| Co-contamination of heavy metals and pesticides caused by industrial wastewater discharge,sewage irrigation,and heavy use of peaticides is widespresd in the agricultural environment,which severely threatens the quality of ecological environment,agricultural safety production,and human health.After the use of organochlorine pesticides is banned,organophosphorus pesticides have become the main pesticides currently used in agricultural production.In this study,trichlorfon（TCF）,one of the most widely used organophosphorus pesticides in China,and cadmium（Cd）,were taken as the research object.We firstly studied the dose-time effect of TCF-Cd combined contamination on soil biological activities.Subsquently,different bioremediation strategies were applied for studying the removal performance of artificial TCF-Cd co-contamination,and the corresponding removal mechanisms were revealed.The main results were summaried as follows:1.The effects of single and combined pollution from different concentrations of TCF（10 and 100 mg/kg）and Cd（0.8,4,and 40 mg/kg）on soil biological activities after exposure for 21 days.The single treatments of TCF with different concentrations and high-concentration Cd（40 mg/kg）,and TCF-Cd co-exposure significantly increased soil basal respiration in the early period（0 to 3 days）.Soil respiration intensity of these treatments decreased significantly from 7 to 14 days,and no significance was observed compared to the control in the late stage.Soil activities of catalase,urease,invertase,and alkaline phosphatase showed changes of inhibition or promotion with the time under the single and combined treatments of TCF and Cd.Among them,the treatments with 40 mg/kg Cd showed inhibitory effects on these soil enzyme activities.The net nitrogen mineralization rate of the soil decreased on the 1st day in all treatments,then increased rapidly from 1 to 3 days,and then remained relatively stable in the later stage.The single treatment of 100 mg/kg TCF increased the soil total DNA content and the community abundance of bacteria and fungi.40 mg/kg Cd single treatment showed the inhibition in total DNA content and bacterial community abundance,and showed no significant effect on the fungal community abundance in the later culture period.TCF-Cd treatment increased the fungal community abundance,and the total DNA content and bacterial community abundance were higher than that of Cd single treatment.TCF showed a rapid dissipation rate in soil,and Cd concentration had no significant effect on TCF dissipation.The analysis of variance showed that the single and combined effects of TCF concentration,Cd concentration,and culture time had significant effects on most of soil biological activity parameters（P<0.05）.2.Simultaneous trichlorfon degradation and Cd adsorption by Aspergillus sydowii.A.sydowii could grow normally in mineral salt medium containing 100 mg/L TCF and different concentrations of Cd（2,5,and 10 mg/L）,and could simultaneously degrade trichlorfon TCF and adsorb Cd.The maximum removal rates of TCF and Cd（II）were55.52%and 57.90%,respectively,in the treatment of 100 mg·L-1 TCF with 2 mg·L-1Cd（II）.With increased initial Cd concentration,the A.sydowii biomass,TCF degradation rate,and Cd adsorption efficiency decreased,while the Cd adsorption capacity onto A.sydowii increased.The additional exogenous glucose and sucrose significantly increased the A.sydowii biomass and TCF and Cd removal.GC-MS and FTIR results showed that the degradation pathway of TCF was through the hydrolysis reaction of P-C bond cleavage,and the Cd removal was mainly through the chelation reaction between-OH and-NH on the surface of A.sydowii and Cd.In addition,it was observed that the grown A.sydowii pellets could remove TCF and Cd,while the sterilized A.sydowii pellets could only adsorb Cd.3.Simultaneous removal of TCF and Cd from aqueous solution by magnetically separable chitosan beads immobilized A.sydowii（MCBAs）.MCBAs were prepared by mixing chitosan,nano-γ-Fe2O3 and A.sydowii spore suspension in certain proportion,and characterized by SEM,BET,FTIR,XRD and VSM analyses,then used to simultaneously remove TCF and Cd from aqueous solution.MCBAs showed an increased special surface area（55.38 m2/g）through immobilizing A.sydowii and its saturation magnetization reached 14.62 emu/g.The equilibrium removal capacities of TCF and Cd were 135.43 mg/g and 56.40 mg/g in the co-system with 200 mg/L TCF and 50 mg/L Cd,respectively.The removal capacities of TCF and Cd were strongly depended on the immobilized A.sydowii spore concentration,initial concentrations of TCF and Cd,and MCBAs dose.FTIR result displayed that-OH and-NH groups on MCBAs mainly participated in the Cd sequestration and the C=O stretching vibration was possibly related to the degradation intermediates of TCF.MCBAs exhibited excellent recyclability upto four cycles and maintained high removal efficiency.4.Phytoremediation of cadmium-trichlorfon co-contaminated water by Indian mustard（Brassica juncea）.The morphological and physiological responses of B.juncea to the single and combined stress of Cd（2,10,and 50 mg/L）and TCF（10,50,and 200 mg/L）,and the phytoremediation potential of B.juncea to Cd and TCF were investigated under hydroponics.Cd exhibited strong inhibition on biomass and root morphological features of B.juncea as the Cd concentration increased.The chlorophyll a fluorescence intensity and chlorophyll content of B.juncea gradually decreased with the increased Cd concentration,whereas the malondialdehyde and soluble protein contents and superoxide dismutase activity increased.TCF with different concentrations showed no marked influence on these morphological and physiological features of B.juncea.B.juncea biomass and physiological status under the co-exposure of Cd and TCF were predominantly regulated by Cd level.The total Cd accumulation and uptake of B.juncea increased with the increase of Cd concentration.And under the50 mg/L Cd treatment alone,the total Cd uptake in roots and shoots of B.juncea was the highest value（11951 mg/kg and 3071 mg/kg,respectively）.B.juncea also exhibited an efficient TCF degradation performance,and the TCF removal rate was the highest（84.60%）under the treatment of 10 mg/L TCF alone.In addition,a mutual inhibitory removal of Cd and TCF was observed under their co-system,and this mutual inhibition was most obvious especially at high concentrations for both（50 mg/L Cd and 200 mg/L TCF）.5.Bioremediation of Cd-TCF co-contaminated soil by B.juncea associated with A.sydowii.Pot experiments were conducted to investigate the concurrent removal of Cd（two levels:Cd L[10 mg/kg]and Cd H[50 mg/kg]）and TCF（100 mg/kg）from co-contaminated soil by comparing the following remediation methods:natural remediation（NR）,soil inoculated with A.sydowii（AS）,soil planted with B.juncea（BJ）,and soil planted with B.juncea and inoculated with A.sydowii（BJ-AS）.The physiological responses of B.juncea,soil enzyme activities and microbial community abundance after remediation were also studied.The results showed that B.juncea grew well in co-contaminated soil at both Cd levels.The biomass and chlorophll content of B.juncea in Cd H-TCF soil were lower than those in Cd L-TCF soil,whereas the contents of malondialdehyde soluble sugar,and activities of catalase,peroxidase and superoxide dismutase of B.juncea in Cd H-TCF soil were higher than those in Cd L-TCF soil.Cd accumulation in B.juncea was high in Cd H-TCF soil,whereas high Cd removal efficiency was observed in Cd L-TCF soil.TCF could be thoroughly degraded within 35days in NR at both Cd-level soils.AS,BJ and BJ-AS promoted TCF degradation and enhanced the activities of catalase,urease,sucrase and alkaline phosphatase in soil compared with the NR.BJ-AS showed the highest phytoextraction ratio（3.32%in Cd L-TCF and 1.34%in Cd H-TCF soil）and TCF degradation rate（half-life of 2.18 and 2.37days in Cd L-TCF and Cd H-TCF soil,respectively）.AS and BJ-AS significantly increased the number of TCF-degrading microorganisms in soil.BJ and BJ-AS significantly increased total DNA content and bacterial community abundance in soil. |
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