Environ. Sci. Technol. 2009, 43, 7536–7542
Origin of Hydroxylated Brominated Diphenyl Ethers: Natural Compounds or Man-Made Flame Retardants? Y I W A N , * ,† S T E V E W I S E M A N , † HONG CHANG,† XIAOWEI ZHANG,† P A U L D . J O N E S , † M A R K U S H E C K E R , †,‡ KURUNTHACHALAM KANNAN,§ SHINSUKE TANABE,| JIANYING HU,⊥ MICHAEL H. W. LAM,∇ AND J O H N P . G I E S Y †,#,∇,O Department of Biomedical Veterinary Sciences and Toxicology Centre, University of Saskatchewan, Saskatoon, Saskatchewan S7N 5B3, Canada, ENTRIX, Inc., Saskatoon, Saskatchewan S7N 5B3, Canada, Wadsworth Center, New York State Department of Health and Department of Environmental Health Sciences, School of Public Health, State University of New York, Empire State Plaza, Albany, New York 12201-0509, Center for Marine Environmental Studies, Ehime University, Matsuyama, Japan, College of Urban and Environmental Sciences, Peking University, Beijing, 100871 China, Department of Zoology and Center for Integrative Toxicology, Michigan State University, East Lansing, Michigan, Centre for Coastal Pollution and Conservation and Department of Biology and Chemistry, City University of Hong Kong, Kowloon, Hong Kong, SAR China, and State Key Laboratory of Marine Environmental Science, College of Oceanography and Environmental Science, Xiamen University, Xiamen, P. R. China
Received May 6, 2009. Revised manuscript received August 5, 2009. Accepted August 6, 2009.
Polybrominated diphenyl ethers (PBDEs) have been widely used as flame retardants. The structurally related hydroxylated PBDEs (OH-PBDEs) and methoxylated PBDEs (MeO-PBDEs) occur in precipitation, surface water, wildlife, and humans. The formation of OH-PBDEs in wildlife and humans is of considerable concern due to their greater toxicities relative to PBDEs and MeO-PBDEs. Research to date suggests that OH-PBDEs are formed by hydroxylation of PBDEs, and MeO-PBDEs are then formed by methylation of the OH-PBDEs. Here we show significant metabolic production of OH-PBDEs from MeOPBDEs while hydroxylation of synthetic PBDEs to OH-PBDEs was negligible. Concentrations of PBDEs, OH-PBDEs, and MeOPBDEs were analyzed in tuna, albatross, and polar bears collected from marine environments worldwide, and we found a closer relationship between OH-PBDEs and MeO-PBDEs than had been previously reported. Furthermore, for the first * Corresponding author tel: (306) 966-4978; fax: (306) 966-4796; e-mail:
[email protected]. † University of Saskatchewan. ‡ ENTRIX, Inc. § Wadsworth Center, New York State Department of Health and Department of Environmental Health Sciences, School of Public Health, State University of New York. | Ehime University. ⊥ Peking University. # Michigan State University. ∇ City University of Hong Kong. O Xiamen University. 7536
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time the metabolic relationships between PBDEs, OH-PBDEs, and MeO-PBDEs were elucidated in vitro using rainbow trout, chicken, and rat microsomes. We propose the production of OHPBDEs from naturally occurring MeO-PBDEs as a previously unidentified mechanism that could be an important contributor for the occurrence of OH-PBDEs found in wildlife from remote areas. Our results suggest that risk assessment paradigms for PBDEs and their metabolites need reevaluation and that human exposure to MeO-PBDEs that occur naturally in marine organisms should be considered.
Introduction Brominated flame retardants (BFRs) have emerged as contaminants of concern due to their widespread use, ubiquitous environmental distribution, great bioaccumulation potential, and toxicity. Polybrominated diphenyl ethers (PBDEs) are one of the most widely used BFRs with an annual global consumption of 70,000 t in 1999 (1). Over the last 30 years concentrations of PBDEs in human blood, breast milk, and other body tissues have been increasing with doubling times of approximately 4-6 years (2, 3). Hydroxylated (OH-) and methoxylated (MeO-) PBDEs, which are analogous to PBDEs in structure, have been found in wildlife tissues (4-8), and laboratory studies have shown the formation of OH-PBDEs after exposure to PBDEs (9-13). There is considerable interest in the origin of OH-PBDEs and MeO-PBDEs in biota and abiotic environmental matrices. The concern over OH-PBDEs is of particular interest since they elicit a variety of effects on exposed organisms including disruption of thyroid hormone homeostasis, oxidative phosphorylation disruption, altered estradiol synthesis, and neurotoxic effects (14-20). The fact that OH-PBDEs were found at greater concentrations than PBDEs in marine algae led to the suggestion that OH-PBDEs can be formed naturally in marine algae or by their associated microorganisms (4, 8). It has also been shown that OH-PBDEs are biotransformation products of PBDEs. This conversion has been reported in fish, rat, and human cell cultures (9, 12, 13). However, the exposure concentrations of PBDEs in these in vitro or in vivo studies were generally great (µg/g level), and the resultant products, OH-PBDEs, occurred at trace concentrations (
