Effects Of Different Additives On The Properties Of Heavy Metals And Phytoremediation In Calcareous Contaminated Soils

Heavy metal pollution of farmland soil poses a threat to both crop quality and human health.A large number of studies have investigated the remediation of soil heavy metal pollution,but these studies are mostly focused on the acidic soil in the south,the remediation of the calcareous heavy metal contaminated soils in the north is not well explored.In this study,remediation of calcareous heavy metal contaminated soil was investigated by indoor pot experiments,indoor soil culture experiments and field experiments.The results are as follows,（1）The results of indoor soil culture experiments show that phosphate+bentonite amendment had lower Olsen-P concentrations（13.0 and 16.3%in the acidic and the calcareous soils,respectively）,compared to the phosphate only treatment.Lime amendment greatly reduced DTPA-extractable concentrations of heavy metal in both soils.In the acidic soil,3 and5 g kg^-1 lime amendment resulted in 23.4 and 35.0%greater Olsen-P concentrations than the control,respectively,while in the calcareous soil,these values were 5.30 and 11.5%,respectively.The results suggest that phosphate+bentonite can be used to reduce heavy metal and P availability in heavy metal contaminated soil,yet when lime is used,caution should be noted with respect to potential soil P losses.（2）The results of indoor pot experiments show that lime amendment resulted in decreased soil DTPA-extractable heavy metal concentrations in both acidic and calcareous soils（54.5 and 15.7%lower than the control in the acidic and calcareous soil,respectively）,increased plant yield,and decreased shoot accumulation of most metals.Calcium nitrate and calcium chloride amendments resulted in decreased plant yield and elevated plant shoot heavy metal concentrations in both soils.The calcium chloride amendment also resulted in elevated soil DTPA-extractable Cd,Zn,and Mn concentrations（32.5-350%greater than the control）and elevated shoot Cd,Zn,and Mn concentrations（11.1-351%）in both soils.The results show that it is feasible to apply lime to calcareous heavy metals contaminated soil in northern China,while calcium chloride and calcium nitrate have strong activation effect on the soil heavy metals（3）Lime and potassium chloride were amended at two dosages in calcareous cadmium polluted soil[lime:0.39（L1）and 0.78 kg m^-2（L2）;potassium chloride:10（P1）and 20 g m^-2（P2）]and Sedum plumbizincicola was planted in a field experiment.The results showed that,compared with the control,soils contents of DTPA-Cd in P1,P2,L1 and L2 treatments changed by 3.72,15.3,-23.6 and-1.46%,respectively;the Cd content of the Sedum plumbizincicola in P2,L1 and L2 treatments changed by 14.9,-6.37 and-5.83%,respectively;the yields of Sedum plumbizincicola of P1,P2,L1 and L2 increased by 30.3,8.24,35.2 and15.5%,respectively,and the cadmium accumulation of Sedum plumbizincicola increased by51.5,29.2,27.2 and 14.3%,respectively.These results indicate that potassium chloride can increased cadmium availability in calcareous cadmium contaminated soils and lime can decreased cadmium availability,but both additives can increased plant yield and absorption of Cd by plants in soil.（4）Sedum plumbizincicol were planted in calcareous cadmium polluted soil,Zea mays L.and Sorghum bicolor（L.）were intercropped with Sedum plumbizincicol to achieve shading effect.The experiment had the following treatments,CK-Sedum plumbizincicol only,C1/S2-one row of corn/sorghum with one row of Sedum plumbizincicol,and C2/S2-one row of corn/sorghum with two rows of Sedum plumbizincicol.The results showed that,compared with the control,C1 increased DTPA-extractable concentrations of Cd,Cu,Mn,Ni,Pb and Zn in soil;Cd content of the Sedum plumbizincicol of treatments C1 and C2 increased by 83.1and 58.7%,respectively;the contents of DTPA extractable heavy metals in S1（except Mn）and S2（except Zn）soils decreased,and the contents of Cd,Zn,Pb and Mn of Sedum plumbizincicol of these two treatments were greater than the control.Compared with the control,Sedum plumbizincicol yield increased of C1 and C2 treatments.These results indicate that intercropping of maize and Sedum plumbizincicol can increase the absorption of Cd by Sedum plumbizincicol and promote phytoremediation.However,the yield of Sedum plumbizincicol on calcareous soil was low,so the cultivation method of Sedum plumbizincicol still needs to be discussed.