| Polychlorinated biphenyls(PCBs)have 209 congeners based on different positions and the number of chlorine atom substitutions.PCBs were used widely as dielectrics in capacitors and also as additives in paints or plastics due to their highly stable physical and chemical properties.However,PCBs exhibit environmental persistence,high biological toxicity,high bioconcentration,and long-range migration,because of which they are now listed as one of the 12 environmental persistent organic pollutants(POPs)to be controlled in 2001.The estimated cumulative global production of commercial PCBs is 1.3 × 106 tons.PCBs still flow into the environment as a by-product of other chlorinated compounds or chlorinated products.The soil environment becomes their largest sink,approximately 93.1%of the PCBs existing in the environment.Therefore,humans would be exposed to soil environments containing these contaminants for decades and even centuries to come.Identifying an efficient and secondary contamination-free method for the remediation of PCB-contaminated soils is a great significance for environmental pollution management and the maintenance of human health.At present,there is a lack of intensive research on plant-microbe remediation technology,and it is necessary to reveal the environmental effect characteristics and influence mechanism of PCBs in plants.In addition,most studies are carried out on the characteristics of PCBs,and people have not studied the comprehensive impact mechanism of its multiple environmental effect characteristics.This study took the characteristics of various environmental effects of PCBs as the breakthrough point,first explored the impact mechanism of the comprehensive environmental characteristics of PCBs.Then the environmental characteristics of PCBs transformation products and their potential environmental risk assessment were carried out to explore the necessity of strengthening the phytodegradation technology of PCBs contaminated soil.The mechanism of plant degradability and phytotoxicity of PCBs was analyzed,and the improvement measures were explored from the internal and external perspectives.Finally,the plant-microbe enhanced remediation technology of PCBs in soil was studied.The 3D-QSAR model assisted by the fractional analysis experimental design method with resolution V and the comprehensive effect 3D-QSAR model modified by the log-normalized method and the vector normalized method were used to investigate the mechanism of the comprehensive effect of PCBs’ bioconcentration(logBCF),migration(KOA and PL),toxicity and flame retardancy,respectively.Based on molecular virtual modification,combined with molecular docking and atom-in-molecule theory(AIM theory),the influence mechanism of PCBs on the characteristics of environmental effects was further analyzed and verified.The results indicate that the hydrogen bond donor and acceptor fields have negligible contributions,and the electrostatic field has the largest influence on the logBCF values of the PCBs.The single modification sites that significantly affected the bioconcentration of PCBs were in the order meta->para->ortho-substitution.The two sites for modification were(R2,R6),(R2’,R3’),(R2’,R6’),and(R5,R6),and those for modification with three sites were(R2,R5,R6).The non-covalent forces near the binding site of PCBs to the receptor protein and the degree of matching between the molecule and its hydrophilic/hydrophobic amino acid residues determine the bioconcentration of PCBs;the comprehensive effect of mobility of PCBs is mainly influenced by the steric and electrostatic fields;the comprehensive effect of PCBs toxicity and flame retardancy is also mainly influenced by the electrostatic field,where PCBs electron density and potential energy density and its electrophilicity are the key factors affecting the toxicity and flame retardancy of PCBs.The complementary construction of PCBs phytotoxicity and biotoxicity 3D-QSAR model,combined with the constructed PCB environmental risk characterization model,was carried out to analyze the transformation path with a significant increase in environmental risks.Their transformation processes were simulated and evaluated for assessing environmental risks.The environmental risks of plant degradation products of PCBs in the environmental media showed the maximum risk,with an increase of 421.71%,indicating that it is essential to improve further the ability of plants to degrade PCBs.In addition,the improvement of some degradation products for PCB derivatives indicates that the virtual modification cannot completely control the potential environmental risks of the molecules,the potential risks of transformation products of PCBs derivatives could not be neglected.The QSAR model of PCBs’ molecular phytotoxicity and plant degradability based on structural parameters were constructed.The phytotoxicity and plant degradability mechanism of PCBs’ molecular homologs are analyzed by combing with the sensitivity analysis.Meanwhile,the 3D-QSAR pharmacophore model of the comprehensive effect of PCBs’phytotoxicity and plant degradability modified by the sine normalization method was constructed to initially carry out a mechanistic analysis.In addition,from the perspective of adding external stimulation conditions and internal modification,formulate measures to slow down the phytotoxicity of PCBs and strengthen the plant degradability of PCBs.Molecular dynamics method,molecular docking technology and quantitative molecular surface analysis were used to further analyze and verify its influence mechanism.The binding energy of all the seven typical PCB interacting with plant toxicity enzyme and degradation enzyme under environmental stimulus conditions improved by 5.79%and 7.32%,respectively.Therefore,it is inferred that the addition of ascorbic acid,tocopherols,and carotenoids can reduce the phytotoxicity of PCBs by the main parameter of EHOMO.The addition of phosphate and urea enhances the degradation of PCBs by the main parameter of logP.The plant-microbe enhanced remediation technology of PCBs in soil was studied.It is found that the ability of plant absorption,degradation and microbial mineralization of PCBs in soil environment is inconsistent,and the three enzymes have the ability to degrade PCBs.PCBs have the strongest binding effect with plant degrading enzymes.Therefore,the plant degradation enzyme was selected as the template for enzyme modification using amino acid recombination and site-directed mutagenesis,and six multifunctional plant degradation enzymes possessing a combination of the three functional roles of absorption,degradation,and mineralization were constructed.The affinity of six multifunctional plant degradation enzymes with mutant acid mutation and the thermal stability of their own structure were increased.The six multifunctional plant degradation enzymes exhibited significantly higher efficiency(2.10-2.38 times)in degrading the PCBs,with a maximum of 2.69 times under suitable external environmental conditions.It was also observed that the priority and the activity of the multifunctional plant degradation enzymes were essentially the same for the degradation of the PCBs,the binding of 4 dioxin-like PCBs individually,and as a whole to the multifunctional plant degradation enzyme(3GZX-1)exhibited synergistic effect. |
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