Abstract
Due to the increasing pollution of tetrabromobisphenol A (TBBPA) in paddy soils, it is of great importance to explore the degradation of TBBPA under repeated anoxic-oxic conditions. In the present study, the degradation of TBBPA (kinetics, metabolites and potential pathways) and the influence of low molecular weight organic acid i.e., lactic acid were investigated in a paddy soil during sequential anoxic-oxic incubations. Under the anoxic condition, TBBPA in the non-sterile soils was efficiently debrominated into three intermediates (including tri-BBPA, di-BBPA and mono-BBPA) and bisphenol A (BPA) with a rate constant (k) of 0.0371 d−1 and a half-life (t1/2) of 60.8 d. The debromination end product (BPA) steadily accumulated. Next, turning to the oxic conditions, the anaerobically accumulated BPA degraded rapidly, while the intermediates and TBBPA were desorbed from the bound residues and were persistent. The detection of tri-BBPA followed by di-BBPA and mono-BBPA thereafter indicated that the dehalogenation of TBBPA was likely a stepwise removal of bromine atoms. A pathway of TBBPA → tri-BBPA → di-BBPA → mono-BBPA → BPA was thus proposed for TBBPA degradation. The degradation of TBBPA and its metabolites was biologically mediated. Moreover, the biodegradation of TBBPA could be significantly accelerated by the addition of lactic acid as an exogenous carbon source and electron donor, with k being increased to 0.0766 d−1 and t1/2 being shortened to 31.9 d. The information will improve our understanding of biotic process associated with agronomic practices (such as applying organic fertilizers) contributing to TBBPA attenuation in the natural soil environment.
Highlights
Tetrabromobisphenol A [4,4′-isopropylidenebis(2,6-dibromophenol); tetrabromobisphenol A (TBBPA)] is one of the most commonly used brominated flame retardants in the world
The sequential anoxic-oxic incubations of TBBPA were performed in a paddy soil from the Longtang area of South China, a main e-waste recycling area which was extensively polluted by TBBPA and bisphenol A (BPA), supplemented by lactic acid as an exogenous carbon source
The intermediates were temporarily detectable at 1.07–7.06%, 1.02–8.21% and 1.25–5.78% of the initially applied TBBPA during 20–110 d for the tri-BBPA, di-BBPA, and mono-BBPA, respectively (Fig. 1b)
Summary
Tetrabromobisphenol A [4,4′-isopropylidenebis(2,6-dibromophenol); TBBPA] is one of the most commonly used brominated flame retardants in the world. In view of the reality of increasing TBBPA contamination and repeated redox cycles in the paddy fields, it is of great importance to investigate the biodegradation of TBBPA in soils during the sequential anoxic-oxic process and to develop abatement measures. The influence of low molecular weight organic acids (e.g., lactic acid) introduced by agronomic practices, such as fertilization, on the degradation of TBBPA in soils is still unclear and needs to be investigated further. The sequential anoxic-oxic incubations of TBBPA were performed in a paddy soil from the Longtang area of South China, a main e-waste recycling area which was extensively polluted by TBBPA and bisphenol A (BPA), supplemented by lactic acid as an exogenous carbon source. The information will improve our understanding of biotic process associated with agronomic practices (such as applying organic fertilizers) contributing to TBBPA attenuation in the natural soil environment
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