EDTA和柠檬酸对污染土壤中重金属的解吸动力学及其形态的影响

利用批处理振荡解吸平衡法研究了0.05 mol/L的乙二胺四乙酸钠(EDTA)和柠檬酸对污染土壤中Cd,Pb,Cu,Zn的解吸动力学特征,并采用优化的BIER(European Community Bureau of Reference)连续提取法分析了EDTA和柠檬酸处理前后土壤中重金属形态和生物有效性的变化.结果表明,污染土壤中重金属Cd,Pb,Cu,Zn的解吸率随着解吸时间的延长而不断增加,但解吸速率随解吸时间的延长而不断降低.EDTA对Pb,Cu的解吸能力显著大于柠檬酸,柠檬酸对Zn的解吸能力显著大于EDTA,柠檬酸和EDTA对Cd的解吸能力相差不大.EDTA和柠檬酸对4种重金属解吸能力的顺序分别为:Pb＞Cd＞Zn＞Cu和CA＞Zn＞Pb＞Cu.双常数方程是描述污染土壤中Cd,Pb,Cu,Zn解吸动力学过程的最佳方程.EDTA去除的重金属主要以酸提取态和可还原态存在,柠檬酸去除的重金属主要以酸提取态存在.EDTA和柠檬酸处理后.污染土壤中Cd,Pb,Cu,Zn的生物有效性降低.     

水分及干燥过程对土壤重金属有效性的影响

土壤水分变化可显著改变土壤性质进而影响土壤重金属有效性。本试验通过测定土壤溶液和采用薄层凝胶梯度法(DGT)表征的Zn、Cd、Cu、Ni浓度,研究土壤含水量变化对重金属有效性的影响。结果表明,不同水分处理显著影响土壤溶液中可溶性有机碳(DOC)含量和土壤中重金属的有效性;随土壤水分降低DGT表征的Zn、Cd、Cu和Ni浓度和土壤溶液中Cu和Ni浓度呈下降趋势,且随干湿交替次数增加而降低;与长期风干土壤相比,经干湿交替后风干土壤重金属有效性降低或显著降低;与土壤溶液法相比,DGT法能反映水分变化对土壤固相金属缓冲补给能力的影响,能更好地表征土壤金属有效性的变化。在农业生产中可通过适当水分管理措施降低重金属的有效性,从而缓解重金属的毒害作用。     

四种改良剂对铜和镉复合污染土壤的田间原位修复研究

研究了石灰、磷灰石、蒙脱石和凹凸棒石对冶炼厂周边Cu、Cd污染土壤的原位修复效果。以黑麦草(Lolium perenne L.)作为田间修复植物,采用植物重金属吸收性、土壤重金属化学提取性及土壤溶液重金属浓度变化等作指标来评价修复效果,并研究了黑麦草对Cu、Cd的吸收与土壤、土壤溶液中Cu、Cd含量的相关性。结果表明,石灰高添加剂量(石灰占污染土壤耕作层质量的0.4%)处理黑麦草对重金属的富集效果最好,显著降低了重金属毒性,促进了黑麦草的生长及其对重金属的富集;石灰和磷灰石各添加剂量均显著降低了污染土壤交换态Cu含量;石灰、磷灰石和蒙脱石各添加剂量均显著提高了土壤溶液pH并显著降低了其Cu、Cd浓度。黑麦草地上部、根中Cu浓度与土壤交换态Cu及土壤溶液Cu浓度呈显著或极显著正相关关系。     

EDTA与EDDS螯合诱导印度芥菜吸取修复重金属复合污染土壤研究

盆栽试验比较研究了EDTA和易降解的EDDS对复合污染土壤中Cu、Zn、Pb、Cd的活化能力及印度芥菜对4种重金属的吸收与转运特征。结果表明:施用量相同的条件下,EDDS活化土壤Cu的能力与EDTA相当;而EDDS活化土壤Zn、Pb、Cd,尤其是活化土壤Pb、Cd的能力小于EDTA,这与两种螯合剂与不同重金属形成螯合物的稳定常数相一致。向复合污染土壤中施入3mmol/kg和6mmol/kgEDDS均可诱导印度芥菜叶中超量积累Cu。本研究中3mmol/kgEDDS的不同施用方式(单次施,分2次和4次施)对印度芥菜叶片Cu含量的影响差异不显著。各处理印度芥菜叶中的重金属浓度要远高于茎中的浓度,茎中的Cu浓度随土壤溶液Cu浓度线性增加,而叶中Cu的浓度随土壤溶液Cu浓度先增加后下降。     

芜湖市工业区土壤重金属污染状况研究

通过对芜湖工业区(四褐山区、马塘区)土壤中重金属污染状况的调查,结果表明:土壤中重金属(Cu、Pb、Zn、Cd)含量绝大部分高于土壤元素背景值。在四褐山工业区,Cu污染最严重,Cd次之;在马塘工业区,Cd污染最严重,Zn次之。土壤中重金属含量基本上与土壤pH呈负相关关系,而重金属总量与可浸提态含量呈正相关关系。土壤中重金属污染来源主要是污水,大气粉尘沉降也是一个重要因素。     

水稻籽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籽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，以及水稻籽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。水稻籽实对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各活性形态对水稻籽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。     

九华铜矿重金属环境污染状况研究

选择江苏九华铜矿区,对其周边土壤和作物的重金属污染状况进行了研究.结果发现,约有一半的采样点土壤全Cu含量超过我国土壤环境质量三级标准(400 mg/kg),其DTPA提取态Cu含量的平均值为117 mg/kg.通过对矿区土壤重金属间的相关分析表明,土壤Cu与Zn、Pb、Cd、Co之间呈极显著的正相关关系(p＜0.01),而与Cr、Ni无显著相关,说明了该铜矿区土壤还伴有外源Zn、Pb、Cd、Co的污染.土壤复合污染指数(PI)＞1.0的土壤样品占57.3%.矿区周围作物可食部位Cu、Zn、Pb、Cd和Cr的含量均较高.     

深圳市主要公园及道路绿地土壤重金属含量状况比较研究

对深圳城市主要公园和道路绿地土壤Cu、Zn、Pb、Cd含量状况进行取样调查分析。研究结果表明,绿地土壤重金属含量与土地利用类型有关,表现为道路绿地土壤Cu、Zn、Pb平均含量高于公园绿地土壤,而Cd平均含量则相反。采用不同土壤重金属污染评价方法对深圳城市绿地土壤进行的环境质量评价均表明深圳城市绿地土壤Cd污染现象显著。在考察的四种重金属元素中,Zn含量与土壤有机质、pH有关,其中pH对Zn含量的影响相对较大;土壤Cu与Pb、Zn呈直线相关,表现出相互依存的关系。     

污染水稻土中有效态重金属的空间分布及影响因子

利用地统计学方法,选择江西省贵溪铜冶炼厂污染区,研究了表层水稻土中有效态重金属的空间变异特征和影响因素.分析表明,土壤有效态Cu、Cd、Pb为中等空间相关性,有效态Zn为弱空间相关性.有效态Cu、Cd分别与有效态Zn和有效态Pb呈显著相关,表现出复合污染的特征.土壤有效态重金属的空间分布有明显的各向异性.土壤有效态重金属的长轴方位角(西北-东南和东北-西南)与污染物的扩散方向(渠道和偏东风向)相近.随污染源距离的增加,土壤有效态Cu含量降低,而有效态Cd和Pb含量增加,有效态Zn含量在西北和东南两个方向上增加.相关分析表明,影响污染区水稻土中重金属有效态含量空间分布的主要因子是离污染源的距离和地形,其次是土壤的吸附能力(土壤SO42-含量)以及土壤pH,土壤有机质和土壤孔隙性的影响较小.     

重金属Cd、Zn、Cu、Pb复合污染对土壤微生物和酶活性的影响

通过野外土样采集及室内测定,研究了云南东川铜矿区土壤酶和微生物特征,并采用盆栽试验研究了重金属Cd、Zn、Cu、Pb复合污染对土壤微生物和酶活性的影响。结果表明,距离矿口越近,土壤有机质、有效N、P、K的含量、土壤pH值亦越低,土壤酶活性和土壤微生物数量、微生物生物量C和N受到的抑制程度也增强,其中土壤酶中的酸性磷酸酶和过氧化氢酶,土壤微生物中的细菌对重金属污染较为敏感。盆栽试验中,Cd、Zn、Cu、Pb复合污染使白菜(Brassica rapapekinensis)生物量明显下降,且随复合污染程度的增加,白菜生物量下降幅度增加。Cd与Zn、Cu、Pb,Zn与Cd、Cu、Pb,Cu与Cd、Zn、Pb的复合效应机制为协同效应,而Pb与Cd、Zn、Cu的复合效应机制为拮抗效应。重金属Cu、Zn、Pb、Cd复合污染使土壤酶活性显著降低,但低量的Cd、Zn、Cu、Pb复合污染刺激了细菌、真菌、放线菌、微生物生物量C和N。重金属Cd、Zn、Cu、Pb对土壤酶活性和土壤微生物数量及微生物生物量C和N的复合效应机制表现出协同和拮抗效应。     

Simultaneous Sorption of Cd,Cu, Ni,Zn, Pb,and Cr on Soils Treated with Sewage Sludge Supernatant

Disposal of sewage sludge creates the potential for heavy metal accumulation in theenvironment. This study assessed nine soils currently used as Dedicated Land Disposal units(DLDs) for treatment and disposal of municipal sewage sludge in the vicinity of Sacramento,California. Adsorption characteristics of these soils for Cd, Cu, Ni, Zn, Pb, and Cr were studiedby simultaneously mixing these elements in the range of 0-50 µmol L-1 with sludgesupernatant and reacting with the soil using a soil:supernatant ratio of 1:30, pH = 4.5 or 6.5, andconstant ionic strength (0.01 M Na-acetate). The concentration of metals in the supernatant wasdetermined after a 24 hr equilibration period. Adsorption isotherms showed that metal sorptionwas linearly related to its concentration in the supernatant solution. The distribution coefficientKd (Kd = concentration on solid phase/concentration in solution phase) was computed as theslope of the sorption isotherm. The distribution coefficients were significantly correlated to soilorganic matter content for Ni, Cu, Cd, and Pb at pH 4.5 and for Ni, Cu, Zn, and Cd at pH 6.5.There was also a correlation between Kd and soil specific surface area but no relationship to othersoil properties such as CEC, clay content, and noncrystalline Fe and Al materials. Therefore, soilorganic carbon and surface area appear to be the most important soil properties influencing metaladsorption through formation of organo-metal complexes. The Kd values for all elements werehigher at pH 6.5 than at 4.5. Selectivity between metals resulted in the following metal affinitiesbased on their Kd values: Pb>Cu>Zn>Ni>Cd≈Cr at pH 4.5 andPb>Cu≈Zn>Cd>Ni>Cr at pH 6.5.     

Prediction of available heavy metals by six chemical extractants in a sewage sludge‐amended soil

Abstract

In a field experiment conducted during three years in a sandy‐loam, calcareous soil, one aerobically digested sewage sludge (ASL) and another anaerobically digested sewage sludge (ANSL) were applied at rates of 400, 800, and 1,200 kg N/ha/year, and compared with mineral nitrogen fertilizer at rates of 0, 200, 400, and 600 kg N/ha/year in a cropping sequence of potato‐corn, potato‐lettuce, and potato, the first, second, and third year, respectively. Results showed that the highest values of soil extractable metals were obtained with aqua regia, whereas the lowest levels with DTPA. All metal (Zn, Cu, Cd, Ni, Pb, and Cr) gave significant correlations between metal extracted with the different extractants and metal loading applied with the sludges. The metal extractable ion increased over the control for Zn, Cu, Cd, Ni, Pb, and Cr extracted with DTPA, EDTA (pH 8.6) and 0.1 N HC1, for Zn, Cd, Ni, Pb, and Cr extracted with EDTA (pH 4.65) and AB‐DTPA, and for Zn, Cd, Ni, and Cr extracted with aqua regia. The level of metal‐DTPA extractable resulted highly correlated with that obtained by the other methods, except the Ni‐aqua regia extractable. The soil extractable elements which showed significant correlations with metals in plant were: Zn, Cu, Cd, and Ni in potato leaves, Cd, Ni, and Pb in corn grain, and Zn and Cd for lettuce wrapper leaves. In general, all the chelate based extractants (DTPA, EDTA pH 4.6, EDTA pH 8.6, AB‐DTPA) were equally useful as indicator of plant available metals in the soil amended with sludge.     

General purpose Freundlich isotherms for cadmium,copper and zinc in soils

Assessing the accumulation and transport of trace metals in soils and the associated toxicological risks on a national scale requires generally applicable sorption equations. Therefore Freundlich equations were derived for Cd, Zn and Cu using multiple linear regression on batch sorption data from the literature with a wide variety of soil and experimental characteristics, and metal concentrations ranging over five orders of magnitude. Equations were derived based on both total dissolved metal concentrations and free metal activities in solution. Free metal activities were calculated from total metal concentrations taking into account ionic activity, and inorganic (all metals) and organic complexation (Cu only). Cadmium and Zn were present in solution predominantly as free ions, while Cu was present as organic complexes. Since actual dissolved organic carbon (DOC) concentrations were not available they were estimated using an empirical field relation between DOC and organic matter content. The logarithmic transformation of the Freundlich constant for Cd was regressed on the logarithmic transformations of cation exchange capacity (CEC) (H⁺) and dissolved Ca, and for Zn with CEC and (H⁺). For Cu the log–log regression model of the Freundlich constant included the solid:solution ratio of the batch to account for dilution of DOC in the batch as compared with the field. The explained variance for the fitted Freundlich equations was 79% for Cd, 65% for Cu and 83% for Zn, using log-transformed adsorbed concentrations and soil solution activities. The Freundlich adsorption models underestimated metal contents determined from 1 m HNO₃ digestion on field samples, up to a factor of 6 (Cd and Cu) or 10 (Zn).     

Modelling trace metal extractability and solubility in French forest soils by using soil properties

Soil/solution partitioning of trace metals (TM: Cd, Co, Cr, Cu, Ni, Sb, Pb and Zn) has been investigated in six French forest sites that have been subjected to TM atmospheric inputs. Soil profiles have been sampled and analysed for major soil properties, and CaCl₂‐extractable and total metal content. Metal concentrations (expressed on a molar basis) in soil (total), in CaCl₂ extracts and soil solution collected monthly from fresh soil by centrifugation, were in the order: Cr > Zn > Ni > Cu > Pb > Co > Sb > Cd , Zn > Cu > Pb = Ni > Co > Cd > Cr and Zn > Ni > Cu > Pb > Co > Cr > Cd > Sb , respectively. Metal extractability and solubility were predicted by using soil properties. Soil pH was the most significant property in predicting metal partitioning, but TM behaviour differed between acid and non‐acid soils. TM extractability was predicted significantly by soil pH for pH < 6, and by soil pH and Fe content for all soil conditions. Total metal concentration in soil solution was predicted well by soil pH and organic carbon content for Cd, Co, Cr, Ni and Zn, by Fe content for Cu, Cr, Ni, Pb and Sb and total soil metal content for Cu, Cr, Ni, Pb and Sb, with a better prediction for acidic conditions (pH < 6). At more alkaline pH conditions, solute concentrations of Cu, Cr, Sb and Pb were larger than predicted by the pH relationship, as a consequence of association with Fe colloids and complexing with dissolved organic carbon. Metal speciation in soil solutions determined by WHAM‐VI indicated that free metal ion (FMI) concentration was significantly related to soil pH for all pH conditions. The FMI concentrations of Cu and Zn were well predicted by pH alone, Pb by pH and Fe content and Cd, Co and Ni by soil pH and organic carbon content. Differences between soluble total metal and FMI concentrations were particularly large for pH < 6. This should be taken into account for risk and critical load assessment in the case of terrestrial ecosystems.     

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。     

石灰石和海泡石组配对水稻糙米重金属积累的影响

为了研究组配改良剂(石灰石+海泡石,LS)对于重金属Pb、Cd、Cu和Zn复合污染稻田的修复效果,在湘南某矿区附近稻田中进行了组配改良剂的田间试验。结果表明:施用0~1.8 kg m-2的组配改良剂LS使土壤pH和CEC显著增加,使土壤中Pb、Cd、Cu和Zn交换态含量显著降低。土壤Pb、Cd、Cu和Zn交换态含量的降低是pH升高,土壤胶体的CEC增加及土壤吸附能力增强的共同作用。施用组配改良剂LS显著降低了3个水稻品种(黄华占、丰优9号、Ⅱ优93)糙米中Pb、Cd和Cu的累积量,最大降幅分别为55.8%、66.9%、37.4%,而对糙米中Zn的含量没有明显影响。当LS施用量为1.8 kg m-2时,能使丰优9号糙米中Cd含量(0.195 mg kg-1)达到国家食品中污染物限量标准(0.20 mg kg-1)以下。土壤中交换态Pb、Cd和Cu含量的降低是糙米中重金属累积量减少的原因。土壤交换态Pb、Cd和Cu含量的对数值(lnC交换态)与其糙米中含量(lnC糙米)的对数值之间存在显著的线性相关关系。     

Mixed chelators of EDTA,GLDA, and citric acid as washing agent effectively remove Cd,Zn, Pb,and Cu from soils

Purpose

Soil washing with chelators is a viable treatment alternative for remediating multi-contaminated soils. The aim of this study was to investigate the removal efficiencies of Cd, Zn, Pb, and Cu in alkaline and acid multi-metal-contaminated soils by washing with the mixed chelators (MC).

Materials and methods

The batch experiments were carried out to evaluate the removal efficiencies of heavy metals in contaminated soils by the MC with different molar ratios of EDTA, GLDA, and citric acid, and evaluated the washing factors, including contact time, pH, MC concentration, and single and multiple washings at the same MC dose, on the removal efficiencies.

Results and discussion

Results showed that the removal efficiencies for Cd, Zn, Pb, and Cu by the MC (the molar ratio of EDTA, GLDA, and citric acid was 1:1:3) were as much as those of the only EDTA washing from both soil at the same application dose of total chelators; moreover, the application dose of EDTA decreased by 80%. For the alkaline-contaminated soil, the removal efficiencies of Cd, Zn, Pb, and Cu decreased with the increasing of the solution pH, which was opposite to acid-contaminated soil. This was attributed to that the metal-ligand complex could be obviously re-adsorbed on the soil surface sites, particularly in low pH values. The removal efficiencies of Cd, Zn, Pb, and Cu depended on MC concentration. A higher MC concentration led to a more effective removal of Cd, Zn, Pb, and Cu in alkaline-contaminated soil; however, their changes were slightly increased in acid-contaminated soil. At the same dose of MC, single washing with higher MC concentration might be favorable to remove heavy metals, moreover, with much less wastewater generation.

Conclusions

The MC (the molar ratio of EDTA, GLDA, and citric acid was 1:1:3) may be a useful, environmentally friendly, and cost-effective chelators to remediate heavily multi-metal-contaminated soil.

     

Inter-relationships between soil properties and the uptake of cadmium,copper, lead and zinc from contaminated soils by radish (Raphanus sativus L.)

Radish was grown in 46 garden plots in England and Wales. Some of the gardens had been contaminated by heavy metals from lead mining. The soils were analysed for pH, organic content and cation exchange capacity; also for Cd, Cu, Pb, and Zn (total, organic bound, exchangeable and specifically sorbed). Acetic acid-soluble P and exchangeable K, Mg and Zn were also determined. Radish bulbs and leaves were analysed for heavy metals. The results were interpreted using linear and multiple linear correlation and regression analysis. Acetic acid satisfactorily predicted Cd uptake and Pb uptake was best predicted by total soil Pb. These regressions were not improved by including other soil properties. Zinc uptake was best modeled using exchangeable Zn and the predictive power of the regression was improved by including pH. However, the pH term was positive suggesting that raising soil pH would increase uptake. A poor relationship between total and exchangeable Zn was changed to a highly significant relationship by including cation exchange capacity and pH. The latter term was strongly negative. Uptake of Cu was not satisfactorily predicted.     

Metal‐Associated Forms and Speciation in Biosolid‐Amended Oxisols

Abstract

The objective of this study was to determine the effects of pH and ionic strength on the distribution and speciation of zinc (Zn), copper (Cu), and cadmium (Cd) in surface soil samples from two Brazilian Oxisols amended with biosolids. Soils and biosolids were equilibrated in an experimental dual‐chamber diffusion apparatus that permits the soils and biosolids to react through a solution phase via diffusion across a membrane. After equilibrium was reached, soil and biosolids samples were sequentially fractionated to identify various solid forms of Zn, Cu, and Cd. Metal concentrations in the solution phase were determined and mass balance calculated. Equilibrating pH had no major effect on Cu solubility from biosolids and, at pH range from 4 to 7, most Cu remained in the biosolids. Soluble Zn and Cd concentration increased with decreasing pH because of the increased solubility of the biosolids. Copper and Zn were primarily associated with the residual fraction and Fe oxides in one soil, but were primarily associated with chemically unstable fractions, or adsorbed to the surface of oxides, in the other soil. In both soils, Cd was primarily associated with readily bioavailable fractions. The effect of pH on the metal distribution was more evident than the ionic strength effect. Free ions were the predominant metal species in solution, especially at lower pH values.     

Dissolved organic carbon and decreasing pH mobilize cadmium and copper in soil

When limed farmland is converted to forestry cadmium (Cd), copper (Cu) and other heavy metals can become mobile because of acidification and increased concentration of dissolved humic substances. The influence of pH and dissolved organic C on amounts and rates of Cd and Cu release was investigated in a cultivated soil by extraction with ～ 1 mm hydrochloric acid at pH 3 with and without dissolved organic C in the batch mode with weekly replacement of the extraction solution. After 88 weeks, 35–50% of aqua regia‐extractable Cd was extracted; addition of 10 mm dissolved organic C had no effect on the amount dissolved, but it increased the initial rate of release because the organic matter buffered the suspension at a lower pH. The solubility and release rate of Cd decreased as the geochemically active fraction was depleted. This suggests that Cd occurs in the soil in a continuum of binding strengths ranging from readily available to strongly bound forms. The repeated extractions resulted in distribution coefficients (K_{d dis}) that have log‐linear relationships with pH. This allows prediction of Cd solubility during acidification of soil. Dissolved organic C enhanced the release of Cu from less than 8% (without) to more than 20% (with) of aqua regia‐extractable Cu. Total contents of Cd and Cu cannot be used as measures of the metals' availability during acidification of former limed farmland. Predictions of availability should be based on the solubility as a function of pH and the degree of Cd or Cu depletion from the geochemically active fraction in soil.