Brominated Flame Retardants: Assessing DecaBDE Debromination in the Environment HEATHER M. STAPLETON (PhD, MS, BS) MAY 2006 28 Boulevard Charlemagne 1000 Brussels (Belgium) Tel.: +32 2 234 3640 Fax.: +32 2 234 3649 [email protected] www.env-health.org About the Author The intent of this overview is to provide a summary Heather Stapleton’s expertise is in the fate and on the significance and extent of DecaBDE biotransformation of organic contaminants in debromination in the environment. If DecaBDE is aquatic systems, focusing on persistent organic a ‘significant’ pathway for the formation of lower pollutants (POPs), such as polychlorinated brominated congeners, there are both potential biphenyls (PCBs) and polybrominated diphenyl adverse environmental and health consequences. ethers (PBDEs). She is presently carrying out The potential persistency and bioaccumulation research on DecaBDE debromination at Duke properties of the lower congeners must be taken University, Nicholas School Faculty, Environmental into consideration in the risk assessment. Sciences and Policy Division in her capacity as an Moreover, there may be legal implications for Environmental Chemist. putting on the market indirectly through DecaBDE and into the environment these lower congeners, such as PentaBDE and OctBDE, which are already I. Context from European Public Health restricted under existing EU regulation. Alliance – Environment Network. The draft addendum environmental risk assessment II. Introduction report for decabromodiphenyl ether (DecaBDE) was distributed to the Technical Committee for Decabromodiphenyl ether (BDE 209) is a multi- New and Existing Substances (TC NES) on August halogenated organic chemical used primarily as a 11, 2005 (The addendum can be found at the flame retardant in a commercial mixture known as European INventory of Existing Commercial DecaBDE. It has been used as an additive flame chemical Substances (EINECS), retardant since the late 1970s, and because it is well [http://ecb.jrc.it/existing-chemicals/]) . The suited to flame retard in particular plastics, its previous risk assessment, agreed in May 2004, had market demand has increased significantly over the concluded that further information was required past few decades with the increasing use of plastics before definitive conclusions could be drawn on the in electrical goods 1. Commercially produced concerns from DecaBDE to the environment. DecaBDE consists primarily of BDE 209 (<97%) with minor contributions (0.3 to 3.0%) of octa- and One of the key areas identified for further nonaBDE congeners (or iso-forms), which are clarification was the extent and importance of the impurities in the technical mixture. A particular debromination of DecaBDE in the environment. concern regarding BDE 209 is the potential for The conclusion in the draft addendum prepared by degradation via debromination. Debromination is a the UK government highlights that it is still not process by which bromine atoms are sequentially possible to give a reliable assessment of the overall removed or cleaved from an organic compound, significance of debromination based on expert resulting in a smaller lower brominated molecule judgment. Although the conclusions state that the which is slightly more water soluble. These lower published data on debromination heightened the brominated congeners have the potential to be more concern, it did not necessary mean that persistent and more bioaccumulative than their debromination was a significant pathway in the larger parent chemical. environment. This view was also elaborated in a TNO report commissioned by the Brominated Science Environment Forum1, an industry based III. Environmental Levels of DecaBDE association. Numerous studies have investigated the prevalence 1 of polybrominated diphenyl ether (PBDE) A.O. Hanstveit MSc, Dr. C.T. Bowmer, Dr. A.P. Freidig. TNO 2, 3 Netherlands Organisation for Applied Scientific Research. A review of congeners in the environment . the anaerobic and abiotic degradation of the flame retardant decabromodiphenyl ether (CAS # 1163-19-5) in the context of an EU BDE 209 is a fully brominated PBDE congener environmental risk assessment report, customer BSEF – Bromine Science and Environmental Forum & The International Organization of containing ten bromine atoms (See Figure 1). A the Bromine Chemical Industry. 17 August 2005 (ECB TRACKING majority of environmental samples, specifically NO. COM013_ENV_IND 09) Brominated Flame Retardants: Assessing DecaBDE Debromination in the Environment 2 2 2' IV. Photolytic Debromination of BDE 209 O 3 3' BDE 209 absorbs sunlight in the UV region of the 4 electromagnetic spectrum that reaches the surface of 6 6' 4' 5 5' the earth. Due to this light absorption, BDE 209 is susceptible to photodegradation, which can occur Brn n=1-10 significantly through debromination. A majority of the UV spectrum is blocked by glass windows and Polybrominated Diphenyl Ether (PBDE) does not reach indoor environments. However, Figure 1. Structure of PBDE molecule. substrates containing BDE 209 in direct sunlight do receive UV radiation. Several studies have investigated the photodegradation of BDE 209 to human and biological samples, contain PBDE determine the time it takes for 50% of the BDE 209 congeners that are dominated by congeners with mass to degrade (known as the half-life). Half-lives four to six bromine atoms 4, 5. PentaBDE and vary from a few minutes up to several years, depending upon the substrate and light source OctaBDE are two additional commercial 13 brominated flame retardant mixtures containing (Table 2). Söderström et al. examined the PBDE congeners with four to eight bromine atoms photolytic decomposition of BDE 209 in several (see Table 1), and are believed to be the source of different types of substrates using both natural these congeners in biological samples. However, sunlight and a UV-lamp. Their study demonstrated debromination of BDE 209 cannot be ruled out as a that BDE 209 degraded very quickly in organic source of these lower brominated congeners. solvents but was slower when adsorbed to sediment and soils. Ahn et al. 14 also observed longer half- BDE 209 has been measured in house dust 6-8 at lives of BDE 209 when adsorbed onto sediment and concentrations up to 10,000 ppb, which could be a minerals compared to dissolution in water and potential pathway of human exposure, particularly organic solvents. These studies suggest that for young children. Toddlers have a predisposition adsorption of BDE 209 onto suspended material in the water column decreases the photodegradation of to put dirty hands and toys in their mouth and 15 inadvertently ingest larger amounts of house dust. BDE 209 in aquatic environments. Stapleton This predilection has been responsible for large exposed BDE 209 spiked house dust to sunlight and cases of lead poisoning in U.S. children,9-11 due to found that the half-life was approximately 220 hours the high lead levels in house dust. No studies have of continuous sunlight exposure, or assuming 10 investigated the levels of PBDEs in children under hours of sunlight a day, approximately 22 days. the age of 5; however, modeling studies suggest However, it is difficult to assess the magnitude and toddlers are receiving greater exposure to PBDEs duration of sunlight that house dust would be than adults because of the high levels in house dust exposed to in an average home. Most windows will 12. In some homes studied, BDE 209 comprises block out UV wavelengths of light which would 90% of the total PBDE burden,7 therefore, BDE hinder degradation. In contrast, car dust has 209 exposure could be unique to young children. recently been found to contain elevated levels of BDE 209 Conclusion (http://www.ecocenter.org/releases/20060111_aut Debromination of BDE 209 cannot be ruled out as otoxics.shtml), which is susceptible to greater a source of lower brominated congeners. sunlight exposure and in which debromination can be expected to occur significantly. DecaBDE is mainly found in dust in the indoor environment including our homes and cars which The degradation products of BDE 209 photolysis may result in elevated exposures in children. are primarily lower brominated PBDE congeners formed via debromination. In soils, sediment and house dust, the primary congeners identified are hepta-, octa- and nonaBDE congeners 13-15, and very little degrades to congeners with fewer than six bromine atoms. When dissolved in water or Brominated Flame Retardants: Assessing DecaBDE Debromination in the Environment 3 organic solvents, BDE 209 degrades quite rapidly resulting in a BDE 209 half-life of about one day. and leads to greater formation of the lower The use of iron sulfide and sodium sulfide reduced brominated congeners, including tri-, tetra- and the debromination/degradation rate to 2 and 33% pentaBDE congeners, and also polybrominated of the rate observed for zero-valent iron. Both the dibenzofurans (PBDFs) 13, 16, 17. In the environment, iron and sulfides resulted in debromination down to it is expected that BDE 209 will be found primarily congeners with two and three bromines. In all bound to solids in the water column, and bound to experiments, the initial rate of degradation was rapid particles in the atmosphere. Therefore, degradation and then decreased over time as lower brominated of BDE 209 dissolved in water (or organic solvents) congeners were formed that appeared to be more is not expected to be of environmental relevance. stable. While this study demonstrates the possibility and feasibility of reductive debromination by Conclusion minerals, this process is unlikely to occur naturally It is difficult to assess the degree of BDE 209 in the environment. PBDEs will have a greater photolytic debromination in house dust, soils and tendency to be bound to natural organic matter and sediments when exposed to light. However, in cars soils in the environment before binding directly to debromination can be expected to occur more the mineral surface, which is necessary for the significantly. Debromination in water is not mineral to act as an oxidant. expected to be of environmental relevance.