Development and validation of a congener‐specific photodegradation model for polybrominated diphenyl ethers

Abstract

With the phaseout of the manufacture of some polybrominated diphenyl ether (PBDE) formulations, namely penta-brominated diphenyl ether (BDE) and octa-BDE, and the continued use of the deca-BDE formulation, it is important to be able to predict the photodegradation of the more highly brominated congeners. A model was developed and validated to predict the products and their relative concentrations from the photodegradation of PBDEs. The enthalpies of formation of the 209 PBDE congeners were calculated, and the relative reaction rate constants were obtained. The predicted reaction rate constants for PBDEs show linear correlation with previous experimental results. Because of their large volume use, their presence in the environment, and/or importance in the photodegradation of the deca-BDE formulation, BDE-209, BDE-184, BDE-100, and BDE-99 were chosen for further ultraviolet photodegradation experiments in isooctane. The photodegradation model successfully predicted the products of the photochemical reactions of PBDEs in experimental studies. A gas chromatography retention time model for PBDEs was developed using a multiple linear regression analysis and, together with the photodegradation model and additional PBDE standards, provided a way to identify unknown products from PBDE photodegradation experiments. Based on the results of the photodegradation experiments, as well as the model predictions, it appears that the photodegradation of PBDEs is a first-order reaction and, further, that the rate-determining step is the stepwise loss of bromine. Our results suggest that, based on photodegradation, over time, BDE-99 will remain the most abundant penta-BDE, while BDE-49 and BDE-66 will increase greatly and will be comparable in abundance to BDE-47.

In vitro biotransformation of PBDEs by root crude enzyme extracts: Potential role of nitrate reductase (NaR) and glutathione S-transferase (GST) in their debromination

“…For the fully brominated BDE-209, debromination products via removal of the ortho-, meta-and para-bromine atoms were all detected, and differences in their concentrations were small. BDE-7 was frequently detected in the debromination products of the four parent PBDEs, probably because of its low enthalpy of formation (Zeng et al, 2008). Detection of BDE-11 (3,3 0 -diBDE) in the BDE-47 and -99 exposed solutions indicated the possibility of bromine rearrangement (Zhao et al, 2012).…”

Uptake, translocation, and debromination of polybrominated diphenyl ethers in maize

“…Figure 7 shows the percentage profiles of the debromination products of BDE-28, -47 and -99 in each part of maize. BDE-28 could be debrominated to BDE-15, -12/13 (co-eluting congeners) and -8; BDE-47 could be debrominated to BDE-28, -15, -12/13 and -8; BDE-99 could be debrominated to was prevalent in the debromination products of all three parent PBDEs probably due to its low enthalpy of formation (Zeng et al, 2008). As for BDE-99, BDE-47 Transpiration rate (mL/day) Fig.…”

Summer atmospheric polybrominated diphenyl ethers in urban and rural areas of northern China

“…On the other hand, the rural field sites are relatively far away from the emission sources and hence have higher R penta/octa ratios, since various BDE congeners behave differently during atmospheric transport. Since the transport potentials of BDE-153 and BDE-154 were lower than that of BDE-47 and low-brominated BDEs like BDE-47 can be formed as the degradation products of higher brominated congeners (Söderström et al, 2004;Zeng et al, 2008), relative accumulation of BDE-47 on the way of air transport can lead to a rise of R penta/octa ratio from sources to receptors.…”