Polybrominated Diphenyl Ethers (PBDEs) as Emerging Environmental Pollutants: Advances in Sample Preparation and Detection Techniques

PBDEs are categorized as probable human carcinogens and are known to bioaccumulate in fatty tissues of animals and humans, reaching toxic levels upon continued exposure. Monitoring of these pollutants is therefore paramount as it contributes to addressing the problem of human exposure and environmental pollution. PBDEs are commonly applied as flame retardants in polymer products such as electronics, plastics, textiles, and building materials. They are characterized by high physical and chemical stability, making them persistent in the environment. PBDEs can be transported away from their sources for long-ranges through aqueous and/or terrestrial environmental compartments. In this context, monitoring and assessment of environmental pollution by these compounds are very important. The determination of PBDEs involves a series of steps from sample pre-treatment to quantification of analytes using various detection systems. Different sample preparation strategies that range from conventional to advanced strategies have been applied for the determination of PBDEs in environmental samples. Some of the conventional sample enrichment methods include Soxhlet extraction and liquid-liquid extraction, while more recent methods such as ultrasound-assisted extraction, pressurized liquid extraction, and solid-phase extraction have exhibited successful extraction of PBDEs from environmental samples. PBDEs comprise of two halogenated aromatic rings bonded by an ester bond and are classified in relation to the number and position of bromine atoms in a particular molecule. They have a general molecular formula of C12H(10 - x) BrxO, where x is the number of bromine atoms in a molecule with numerical values [x = 1, 2, 3, …, 10 = m + n]. Substitution of bromine atoms can take place at 10 possible positions on the two benzene rings resulting in 209 possible congeners. Different congeners are easily identified by their corresponding IUPAC numbers ranging from 1 to 209. The global production of commercial PBDE formulations was approximately 67,000 tons in the ratio 1:1.98:14.8 for octa-BDE, penta-BDE, and deca-BDE respectively, of which the United States production was approximately 50% of the global production. Several governmental regulations and international environmental agencies have restricted and completely banned the use and production of some PBDE congeners. In 2004, the European Union phased out the use and production of penta-BDE and octa-BDE, and in December 2004, Great Lakes Chemical Corporation, a sole manufacturer of penta-BDE and octa-BDE in North America, voluntarily phased out the production of these BDE formulations. PBDEs are still reported in air, soil, and aquatic environments, which is attributed to their stability and subsequent release from technoeconomic systems, and production of deca-BDE, which still continues to be produced in some countries. There are diverse pathways by which PBDEs enter the environment, including leakage from consumer products and industrial facilities that synthesize PBDEs or PBDE-containing products, as well as illegal disposal of obsolete electrical appliances and electronic devices.