Studies On Reductive Degradation And Quantitative Structure-property Relationship(QSPR) Of Polybrominateddiphenyl Ethers(PBDEs)

Polybrominated diphenyl ethers(PBDEs) are a category of emerging persistent organic pollutants(POPs), which have 209 congeners. They have been widely used in electronic equipments, plastics, transportations and textiles as a category of additive brominated flame retardants. During the use of these products, PBDEs can enter the environment through volatilization and leakage. Nonstandard incineration of garbage or other waste disposal methods will lead a large number of PBDEs and other toxic emissions into the atmosphere, soil and water. The content of PBDEs in the environment has increased year by year. Nowadays, PBDEs were detected not only in water, air, soil, but also in human body, and most of them are toxic and carcinogenic. Therefore, how to degraded the PBDEs in the environment has become an urgent problem which needs to be solved. Zero valent iron(ZVI) has unique physical properties and high reducibility, the preparation method of ZVI is simple, and the price is low. Therefore, ZVI has been widely used in the degradation of a variety of organic compounds in the previous studies. This study discussed the reductive degradation effect of PBDEs by microorganism, unsupported and supported ZVI particles, which were stressed with the hope of providing some meaningful advices for the practical application.Quantitative structure-property relationship(QSPR) methodology is based on the development of the mathematical relations between the macroscopic properties and the molecular structure for a particular set of similar compounds. In this study, linear(multiple linear regression(MLR), the partial least squares regression(PLSR), principal component analysis multiple linear regression analysis(PCA-MLR)) and non-linear(back propagation artificial neural network(BP-ANN)) models were employed for QSPR studies between the molecular descriptors and the logarithm of normalized reaction rate constants of fourteen selected BDE congeners obtained from the previous experiments and approaches.The main conclusions of this paper are as follows: The contents of eight BDE congeners in sixteen sampling points of the Baihua Lake were determined. The concentrations of tri-BDE(BDE-28), tetra-BDE(BDE-47), penta-BDE(BDE-99 and bde-100), hexa-BDE(bde-153 and bde-154), hepta-BDE(bde-183) and deca-BDE(BDE-209) were: nd-14.443 ng/g, 0.554-30.011 ng/g, 0.0526-14.226 ng/g, nd-8.773 ng/g, nd-11.101 ng/g and nd-22.350 ng/g. The total concentration range of PBDEs were 0.774-100.903 ng/g, and the average concentration was 20.461 ng/g. The detection rate of PBDEs was 43.75%- 100%, BDE-28,-47,-99 and-100 were the primary BDE congeners in the sediments of Baihua Lake. In comparison with other places, the pollution levels of PBDEs in surface sediments of the Baihua Lake were higher, which needs more attention to reduce the damage to the environmental.(1) ZVI particles were synthesized by the aqueous phase reduction, and the tapping mode image of atomic force microscope(AFM) showed that the diameter of the ZVI particles was in the range of 90 nm- 400 nm. By comparison of the reductive degradation of BDE-47 by sunlight, ZVI, ZVI impregnated activated carbon(ZVI/AC) and ZVI impregnated ion exchange resin(ZVI/IER), the effect was found to descend in the following order: ZVI/AC > ZVI/IER > ZVI > sunlight. Second order and first order kinetic models were used for the fitting of the degradation data of BDE-47. Results showed that the degradation data of BDE-47 by the sunlight, ZVI, ZVI/AC and ZVI/IER in the current study were generally best described by the pseudo first order equation.(2) In this paper, the reductive degradation ability for BDE-47 and BDE-99 by aerobic bacteria was better than that by anaerobic bacteria. The degradation rate of BDE-47 was greater than that of BDE-99 by both microorganisms. The reductive degradation rates of BDE-47 and BDE-99 by aerobic and anaerobic microorganisms were generally best described by the first order equation.(3) In this study, quantum chemical method was chosen to calculate the degradation pathways of BDE-47 and BDE-99 in gas-phase and solvent(water). The calculation results showed that the degradation pathways of BDE-47 and BDE-99 were similar to the previous laboratory study. This showed that quantum chemical method could calculate the degradation pathway of PBDEs in molecular level accurately and effectively.(4) The best QSPR model for the BDE congeners was log KSA = – 0.001(±0.118) μ – 29.547(±20.016) ELUMO – 59.349(±15.367) EHOMO + 0.065(±0.205) NBr – 19.301(±3.678). The MLR, PLSR, PCA-MLR and BP-ANN methods were employed for QSPR studies on the reductive degradation reactivity of the BDE congeners. All methods could predict the log KSA of the BDE congeners in test set satisfactorily, with the RMSE values less than 0.3. The BP-ANN model had better description ability and more accurate prediction results than the models from the PLSR and PCA-MLR approaches.