Free and bound polybrominated diphenyl ethers and tetrabromobisphenol A in freshwater sediments

Both free and bound fractions of polybrominated diphenyl ethers (PBDEs) and tetrabromobisphenol A (TBBPA) in sediment were examined. The free fraction was operationally defined as the fraction of each target compound extracted with a solvent mixture of hexane/acetone by Soxhlet extraction, while the bound fraction was the portion released from the sediments by alkaline hydrolysis following the solvent extractions. Tri- to hepta-BDEs and TBBPA were detected in the bound fraction. Bound PBDEs accounted for 0.2–2.8% of the total PBDEs and bound TBBPA accounted for 6.5–48% of the total TBBPA, in surface sediments. In sediment cores, these percentages ranged from 1.8% to 42% for bound PBDEs and 22–92% for bound TBBPA. The percentages of bound materials showed an increasing trend with the sediment depth. Sequestration of PBDEs and TBBPA within sediments might be an important geochemical fate of these brominated flame retardants.