Solubility and uptake of heavy metals from a Swedish soil

Samples of the surface layer (Ap) and of grass, collected from: (1) grass ley fertilized in the normal way; (2) permanent pasture fertilized in the normal way; and (3) permanent pasture treated with large amounts of sewage sludge five years earlier, were analysed for Mn, Zn, Cu, Cr, Co, Ni, Pb, and Cd.The soil samples were extracted with: (1) distilled water saturated with CO₂; (2) 1 M neutral ammonium acetate; (3) ammonium acetate + acetic acid, pH 4.75; and (4) 2 M nitric acid on a waterbath. The efficiency of these extractants differed greatly and, in relative values, was: 1 for H₂O + CO₂, 3.4 for NH₄OAc, 20.7 for NH₄OAc + HOAc, and 343 for 2 M HNO_3- The dissolving effects of the extractants differed markedly with the kind of element.Grass from the field treated with sewage sludge showed much higher contents of Mn and Zn and somewhat higher contents of Cu and Pb than grass from the untreated field. The levels of Cr, Co, Ni, and Cd were practically uninfluenced by the treatment. Grass from a field close to a highway accumulated large amounts of air-borne Pb and Cd during the summer.It is concluded that the total contents of heavy metals in soils have only limited importance for the uptake by plants. Weak extractants therefore give better information about the plant-available amounts in soils.     

Remediation of a grey forest soil contaminated with heavy metals by means of leaching at acidic pH

Purpose

The purpose was to study the heavy-metal leaching from topsoil when acidolysis or combination of acidolysis/complexolysis was applied as an approach for in situ soil remediation. The question was how the acidolysis of ferric iron hydroxides from topsoil would effect on the heavy-metal leaching when soil pH was lowered with sulfuric acid in or without the presence of cut straw into the soil.

Materials and methods

Four zero-suction lysimeters were used in this study. The heavy-metal acidolysis was studied by the soil irrigation with diluted solutions of sulfuric acid or its in situ generation as a result of the bacterial oxidation of S° by Acidithiobacilus thiooxidans.The sulfur requirement was calculated having in mind the higher amount of acid soluble iron in the topsoil due to its contamination by AMD. The combination of acidolysis/complexolysis was studied by cut straw addition to S° at ratio 1:1 and 3:1, respectively. Regular sampling and analyses of the pregnant soil solutions was applied. The pollutant content, their distribution among the geochemical fractions, and the content of amorphous ferric iron hydroxides were determined before and after soil bioremediation.

Results and discussion

The reducible mobile fraction was the main fraction in which almost 50 % of each heavy metal was entrapped as a result of the soil pollution by AMD. The combination of acidolysis/complexolysis, realized by elemental sulfur and cut straw addition to horizon A of the AMD-affected soil at ratio of 1:1, allowed the concentration of lead, uranium, and arsenic after 9 months of remediation to be decreased near the relevant maximum admissible concentration (MAC), as their content in the exchangeable and specific adsorbed mobile fraction were drastically reduced. It determined the lower bioavailability of the pollutants at the end of the leaching stage.

Conclusions

A mixture of elemental sulfur and cut straw at a ratio of 1:1 was an efficient method for in situ bioremediation of AMD-affected soil. The heavy-metal leaching from easily leachable fractions was a result of the joint action of acidolysis/complexolysis, and as a result, the contaminant content in horizon A was significantly reduced.

     

Remediation of a soil contaminated with heavy metals by immobilizing compounds

The labile fraction of heavy metals (HM) in soils is the most important for toxicity for plants and microorganisms. Thus, it is crucial to reduce this fraction in contaminated soils to decrease the negative effect of HM. In a greenhouse experiment, the effects of several additives on the labile fractions of Zn, Cd, Cu, Ni, and Pb were investigated in a soil contaminated during long‐term sewage‐sludge application. The accumulation of HM was studied in the aboveground biomass of wheat (Triticum aestivum L.). The additives used were the clay minerals Na‐bentonite, Ca‐bentonite, and zeolite; the Fe oxides hematite and goethite; the phosphate fertilizers superphosphate and Novaphos. Wheat was planted three times during 5 months, allowed to grow for 7 w, and harvested. Dry matter and HM content of shoots were determined after each harvest. Soil samples were taken after the first and third harvest, and the NH₄NO₃‐extractable HM contents were determined. After the addition of 2% Na‐bentonite as well as 2% Ca‐bentonite, a strong reduction of the labile HM soil fraction and shoot HM concentration was observed. At the end of the experiment, the labile fraction was reduced due to the addition of Na‐bentonite and Ca‐bentonite by 24% and 31% for Zn, by 37% and 36% for Cd, by 41% and 43% for Cu, by 54% and 61% for Ni, and by 48% and 41% for Pb, respectively. Furthermore, the shoot HM concentrations with the exception of Zn were reduced below the phytotoxicity range. Accordingly, the shoot dry‐matter production was significantly increased. The addition of phosphate fertilizers (notably Novaphos) strongly reduced the bioavailability of Pb for wheat plants. By addition of 0.05% Novaphos, the labile fraction and the shoot concentration of Pb were lowered by 39% and 64%, respectively. However, the addition of Fe oxides and zeolite resulted only in a small reduction in HM bioavailability to wheat plants. Among the studied additives, Na‐bentonite and Ca‐bentonite have the most promising potential to reduce the bioavailability for the studied HM.     

Pig manure digestate-derived biochar for soil management and crop cultivation in heavy metals contaminated soil

Management of heavy metal-contaminated soil under drought and other harsh hydrological conditions is critical for protecting soil ecosystem services. In this study, we examined the effect of pig manure digestate-derived biochar as a soil amendment (15 t ha⁻¹) with N fertilizer (180 kg ha⁻¹) on soil and plant heavy metal levels and nutrient availability under various moisture regimes (optimal moisture ~15%, drought condition ≤5%, and flooded condition ≥35% wt.). It was observed that biochar applications significantly decreased heavy metals in the spring wheat plants, lowering Cr by 90%, Ni by 50%, Cd by 9% and Pb by 34% compared to non-biochar (control) treatments. However, the pig digestate-derived biochar increased heavy metals in soil under all moisture regimes, increasing soil Cr by 21%, Ni by 43%, Cu by 55%, Zn by 70%, and Pb by 12%. The availability of macroelements also increased with the biochar applications under the optimum moisture regimes in both soil and plants, increasing Mg²⁺ by 11%, P by 4%, K⁺ by 50%, and Ca²⁺ by 56% in the soil, and Mg²⁺ by 13%, P by 69%, K⁺ by 29, and Ca²⁺ by 39% in plants. Biochar addition also improved chlorophyll fluorescence (CF) levels in the crop for the entire season (12^th to 62^nd day) and the aboveground crop biomass and dry matter contents both increased. Consequently, the use of pig manure digestate-derived biochar with N fertilizer under normal moisture conditions was able to reduce heavy metal availability to plants and thus could be used in contaminated soils to maintain better crop growth and development.     

改良剂原位修复重金属污染土壤研究进展

改良剂原位修复重金属污染土壤因其成本低廉、易于实施,已经得到广泛应用。然而,改良剂对土壤重金属的修复仍然存在着一定的局限性和潜在风险。无机和有机改良剂的修复效果不仅与重金属离子的种类有关,而且还受作物、土壤类型及环境因子的制约。本文就目前常用改良剂的修复效果,存在的问题,改良剂原位修复重金属污染土壤的作用机制以及国内外研究进展作简要综述,并对此方面研究的未来趋势提出展望。     

Effects of soil redox potential (Eh) and pH on growth of sunflower and wheat

ABSTRACT

Soil redox potential (Eh) and pH are fundamentals parameters for plants growth. Measuring soil Eh is essential but complex due to the lack of measurement reliability resulting from high temporal variability and metrological challenges. This paper proposes practical advancements for measuring Eh in aerobic soils using combined electrodes (improvements in methodology specific to cleaning electrodes, measurement time, cleaning the dataset). The study of soil Eh and pH on sunflower and wheat in pot experiments has highlighted the relationship between Eh_cumul (Eh associated with a dimension of time) and the portion of porosity that is accessible to air. For reduced soil conditions, sunflower positively reacts to better aeration. Strong correlations exist between the duration of each potential range and the growth of sunflower. The study of sunflower growth in soil reveals extremely harmful impact resulting from too high and/or too low Eh values.     

Microbial community structure and function in a soil contaminated by heavy metals: effects of plant growth and different amendments

We studied the effects of in situ remediation of a heavy metal (HM) contaminated soil on some soil chemical properties, microbial function and microbial structural diversity after 18 months. The experiment was carried out at semifield scale in containers filled with HM contaminated soil from the Aznalcóllar mine accident (Southern Spain, 1998). The remediation measures consisted of the application of different amendments and/or establishment of a plant cover (Agrostis stolonifera L.). Seven treatments were established: four organic treatments (municipal waste compost (MWC), biosolid compost (BC), leonardite (LEO) and litter (LIT)), one inorganic treatment (sugar beet lime (SL)) and two controls (control with plant cover (CTRP) and control without plant cover (CTR)). Several soil chemical (pH, soluble HM, total organic C (TOC), water-soluble C (WSC) and available-P) and biochemical properties (microbial biomass C (MBC), MBC/TOC ratio and enzyme activities) were determined. Microbial community structure was studied by means of ARDRA (amplified ribosomal DNA restriction analysis). The SL, MWC and BC treatments were the most efficient to raise soil pH and decrease soluble HM concentrations. Total organic C was increased in the organic treatments by 2 to 4-fold, whereas water-soluble C was statistically similar in the CTRP, SL and the organic treatments, probably due to the presence of a root system in all these treatments. Available-P was also increased in the BC, SL and MWC treatments due to the higher P content of the amendments applied in these treatments. Soil microbial function was generally enhanced in the amended and CTRP treatments. The MWC, BC and SL treatments were particularly efficient to increase microbial biomass C, the MBC/TOC ratio and the dehydrogenase and aryl-sulphatase enzyme activities. These results could be attributed to the amelioration of some of the soil chemical properties: increase in soil pH and water-soluble C and decrease of HM soluble concentrations. ARDRA analyses showed changes in structural diversity in both the bacterial and fungal community under the different treatments. Fingerprinting patterns of the 16S rDNA obtained with Hinf-I and of the 18S rDNA with Hpa-II revealed higher similarity percentages among samples from the same treatment compared with samples from the other treatments. In addition, a higher similarity was found between samples from all treatments under the Agrostis influence. The use of certain amendments and/or a plant cover is important for in situ remediation of HM contaminated soils, since these practices can affect soil chemical properties, as well as the microbial community function and structure.     

Application of composted sewage sludges contaminated with heavy metals to an agricultural soil

To elucidate the mechanism of transfer of heavy metals into the food chain, an experiment was carried out with a calcareous soil, to which two different doses of a sewage sludge compost contaminated with either Cd or Zn, Cd, Cu, and Ni were applied. A crop of lettuce was then grown in the amended soils. The application of sewage sludge composts to a calcareous soil lowered the soil's pH, although the value was always around 8 at the end of the experiment. Electric conductivity rose with organic amendment. As anticipated, such an amendment improved the nutritional level of the soils, particularly Nand P, both total and available. Plant yields were negatively affected by organic amendments contaminated with heavy metals, the most dangerous in our experiment being Cd and Zn since this metals easily taken up by plants. As Ni and Cu form insoluble complexes with the organic matter of the sewage sludge composts they are not readily absorbed. Of the metals studied, Cd and Zn showed the highest bioavailability index.     

Effects of organic amendments on rice (Oryza sativa L.) growth and uptake of heavy metals in contaminated soil

Journal of Soils and Sediments - Previous studies showed that rapeseed cake increased rice grain yields and significantly lowered the heavy metal concentrations in the brown rice. The pH, dissolved...     

复合污染土壤中土霉素的吸附行为及其对土壤重金属解吸影响的研究

参考经济合作与发展组织(OECD)化学品试验导则No.106,采用批量平衡试验的方法,探讨了土霉素(Oxytetracycline,OTC)在3种土壤中的吸附解吸特性,并考察了土霉素外加量对土壤中4种代表性重金属元素(铜、锌、铅、镉)解吸量的影响。试验设置的土霉素初始浓度为0.01、0.1、1.0、5.0、10.0、25.0、50.0、100、200和400 mg L-1。结果表明:(1)存在一个土霉素特征浓度,高于或低于该浓度值时土霉素的吸附性质有所差异,且高低两个浓度范围内的数据均能用Freundlich模型与Langmuir模型较好地拟合;(2)当土霉素浓度在0~25 mg L-1之间时,能在土壤表面与重金属发生竞争吸附,且重金属解吸量随土霉素浓度的增加而增加;当土霉素浓度在25~100 mg L-1之间时,部分游离态重金属以与土霉素的络合物形式重新固定于土壤表面,土壤重金属的解吸量随土霉素浓度增加而减少;土霉素浓度高于100 mg L-1时,体系p H相对于对照有明显下降,土壤重金属的解吸量与土霉素浓度又呈正相关。     

火焰原子吸收分光光度法测定污染土壤中5种重金属

采用微波消解法预处理待测土壤,火焰原子吸收分光光度法测定污染土壤消解液中的锌、铜、铅、镉、铬5种重金属.方法简便、灵敏、准确,土壤中锌的相对标准偏差为1.2%;铜的相对标准偏差为1.9%;铅的相对标准偏差为1.2%;镉的相对标准偏差为5.2%;铬的相对标准偏差为1.8%.方法的加标回收率锌为76.8%～104%;铜为86.9%～95.3%;铅为83.0%～94.4%;镉为83.2%～91.9%;铬为90.9%～96.1%,适用于污染土壤中重金属含量的测定.     

Sorption-desorption behaviors of heavy metals by biochar-compost amendment with different ratios in contaminated wetland soil

Purpose

Heavy metal pollution in soils has become a global environmental concern. The combination of biochar and compost has already been proved to be an attractive method in contaminated soil. The objective was to study the sorption-desorption characteristics of Cd, Cu, and Zn onto soil amended with combined biochar-compost.

Materials and methods

In this study, the soil was amended with combinations of biochar and compost with different ratios at 10% (w/w). To determine the sorption-desorption behaviors of heavy metals by biochar-compost amendment with different ratios, we determine the effects of different ratios on soil properties and use batch experiments to investigate sorption-desorption behaviors of Cd, Cu, and Zn.

Results and discussion

The results show that the Langmuir and Freundlich model can well describe the adsorption isotherm of Cd, Cu, and Zn in the soils with or without biochar-compost combinations. The incorporation of amendment combinations into soil significantly promotes the sorption affinity of soil on metals. The sorption capacity of Cd and Zn was improved as the compost percentage rose in biochar-compost more likely due to the increase of organic matter and available phosphorus, while that of Cu was stronger with 10 and 20% biochar addition in biochar-compost combinations likely as the result of the formation of new specific adsorption sites and the mobile Cu adsorption in compost after adding a certain amount of biochar in amendment mixtures. Additionally, a certain proportion of biochar applied into amendment mixtures could suppress desorption of Cd and Cu by pH change, and the Zn desorption rate gradually decreased as the compost ratio increased in amendment mixtures.

Conclusions

The results indicated that the various ratios between biochar and compost have a significant effect on sorption-desorption of metals in soil, which helps us consider the effective combination of biochar and compost in soil.

     

Effects of heavy metals on the structure and functioning of detritivore communities in a contaminated floodplain area

The aim of this study was to determine the effects of heavy metal pollution on the structure and functioning of detritivore soil communities that consist of isopods, millipedes and earthworms, in 15 heavily polluted flood plain soils, located in the delta area of the rivers Rhine and Meuse, in the Netherlands. The 15 study sites represent a gradient in Zn, Cu and Cd concentrations. The structural attributes of the detritivore community, which were assessed, were the species richness and densities in the field sites. The functioning of the detritivore community was studied by determining organic matter decomposition using litter bags and feeding activity with the bait-lamina method. Concentrations of Cd, Cu and Zn were measured in soil, pore water and 0.01 M CaCl₂ extracts of the soil, in adult earthworms and plant leaves. Results show that metal pollution is not a dominating factor determining the species richness and densities of the selected detritivore groups, although the biomass of the earthworm Lumbricus rubellus was positively and significantly correlated to Zn concentrations in pore water and 0.01 M CaCl₂ extracts. Litter decomposition was significantly and positively correlated to detritivore biomass and 0.01 M CaCl₂ extractable Cd concentrations in soil and negatively to pH-CaCl₂, although the range of pH values was very small. It can be concluded that in spite of high metal levels in the soil, bioavailable concentrations are too low to result in clear negative effects on the structure and functioning of detritivores in the Biesbosch, the Netherlands.     

N2O Emission and changings of redox potential and pH in submerged soil samples

The formation of N₂O as a result of denitrification was monitored under laboratory conditions in samples of a waterlogged Italian soil that had been amended with rice straw, KNO₃ and (NH₄)₂HPO₄. Redox potential and pH were also monitored. After four days of incubation N₂O-N production reached a peak of 184.2 μg/d which declined to 29.05 μg/d on the seventh day. The production of N₂O stabilized around this level for about 10 days and then declined to 1.57 μg/d, where it remained till the end of the experiment.     

Nitrate and nitrite reduction in flooded gamma-irradiated soil under controlled pH and redox potential conditions

Nitrate and nitrite reduction was studied in a waterlogged soil after γ-irradiation with 2.5 Mrad. Before irradiation and mineral-N addition the pH was controlled at 4.5, 6 and 8, and the redox potential controlled at 0, +200 and +400 mV Nitrate reduction rate increased with increasing pH as well as with decreasing redox potential. Nitrate reduction rate was doubled by decreasing the redox potential from +400 to 0 mV. At pH 4.5 almost no nitrite accumulated regardless of redox potential, while at pH 6 and 8 marked nitrite accumulation occurred at low redox potential. In relation to non-irradiation. γ-irradiation had a stimulating effect on nitrate reduction at pH 6 and 8 but a retarding effect at pH 4.5; nitrite reduction proceeded slower at pH 6 and 8 but at the same rate at pH 4.5. It has been demonstrated that nitrate and nitrite reduction can be carried out by radiation-resistant enzyme systems of non-proliferating cells of denitrifying organisms.     

Effects of heavy metals in soil on microbial processes and populations (a review)

The effects of Cd, Cu, Zn, and Pb on soil microorganisms and microbially mediated soil processes are reviewed. The emphasis is placed on temperate forest soils. The sensitivity of different measurements is discussed, and data compiled to compare relative toxicity of different metals. On the whole the relative toxicity of the metals (on a μg g^?1 soil basis) decreased in the order Cd > Cu > Zn > Pb, but differences between different investigations were found. The influence of abiotic factors on metal toxicity is briefly discussed and especially examplified by different soil organic matter content. Evidence of tolerance and adaptation in the soil environment and the time scale involved in the evolution of a metal-tolerant microbial community after metal exposure are also considered.     

Incidence of heavy metals in street surface sediments: Solubility and grain size studies

Samples of surface and gutter sediment from roads within N.W. London have been analyzed for levels of Cd, Cu, Fe, Mn, Pb, and Zn. Sediment and associated metal grading curves are presented and apart from Mn and Fe which reflect natural background levels, the remaining metals show distributions which relate to road type and traffic conditions. For highways carrying the highest traffic densities the concentrations of Cd and Pb are greatest for grain sizes between 100 and 500 µm and an aggregation process is postulated. Residential side street samples show a marked affinity of Cd, Fe, and Zn for the coarsest grain fractions. Laboratory sorption and desorption studies are described and solution concentrations are obtained for Cd, Cu, Mn, Pb, and Zn over 1 to 30 day time periods. Solubility curves are typically variable with time. The relationship of leachate patterns to particle size and sample site location is discussed and its relative importance to Stormwater loadings is considered. Extraction efficiencies for the five metals are found to be independent of road type and in the order Cd > Zn, Cu > Mn > Pb. The relevance of this hierarchy to Stormwater toxicity is discussed.     

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。     

草甘膦对重金属污染土壤中铜、锌淋溶的研究

草甘膦分子结构中含有膦酸基、羧基和胺基等,具有强的络合重金属离子的能力,从而影响重金属在土壤中的环境化学行为.本文采用土柱淋溶方法,研究了不同浓度草甘膦溶液( 0、5 、20 和 50 mg/L)对污染土壤中重金属溶出的影响.草甘膦的存在降低了淋滤液的pH,增加了淋滤液中Cu和Zn的含量.逐层采样并分析了土壤中重金属的生物有效性含量,发现草甘膦的存在增加了土柱下层土壤重金属的生物有效性浓度.大量使用草甘膦会导致污染土壤中重金属的溶出,进而污染地下水.     

稻田土壤和稻米中重金属潜在污染风险评估与来源解析

该文选择贵州省典型城市(都匀市)周边水稻种植区为研究区,系统采集了稻田土壤和稻米样品各110个,测定土壤和稻米中Cd、Hg、As、Pb和Cr含量,基于多元统计分析和污染风险评价等分析方法,揭示了研究区稻田土壤重金属污染的主要来源及土壤和稻米中重金属存在的潜在风险。结果表明,与贵州土壤重金属背景值相比,稻田土壤中Cd、Hg、As、Pb和Cr超标率分别为14.55%、40.00%、16.36%、22.72%和13.64%,主要以Hg污染问题最为突出。稻米中只存在3.64%Cd超标,Hg、As、Pb和Cr平均含量均低于国家食品安全标准限定值(GB 2762-2017),说明当地居民食用稻米存在最大的潜在威胁为Cd污染稻米。稻田土壤重金属来源分析结果表明,稻田土壤中Cd、Hg、As和Pb之间呈显著正相关关系,说明土壤中Cd、Hg、As和Pb具有相同的来源,主要来源于当地铅锌矿冶炼、火电厂等污染点源排放的污染物;Cr与其他元素相关性不显著,主要来源于成土母质,为自然来源元素。