| Dechlorane Plus（DP）is a typical halogenated flame retardant with persistence,biotoxicity and ecological risk.The study on the migration and transformation mechanism of DP in soil-plant system can provide a theoretical basis for the research and development of safe and effective phytoremediation technology,and has important practical significance for preventing halogenated flame retardant pollution in soil and ensuring the safety of human settlements.In this paper,the distribution of DP and the changes of its isomers in roots,stems and leaves of three plants and their corresponding rhizosphere and non-rhizosphere soils in e-waste recycling sites were studied,and the main intermediate degradation products and degradation pathways of DP in soil-plant system were preliminarily identified according to the chromatograms and secondary mass spectra obtained by full scanning mode of gas chromatography-triple quadrupole mass spectrometry（GC-MS/MS）.According to the results of semi-quantitative analysis of degradation products by using peak area ratio,the distribution of degradation products was discussed,and according to the results of the research on DP and its degradation products,it was concluded that Solanum nigrum had the best advantage in remediation of DP pollution in soil.Through the experiment of planting Solanum nigrum in DP contaminated soil,the germination of Solanum nigrum seeds under DP stress was discussed,and the changes of bacterial and fungal communities in soil were analyzed by high-throughput sequencing technique.The effects of laccase concentration,p H value in soil,temperature and the condition of adding manganese dioxide on the degradation of DP by laccase were studied by the method of controlling variables.By studying the above contents,four main results in this paper was obtained as follows:（1）DP concentration of the whole plant showed the rule of Solanum nigrum>Poa pratensis>Solidago decurrens Lour.Due to the adsorption of roots,the concentration of DP in rhizosphere soil was higher than that in non-rhizosphere soil.Due to the different accumulation abilities of plants,the accumulation of DP in the roots of Solanum nigrum was higher than that of Poa pratensis and Solidago decurrens Lour.The transport abilities from root to stem and leaf of the three plants were weak,and there was no significant difference.There existed the phenomenon of preferential enrichment of syn-DP or preferential degradation of anti-DP in rhizosphere soil.（2）23 kinds of intermediate degradation products were identified,which were summarized as dechlorination,oxidation,cracking and isomerization,including dechlorination,ring opening,reverse diene synthesis,aldehyde,carboxylation,hydroxylation,epoxidation,isomerization and so on.It was speculated that they may eventually be mineralized into H2O and CO2,or converted into biomass.According to the distribution of the ratios of all products,combined with the distribution of DP,it was determined that Solanum nigrum was dominant in the degradation of DP in soil,especially its root enrichment,organic matter secretion,degradation and so on.（3）Obviously,Solanum nigrum seeds showed low tolerance to DP concentration of 3000 ng·g-1 in soil,the dormancy period of seeds was prolonged and the germination rate decreased,while DP with concentration of 200-2000 ng·g-1 in soil could stimulate the germination of Solanum nigrum seeds.From the changes of microbial community,DP stress and Solanum nigrum planting increased the abundance and species diversity of bacteria in soil;in fungus,Solanum nigrum promoted abundance and diversity,but DP reduced fungal diversity.In terms of the contribution of the two factors,the differences of bacterial species caused by plant was higher than that caused by DP pollution,which was on the contrary in the changes of fungal community,so the microbial abundance and diversity under the combined action of two factors depended on the degrees of contribution of single factors.（4）In the range of laccase concentrations from 0 to 14 U/g in soil,the DP degradation rate increased with the increase of enzyme concentration,while the increase of DP degradation rate decreased.The optimum p H value of degradation was about 4.5 and the optimum temperature is about 25℃.Manganese dioxide itself could degrade DP.The degradation rate of DP can reach 70.28%under the action of 2%manganese dioxide alone,and 59.85%under the action of laccase alone,and 87.34%when they acted together,which is less than the sum of individual degradation rates.The results proved that manganese dioxide can reduce the activity of laccase to a certain extent,thus inhibiting the degradation of DP by laccase. |
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