11. Brominated Flame Retardants: Analytical, Toxicological and Environmental Aspects

Brominated flame retardants (BFRs), such as polybrominated diphenyl ethers (PBDEs), hexabromocyclododecanes (HBCDs) and tetrabromobisphenol-A (TBBP-A), have routinely been added to consumer products for several decades in a successful effort to reduce fire-related injury and property damage. Recently, concern for this emerging class o f chemicals has risen because o f their occurrence in the environment and in human biota. Here we briefly review scientific issues related to analytical, toxicological and environmental aspects o f these BFRs and discuss data gaps. 1. General Information Concerning Flame Retardants Flame retardants are materials that inhibit or resist the spread of fire that are added to polymers which are used in plastics, textiles, electronic circuitry or other mate­ rials (WHO/ICPS, 1994, 1997). The different classes of flame retardants include naturally occurring substances (asbestos), synthetic inorganic materials, such as antimony oxides, aluminium hydroxide, magnesium hydroxide, and borates, organic phosphate esters with or without halogens and chlorinated and brominated organic compounds (WHO/ICPS, 1997). The most used brominated flame retardants (BFRs) are polybrominated diphenyl ethers (PBDEs), hexabromocyclododecane (HBCD), tetrabromobisphenol-A (TBBP-A) and polybrominated biphenyls (PBBs). Flame retardants act by different mechanisms depending on the respective chemical class: some compounds break down through endothermie processes when subjected to high temperatures (e.g., aluminium and magnesium hydroxides), while other compounds act as diluents of fuel or of the gas phase and thus lower­ ing the combustible portion of the material (calc, calcium carbonate or inert gases, most often carbon dioxide or water). Another way to stop the flame spreading is to create a thermal insulation barrier between the burning and unbumed parts of a material (e.g., intumescent additives). Chlorinated and brominated flame retardants under thermal degradation condi­ tions release hydrogen chloride and hydrogen bromide. These reaction products react with highly reactive II' and HO' radicals present in the flame resulting in the formation of inactive molecules and of Cl' ox Br' radicals. The halogen radical has "•"Corresponding author. E-mail: [email protected] C. Popescu et al. (eds.), Applications o f Mass Spectrometry in Life Safety. © Springer Science + Business Media B.V. 2008 153 154 A. CO YACI AND A. C. DIRTU much lower energy than //• and HO', and therefore much lower potential to propagate the radical oxidation reaction and therefore the flame. Despite of their benefits for reducing fire-related injury and property damage, growing concern for BFRs has risen because of their occurrence and persistence in the environment, biota and humans, in a similar way to other persistent organic pollutants (de Wit, 2002; Birnbaum and Staskal, 2004). 2. Brominated Flame Retardants: Uses and Production Levels 2.1. POLYBROMINATED DIPHENYL ETHERS PBDEs are flame retardant additives which are used in a wide array of household products in concentrations up to 30% by weight, typically between 2% and 6%. They are structurally related to polychlorinated biphenyls (PCBs) and are pro­ duced commercially as mixtures. However, PBDE mixtures contain fewer conge­ ners than the commercial PCB mixtures. The three commercially mixtures of PBDEs are Penta-BDE, Octa-BDE and Deca-BDE according to the number of bromine atoms in the dominating congeners of the mixtures. The three PBDE mixtures have different applications: Penta-BDE mixture is primarily used in foams, such as seat cushions and other household upholstered furniture, as well as in rigid insulation. Octa-BDE is used in high impact plastic products, such as housing for fax machines and computers, automobile trim, telephone handsets and kitchen appli­ ance casings. Deca-BDE is used in plastics, such as wire and cable insulation, adhesives, coatings and textile coatings. Typical end products include housing for televi­ sion sets, computers, audiotape cassettes stereos and other electronics. DecaBDE is also used as a fabric treatment and coating on carpets and draperies, but it is not used in clothing. The European Union has banned since August 2004, the use of Pentaand Octa-BDE technical mixtures, but the use of Deca-BDE mixture is unrestricted following favorable risk assessment in May 2004 (BSEF, 2007). In U.S., only California has banned the use, by the end of 2008, of Pentaand Octa-BDE mix­ tures and other U.S. states are in the phase out legislation for PBDEs. 2.2. HEXABROMOCYCLODODECANE Structurally, HBCD is a cyclic aliphatic ring consisting in twelve carbon atoms with six bromine atoms tied to the ring. The commercial HBCD consists in a mix­ ture of the a -, ß and y-HBCD diastereomers, with the y-HBCD isomer being dominant (>70%). With a worldwide production of 16,700 t in 2001, HBCD is the third most widely used BFR in the world and on the second place in the European ANALYTICAL, TOXICOLOGICAL AND ENVIRONMENTAL ASPECTS 155 Union. HBCD is considered to be a high-production-volume chemical and a prior­ ity pollutant under the “Existing Substance Regulation” of the European Chemi­ cals Bureau. It is mostly used in extmded (XPS) and expanded (EPS) polystyrene foams, but also is used as insulation material in construction industry. HBCD is highly efficient so that very low levels are required to reach the desired flame retardancy. Typical HBCD levels in EPS are 0.7% and in XPS 2.5%. At present, HBCD is the only suitable flame retardant for these applications. Other uses of HBCD are upholstered furniture, automobile interior textiles, car cushions and insulation blocks in tracks, packaging material, video cassette recorder housing and electric and electronic equipment. In Europe and the United States, HBCD is not subject to regulatory restriction, whereas in Japan it is classified as a type I monitoring substance together with PBDEs and TBBP-A. 2.3. TETRABROMOBISPHENOL-A (TBBP-A) With a global production of 170,000 t in 2004 (BSEF, 2007), TBBP-A is the larg­ est used BFR. TBBP-A is mainly used as reactive BFR in laminates for printed wiring boards which are commonly used in electronic devices. Additionally, TBBP-A is used as an additive BFR in acrilonitrile-butadiene-styrene (ABS) polymers plastic housings, but it is also used as an intermediate in the production of other BFRs, such as TBBP-A derivatives and brominated epoxy oligomers. Following favorable risk assessments, the use of TBBP-A is not restricted in any country (BSEF, 2007). 2.4. OTHER BROMINATED FLAME RETARDANTS There are in total a number of 75 different types of BFRs. Besides the above mentioned compounds, the most important group of BFRs according to its impact on environment are polybrominated biphenyls (PBBs). As a BFR, PBB was used in epoxy and phenolic resins, industrial plastics, such as high-impact polystyrene. Combusted PBB-containing materials may produce highly toxic brominated diox­ ins and furans. Since they have been found to be persistent, bioaccumulative toxins, being also classified as potential carcinogens, most of the production of PBBs was ceased in 1970s (BSEF, 2007). 3. Analytical Methodologies Due to the observed increasing temporal trends in humans or biota, BFRs are being determined in a growing number of laboratories. Analytical methods for the deter­ mination of BFRs have shown a rapid development and they were in most of the cases based on protocols previously established for persistent organic pollutants 156 A. CO YACI AND A. C. DIRTU (POPs), such as organochlorine pesticides, PCBs or polychlorinated dioxins and furans (PCDD/Fs). Even if different properties of BFRs, such as polarity or vapor pressure, suggest that different procedures should be applied for their analysis from environmental samples, some common approaches can still be underlined depending also on the type of sample or the detection method (de Boer et al., 2001; Covaci et al., 2003, 2007; de Boer et al., 2007). Indeed, due to particular physico-chemical properties, the determination of individual HBCD diastereomers and TBBP-A may require specific analytical approaches. In general, the methods used for the determination of BFRs in different matri­ ces are very sensitive and thus able to detect extremely low amounts of these compounds. The methods described in the literature have been recently reviewed (Covaci et al., 2003; Stapleton, 2006; Covaci et al., 2007). Some basic steps of the BFR determination are sample pre-treatment, extraction, clean-up and instrumen­ tal analysis. However, being present in all environmental compartments, labora­ tory contamination during each analysis step can easily occur. 3.1. SAMPLE PRE-TREATMENT Various sample pre-treatments are used depending on the employed extraction method. For solid samples (sediment, soil, dust, biological tissues), sample pre­ treatment involves usually the drying of the sample. Dry samples are more effec­ tively homogenized, allowing accurate sub-sampling for parallel analyses for other determinants (e.g., organic carbon). In addition, storage and transport may be eas­ ier. The absence of water in the samples avoids laborious extraction with separa­ tion funnels and makes the sample matrix more accessible to organic solvents. As an alternative to drying through evaporation, several methods can be applied for water binding and the most easily to perform is chemical drying by grinding of the sample with anhydrous Na2S04. Freeze-drying (water evaporation below 0°C under vacuum conditions) can also serve for sample drying (Smedes and de Boer, 1997).