Abstract

Purpose

Magnetic removal techniques using functionalized magnetic nanoparticles as adsorbents have been frequently tested for use in the removal of heavy metals in aqueous solution, but seldom in farmland soil. Here, a novel magnetic microparticle solid chelator (MSC) was employed as the adsorbent for magnetic removal and/or immobilization of Cd and Zn in a paddy soil (PS), an upland soil (US), and a paddy–upland rotation soil (RS) with different degrees of pollution.

Materials and methods

MSC was applied to 14 kg air-dried soil samples (PS, US, and RS) at the dosage of 1% (w/w), and then watered, and intermittently stirred. Finally, the MSC–metal complexes were retrieved using a magnetic device (MCR treatment) or not (MC treatment), and the removal efficiency of soil Cd and Zn in MCR treatment was evaluated. After magnetic separation of MSC–metal complexes, pot experiments were performed to investigate the impacts of the magnetic remediation process on rice growth, the phytoavailability of soil Cd and Zn, and the accumulation of Cd and Zn in rice plants.

Results and discussion

The MCR treatment exhibited recovery rates of 55.4%, 49.6%, and 19.0% for MSC–metal complexes in PS, US, and RS, respectively, which brought about removal efficiencies of 2.2–12.2% for Cd and 1.9–4.6% for Zn. The MC and MCR treatments substantially decreased the availability of soil Cd, but not soil Zn; this effect was more remarkable when using CaCl₂ instead of DTPA as the extractant for determination of bioavailable metals. Furthermore, the CaCl₂-extractable Cd and Zn had a more significant relationship with Cd and Zn concentrations in rice roots. The MC and MCR treatments led to dramatic reductions in rice grain Cd of 23.9–72.1% and 37.3–63.9%, respectively, in the three soils relative to the respective controls. The MC and MCR treatments also exhibited an inhibitory effects on rice grain Zn accumulation in US (10.6% and 4.3% decreases, respectively) and RS (9.3% and 19.5% decreases, respectively), but not in PS. Moreover, the grain yield was unaffected under the MCR treatment in the three soils, and significantly increased by 29.8% under the MC treatment in US.

Conclusions

Our study suggests that MSC-based magnetic remediation technique can effectively immobilize and/or remove Cd and Zn in farmland soils, decreasing their uptake by rice plants, with no adverse effects on grain yield.

中文翻译：

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磁性微粒固体螯合剂对污染土壤中的镉和锌的磁性去除/固定及其对水稻种植的影响

摘要

目的

使用功能化磁性纳米粒子作为吸附剂的磁性去除技术已被频繁测试用于去除水溶液中的重金属，但很少在农田土壤中使用。在这里，一种新型的磁性微粒固体螯合剂（MSC）被用作吸附剂，用于在稻田（PS），旱地（US）和稻田-旱地旋转土壤（C）中磁性去除和/或固定Cd和Zn。 RS）具有不同程度的污染。

材料和方法

将MSC以1％（w / w）的剂量应用于14 kg风干的土壤样品（PS，US和RS），然后浇水并间歇搅拌。最后，使用或不使用磁性装置（MCR处理）（MC处理）回收MSC-金属配合物，并评估了MCR处理中土壤Cd和Zn的去除效率。磁性分离MSC-金属配合物后，进行盆栽实验，研究磁修复过程对水稻生长，土壤Cd和Zn的植物利用率以及水稻植物中Cd和Zn积累的影响。

结果和讨论

在PS，US和RS中，MCR处理对MSC-金属配合物的回收率分别为55.4％，49.6％和19.0％，这对Cd和Zn的去除效率分别为2.2-12.2％和1.9-4.6％。 。MC和MCR处理大大降低了土壤Cd的利用率，但不降低土壤Zn的利用率。当使用CaCl ₂代替DTPA作为确定生物利用金属的萃取剂时，该效果更为显着。此外，CaCl ₂可提取的Cd和Zn与水稻根中Cd和Zn的浓度之间存在更显着的关系。相对于相应的对照，MC和MCR处理使三种土壤中的水稻籽粒Cd分别显着降低了23.9-72.1％和37.3-63.9％。MC和MCR处理对美国（分别降低10.6％和4.3％）和RS（分别降低9.3％和19.5％）的水稻籽粒锌积累也表现出抑制作用，而在PS中则没有。此外，在三种土壤中，MCR处理对谷物产量没有影响，而在美国，MC处理使谷物产量显着增加了29.8％。

结论

我们的研究表明，基于MSC的磁修复技术可以有效地固定和/或去除农田土壤中的Cd和Zn，从而减少水稻植物对Cd和Zn的吸收，而对谷物产量没有不利影响。