| Recently, the Cd pollution of soil has posed a serious threat to food safety and human health, which has attracted more and more attention. Among the remediation technologies for soil heavy metal pollution control, in situ chemical immobilization technology is prospective because of its high remediation efficiency and low cost. Seeking the effective amendments are the focus for the successful remediation. The remediation results were different from the soil properties, the types and extent of heavy metal elements, the types and amounts of passive materials. In this study, five materials were selected by soil incubation experiment from ten materials. The corresponding passivation influence of different addition of the five materials soils was studied under pot conditions. The effect of the five materials applied in Cd polluted farmland was discussed as well. The main results are presented as follows:(1) The results of soil incubation experiment showed that, the ten materials (straw biochar, building biochar, sepiolite, Ca-bentonite, white marble, mushroom residue, fly ash, slag, diatomite and shale) could significantly reduce the available Cd content in neutral and acid Cd-contaminated soil in different incubated time, and the lower range increased with the increasing amount of materials. With the extension of incubated time, the available Cd content of the two kinds of soil both showed the trend of decreasing firstly and then stable. After 60 days incubated, the available Cd content in neutral and acid soil were decreased by 9.13%～39.29% and 3.10%c31.52%. The effects of ten materials on the Cd forms in the two kinds of soil were mainly the transformation from the acid extractable Cd to the residual Cd when incubated for 60 days. Meanwhile, the percentage of acid extractable Cd in neutral and acid soil decreased 0.73%～8.30% and 1.08%～13.33% respectively, and that of residual Cd increased 0.43%～5.92% and 1.35%～10.04%. Among the ten materials, building biochar, fly ash, straw biochar, sepiolite, white marble and shale had better passivation effect than other materials in both neutral and acid Cd-contaminated soil.(2) The results of the pot experiment indicated that straw biochar, fly ash, sepiolite, white marble and shale increased the neutral and acid Cd-contaminated soil pH and CEC. Under the amendment treatments, the pH in the neutral and acid soil increased 0.16～0.99 and 0.22～1.88 unit, and the CEC increased by 1.71%～48.52% and 0.80%～43.91%, compared with the control. The soil available Cd content in neutral and acid soil were significantly reduced by 4.61%-26.48% and 6.44%～37.22% in a dose-effect manner. Applying the five amendments made the acid extractable Cd in the two kinds of soils transform to the residual Cd, and that changed more obviously with the increase of application of materials. Compared with the control, the percentage of acid extractable Cd in neutral and acid soil decreased 0.73%～8.30% and 1.06%～13.33%, and that of residual Cd increased 0.43%-5.92% and 1.35%～10.04% respectively. The five amendments significantly reduced the Cd content in edible part of Brassica chinensis L. grown in two kinds of Cd-contaminated soil, which presenting good after effect. Compared with the control treatment, the Cd content in edible part of Brassica chinensis L. grown in neutral and acid soil decreased by 22.35%～77.65% and 14.84%-91.02%, respectively. Therefore, straw biochar, fly ash, sepiolite, white marble and shale could effectively reduce the bioavailability of Cd.(3) The biomass in shoot of Brassica chinensis L grown in two kinds of Cd-contaminated soil significantly increased under straw biochar, fly ash, sepiolite, white marble and shale treatments, which was 2.25～11.78 times higher than the control treatment in acid soil, and that increased by were 0.56%～44.42% in neutral soil. With the increase amount of the amendments, the biomass of Brassica chinensis L. grown in neutral Cd-contaminated soil firstly increased and then decreased, while that in acid Cd-contaminated soil increased firstly and then had no obvious change. Compared with the control, the vitamin C, soluble sugar and soluble protein content of Brassica chinensis L. grown in neutral soil under amendment treatments increased by 1.58%～22.92%,1.29%～17.16% and 1.78%～16.4% respectively, and that in acid soil presented as 2.92%-33.82%,1.95%～36.38% and 1.10%-28.37%. At the same time, the content of nitrate reduced by 1.48%～16.77% and 0.60%～25.27% respectively. The straw biochar, fly ash, sepiolite, white marble and shale not only effectively promoted the growth of Brassica chinensis L., but also improved its quality.(4) The field experiments indicated that straw carbon, fly ash, sepiolite, white marble and shale increased paddy (first crop) and upland (second crop) soil pH and CEC, and decreased the available Cd content by 12.21%-22.53% and 14.04%-25.00% respectively. Under the amendment treatments, the acid extractable Cd translated into the residual Cd in paddy soil, while the acid extractable Cd translated into the reducible Cd and residual Cd in upland soil. Five amendments all dramatically reduced the Cd content in each part of rice and Brassica chinensis L. And the Cd content in brown rice and edible part of Brassica chinensis L. were reduced by 35.65%-58.65% and 31.67%-49.17%. Furthermore, the Cd content in brown rice under straw carbon and white marble treatments and the Cd content in edible part of Brassica chinensis L. under amendment treatments were all lower than the National Food Safety Standard. Five amendments had no significant effect on rice yield, but the yield of Brassica chinensis L. significantly increased under straw biochar and fly ash treatments.Overall, straw carbon, fly ash, sepiolite, white marble and shale could reduce the Cd activity in soil and the Cd content of crops, as well as make the yield of crops stable or improved. Straw biochar, white marble and fly ash performed more prominent, therefore, they could be used as better amendments for the remediation of Cd-contaminated soils. |
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