Application of a congener‐specific debromination model to study photodebromination, anaerobic microbial debromination, and FE⁰ reduction of polybrominated diphenyl ethers

Abstract

A model was used to predict the photodebromination of the 197, 196, and 153, the major components of the octa-polybrominated diphenyl ether (PBDE) technical mixture, as well as BDE-47, and the predicted results were compared to the experimental results. The predicted reaction time profiles of the photodebromination products correlate well with the experimental results. In addition, the slope of the linear regression between the measured product concentrations of the first step of the photodebromination products and their enthalpies of formation was found to be close to their theoretical value. The photodebromination results of the octa-BDE technical mixture were compared with anaerobic microbial debromination results and were found to be the same in both experiments. The debromination pathways of technical octa-BDE mixture were identified and BDE-154, 99, 47, and 31 were found to be the most abundant hexa-, penta-, tetra-, and tri-BDE debromination products, respectively. In addition to photodebromination and anaerobic biodebromination, the model prediction was also compared to the zero-valent iron reduction of BDE-209, 100, and 47 and the same debromination products were observed. Good correlation was observed between the photodebromination rate constants of fifteen PBDE congeners and their calculated lowest unoccupied molecular orbital (LUMO) energies, indicating that PBDE photodebromination is caused by electron transfer. Furthermore, the rate constants for the three different PBDE debromination processes are controlled by C-Br bond dissociation energy. With the model from the present study, the major debromination products for any PBDE congener released into the environment can be predicted.

Species‐specific and structure‐dependent debromination of polybrominated diphenyl ether in fish by in vitro hepatic metabolism

“…For example, the formation rate of BDE 28 (removal of the meta-bromine) was 2 times that of BDE 25 (removal of the para-bromine) by in vitro incubations with BDE 66 (Table 1). However, compared with the biotransformation in fish, photobromination experiments showed a different trend, with ortho-and meta-substitutions as the dominant metabolic approaches [15,35]. A similar situation was also found in the debromination of BDE 42 and BDE 99 ( Table 1).…”

“…Although the transformation rate of BDE 99 was faster than that of BDE 85, the remaining mass of BDE 99 was still 2 times that of BDE 85, indicating a faster removal rate for doubly flanked bromine than singly flanked bromine. Given that repulsion between adjacent bromines results in increased enthalpies of formation, it is not surprising that doubly flanked bromines are removed more frequently than singly flanked bromines [35]. Given that repulsion between adjacent bromines results in increased enthalpies of formation, it is not surprising that doubly flanked bromines are removed more frequently than singly flanked bromines [35].…”

Kinetics and pathways for the debromination of polybrominated diphenyl ethers by bimetallic and nanoscale zerovalent iron: Effects of particle properties and catalyst

“…The main debromination mechanisms for unamended Fe° appears to be a direct electron transfer (Zhuang et al, 2010). Similarly, PBDE photodebromination is also caused by electron transfer, as there is a correlation between the debromination rate constants and the calculated lowest unoccupied molecular orbital energies (E LUMO ) (Zeng et al, 2010; Zhuang et al, 2010). Fe° reduction and photodebromination of PBDEs have similar major products (Zeng et al, 2010).…”

“…al. were able to build an energy-based debromination model to predict the major congeners and kinetics for PBDE-Fe° reduction and photodebromination, where the reactions are governed by the enthalpy of formation (Keum and Li, 2005; Zeng et al, 2008; Zeng et al, 2010). …”

“…Compared to reactions on an iron surface, the debromination reactions on a palladium surface highlight the steric hindrance and rapid sequential debromination of adjacent bromines, indicating the importance of surface precursor complex formation. Similarly, in addition to the enthalpy of formation and the type of microbial culture, steric effects also control PBDE anaerobic microbial debromination (Zeng et al, 2010). Moreover, preferential removal of para- and meta-bromines was observed in the PBDE debromination tests with sewage sludge collected from a mesophilic digester (Gerecke et al, 2005) and three microbial cultures (Robrock et al, 2008).…”