工业和农业污染稻田土壤重金属的赋存形态及水稻吸收运移比较

[目的]稻田土壤重金属污染是当前农产品安全生产关注的重要问题.本文比较分析工业和农业污染源稻田土壤重金属的赋存形态及水稻吸收运移,以期为稻田土壤重金属污染控制提供参考.[方法]在长江中下游地区调查选取工业源和农业源重金属污染稻田各27块,在水稻成熟期使用抖根法采集根际土壤及水稻根系和籽粒样品,采用Tessier七步提取...     

Cadmium contamination of soils and rice plants caused by zinc mining V. Removal of soil cadmium by an HCl-leaching method for the control of high Cd rice

Abstract

A method of leaching polluted soil with diluted HCl solution was investigated for controlling high Cd in rice. Results obtained in the pot and field experiments are summarized as follows:

1. By leaching the soil in the pot with 0.05 or 0.1 N HCl solution followed by washing with water, soluble heavy metals were remarkably removed in the order of Cd>Cu>Zn?Pb; the Cd content decreased to half with 0.1 N HCI treatment.

2. Heavy metal contents of the plants decreased with the treatments. Especially, Cd content in straw and rice of the soil applied with CaCO₃ after the treatment was one-third and one-fifteenth of the control, respectively.

3. A contaminated paddy field was similarly treated using industrial cone. HCl. One-fourth of the soluble Cd in the surface soil was removed by this method, and the Cd content of the unpolished rice decreased from 0.33 ppm to 0.06 ppm in the plot treated with fused magnesium phosphate and calcium silicate after the treatment.

4. Cd concentration of the drained water from the treated field could soon be diluted far below the allowable limit with the abundant river current. A sufficient supply of calcareous materials was needed to compensate for the lost bases in the soil.     

稻壳基生物炭对生菜Cd吸收及土壤养分的影响

探讨稻壳基生物炭对Cd污染土壤上叶菜吸收Cd和土壤Cd形态的影响作用,明确稻壳基生物炭对土壤Cd污染的调控效应,可为合理利用稻壳基生物炭降低叶菜Cd含量提供参考。采用盆栽试验,研究了稻壳基生物炭在不同用量水平下对2茬生菜地上部Cd含量、土壤养分含量及Cd赋存形态的影响。结果表明,在5~25 g-kg-1用量范围内,稻壳基生物炭显著降低了2茬生菜地上部和根系Cd含量,且在最大用量25 g-kg-1时效果最好,地上部Cd含量分别比未施稻壳基生物炭的对照处理降低了19.6%和45.8%,根系Cd含量分别降低了36.8%和28.0%。在25 g-kg-1用量水平下,稻壳基生物炭对土壤p H、有效磷、速效钾及有机质含量提升效果明显,但显著降低了土壤碱解氮含量。施加稻壳基生物炭对土壤有效态Cd含量及Cd化学形态也有不同影响。随着稻壳基生物炭用量的增加,土壤NH4OAc提取态Cd含量和弱酸提取态Cd含量显著降低,在用量为25 g-kg-1时,分别比对照降低17.9%和10.4%,可还原态Cd含量无显著变化,可氧化态Cd含量呈减低趋势,残渣态Cd含量增加17.6%。因此推测,提升土壤p H、降低土壤有效态Cd含量、增加残渣态Cd含量可能是稻壳基生物炭降低生菜体内Cd含量的主要原因。稻壳基生物炭可以作为土壤改良剂,抑制Cd污染土壤上叶菜对Cd的吸收,改善土壤养分状况。     

我国稻田土壤镉污染现状及安全生产新措施

水稻是我国重要的粮食作物,由于受重金属污染威胁日益增大,其安全生产问题备受关注。通过综述我国稻田土壤及稻米镉污染现状、镉污染土壤改良剂研究进展以及稻米对镉富集的品种间差异,认为在土壤中镉的去除修复技术无法在短时间内实现的前提下,镉排异型水稻品种的筛选与利用是实现其安全生产的一个新的有效措施。在此基础上,配合一些污染土壤改良剂的使用,会进一步增强其安全生产水平。     

石灰组配土壤改良剂抑制污染农田水稻镉吸收

为达有效地调控污染稻田水稻糙米对Cd吸收,该研究选取湖南省长株潭地区的湘潭、醴陵和株洲3处不同Cd污染程度田块,研究石灰配施海泡石、钙镁磷肥、有机肥对水稻Cd吸收和累积的影响。结果表明,施用石灰及其组配改良剂均可明显提高土壤pH值,有效降低土壤中酸提取态Cd含量和水稻中Cd含量。与不施用改良剂相比,石灰配施海泡石或有机肥、配施海泡石和有机肥,Cd污染稻田土壤pH值平均升高1.08,0.96和0.93个单位,酸提取态Cd质量分数分别平均降低20.6%,15.6%和21.2%。石灰配施海泡石、有机肥或钙镁磷肥处理下在轻度Cd污染田块中糙米Cd含量较对照分别显著降低了48.3%,46.7%和34.2%,石灰配施有机肥、钙镁磷肥或钙镁磷肥和有机肥处理下在中度Cd污染田块中糙米Cd含量较对照分别显著降低了52.8%,47.8%和37.5%,石灰配施钙镁磷肥和有机肥、有机肥或海泡石处理下在重度Cd污染田块中糙米Cd含量较对照分别显著降低了51.2%,44.6%和42.5%,均低于食品安全国家标准中糙米限量值0.2 mg/kg(GB2762-2017)。相关分析表明,土壤中酸提取态Cd含量与水稻根、茎叶和糙米中Cd含量呈显著正相关关系(P0.05),说明土壤酸提取态Cd含量是影响糙米对Cd吸收的关键因素之一。上述结果说明,石灰配施海泡石、有机肥或钙镁磷肥+有机肥可有效调控污染稻田土壤中Cd进入水稻,实现水稻安全生产。     

阻隔主要外源输入重金属对土壤-水稻系统中镉铅累积的影响

土壤-水稻系统中重金属输入输出调控对稻田污染防治和水稻安全生产具有重要意义。该文研究稻草移除、截断大气沉降、清洁水灌溉等调控措施对稻田土壤-水稻系统中重金属Cd和Pb的累积与运移特征的影响。结果表明,稻草移除、截断大气沉降和清洁水灌溉均能明显降低污染土壤中有效态重金属含量和水稻中重金属的累积量。与稻草还田对照处理相比,除种植早稻后的土壤有效态Pb含量外,稻草移除处理下土壤中有效态Cd、Pb含量均略有降低,且在该处理下,早稻糙米中Pb含量与晚稻糙米中Cd、Pb含量显著降低,降幅分别为3.6%、10.4%和32.4%;稻草移除+截断大气沉降处理下,土壤中有效态Cd、Pb含量均不同程度地下降,种植晚稻后的土壤有效态Pb含量显著降低,除早稻的根和糙米中Cd含量外,其余早晚稻水稻各部位Cd、Pb含量均显著降低,水稻根和茎叶Cd、Pb含量平均降幅分别为32.8%、36.8%和32.2%、24.8%,晚稻糙米Cd、Pb累积量分别显著降低66.3%和22.2%;稻草移除+清洁水灌溉处理下,种植早晚稻后的土壤有效态Cd、Pb含量平均下降幅度分别为11.7%和15.9%,早晚稻各部位Cd、Pb含量降低幅度较大,早晚稻根和茎叶Cd、Pb含量平均降幅分别为38.34%、30.35%和43.4%、13.2%,晚稻糙米中Cd、Pb累积量降幅分别为39.4%、67.2%。分析水稻地上部的Cd、Pb富集与转运系数表明,稻草移除结合截断大气沉降或清洁水灌溉等控源措施可显著降低Cd、Pb在水稻地上部位的富集系数,减少地上部位重金属的累积量。上述结果表明,采用稻草移除结合截断大气沉降或清洁水灌溉措施可进一步降低土壤中有效态Cd、Pb含量和水稻中Cd、Pb富集。因此,控制区域大气污染,净化农田灌溉水等控源措施,同时施行稻草移除等输出污染农田土壤中重金属等策略,可有效实现污染农田土壤安全利用和水稻安全生产。     

不同水分管理模式下坡缕石修复稻田土壤镉污染效果

  目的  探究在合理的水分管理模式下提高坡缕石钝化稻田土壤镉的效率,及坡缕石施加对土壤理化性质、环境质量和水稻抗氧化胁迫的影响。  方法  采用盆栽试验方法,试验设置长期淹水、传统灌溉和湿润灌溉3种水分管理措施,每一水分管理模式下设0%、0.5%、1.0%、1.5%、2.0%和2.5% 6个坡缕石施加浓度,共18个处理,通过测定土壤pH、zeta电位、有效态镉、稻米生物量、稻米镉含量、土壤酶和叶抗氧化酶活性,分析不同水分管理措施与坡缕石用量组合修复镉污染的效果。  结果  长期淹水、传统灌溉和湿润灌溉下,坡缕石处理土壤pH分别增加0.49 ~ 1.24、0.49 ~ 1.47和0.42 ~ 1.64个单位,0.025 mol L?1 HCl提取态镉含量分别下降15.4% ~ 46.2%,11.5% ~ 39.7%和11.4% ~ 32.4%,毒性浸出法提取态镉最大降幅分别为47.4%、42.4%和40.2%（P < 0.05）。未施加坡缕石条件下,与传统灌溉比,长期淹水、湿润灌溉的稻米生物量降低11.2%和19.3%（P < 0.05）。3种水分管理模式下,坡缕石处理的稻米镉含量分别下降21.9% ~ 75.0%,17.8% ~ 70.2%和17.4% ~ 66.5%,土壤磷酸酶活性最大增幅分别为40.0%、57.1%和40.9%,叶超氧化物歧化酶活性最大增幅分别为33.9%、50.2%和37.4%（P < 0.05）。  结论  长期淹水下坡缕石钝化土壤镉的效率最高,1.0%坡缕石施加使稻米镉含量降至我国食品污染物含量限量标准0.20 mg kg?1（GB 2762—2012）以下,长期淹水联合坡缕石施加组合为镉污染稻田土壤修复技术。     

改良剂对镉污染酸性水稻土的修复效应与机理研究

为探明田间条件下施用石灰、钙镁磷肥、海泡石和腐殖酸等改良剂对Cd污染酸性水稻土的修复效应和作用机理, 通过在Cd污染区建立田间小区试验, 研究了改良剂单施和与石灰配施对Cd污染酸性水稻土中Cd作物有效性的影响。结果表明, 施用改良剂有效地改变了土壤中Cd的存在形态, 除腐殖酸外, 其他改良剂均使土壤酸提取态Cd不同程度地转化为可还原态Cd和残渣态Cd; 施用改良剂可使0.1 mol·L^-1 NaNO₃和 0.01 mol·L^-1CaCl₂提取态Cd 降低26%~97%, 降低效果为石灰+海泡石>海泡石>石灰+钙镁磷肥>钙镁磷肥>石灰>石灰+腐殖酸>腐殖酸; 改良剂使水稻地上部分的Cd吸收量降低6%~49%。试验结果还显示, 施用改良剂提高土壤pH是引起土壤中Cd作物有效性降低的主要原因之一。根据田间试验的结果, 海泡石可推荐作为Cd污染酸性水稻土的改良剂, 而腐殖酸则不宜使用。     

Using profitable chrysanthemums for phytoremediation of Cd- and Zn-contaminated soils in the suburb of Shanghai

Purpose

We studied the profitable phytoremediation method with commercial chrysanthemum (Chrysanthemum indicum L.) in order to remediate the soils contaminated with heavy metals and generate economy income from the contaminated sites.

Materials and methods

A field experiment was carried out to remediate the contaminated soil through growing the commercial chrysanthemum plants in a farmland polluted with heavy metals of Cd and Zn due to application of creek sediments in the western suburb of Shanghai, Southeast China, since June 2013.

Results and discussion

After the consecutive 3 years of phytoremediation, Cd and Zn contents in the soil were reduced by 78.1% and 28.4%, respectively. We also found that the rice grain growing on the 3-year phytoremediated soil met the requirements of dietary safety, so did the vegetable growing on the 5-year phytoremediated soil.

Conclusions

Growing chrysanthemum plants as a method of phytoremediation can not only remove a large amount of toxic heavy metals from the contaminated soil but also be highly profitable from the sales of chrysanthemum flowers.

     

水稻子实对不同形态重金属的累积差异及其影响因素分析

在分析成都平原核心区土壤重金属(Cd、Cr、Pb、Cu、Zn)全量、各形态含量及相应点位种植的水稻子实重金属含量的基础上,通过统计分析、空间插值及线性回归方程的模拟,研究了土壤Cd、Cr、Pb、Cu、Zn全量的空间分布状况、各形态重金属含量统计特征,以及水稻子实对重金属各形态的累积差异及其影响因素。结果表明,成都平原水稻土重金属污染较轻,除Cd外,均低于国家土壤环境质量二级标准。土壤中重金属的可交换态含量均较低,Cd主要以铁锰氧化态存在,Cr、Cu、Zn、Pb主要以残渣态存在。水稻子实对5种重金属的累积效应顺序为:Cd>Zn>Cu>Pb>Cr。与水稻重金属累积关系密切的重金属活性形态(可交换态、碳酸盐结合态、铁锰氧化物结合态和有机物结合态)主要有:Cd的碳酸盐结合态、Cr的可交换态、Pb的有机物结合态和Cu的碳酸盐结合态含量;Zn各活性形态对水稻子实含量的影响不明显。土壤理化性质对不同活性形态重金属元素的影响效应各不相同。活性态Cd主要受有机质、pH和容重的影响;活性态Cr与pH、有机质、CEC和容重密切相关;活性态Pb与有机质、容重、中细粉粒、砂粒等均有密切的关系;Cu的活性主要受粘粒、有机质含量的影响;Zn的有效性主要受pH、有机质、砂粒、容重的影响。总的看来,对土壤Cd、Cr、Pb、Cu、Zn各活性形态含量影响效应较强的是有机质、pH、容重,而与土壤吸附性能密切相关的颗粒组成、CEC的影响不甚明显。     

生物质炭与氮肥配施降低水稻重金属含量的盆栽试验

针对重金属污染严重的土壤,探索施用氮肥和生物质炭减少水稻重金属吸收的可行性。该研究采用盆栽试验,选用生物质炭、硫硝铵氮肥(简称普通氮肥)和含硝化抑制剂3,4-二甲基吡唑磷酸盐的硫硝铵氮肥(简称3,4-dimethylpyrazolephosphate,DMPP氮肥),设置了5种处理包括对照即未添加氮肥和生物质炭、普通氮肥添加、DMPP氮肥添加、生物质炭+普通氮肥添加和生物质炭+DMPP氮肥添加,研究了不同处理对水稻华航丝苗(Oryza sativa L.)生长和重金属Cu、Zn和Cd吸收特性的影响。结果表明,不配施生物质炭时,DMPP氮肥对水稻籽粒产量无显著(P0.05)影响;生物质炭与普通氮肥或DMPP氮肥配施均能增加水稻籽粒产量:与单施普通氮肥相比,生物质炭与普通氮肥配施水稻籽粒产量显著(P0.05)增加20.3%;与单施DMPP氮肥相比,生物质炭与DMPP氮肥配施水稻籽粒产量显著(P0.05)增加49.3%。与不施肥对照相比,生物质炭与DMPP氮肥配施能降低籽粒Cu、Zn和Cd含量,其籽粒Cu、Zn和Cd质量分数分别显著降低20.0%、21.4%和11.6%。未配施生物质炭时DMPP促进Cu从秸秆向籽粒的转移,配施生物质炭时DMPP促进Cu和Cd从根向秸秆的转移;生物质炭与不同氮肥配施对水稻籽粒/秸秆和秸秆/根Cu、Zn和Cd转运系数的影响因配施氮肥品种不同而存在差异。综上,生物质炭与DMPP氮肥配施可降低籽粒中重金属Cu、Zn和Cd质量分数,促进水稻生长,增加水稻籽粒产量,适宜在多重金属污染稻田施用。     

大冶市农田土壤中镉的空间分布特征及污染评价

矿山开采和冶炼是造成土壤重金属Cd污染的主要原因,了解典型区域土壤中Cd的空间分布特征及其污染现状,可为区域土壤污染防治与安全利用提供重要信息。本研究针对湖北省大冶市所有农田采集92个表层土壤样品和3个土壤剖面,利用GIS方法对土壤重金属Cd空间分布特征及污染状况进行了研究。结果表明大冶市土壤中Cd的含量范围为0.6 ~ 4.6 mg/kg,平均值为1.41 mg/kg,Cd迁移深度可达 40 cm。区域内土壤Cd污染范围较广,空间变异较大,还地桥镇、罗桥街办、陈贵镇等地农田土壤Cd含量较高。地积累指数评价结果显示大冶市大部分农田土壤为轻度、中度污染程度,在合理调整种植结构等方式下仍可保障农田安全利用。     

Effects of water and organic manure coupling on the immobilization of cadmium by sepiolite

Purpose

Natural sepiolite (SP) has proven effective on the in-situ immobilization remediation of Cd-contaminated soils. But the practical remediation effect may largely influenced by water management and the application of organic manure. The effects of chicken manure (CM) on SP-amended soils were investigated under normal and saturated water conditions using a pot experiment with Brassica campestris L.

Materials and methods

Cd-contaminated paddy soils were amended with CM, SP, and CM?+?SP with no amendment as control. The amount of sepiolite was 0.5% (w/w, the same below) either in SP or CM?+?SP amended soils, while the amount of CM was 0.5, 1.0, and 2.0% in CM and CM?+?SP-amended soils. The plant metal contents, fresh weight, and soluble sugar content of plant edible parts were measured on harvest. Soil Cd was extracted by diethylenetriaminepentaacetic acid (DTPA) and HCl to estimate the mobility of heavy metal. Soil pH and dissolved organic matter (DOM) of rhizosphere soil were determined. The electronegative charges of soils were also measured using the zeta potential.

Results and discussion

The application of CM and increasing soil moisture on SP-amended soil increased plant growth to a greater extent than the application of SP alone. The application of CM along with the increase of soil moisture decreased Cd uptake and translocation in plants grown on SP-amended soil compared to the application of SP alone. Cd content of edible plant parts reached a minimum of 0.24 mg kg^?1 with the application of 2.0% CM on SP-amended soils under water-saturated conditions, which was approximately 50% lower than the Cd concentration found when applying SP alone.

Conclusions

The results of this study suggest that the application of sepiolite on Cd contaminated soil can effectively reduce Cd uptake by B. campestris L., and the addition of CM combined with effective water management also appears to further reduce Cd absorption and accumulation.

     

硫在稻根微域中化学行为及其对水稻吸收重金属的影响机理

我国水稻种植面积和产量分别占世界23%和40%.人类活动,如农药和除草剂施用、采矿、污水灌溉,已经导致了一些地区水稻土污染.开发能够控制、减少水稻对重金属吸收和经食物链传递的技术与方法,对确保食物安全具有重要意义.硫(S)有6个化合态,土壤硫化合物种类多,其在土壤中转化相当复杂,在土壤环境化学研究中具有重要地位.本文收集了国内外有关文献,评述了S在水稻土中的含量、形态及转化,重点阐述了S在根际微域化学行为及其与水稻吸收重金属之间的关联,并提出了未来应开展的主要研究方向.     

Risk assessment,spatial distribution,and source identification of heavy metal(loid)s in paddy soils along the Zijiang River basin,in Hunan Province,China

Purpose

This study aimed to reveal spatial distribution of As, Cd, Cr, Cu, Mn, Ni, Pb, Sb, V, and Zn in paddy soils in the Zijiang River basin and to evaluate its pollution status and potential ecological risks, and thus to provide basic information for rational utilization of paddy soils in the study area.

Materials and methods

The heavy metal(loid) concentrations in one hundred and thirty-five paddy soil samples (these samples were collected from the top 0–20 cm layer) were measured by inductively coupled plasma-optical emission spectrometry. The spatial distribution characteristics of the heavy metal(loid)s were depicted by the Ordinary Kriging interpolation analysis. The contamination degree and potential ecological risks of the heavy metal(loid)s in paddy soils were assessed by Nemerow’s comprehensive index, geoaccumulation index, potential ecological risk factor, and potential ecological risk index. The potential sources of the heavy metal(loid)s were deduced by Pearson’s correlation analysis, hierarchical cluster analysis, and principal component analysis.

Results and discussion

The mean concentrations of the heavy metal(loid)s decreased in the order of Mn?>?V?≈?Zn?>?Cr?>?Ni?≈?Pb?>?Cu?≈?Sb?>?As?>?Cd. Except for Cd and Sb, the mean concentrations of As, Cr, Cu, Mn, Ni, Pb, V, and Zn were close to the background reference values. The concentration of Cd in 94.8% of samples exceeded the soil quality standard value (grade II, 5.5?<?pH?<?6.5, GB 15618–1995). According to the assessments of pollution and potential ecological risks for the heavy metal(loid)s, 45.2% and 46.7% of samples were severely polluted and moderately polluted, respectively. The potential sources analysis indicated that Cd, Sb, and Zn mainly originated from agricultural, mining, and smelting activities; As, Cu, and Pb mainly originated from agricultural activities, while coal combustion by-products was another major source of these heavy metal(loid)s in paddy soils near the thermal power plant in the southwest corner of the study area; Cr, V, Mn, and Ni mainly originated from natural source.

Conclusions

Cadmium and Sb are the main contaminants in paddy soils in the study area, and there are hot-spot pollution areas.

     

利用Illumina高通量测序对复合重金属污染下根际和非根际稻田土壤细菌的研究

There is an increasing concern about rice (Oryza sativa L.) soil microbiomes under the influence of mixed heavy metal contamination.We used the high-throughput Illumina MiSeq sequencing approach to explore the bacterial diversity and community composition of soils in four paddy fields,exhibiting four degrees of mixed heavy metal (Cd,Pb and Zn) pollution,and examined the effects of these metals on the bacterial communities.Our results showed that up to 2 104 to 4 359 bacterial operational taxonomic units (OTUs) were found in the bulk and rhizosphere soils of the paddy fields,with the dominant bacterial phyla (greater than 1％ of the overall community) including Proteobacteria,Actinobacteria,Firmicutes,Acidobacteria,Gemmatimonadetes,Chloroflexi,Bacteroidetes and Nitrospirae.A number of rare and candidate bacterial groups were also detected,and Saprospirales,HOC36,SC-I-84 and Anaerospora were rarely detected in rice paddy soils.Venn diagram analysis showed that 174 bacterial OTUs were shared among the bulk soils with four pollution degrees.Rice rhizosphere soils displayed higher bacterial diversity indices (ACE and Chao 1) and more unique OTUs than bulk soils.Total Cd and Zn in the soils were significantly negatively correlated with ACE and Chao 1,respectively,and the Mantel test suggested that total Pb,total Zn,pH,total nitrogen and total phosphorus significantly affected the community structure.Overall,these results provided baseline data for the bacterial communities in bulk and rhizosphere soils of paddy fields contaminated with mixed heavy metals.     

Soil Factors Affecting Heavy Metal Solubility in Some New Zealand Soils

Heavy metal contamination of soils is usually quantified and guidelines set solely on the basis of total heavy metal content. However, it is recognised that water soluble heavy metal concentrations may provide a better indication of the potential risk that heavy metals may pose to the soil environment. The aim of this study was to use a semi-empirical model based on the competitive adsorption of metal and H⁺ ions [dependent on solution pH, total metal content, total carbon content and soil oxide content] to predict water soluble Cu, Cr, Cd, Pb, Ni and Zn concentrations in a range of field contaminated soils. The results of multiple linear regressions showed that basic soil properties could predict 85, 72, 66, 78, 50 and 75% of the variation in soluble Ni, Cu, Cr, Pb, Cd and Zn concentrations respectively. Water soluble metal concentrations were best predicted using empirical linear regressions which included total metal content, while the importance of other soil properties such as soil pH, total carbon and oxalate extractable Fe and Al oxides varied between metals. The models have the potential to provide valuable information on metal availability in contaminated soils and offer an indication of the potential risk a metal may pose to a given soil environment, along with providing a basis for developing soil quality guidelines for the prevention, investigation and clean-up of soil metal contamination.     

Heavy metal contamination of agricultural soils around a chromite mine in Vietnam

Abstract

In Vietnam, the Co Dinh mine is the largest chromite mine in the country. Mining, ore dressing and disposal of the tailings provide obvious sources of heavy metal contamination in the mine area. The present study examined the influence of chromite mining activities on the adjacent lowland paddy field by investigating heavy metal and As levels in the mine tailings, sediments, paddy soils and water. At paddy fields located near the mine tailings, the total contents of Cr, Co and Ni were 5,750, 375 and 5,590?mg?kg^?1, and the contents of their water-extractable form were 12.7, 1.16 and 32.3?mg?kg^?1, respectively. These results revealed severe contamination of lowland paddy soils with Cr, Co and Ni as a result of mining activity, suggesting serious health hazards through agricultural products, including livestock in this area. The principal source of the pollution was sediment inflow owing to the collapse of the dike, which was poorly constructed by heaping up soil. Moreover, water flowing out from the mining area was also polluted with Cr and Ni (15.0–41.0 and 20.0–135?μg?L^?1, respectively). This might raise another problem of heavy metal pollution of watercourses in the area, indicating the need for further investigation and monitoring of fluctuations of water quality with seasonal changes.     

Cadmium contamination of soils and rice plants caused by zinc mining IV. Use of soil amendment materials for the control of Cd uptake by plants

In view of the difficulty in practicing water management as a measure to prevent the production of high Cd rice, alkaline or calcareous soil amendment materials were examined, concerning their pH effect on the availability of soil heavy metals.

1. In the experiment conducted on the contaminated paddy field, the essential Cd uptake by the plant occurred after the ear-forming stage and was reduced remarkably by a basal application of the amendment materials followed by top application, depending on the activity of raising the soil pH. Combined use of calcium silicate and fused magnesium phosphate for a basal dressing was most effective on Cd uptake, producing rice of the lowest Cd content, one fifth of the control.

2. The content of Cu in rice also decreased with the treatment to an extent second to Cd, while that of Zn and Pb decreased in straw but hardly changed in rice. Cu seemed fastest in the straw-to-grain movement which was also promoted by the treatments.

3. Soil Cd and Cu were less soluble in 0.1 N HCl solutions than were Zn and Pb, with the application of fused phosphate. Soil Cd became more insoluble in the incubated soil in a submerged condition and its solubility appeared to be depressed by the addition of ammonium sulfate.

4. Based on the good results for the control of high Cd rice obtained through three years' survey in the problem area, it was recommended that these materials be used in sufficient quantity to raise soil pH, taking care not to cause delay in the first growth.     

Magnetic removal/immobilization of cadmium and zinc in contaminated soils using a magnetic microparticle solid chelator and its effect on rice cultivation

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.