Phytoremediation Of Heavy Metal Contaminated Soils With Mobilizing Amendments

Heavy metal pollution is one of the most serious environmental problems across the world.Heavy metals can not only do harm to the ecosystem,but also endanger human health.Heavy metal contaminated soils in northern China are calcareous soils with high p H,heavy metals in these soils are difficult to be stabilized.Phytoremediation may be a decent remediation choice for heavy metal contaminated calcareous soils,however,so far there is no successful phytoremediation technology for calcareous soils.The main purpose of this study is to explore the feasibility of soil mobilizing amendments combined with phytoremediation for the remediation of calcareous soil,and to evaluate the environmental risk of amendment application in soil,so as to provide reference for the remediation of heavy metal calcareous contaminated soil in northern China.Main results of this work are as follows,（1）Four chemicals（Na Cl,HCl,EDDS and citric acid）were added to two soils(Xinxiang soil,total Cd:6.77 mg kg^-1,<0.01 mm particle:9.8%;Jiyuan soil,total Cd:5.72mg kg^-1,total Pb:312 mg kg^-1,<0.01 mm particle:29.8%)and then cultivated.The results showed that the activation efficiency of Na Cl and HCl on Cd were significant,reaching71.87%and 74.87%in Xinxiang soil,respectively;the activation efficiency of Na Cl and HCl on Cd were significant,reaching 53.44%,48.44%in the Jiyuan soil,respectively;the activation efficiency of EDDS on Pb was significant,reaching 55.21%in the Jiyuan soil.Our study indicated that soil texture may play an important role on the activation efficiency of heavy metal in these two soils.（2）Field experiments were conducted to study the remediation effects of the combined amendments（sodium chloride and citric acid）of Bidens pilosa L and Solanum nigrum L on the heavy metal contaminated farmland soil(total Cd:3.06 mg kg^-1)in Xinxiang,Henan Province.The results showed that sodium chloride contributed more to the plant accumulation of Cd,the accumulation of Cd of Solanum nigrum L with sodium chloride amendment increased by 15.72%than the control.Citric acid contributed more to the accumulation of Cd in Bidens pilosa L the accumulation of Cd of Bidens pilosa L increased by 4.76%with citric acid amendment than the control.The accumulation of Cd in Solanum nigrum L was 1.94-2.32 times fo that of Bidens pilosa L Therefore,sodium chloride combined with Solanum nigrum L had better remediation effect for the cadmium contaminated farmland in this work,but the efficiency of phytoremediation still needed to be improved.（3）Two irrigation rates（1 time and 3 times of precipitation）and two amendments（sodium chloride and citric acid）were used to conduct simulated leaching tests on indoor soil columns to investigate their effects on heavy metal leaching in soil.The results show that,Cd and Zn migrated 1-2 cm in the soil profile,while Cu migrated 1-5 cm,indicating that Cu is more mobile than Cd and Zn.Compared with citric acid treatment,sodium chloride treatment is more conducive to the migration of heavy metals in the soil.In addition,Cd can migrate more than 2 cm while Cu can migrate more than 5 cm under three time precipitation irrigation with citric acid and sodium chloride amendments,indicating that increasing irrigation rate can promote the leaching of heavy metals in the soil.（4）In order to explore the time effect of the amendment,two chemicals（EDDS and sodium chloride）were applied in a contaminated soil with plant,and then the soil and plants were sampled and analyzed at four time intervals.The results showed that,the contents of DTPA-extractable Pb,Cd,Cu and Zn in soil significant increased after 3 to 10 days of EDDS treatment.After 25 days,there was no significant difference in the content of DTPA-extractable heavy metals compared with the control.After 3 to 10 days of sodium chloride amendment,the contents of DTPA extractable heavy metals were not significantly different from the control,but increased significantly after 25 days.Twenty-five days after EDDS and sodium amendment,the accumulation of Cd in the plants reached the maximum of 34.97 and 41.85μg pot^-1,respectively,which increased by 0.16%and 10.92%compared with the control,respectively.The above results indicated that due to the degradation of EDDS in soil,the activation of soil heavy metals could only last for less than 20 days,while the amendment of soil heavy metals by inorganic amendments could last longer.