| Tetrabromobisphenol A(TBBPA)[4.4'-isopropylidenebis(2,6-dibromophenol)]is the preferred brominated flame retardant in industry.used as an additive in,e.g.,construction materials,textiles,and electronic equipment.The presence of TBBPA as an environmental contaminant has raised increasing concern,because TBBPA has been shown to act as an endocrine disruptor with thyroid hormone activity and to exert toxicity and oxidative stress in organisms.In the environment,one of the sinks for TBBPA is soil.TBBPA can be accumulated in the soils via many ways.Previous studies showed that most of TBBPA in soil become bound residues.However,detailed studies of the release and satability of the TBBPA-derived bound residues and effects of Cu2+ on fate of TBBPA in soil under oxic conditions are scarce.There are scarce reports about the fate of TBBPA in the rice-wheat rotation and reed field.TBBPA affects the plants,and plants may enhance the biotransformation and biodegradation.The results are follows:1 The formation,characterization,and mineralization of bound residues of TBBPA in silty clay under oxic soils.We studied the nature and stability of bound residues derived from TBBPA in fine-texture soil.We incubated 14C-labelled TBBPA in silty clay rice paddy soil for 93 days under oxic conditions.TBBPA dissipated with a first-order kinetic constant kd of 0.0474 ± 0.0017 day-1(t1/2 14.6 ± 0.3 days)and mineralized with a km of 0.0011 ±0.00002 day-1.At the end of the incubation,four metabolites,including two methylation products(TBBPA monomethyl and dimethyl ether),accounted for 7.9 ±0.1%of the initial TBBPA.The BRs continuously increased in amount to a maximum of 80.1 ± 3.6%.About 86.3 ± 0.9%of the BRs localized in the humin fraction and 55.9 ± 1.5%was hydrolyzable with strong alkali(SAH-BRs),which represents reversible BRs.When BRs-containing soil was incubated with fresh soil for 231 days,9.2 ± 0.3%was mineralized(km 0.00047 ±0.00002 day-1)and SAH-BRs decreased to 34.1 ± 1.1%,accompanied by transformation into other BR forms.2.When BRs were incubated with Ochrobactrum sp.T for 214 days,6.8 ± 0.4%was mineralization and HA increased to 14.7 ± 1.2%.The organic extracts was increased and the BRs ware redistribution with Ochrobactrum sp.T.3.Impact of Cu2+ on the fate of TBBPA in oxic conditiond.During 91 days incubation,high concentration of Cu2+ decreased the mineralization of TBBPA.8.7 ±0.08%(km 0.00155 ± 0.00006 day-1)and 6.6 ± 0.6%(km 0.00085 ± 0.00002 day-1)of TBBPA were mineralized in the absence and presence of Cu2+(400 mg·kg-1)respectively.Cu2+(400 mg·kg-1)promoted formation of BRs,at 0 days.At the end of the incubation,the amount of BRs with Cu2+(400 mg·kg-1)was slighter higher than without Cu2+.In the sterilized soil,there was no mineraliztion during the incubation.4.The fate of TBBPA in field soil with rice-wheat rotation and reed plants.In the field experiment,the concentration of TBBPA was 100 mg·kg-1.At end of harvest of rice and reed,TBBPA in the organic extracts of control soil,soil with rice and reed were 45.8 ±3.1%,40.8 ± 2.3%,and 30.1 ± 2.7%respectively.After harvesting wheat,21.3.8 ± 0.9%,17.7 ± 1.0%,and 15.4 ± 2.7%of TBBPA were remained in organic extractsin of control soil,wheat and reed field respectively.At the 4th year,the concentration of TBBPA was below 0.5 mg·kg-1,and most of TBBPA dissipated.In the first year,we detected the metabolites of TBBPA.During the rice season.TBBPA was transformed to low brominated intermediates and BPA.In the wheat seasons,we detected O-methylation metabolites of TBBPA.5.The fate and metabolites of TBBPA in rie cell suspension culture.We studied the fate,metabolites,and transformation of 14C-labeled TBBPA in rice cell suspension culture.During the incubation for 14 days,TBBPA degradation occurred continuously in the culture,accompanied by formation of one anisolic metabolite(DBHPA)(50%of the degraded TBBPA)and cellular debris-bound residues(46.4%)as well as mineralization(3.6%).The cells continuously accumulated TBBPA in the cytoplasm,while a small amount of DBHPA(2.1%of the initially applied TBBPA)was detectable inside the cells only at the end of incubation.The majority of the accumulated residues in the cells was attributed to the cellular debris-bound residues,accounting for 70-79%of the accumulation after the first incubation day.About 5.4%of the accumulation was associated with cell organelles,which contributed 7.5%to the cellular debris-bound residues.Based on the fate and metabolism of TBBPA in the rice cell suspension culture,a type ? ipso-substitution pathway was proposed to describe the initial step for TBBPA degradation in the culture and balance the fate of TBBPA in the cells.As mentioned above,we first studied the fate and metabolites of TBBPA in rice cell suspension,and found formation of BRs in rice cell walls.Then we in vestgated the formation and nature of the BRs in silty clay soil.The rice root exudates cannot accelerate the release of the TBBPA-derived BRs,while ester-linkage and ether-linkage BRs may be transformed into other BR forms.Ochrobactrum sp.T.TBBPA degrader can promote the release of BRs and increase the transformation of BRs into CO2(mineralization),organic extracts,and HA.For the future work,the followings should be studied the molecular mechanism of degradation of TBBPA in rice cells and formation of BRs;the stability of BRs derived from plant;the stability of BRs with rice or wheat;analysis of bacterial in the field experiment. |
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