Study On Phytoremediation Of Soil Co-contaminated By Heavy-metal And Tetracycline

With the rapid development of economy and society,people's living standards have been constantly improved,intensive livestock and poultry breeding industry has been developing rapidly.At the same time,a large number of untreated livestock and poultry manure is applied to farmland as fertilizer.Heavy metals and antibiotics in livestock and poultry manure then enter farmland,which causes the co-contamination of farmland and poses a serious threat to agricultural production and the soil ecosystem.After the pollutant enter the soil environment and enter the human body through the food chain and other means,the accumulation of pollutants in the body through biomagnif ication effect will inevitably lead to serious consequences.Therefore,it is urgent to explore the technology of economical,environmentally friendly and efficient remediation technology for contaminated soil.In this study,the common hyperaccumulators,Tagetes patula L.,Medicago sativa L.,and Mirabilis jalapa L.were used as tested plants,and cadmium(Cd),copper(Cu)and tetracycline antibiotics(TCs)were used as contaminant.Pot experiments were conducted to explore the remediation effect of different methods on co-contaminated soil,and to explore species and planting patterns(monoculture and intercropping)on the influence mechanism of the morphology of heavy metals in the rhizosphere of plants and pollutant removal capacity.The main findings are as follows:(1)In the co-contamination treatment,low concentration of heavy metal stress(Cd 2.5mg/kg,Cu 200mg/kg),M.jalapa growth is inhibited,while the medium concentration(Cd 5mg/kg,Cu 400mg/kg)and high concentration(Cd 10mg/kg,Cu 600mg/kg)heavy metal stress,M.jalapa growth is promoted,but the promoting effect gradually decreased with the increase of TCs concentration.Intercropping of T.patula and M.sativa,TCs stress inhibited the growth of T.patula and promoted the growth of M.sativa;while heavy metal stress inhibited the growth of T.patula,the growth of M.sativa was promoted in low concentration,and the high concentration was inhibited;The growth of T.patula and M.sativa was inhibited under co-contamination stress.The biomass of T.patula of intercropping was significantly lower than that of monoculture,and the corresponding treatments decreased by 67.16%,49.20%,79.34% and 43.75%,respectively,while the biomass of M.sativa of intercropping was lower than that of monoculture.(2)M.jalapa Cd,Cu concentration and accumulation are higher than single heavy metal stress under co-contamination treatment,treated in C1T2(Cd 2.5mg/kg,Cu 200mg/kg,TCs 2.0mg/kg),the concentration of Cd in root,stem and leaf increased by 55.97%,10.21% and 13.37% compared to C1T0(Cd 2.5mg/kg,Cu 200mg/kg,TCs 0mg/kg)respectively.It is shown that the co-contamination of TCs and heavy metal can promote the absorption and accumulation of heavy metals to M.jalapa.Intercropping of T.patula,the concentration of heavy metal is higher than monoculture,and Cd transport capacity is higher than monoculture,but because its biomass is signif icantly lower than monoculture,so the accumulation is lower than monoculture;T.patula enrichment and transport capacity of heavy metals is higher than M.sativa,and the enrichment ability under the stress of low-concentration heavy metals is higher than in high concentrations,while TCs co-contamination promotes the Cd transport capacity of T.patula.(3)The concentration of available heavy metal in the M.jalapa rhizosphere was higher than that in the CK group,and the co-contamination group is higher than that of single heavy metal contamination group,which show n that M.jalapa can activate the rhizosphere heavy metal,and the combination of TCs and heavy metal can further enhance the concentration of available heavy metal.M.jalapa can absorb freely dissolved Cd in soil solution to make it lower than the CK group,in C2(Cd 5mg/kg,Cu 400mg/kg)treatment,M.jalapa rhizosphere freely dissolved Cd compared with CK group reduced by 27.57%,9.11%,5.68%,14.69%,respectively.M.jalapa can improve soil environmental quality and morphology of heavy metals in rhizosphere soil,and ultimately affect the biomass and heavy metal content of corn.Intercropping of T.patula and M.sativa also can activate the rhizosphere heavy metal,improve it the biological availability concentration.Cu concentration of freely dissolved sequence is: monoculture > intercropping >CK.The ability of Cd activation of intercropping is stronger than monoculture,and there are significant differences in the activation ability of Cd and Cu.(4)The concentration of heavy metals in M.jalapa tissue was positively correlated with the bioavailability state,free dissolved state,weak acid extractable state and reducible state heavy metals in soil,and the correlation coefficient with Cd was greater than that with Cu.There was a signif icant positive correlation between the Cd content in the shoot of T.patula and the bioavailability state,free dissolved state,and oxidizable heavy metal states of soil(p < 0.01),and there was also a signif icant positive correlation between the Cd concentration in the shoot and in the root(p<0.01).The concentration of heavy metals in M.sativa tissues had the highest correlation with the concentration of the bioavailability state and the extractable state of the weak acid state.(5)In all treatments,the removal rate of TCs was higher than 98%,and the residual amount of TCs was in the order of TC > OTC > CTC.In low conc entration TCs co-contamination treatment,M.jalapa remediation promoted the removal of TC;M.jalapa reduced the removal rate of TC in high concentration TCs co-contamination treatment.Remediation of M.jalapa inhibited OTC and CTC degradation in rhizosphere soil.Compared with the control group(CK),the degradation of TC and CTC in rhizosphere was promoted by monoculture of T.patula.,the removal effect of TCs by M.sativa monoculture was better than intercropping,and the intercropping of T.patula and M.sativa can promote the removal of TC and OTC in rhizosphere and inhibit the removal of CTC in rhizosphere.The residual amount of TCs in the co-contamination treatment was lower than that in the treatment of TCs alone.