Promotion Of Microbial Remediation For Polychlorinated Biphenyls Contaminated Soil By Magnolol

Polychlorinated biphenyls (PCBs) are typical persistent organic pollutants in soil. At present,the remediation technology of PCBs contaminated soil is mainly divided into physical remediation technology, chemical remediation technology and biological remediation technology. Bioremediation technology can make up for the shortcomings of physical and chemical remediation technology, and microbial remediation technology is the most promising.Biodegradation of PCBs by microorganisms is usually carried out in a cometabolic manner.Cometabolism substrates play a crucial role in microbial remediation. For the first time using magnolol with biphenyl structure of natural as cometabolism substrate, the study used the PCBs degrading strain Rhodococcus biphenylivorans TG9T isolated from soil by our group. To study the remediation potential for PCBs contaminated soil, the degradation of PCBs in solution and soil microcosm had been investigated, and semi-field soil tests had been conducted. The other cometabolism substrates were compared as well, and the mechanism of degradation had been explored. The main results are as follows.(1) The low concentration of magnolol (0.1 mg/L to 1 mg/L) did not inhibit the growth of TG9, while the higher concentration of magnolol (3 mg/L to 5 mg/L) had inhibitory effect on TG9. The delay time for growth was longer at higher concentration.(2) In solution culture system, strain TG9 could degrade magnolol. With initial concentration of 1 mg/L for 5 days the degradation rate reached 36.5%. The magnolol could promote degradation of PCB31 as cometabolism substrate. Compared to the control, the degradation rate of PCB31, the initial concentration about 10 mg/L, increased by 17.3%, to 64.5%, after 100 h. When compared with the classical cometabolism substrate, promoting rate of PCB31 degradation was almost equal, while the degradation was slightly delayed. After 28 h,the degradation rate of magnolol experimental group was significantly higher than that of limonene, carvone, hesperidin, salicylic acid experimental groups (P < 0.05). Biphenyl was detected during the metabolism of magnolol. It was speculated that biphenyl was the metabolite of magnolol with TG9, and then promoted the degradation of PCB31 by TG9. This could explain delayed effect of magnolol for PCB31 degradation by TG9.(3) The promotion effect for PCBs degradation were studied by substrates including magnolol, biphenyl, limonene, carvone, hesperidin, salicylic acid and so on. In the laboratory simulation of soil microcosm experiments, all of the substrates above could promote degradation of PCBs. The initial concentration of the total PCBs in the tested soil was 126.6?131.8 mg/kg.Magnolol had the best promotion effect, and the cumulative degradation rate reached 82% in 50 days, which was the best among above natural products. It was worth mentioning that magnolol had the best effect on promoting tri-PCBs and the degradation rate was up to 79.2%,significantly better than other substrates. While the tetra-PCBs degradation rate reached 82.9%,which was the same as that of biphenyl, carvone, hesperidin and better than that of the other substrates.(4) The plant crude extracts containing above natural products could promote the degradation of PCBs in semi-field soil remediation experiments. The cumulative degradation rate was 45% by adding extracts of Magnolia officinalis in 40 days. The initial concentration of PCBs in the original soil was 17.6?18.8 mg/kg. The degradation rate of the experimental group with the Magnolia officinalis crude extract (containing magnolol) was 44.1% after 40 days.Magnolia crude extracts of tri-PCBs degradation rate was 45.3%, which promoting effect was similar with dill seed crude extract (containing limonene and carvone) and were both better than the others. Magnolia crude extracts of tetar-PCBs degradation rate was 43.4%, which promoting effect was not as better as that of dill seed extracts, but was better than that of the other extracts.In this study, a new natural substrate of co-metabolism and degradation was identified: magnolol.Which verified its promoting effect on bioremediation of PCBs contaminated soil and preliminarily clarified its mechanism, and laid the foundation for further field application and mechanism clarifying.