Fate Of Tetrabromobisphenol A In Paddy Soil Under Different Reducing Conditions And Sequential Anoxic-oxic Conditions

Tetrabromobisphenol-A (TBBPA)[4,4’-isopropylidenebis (2,6-dibromophenol)] is one of the most commonly used brominated flame retardants (BFRs), being used as additives in many commercial and industrial products. Given its widespread use all over the world, TBBPA has been frequently detected in environmental samples, such as sediment and soil. Paddy field is an important agricultural ecosystom in China and Asia and is one of the main sinks for TBBPA. It is of significance to study the behaviors of TBBPA under different environmental conditions in paddy soil in order to evalutate its ecological risk. Using C-14isotopic tracer method, we investigated the degradation, metabolism, and formation and release of bound residues of TBBPA under sulfate and iron reducing conditions. Also, we established a sequential anoxic-oxic incubation system to study the fate of TBBPA under anoxic-oxic conditions.During195days of anoxic incubation, trace TBBPA (1.3%) was mineralized to CO2and most of TBBPA was reductively debrominated with a disspation half-life of36days. To promote sulfate and iron reducing condition,20mM sodium sulfate and160mM amorphous Fe(OH)3were added to soil. Under the sulfate-reducing condition, the dissipation half-life of TBBPA was31days. The amendment of Fe(OH)3showed great influence on behavior of TBBPA at the beginning of incubation. Most of TBBPA was adsorbed to Fe(OH)3and couldn’t be extracted by organic solvents. As Fe(Ⅲ) were reduced to Fe(Ⅱ) during the incubation, part of the adsorbed TBBPA was released as extractable residues. Four metabolites were detected via radioactive detector (HPLC-14C-LSC) and were analyzed as mono-, di-, tri-brominated bisphenol A(mono-, di-, tri-BBPA), and bisphenol A (BPA) by LC-MS.During the anoxic incubation, formation of bound-residue was detected in all treatments. Compared to natural treatment, more bound residues was formed at the first30days of incubation in sulfate reducing treatment, which accouted for53%of applied radioactivity. Due to the special structure of amorphous Fe(OH)3, most TBBPA was recovered as bound residues at the beginning of incubation. When ammonium oxalate (pH3.25) was applied to dissolve the amphours Fe(OH)3, the initially bound radioactivity can be completely released. Along with the incubation, the percentage of ammonium oxalate-extractable radioactivity in the bound residues decreased. The components of these released radioactivity included TBBPA and its debromination metabolites, which was different at different incubation time. Beside, we study the release of bound residues in fresh soil. The results showed that bound residues didn’t release but some mineralization was detected.To establish a sequential anoxic-oxic incubation, the water layer in the samples after125days of anoxic incubation was removed and the solid fractions were incubated under oxic condition for another70days. At the end of the anoxic incubation, most of the TBBPA and all of the low brominated intermediates had been transformed to BPA or bound residues. After altering the incubation to oxic condition,9.5%of the anaerobically accumulated BPA was mineralized to CO2, which accounted for5.9%of applied radioactivity. Meanwhile, most of the BPA was transformed to bound residues with a half-life of11days. We also observed the release of anaerobically formed bound residues after incuabtion condition alteration including TBBPA and its low brominated intermediates. The total released anaerobically formed bound residues was about12.4%of applied radioactivity. These released TBBPA and intermediates was persisitent during a70days of oxic incubation.We evaluated for the first time the feasibility of sequential anoxic-oxic incubation to remove the brominated flame retardant TBBPA from environmental matrix. The results proved that TBBPA may be effectively debrominated to BPA during anoxic incubation and that BPA degrades rapidly during subsequent oxic incubation. However, the release of TBBPA and the less debromination metabolites during the subsequent oxic incubation indicate that the sequential anoxic-oxic incubation is not able to completely remove TBBPA and its metabolites from soil. A second round of the sequential anoxic-oxic incubation might improve the removal efficiency.