| Polychlorinated Biphenyls (PCBs) are one of the twelve preferential restricted persisted organic pollutants, because of the toxicity, carcinogenicity, persistance and bioaccumulation. PCBs are difficult to be degraded, they can accumulate into the environment by water, soil, atmosphere and other ways. PCBs were widely used for industry production. Power capacitors with PCBs were stacked outsides, leaking out, imperfect combustion during the process of use, disposition and dismantling, which lead to the environment pollution of PCBs. Soil is the main sink of PCBs.In this study, the pollution characters, contents, substances distribution of PCBs in the soils surrounding a E-waste recycling area in Yangtze River Delta were investigated. A PCBs-degrading strain was isolated; the capability of the strain on PCBs degrading was studied, with different PCBs congeners as the sole carbon source; the optimum PCBs-degrading conditions were explored by orthogonal and co-metabolism experiments. The combined remediation effects of plant-microbe on PCBs contaminated soil were also studied using pot experiment. The results were as follows:1. The detection rates of PCBs homologue in all soil samples near a E-waste recycling area in Yangtze River Delta were 100%, the average of PCBs was 33.9μg/kg. The main congeners were 4-5-chlorinated biphenyls and the high-chlorinated biphenyls also took account for some proportion.2. A PCBs-degrading strain was isolated. Molecular, physiological and biochemical assays identified the strain was Sinorhizobium melilon, named SL1 (GenBank Accession No. KF98277).3. The strain SL1 could use 2,4,4’-TCB,3,3’,4,4’-TCB and 21mixed PCBs congeners as the sole carbon source. The degradation rates of Sinorhizobium melilon to 2,4,4’-TCB, 3,3’,4,4’-TCB and 21mixed PCBs congeners were decreased gradually with the concentration increased. The degradation rates for 2,4,4’-TCB were 93.3% of 1.0 mg/L and 65.1% with the highest concentration up to 50.0 mg/L for 7 days, respectively. The degradation rates were 56.2%of 1.0 mg/L and 22.8% with the highest concentration of 25.0 mg/L for 3,3’,4,4’-TCB after 7 days, individually. The degradation rates under 4.2,105.0 mg/L concentration of 21 mixed PCBs were 46.9% and 12.5% after 7 days, and the results showed obvious degradation effect for 2-5-chlorinated biphenyls by SL1. The orthogonal experiment indicated that the optimal conditions for degradation process were as follows: pH=7.0, temperature 30 ℃, inoculation volume 4.5 mL, medium cubage 25 mL/250 mL. Under these conditions, the degradation rate for 2,4,4’-TCB under 10.0 mg/L was increased from 54.8%to 83.6% by SL1 after 7 days. The pH had significant effect on experiment results. In addition, the degradation rates of PCBs were increased with limonene, mannitol and carvone as co-metabolism substrates by Sinorhizobium melilon,89.4%,77.8%,66.6%, respectively.4. The combined remediation effects of inoculation with or without Sinorhizobium melilon with a host plant (alfalfa) on the spiked PCBs soils were studied using pot experiment. The removal rates of different treatments with Sinorhizobium melilon, plant, pant and Sinorhizobium melilon were 29.5%,33.4%,47.2%, significantly higher than control group(10.4%). The effect of treatment with alfalfa and Sinorhizobium melilon was higher than other two treatments. Sinorhizobium melilon combined with alfalfa could significantly promote the growth of the plant, change the structure of the rhizosphere microorganisms, enhance the activity and diversity of soil microbial community, and even facilitate the absorbability and the transportation of the PCBs in plants. |
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