Transport And Distribution Of Decabrominated Diphenyl Ether In Soils And Photolysis Of Decabrominated Diphenyl Ether In Soil Suspensions

Polybrominated diphenyl ethers?PBDEs?is widely used as a brominated flame retardant.Because of its persistent and biological toxicity,and it has been widely detected in various environmental media,it poses a threat to the ecological security.Decabrominated diphenyl ether?BDE-209?is the main persistent organic pollutants in the electronic waste dismantling area.Due to its extreme hydrophobicity,it is mainly absorbed in soils,sediments and organic matters,and could be photodegradated under the irradiation of sunlight.Therefore,based on the natural phenomena,this study firstly investigated the distribution characteristics of BDE-209 in the soils of e-waste dismantling areas and then investigated the photodegradation of BDE-209 in soil suspensions.Finally we revealed the distribution and transport mechanism of BDE-209 in the soils of e-waste dismantling areas and the photodegradation mechanism of BDE-209 in soil suspensions.The main findings are as follows:?1?The contents of BDE-209 on surface soil and vertical scale samples were purificated by using self-made purification column and determined by using high performance liquid chromatography.The results show that the soils in the e-waste dismantling areas are significantly polluted by BDE-209.The concentration of BDE-209 in the soils are high?0.10to 5.47 mg/kg?,and the average content of BDE-209 in the paddy field is higher than that in vegetable field caused by irrigation sewage.BDE-209 transports very little over long distances with runoff and the atmospheric deposition causes BDE-209 to migrate to the downwind region.On the vertical scale,with the increasing of soil depth,the content of BDE-209 in soil gradually decrease,and BDE-209 is not detected in soils below 50 cm depth.As the input intensity increasing,BDE-209 migrates deeper in soils in vertical direction.?2?In aqueous soil suspensions system,the photodegradation of BDE-209 accords with the pseudo-first-order kinetics law.Different light sources have a greater influence on the photodegradation of BDE-209 in aqueous soil suspensions.The photodegradation rate is 500W Mercury Lamps>300 W Mercury Lamps>500 W Xenon Lamps>300 W Xenon Lamps.The light shielding effect of soil particles inhibits the photodegradation reaction of BDE-209 in aqueous soil suspensions.The higher pH value has an effect on the photodegradation rate of BDE-209 in the aqueous soil suspensions.At pH=9.5,the photodegradation rate of BDE-209is fastest,reaches 0.071 h^-1.The photodegradation products show that the mainly photodegradation mechanism of BDE-209 is debromination reduction reaction and formating di-to nona-brominated diphenyl ethers.The degradation pathway is sequencing debromination to generate low-brominated biphenyls ethers.In addition,at the presence of metal ions and humic acids,Fe?III?and Cu?II?compete with BDE-209 for absorption of photons that inhibits the direct photodegradation reaction of BDE-209 in the soil suspensions.The shielding effect and quenching of the active material of humic acid also inhibit the photodegradation of BDE-209.?3?In the organic solvents soil suspensions,the solvent characteristics have an effect on the photodegradation of BDE-209.Using 500 W mercury lamp as the light source,the photodegradation rate of BDE-209 is successively that of acetonitrile soil suspension(0.031 h^-1)>Methanol soil suspension(0.027 h^-1)>Acetone soil suspension(0.009 h^-1).Acetone can absorb ultraviolet light so that inhibits the photodegradation of BDE-209.The degradation products were detected.The results show that BDE-209 could formate di-to nona-brominated diphenyl ethers in methanol soil suspensions through sequencing debromination.The content of debromination products of BDE-209 in the soil suspensions of acetonitrile and acetone is less.The composition of photodegradation products is not much different with that reported in the pure solvents,and the most products are debromination products.That indicates the presence of soil particles does not change the photodegradation mechanism.