significant concentrations have been reported in air, water, soil, sediment, and sewage samples, in aquatic and terrestrial organisms [45], and in human breast milk [46]. Little is known about their toxicity on organisms in the environment however, there is indication that they are endocrine disrupters capable of affecting the thyroid system [47]. 

EnvirOTimental trends are having an impact on electrical applications. Waste legislation includes WEEE (Waste of Electrical and Electronic Equipment) directive 2002/%/EC which holds producers responsible for collection and recovery of materials at end of Ufe. Additionally, materials that contain bromine-based flame retardants must be removed from the waste and handled separately. In restrictions on use of hazardous substances (ROHS) directive 2002/95/EC, the use of various hazardous materials is restricted. These include lead, mercury, cadmium, hexavalent chromium, polybrominated biphenyls, and polybrominated diphenyl ether. Since the introduction of Blue Angel in Germany in 1978, several other eco-labels have been implemented. These include TCO (Sweden), Nordic Swan, Milieukeur (Netherlands), and the EU Ecolabel. The general purpose of these labels is to provide cmisumers with information relating to the environmental impact of the products they purchase. 

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