On the identity and formation routes of environmentally abundant tri- and tetrabromodibenzo-p-dioxins

Ten previously unidentified polybrominated dibenzo-p-dioxins (PBDDs) were identified or tentatively identified in samples of Baltic Sea sediment and biota. Five tetrabrominated dibenzo-p-dioxins (TeBDDs) were identified using authentic reference standards, including the four most abundant (previously denoted 4U1 through 4U3). In addition, five tribromodibenzo-p-dioxins (TrBDDs) were tentatively identified using retention times and analysis of TeBDD debromination products (including a moderately abundant compound previously denoted 3U1). An attempt was made to improve the gas chromatographic separation of the major TeBDDs, but with limited success. The data generated were used as basis for a discussion on the potential PBDD formation routes. No single formation pathway could explain the PBDD patterns found. Instead, a combination of a number of potential formation processes is suggested, including enzymatic and photolytic coupling of environmentally abundant bromophenols or hydroxyl diphenyl ethers (OH-PBDEs), and debromination of PBDDs to lesser brominated products.