| The coexistence of heavy metals and phthalates was common in vegetable base soils in China attributed to the extensive use of sewage irrigation,sludge farming,pesticides,fertilizers,plastic films and other products.The detection rate of Cd and DnBP was high and the pollution was serious.Heavy metals and organic compounds interacted with each other when they entered into the soil,which changed the existing forms of the two kinds of pollutants in the soil and affects their ecological toxicity and environmental behavior.In this paper,the soil of Xinmin Vegetable Base in Shenyang was used as the test soil to study the response law of the forms of Cd and DnBP in soil,the microbial degradation law of DnBP,the soil microbial activity and the composition of soil bacterial community to compound pollutants.It could be used to reveal the changes andmechanismof bioavailability of Cd and DnBP under the condition of compound contamination and provide scientific basis for the evaluation,early warning and remediation of farmland soil contamination.The effect of DnBP compound pollution on the bioavailability of cadmium in soil was studied by BCR four-state extraction combined with flame atomic absorption spectrometry.The results showed that the bioavailability coefficients of Cd in the soils treated with combined contamination were significantly lower than those of the control group on the 7th to 42th day,but there was no significant difference among the treatments on the 56th day.It indicated that the bioavailability coefficient of Cd decreases under the condition of combined pollution,and DnBP had antagonistic effect on the bioavailability of Cd,but the antagonistic effect gradually weakened with the prolongation of pollution time.The effect of Cd compound pollution on the forms of DnBP in soil and the degradation of DnBP by microorganisms was studied by means of comprehensive separation of soil humus and ultrasonic extraction-gas chromatography.The results showed that with the increase of Cd concentration,the content of DnBP in humin,fulvic acid and water-soluble substances decreased,and that of DnBP in humic acid increased gradually.The microbial degradation curves of DnBP in soils accorded with the first-order kinetic equation.The half-lives of DnBP(100 mg·kg-1)and 0.5,1,5,10,20mg·kg-1 Cd were 4.847,5.545,5.975,6.027 and 6.189,respectively.With the increase of Cd concentration in soil,the half-life of DnBP degradation was prolonged,which indicated that Cd inhibited the microbial degradation of DnBP in soil and showed antagonistic effect.Soil culture experiment,gas chromatography,spectrophotometry and 16S rDNA high-throughput sequencing were used to study the response of soil basic respiration,soil dehydrogenase activity and soil bacterial community composition to repeated pollution.The results showed that low concentration of Cd promoted soil basal respiration at the initial stage,then turned to inhibition,while high concentration of Cd inhibited it,and the inhibition effect increased with the increase of Cd concentration.Compound pollution with DnBP changed soil microbial community structure and decreased soil microbial richness,diversity and evenness.Cd inhibited Chloroflexi and Acidobacteria and promoted Firmicutes,but had no obvious effect on Proteobacteria,Planctomycetes,Bacteroidetes and Actinobacteria.Redundancy analysis showed that11 kinds of bacteria were correlated with DnBP degradation in soil.The abundance ofDyella and Acidobacteriaceaehad a significant positive correlation with Cd treatment concentration,others were negatively correlated with Cd treatment concentration,among which Ralstonia was negatively correlated with Cd treatment concentration. |
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