| Soil serves as a source and sink for pollutants.With industrialization and urban expansion,significant accumulation of pollutants occurs in urban soils,posing threats to ecological security and human health.Therefore,the development of environmentally friendly soil remediation technologies is crucial to ensure the safety of urban soils.Dechlorane Plus(DP)and its related compounds(Dechloranes,DPs)are highly chlorinated flame retardants that have been widely added to electrical wire coatings.DPs are biotoxic,long-range transportable,and difficult to degrade,but few techniques have been reported for the detection and removal of DPs from soil.Based on this,this study developed a universal quantification technique for soil DPs by considering the current situation that soil DPs extraction and detection methods use more organic reagents,complicated pre-treatment,and cannot analyze many DPs simultaneously,and the factors such as high sensitivity,high recovery and stable results of accelerated solvent extraction(ASE)combined with gas chromatography-mass spectrometry(GCMS)testing through literature research;for The effectiveness and environmental sustainability of soil microbial remediation,the structural properties of DPs,the screening of DPs-specific degrading bacteria,surfactants and plants suitable for soil DPs remediation,and the development of surfactant-enhanced plant-microbial combined remediation technology suitable for DPs-contaminated soils were considered,and the specific research contents and results are as follows:(1)We developed an accelerated solvent extraction(ASE)combined with gas chromatography-mass spectrometry(GC-MS)method,taking into consideration factors such as high sensitivity,high recovery rates,and result stability.Through optimization experiments of the ASE extraction and purification conditions for soil DPs,as well as GC-MS conditions,we established a rapid ACE-GC-MS quantitative method for the simultaneous detection of five types of DPs.The developed method was validated by analyzing soil samples from an electronic waste disposal site and a cable processing workshop in Shenyang City.The method exhibited detection limits ranging from 0.135 to 1.564 μg·kg-1,recovery rates of 90.9%to 94.3%,precision and accuracy of 0.98-0.99,and good reproducibility.The detection rate of DPs in the two sites in Shenyang City(a waste recycling station and a cable processing workshop)was 100%.The concentrations of DP pollutants ranged from 70.07 to 1637.83 mg·kg-1,syn-DP and antiDP concentrations ranged from 35.93 to 804.17 mg·kg-1 and 34.13 to 833.67 mg·kg-1,respectively.The concentrations of Dec 602,Dec 603,and Dec 604 were in the ranges of 20.07-171.82 mg·kg-1,16.23-198.80 mg·kg-1,and 5.08-224.31 mg·kg-1,respectively.(2)By combining traditional enrichment cultivation methods with degradation performance experiments,we screened out two specific DPs-degrading bacteria,namely Cellulosimicrobium cellulans(Strain A)and Streptomyces azureus(Strain M).Both strains were able to utilize DPs as their sole carbon source for growth.The optimal pH,temperature,and growth conditions of the strains were in line with the natural environment,and they exhibited a high adaptability to common carbon sources under natural conditions.The optimal degradation conditions for soil DPs by Degradation Strain A and Degradation Strain M were as follows:temperature of 30℃,inoculum size of 100 mL(1 ×108 CFU)degradation bacteria per 100g of contaminated soil,pH of 7.0,and a cultivation time of 9 days.Glucose was found to be the most suitable carbon source.Under these optimal conditions,Degradation Strain A achieved removal rates of 33.33%to 46.04%for the five DPs,while Degradation Strain M achieved removal rates of 37.07%to 43.23%for DPs.(3)Surface active agents suitable for the remediation of soil DPs and their concentrations were screened through washing experiments with different surface active agents,microbiological toxicity experiments,and simulated remediation experiments.Using the surfactants rhamnolipid(RL)and polyethylene glycol dodecyl ether(brij 35),the washing rates of the five DPs in the soil were 51.6%-57.2%and 40.2%-47.1%,respectively,and relatively low toxicity(50.3%-54.8%increase of OD600A in the RL500 group compared with the CK group and 60.3%-64.8%increase of OD600M in the brij 35-600 group compared with the CK group).The removal rates of soil DPs using the combination of degrading bacteria A and RL-500 and degrading bacteria M and brij 35600 were 51.6%-75.34%and 61.29%-75.84%,respectively.Considering the aesthetics of urban remediated soil,seed germination experiments and plant pot experiments were conducted to investigate the germination rate of plant seeds in DPs contaminated soil and the effects of different plants on the removal rate of soil DPs.Lavender(L)and rapeseed(R)were selected as the above-ground plants,and after one growth cycle,the removal rates of the five DPs in the soil were 17.6%-33.4%and 2.6%-33.6%,respectively.(4)Pot experiment was conducted to investigate the surfactant-enhanced phytoremediation and microbial remediation of DPs-contaminated soil.The study identified the removal efficiency of soil DPs by different types of surfactant-enhanced phytoremediation and microbial remediation,and screened suitable surfactant-enhanced phytoremediation and microbial remediation technologies for soil DPs remediation.Among them,the A+RL-500+L treatment had the most significant effect on the removal rate of soil DPs with 67.2%-85.1%,followed by the M+brij 35-600+R treatment with 62.4%-83.8%removal rate of soil DPs.(5)The effects of soil dominant microbial composition and their interactions and soil enzyme activities on the removal rate of soil DPs were investigated by highthroughput sequencing and enzyme activity experiments.It was clarified that the interaction between surfactant-enhanced plants and microorganisms in the combined treatment of soil with actinomycetes and their closely related dominant microorganisms promoted the removal of soil DPs,with the most significant effects of Actinobacteriota,Firmicutes and MBNT15 bacteria;soil convertase,laccase,polyphenol oxidase,urease and β-glucosidase had significant promotion effects on the removal of soil DPs;based on the enzyme committee number database(EC)comparison results,non-specific oxidases(oxygenases,dehalogenases,hydrogenases,and hydrogenases)produced by soil microbial interactions were identified as the main mechanisms for the ring opening,dechlorination,and removal of soil DPs,and the ring opening degradation pathways of DPs were postulated. |
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