Purpose

This study aims to investigate the dynamic changes over time in the immobilization efficiency of hydroxyapatite, bentonite, and biochar for Cd and Pb co-contaminated soil given the potential remobilization of immobilized heavy metals for long-term stabilized soils.

Materials and methods

Hydroxyapatite, bentonite, and biochar were applied only once at 2.5% (w/w) of soil during a 5-year pot experiment with pepper-cabbage (Capsicum annuum L.-Brassica pekinensis) rotation. The dynamic changes of soil pH, soil organic carbon (SOC), TCLP (toxicity characteristic leaching procedure)-, DTPA-, and PBET (simulated human gastric solution extraction)-Cd and Pb in soil, fractionation of Cd and Pb in soil, as well as the dynamic variations of bioaccessible Cd and Pb in vegetables were determined.

Results and discussion

The results indicated the application of hydroxyapatite, bentonite, and biochar significantly increased the proportion of residual fraction of Cd and Pb, and reduced the mobility, bioavailability, and bioaccessibility of Cd and Pb analyzed by TCLP, DTPA, and PBET, respectively. Moreover, the concentrations of TCLP-, DTPA-, and PBET-Cd and Pb gradually increased over time. The proportions of acid-extractable Cd and Pb in amended treatments in 2019 were higher than those in 2016. The increment for acid-extractable Cd fraction was 4.69%, 5.53%, and 4.19% in hydroxyapatite, bentonite, and biochar, respectively. While the increment for acid-extractable Pb fraction was 1.48%, 2.08%, and 1.91%, respectively. The bioaccessible Cd and Pb in pepper and cabbage significantly decreased after remediation while no remarkable changes were observed for Pb from 2017 to 2019.

Conclusions

The three amendments were effective ameliorants for Cd and Pb co-contaminated acidic soil, but the immobilization efficiency decreased over time. Moreover, hydroxyapatite showed the highest efficiency on metal stabilization and vegetable safety.

中文翻译：

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将镉和铅固定在受污染的酸性土壤中，并用羟基磷灰石，膨润土和生物炭进行改性

目的

这项研究旨在研究在固定化重金属对长期稳定化土壤的潜在迁移作用下，羟基磷灰石，膨润土和生物炭对Cd和Pb共污染土壤固定化效率随时间的动态变化。

材料和方法

羟基磷灰石，膨润土，和生物炭是在土壤的2.5％（W / W）一个5年的盆栽试验过程中施加一次辣椒，白菜（辣椒L.-大白菜）旋转。土壤pH，土壤有机碳（SOC），TCLP（毒性特征浸出程序）-，DTPA-和PBET（模拟人胃液提取物）-土壤中Cd和Pb的动态变化，土壤中Cd和Pb的分馏，确定了蔬菜中生物可利用的镉和铅的动态变化。

结果与讨论

结果表明，分别通过TCLP，DTPA和PBET分析，应用羟基磷灰石，膨润土和生物炭显着增加了Cd和Pb的残留分数，降低了Cd和Pb的迁移率，生物利用度和生物可及性。而且，TCLP-，DTPA-和PBET-Cd和Pb的浓度随时间逐渐增加。修订后的处理方法中，2019年可提取酸的Cd和Pb的比例高于2016年。羟基磷灰石，膨润土和生物炭中可提取酸的Cd比例分别为4.69％，5.53％和4.19％。酸可萃取的Pb分数的增量分别为1.48％，2.08％和1.91％。

结论

这三种改良剂是对Cd和Pb共同污染的酸性土壤的有效改良剂，但固定效率随时间降低。此外，羟基磷灰石在金属稳定性和蔬菜安全性方面显示出最高的效率。