Study On Remediation Of Cd Contaminated Soils By Mixed Amendments

Cadmium(Cd)is the most concerning soil pollutant and threat to human health in China,in the views of increasing soil Cd pollution,in-situ immobilization by amendments,is one of the most widely adopted method to remedy soils contamination by heavy metals at national and international levels.In this study,we used two mixed amendments M1 and M2 that consist of lime,zeolite,calcium superphosphate and biochar with 47:47:5:1 and 71:23:5:1 ratio as for the study objectives,amendments were added in Cd enriched soils prepared artificially in lab,incubation study was done in lab and pot experiment was done in greenhouse by adopting rotation of rice and rape(Brassica Chinensis L.),moreover field experiment in Cd-contaminated soil was also performed.we studied the effect of types and doses of mixed amendments on soil exchangeable Cd,bioavailable Cd in plants and crop yield.According to experimental designs the main findings are as follows:1.Incubation study:5 levels(T1:0.5%;T2:1%;T3:2%,T4:4%;T5:10%)of mixed amendments(Ml,M2)were added in Cd-contaminated soil which showed remediation effects mainly by increasing soil pH to reduce the contents of exchangeable Cd in soil.Higher levels of amendments(T3,T4 and T5)significantly decreased soil exchangeable Cd contents at the early stage of incubation,while lower level(T1 and T2)continued to decrease soil exchangeable Cd contents during the incubation period.After pre-incubation,on the first day of samplings,soil exchangeable Cd contents decreased by 99.42%and 99.79%in M1T4 and M2T3 treatments compared with CK,soil exchangeable Cd contents decreased by 81.36%to 94.29%in M1T1,M1T2 and M2T1 treatments after 90 days of incubation.2.Pots experiment:Soil pH was the main factor affecting the yield and bioavailability of Cd in rice and rape.Compared with CK,the yield of rice under treatments of M1T1 and M2T1 increased by 8.93%and 8.36%respectively and the biomass(fresh weight)of rape under treatments of M1 and M2 increased by 2.52-2.98 times and 0.76-2.89 times respectively under all levels except M1T4.Mixed amendments M1 and M2 could significantly reduce the total Cd in rice and rape,and the total Cd in plant decreased with the increase in the level of amendments.However,at the same level,the effect of mixed amendments of M2 was slightly better than that of mixed amendments M1.The total Cd in brown rice treated with M1T3 and M2T3 compared with CK decreased by 89.25%and 93.16%respectively,and the total Cd in rape(fresh weight)under M1T4 and M2T4 decreased by 94.14%and 94.47%respectively.Moreover,the abundance of ammonia oxidation and denitrification microorganisms mainly affected by Soil pH.When the amendments level increased from T1 to T4,the gene abundance of AOA,AOB,nirK,nirS and nosZ(I)tended to decrease in rice season;on the other hand,the gene abundance of AOB,nirS and nosZ(I)increased first and then decreased,and the gene abundance of AOA and nirK showed reduction overall in rapes season.3.Field experiment:Mixed amendment M2(3 levels of RM1:0.1%;RM2:0.2%;RM3:0.5%)and pure lime(LM:0.5%lime)were selected for field experiment of wheat-rice rotation.Results showed that mixed amendments decreased the bioavailability of Cd in soil which was mainly due to increase in soil pH,additionally due to the external factors such as weather,tillage and the time of amendments application in the soil had an important impact on the effectiveness of mixed amendments.Mixed amendments significantly increased soil pH and EC,decreased soil exchangeable Cd,and increased wheat yield,but did not showed significant difference in rice yield.In wheat season,under each treatment,soil pH compared with CK increased by 12.92%-36.53%,soil exchangeable Cd decreased by 71.52%-97.07%,and wheat yield increased by 20.90%-61.58%.In rice season,in all treatments,soil pH increased by 2.37%-17.93%,and soil exchangeable Cd was comparatively higher than that of wheat season.The total Cd in rice roots and shoots is higher than wheat.The total Cd in wheat grains treated with RM1,RM3 and LM,and brown rice treated with other treatments except RM1 could meet the food safety standard by adopting our designed treatments.However,adding mixed amendments can reduce the total Cd contents in wheat and rice.