Mobility Of Heavy Metals In Soil Research Articles

Effectiveness of constructed wetland technology-treated industrial wastewater on the spinach (Spinacia oleracea) health risks and biochar efficiency.

In peri-urban areas, use of industrial wastewater for irrigation is a common practice. Industrial wastewater contains cadmium, chromium, lead, nickel, and other elements that deteriorate food quality and affect human health. Biochar has been proven to remediate heavy metal contaminated soil by reducing their mobility and bioavailability. A pot experiment was conducted to evaluate the efficiency of different levels of biochar on spinach growth with low heavy metal concentration and to minimize associated health issues. The experiment lasted two months and the treatments: Control (tap water), untreated and treated industrial wastewater and both in combination with biochar (0.5% and 1%) were applied in completely randomized design. Findings suggested that treated industrial wastewater with 1% biochar resulted in maximum plant height, shoot weight, chlorophyll contents (SPAD value), photosynthetic and transpiration rate. Biochar significantly reduced heavy metal mobility in soil due to its porous structure, high pH, higher CEC, and variety of surface functional groups. The cumulative hazard index (HI), hazard quotient, cancer risk, and total cancer risk (TCR) were calculated using method provided by US-EPA for each metal. All treatments had HI values of < 1, however applying 1% biochar significantly reduced the HI values to 2.00E-01 and 2.88E-01 in adults and children, respectively. TCR for all treatments was < 1, while treated industrial wastewater and biochar (1%) has significantly reduced to 1.55E-02 and 1.91E-03 for adults and children, respectively. Thus, it was determined that irrigation with industrial effluents caused toxicity in vegetables, which had a negative impact on human health. Biochar effectively mitigated metal toxicity in both soil and spinach plants that resulted in reduced health/cancer risk.

Temporal changes in the mobility of As, Pb, Zn, and Cu due to differences in biochar stability caused by lignin content

Understanding biochar aging is a critical factor in predicting its long-term effects when added to soil. This study explores the complex links between lignin content in biochar feedstock and biochar stability during accelerated aging, including its influence on heavy metal mobility in soil. In this study, nine types of biochar based on fir (F), pine (P), and oak (O) sawdust were produced at 400 °C, and lignin was extracted from them using ammonia after 0, 3, and 7 days (named as 0FB, 3FB, 7FB, 0PB, 3PB, 7PB, 0OB, 3OB, and 7OB). Subsequently, each biochar was subjected to 25 cycles of wet-dry (WD) and freeze–thaw (FT) aging. The aged low-lignin biochars (7FB, 7 PB, and 7OB) released more dissolved organic matter (DOM) and contained more oxygen-containing surface groups on their surfaces than the high-lignin biochars (0FB, 0PB, and 0OB). The low-lignin biochars with high DOM leaching released 37–85 % more anionic arsenic (As) from biochar-amended soil after 25 cycles of aging than the high-lignin biochars. The stabilities of lead (Pb), zinc (Zn), and copper (Cu) were increased due to strong binding to surface functional groups on the low-lignin biochar. The acid-soluble fractions of Pb, Zn, and Cu were converted to organic-bound fractions as biochar aging progressed, with the degree of transformation being inversely proportional to the lignin content of biochar. This research highlights the crucial role of lignin in shaping biochar stability, and reveals how biochar stability impacts soil heavy metals speciation, opening new avenues for effective biochar-based environmental solutions and the promotion of soil health.

Impact of thermal soil treatment on heavy metal mobility in the context of waste management.

Thermal soil treatment is a well-established remediation method to remove organic contaminants from soils in waste management. The co-contamination with heavy metals raises the question if thermal soil treatment affects heavy metal mobility in soils. In this study, four contaminated soils and a reference sample were subjected to thermal treatment at 105°C, 300°C and 500°C for 7 day. Thermogravimetry and differential scanning calorimetry were used to understand the reactions, and resulting gases were identified by Fourier-transformed infrared spectroscopy. Treated and untreated samples were characterised by X-ray diffraction (XRD) and electron microprobe analysis and subjected to pH-dependent leaching tests, untreated samples additionally by X-ray-fluorescence (XRF) and inductively coupled plasma mass spectroscopy (ICP-MS). Leachates were analysed using ICP-MS and ion chromatography. Maximum available concentrations were used for hydrogeochemical modelling using LeachXS/Orchestra to predict leaching control mechanisms. Leaching experiments show that thermal treatment tends to decrease the mobility at alkaline pH of Pb, Zn, Cd, As and Cu, but to increase the mobility of Cr. In the acidic to neutral pH range, no clear trend is visible. Hydrogeochemical modelling suggests that adsorption processes play a key role in controlling leaching. It is suggested that the formation of minerals with a more negatively charged surface during thermal treatment are one reason why cations such as Pb2+, Zn2+, Cd2+ and Cu2+ are less mobile after treatment. Future research should focus on a more comprehensive mineralogical investigation of a larger number of samples, using higher resolution techniques such as nanoscale secondary ion mass spectrometry to identify surface phases formed during thermal treatment and/or leaching.

Heavy Metal Migration in Soil-Plant System in Conditions of Urban Environmental Pollution

This study is devoted to heavy metal soil migration to coltsfoot in urban pollution of Tyumen city. Soil and plant samples were collected in the summer of 2017 to 2020 at the control site, highway, engine-building, oil refinery, battery manufacturing, and metallurgical plants. Heavy metals (Cu, Zn, Fe, Mn, Pb, Cd, Ni, Co, and Cr) mobile and acid-soluble forms in soils, and metals concentration in plants were analyzed by atomic absorption and atomic emission spectroscopy. Metals concentration in soils of urban area exceeded the control by 1.1 to 20 times. Relative accumulation of metals decreased in the order: Pb &gt; Cu &gt; Zn &gt; Ni &gt; Cr &gt; Fe &gt; Co &gt; Mn &gt; Cd. Heavy metals mobility in soils decreased in the order: Cd &gt; Mn &gt; Pb &gt; Zn &gt; Ni = Cu &gt; Co &gt; Cr &gt; Fe. Coltsfoot metal accumulation changed in the order: Fe &gt; Zn = Mn &gt; Pb &gt; Cu &gt; Cr &gt; Co &gt; Ni &gt; Cd. The highest contamination for most of the metals was at the metallurgical plant, while Ni and Co concentrations were maximum at the oil refinery. Content of Cu, Zn, Fe, Cd, Ni, and Co in coltsfoot correlated with a concentration in soils. Bioconcentration factor showed the following metal bioavailability: Cu &gt; Zn &gt; Cd &gt; Pb &gt; Ni &gt; Mn &gt; Cr &gt; Co &gt; Fe. Heavy metal accumulation in coltsfoot should be taken into account during sanitary control of herb drugs based on this plant.

Transferring waste red mud into ferric oxide decorated ANA-type zeolite for multiple heavy metals polluted soil remediation

Herein, a novel "waste reclamation for soil remediation" strategy has been developed for both alkaline waste red mud (RM) recycling and heavy metal (HM) polluted soil remediation. Through a direct one-pot hydrothermal reaction process, the Al, Si, alkali, and Fe2O3 components in waste RM have been transferred into ferric oxide decorated ANA-type zeolite (Fe2O3-ANA). As tested by the HMs polluted soil remediation and oilseed rape planting experiment, when 25 g/kg Fe2O3-ANA is added into the Pb2+, Cu2+, Cr3+ and anionic AsO2- polluted soil (HM concentration: 100–200 mg/kg), it can effectively suppress the HMs mobility in soil and reduce the bio-accumulation concentrations of HMs in the harvested oilseed rape (reduce ratio: 37.9–69.5%). The detailed mechanism study using energy dispersive X-ray energy spectroscopy, in-depth X-ray photoelectron spectroscopy and density function theory calculation concludes that the Cu2+, Pb2+ and Cr3+ in soil have been adsorbed and trapped in the framework structure of ANA in Fe2O3-ANA mainly via the cation exchange process. While the anionic AsO2- species are mainly caught by the Fe2O3 component in Fe2O3-ANA via surface adsorption. Overall, this work firstly transforms waste RM into Fe2O3-ANA for soil remediation, which is valuable to waste resource recycling and environmental conservation.

Effects of Co-composting of Municipal Solid Waste and Pigeon Pea Biochar on Heavy Metal Mobility in Soil and Translocation to Leafy Vegetable Spinach.

An experiment was conducted to study the effects of co-composted products of municipal solid waste (MSW) and pigeon pea biochar (PPB) on heavy metal mobility in soil and its uptake by spinach. Application of municipal solid waste biochar co-compost (MSWBC) significantly (p ≤ 0.05) reduced the heavy metal content in spinach leaves and roots compared to municipal solid waste compost (MSWC) amended soil. The percent decrease in spinach leaf following the application of MSWBC-10% PPB compared to MSWC was 20.62%, 28.95%, 36.02%, 41.88%, 41.50%, and 41.23% for Cu, Cd, Pb, Cr, Ni, and Zn, respectively. The dry matter yield of spinach and soil organic carbon (SOC) content in soil amended with MSWBC-10% PPB was significantly increased by 32.75% and 47.73%; and 17.62% and 27.45% relative to control and MSWC amended soil. The study concludes that co-composted product, MSWBC, stabilized heavy metals in MSW, reduced their uptake by spinach and thus making it a viable option for safe disposal of MSW.

Microbially Mediated Coupling of Fe and N Cycles by Nitrate-Reducing Fe(II)-Oxidizing Bacteria in Littoral Freshwater Sediments.

Nitrate-reducing iron(II)-oxidizing bacteria have been known for approximately 20 years. There has been much debate as to what extent the reduction of nitrate and the oxidation of ferrous iron are coupled via enzymatic pathways or via abiotic processes induced by nitrite formed by heterotrophic denitrification. The aim of the present study was to assess the coupling of nitrate reduction and iron(II) oxidation by monitoring changes in substrate concentrations, as well as in the activity of nitrate-reducing bacteria in natural littoral freshwater sediment, in response to stimulation with nitrate and iron(II). In substrate-amended microcosms, we found that the biotic oxidation of ferrous iron depended on the simultaneous microbial reduction of nitrate. Additionally, the abiotic oxidation of ferrous iron by nitrite in sterilized sediment was not fast enough to explain the iron oxidation rates observed in microbially active sediment. Furthermore, the expression levels of genes coding for enzymes crucial for nitrate reduction were in some setups stimulated by the presence of ferrous iron. These results indicate that there is a direct influence of ferrous iron on bacterial denitrification and support the hypothesis that microbial nitrate reduction is stimulated by biotic iron(II) oxidation.IMPORTANCE The coupling of nitrate reduction and Fe(II) oxidation affects the environment at a local scale, e.g., by changing nutrient or heavy metal mobility in soils due to the formation of Fe(III) minerals, as well as at a global scale, e.g., by the formation of the primary greenhouse gas nitrous oxide. Although the coupling of nitrate reduction and Fe(II) oxidation was reported 20 years ago and has been studied intensively since then, the underlying mechanisms still remain unknown. One of the main knowledge gaps is the extent of enzymatic Fe(II) oxidation coupled to nitrate reduction, which has frequently been questioned in the literature. In the present study, we provide evidence for microbially mediated nitrate-reducing Fe(II) oxidation in freshwater sediments. This evidence is based on the rates of nitrate reduction and Fe(II) oxidation determined in microcosm incubations and on the effect of iron on the expression of genes required for denitrification.

The influence of particle size and feedstock of biochar on the accumulation of Cd, Zn, Pb, and As by Brassica chinensis L.

Biochar produced from rice straw (RC) and maize stalk (MC) was amended to the heavy metal-contaminated soil to investigate the effects of different biochar feedstock and particle size (fine, moderate, coarse) on the accumulation of Cd, Zn, Pb, and As in Brassica chinensis L. (Chinese cabbage). The concentrations of Cd, Zn, and Pb in shoot were decreased by up to 57, 75, and 63%, respectively, after biochar addition (4%). Only MC decreased As concentration in B. chinensis L. shoots by up to 61%. Biochar treatments significantly decreased NH4NO3-extractable concentrations of Cd, Zn, and Pb in soil by 47-62, 33-66, and 38-71%, respectively, yet increased that of As by up to 147%. Amendment of RC was more effective on immobilizing Cd, Zn, and Pb, but mobilizing soil As, than MC. A decrease in biochar particle size greatly contributed to the immobilization of Cd, Zn, and Pb in soil and thereby the reduction of their accumulations in B. chinensis L. shoots, especially RC. Increases in soil pH and extractable P induced by biochar addition contributed to the sequestration of Cd, Zn, and Pb and the mobilization of As. Shoot biomass, root biomass, and root system of B. chinensis L. were enhanced with biochar amendments, especially RC. This study indicates that biochar addition could potentially decrease Cd, Zn, Pb, and As accumulations in B. chinensis L., and simultaneously increase its yield. A decrease in biochar particle size is favorable to improve the immobilization of heavy metals (except As). The reduction in Cd, Zn, Pb, and As levels in B. chinensis L. shoots by biochar amendment could be mainly attributed to a function of heavy metal mobility in soil, plant translocation factor, and root uptake.

Barium (Ba) leaching from soils and certified reference materials

Despite the position of Ba as the 14th most abundant element on Earth, relatively few studies have examined the occurrence of Ba in soil. Information on how changing environmental conditions can potentially affect Ba mobility, which is obtained from laboratory or field investigations, is scarcely available. In the present study, the release of Ba from soil samples that have varying organic matter, iron, calcium, and sulfur contents and a wide range of total Ba concentrations was investigated using commonly applied single and sequential extractions, pHstat leaching tests and column tests. Additionally, certified reference materials (soil and sediment) were analyzed to provide data for Ba that are not yet available. Despite relatively high pseudo-total concentrations in soil (69–709 mg/kg) compared to commonly investigated trace elements, such as Cd, Zn, Pb, Cu and Ni, Ba showed low mobility in the soils investigated in the present study, indicating that only a very small proportion of Ba is readily available for leaching or uptake by plants. Ammonium-EDTA only extracted small amounts of Ba from the soils (<3% of the total content, except in one sample). Acidification of the soils (below pH 4) caused a substantial release of Ba (between 3 and 14% of its pseudo-total content). The investigation of Ba leaching as a function of time in combination with geochemical modeling showed that unintended side effects, such as precipitation of BaSO4 during leaching tests, can influence the results. Leaching tests and extractions that have been developed to evaluate heavy metal mobility in soils require careful interpretation when Ba is considered and are likely to not always be suited for Ba because of unintended side effects, such as precipitation reactions. Single extractions with ammonium-EDTA are not suitable for determining the ‘potentially mobile pool’ of Ba in soils because of the low stability constant of Ba-EDTA complexes. Single extractions with 0.01 mol/L CaCl2 and 0.43 mol/L acetic acid solutions can offer a fast preliminary screening of Ba mobility. Investigating the kinetics of Ba release, for example, in pHstat leaching tests, can provide useful information about reactions that occur during leaching tests.

Effects of clay minerals, hydroxides, and timing of dissolved organic matter addition on the competitive sorption of copper, nickel, and zinc: A column experiment

Infiltration of heavy metal (HM) polluted wastewater can seriously compromise soil and groundwater quality. Interactions between mineral soil components (e.g. clay minerals) and dissolved organic matter (DOM) play a crucial role in determining HM mobility in soils. In this study, the influence of the timing of addition of DOM, i.e. concurrent with or prior to HMs, on HM mobility was explored in a set of continuous flow column experiments using well defined natural soil samples amended with goethite, birnessite and/or smectite. The soils were subjected to concurrent and sequential additions of solutions of DOM, and Cu, Ni and Zn. The resulting breakthrough curves were fitted with a modified dose-response model to obtain the adsorption capacity (q0). Addition of DOM prior to HMs moderately enhanced q0 of Cu (8–25%) compared to a control without DOM, except for the goethite amended soil that exhibited a 10% reduction due to the blocking of binding sites. Meanwhile, for both Zn and Ni sequential addition of DOM reduced q0 by 1–36% for all tested soils due to preferential binding of Zn and Ni to mineral phases. In contrast, concurrent addition of DOM and HMs resulted in a strong increase of q0 for all tested metals and all tested soil compositions compared to the control: 141–299% for Cu, 29–102% for Zn and 32–144% for Ni. Our study shows that when assessing the impact of soil pollution through HM containing wastewater it is crucial to take into account the presence of DOM.

Assessment of metal transfer factor under irrigation with treated municipal wastewater

The knowledge of the optimum transfer factor (TF) of heavy metals from soil to plant is of vital importance, because TF is an indicator of heavy metal mobility in soils and a factor that quantifies the existing differences in the bioavailability of metals to plants. Optimum heavy metal transfer factors were found during multiple linear regression analysis (MLRA), under the effect of treated municipal wastewater (TMWW), in the context of a greenhouse randomized blocks experiment. The treatments used were: control (fresh well water), 25%, 50%, 75%, and 100% TMWW in four replications. Cabbage (Brassica oleracea var Capitata) was used as test plant. The optimum metal TF was expressed, as a function of: (i) dry matter (dm) yield of cabbage plant parts (roots, leaves, stems, head) and whole plant, (ii) dm metal content (DMMC), and (iii) pollution load index (PLI). Based on the parameters used in the multiple regression equation, the DMMC and the PLI were found to be statistically, significantly related to TF. Optimum metal transfer values were also calculated as the geometric mean of all metal TFs for each plant part (root, leaves, stems, heads). The geometric mean TF values found, reflecting the whole plant, were 3.44 for Zn, 0.93 for Cu, 4.32 for Cd, 116.67 for Cr, 2.86 for Ni, and 0.56 for Pb.

Sorption of copper, zinc and lead on soil mineral phases

Soil mineral phases play a significant role in controlling heavy metal mobility in soils. The effective study of their relation needs the integrated use of several analytical methods. In this study, analytical electron microscopy analyses were combined with sequential chemical extractions on soils spiked with Cu, Zn and Pb. Our aims were to study the metal sorption capacity of soil mineral phases and the effect of presence of iron oxide and carbonate on this property of soil minerals. Copper and Pb were found to be characterized by higher and stronger sorption on the studied samples than Zn. Only the former two metals showed significant differences in their immobilized metal amounts on the studied samples and soil mineral particles. Highest metal amounts were sorbed on the swelling clay mineral particles (smectites and vermiculites), but iron-oxide phases may also have similar lead sorption capacity. Alkaline conditions due to the carbonate content of soils resulted both in increased sorption on the mineral particles for Cu and in enhanced role of precipitation for all the studied metals. On the other hand, the intimate association of phyllosilicates and iron resulted in significant increase in metal sorption capacity of the given particle. The results of sequential extractions could be successfully completed by the analytical electron microscopy analyses for studying the sorption capacity of discrete mineral particles. Their integrated use helps us in better understanding the heavy metal–mineral interactions in soils.

Speciation of Zn, Cu, and Pb in the soil depending on soil texture and fertilization with sewage sludge compost

Heavy metal (HM) mobility in soil depends on the HM species in it. Therefore, knowledge of the HM speciation in soil allows the prediction of HM impact on the environment. HM speciation in soil depends on the metal chemical origin, soil texture, and other factors such as the origin and level of soil contamination. Recently, the problem of organic waste utilization is of great importance as the amount of this recyclable material is continually increasing. One of the possible ways of recycling is the use of processed organic wastes for agricultural needs. In this research, aerobically composted sewage sludge was used, the utilization of which is of essential importance. But one of the most serious restrictions is HM transfer from such material to the soil. Therefore, a prediction of HM mobility in soil and its migration in the environment is an important issue when using sewage sludge compost (SSC) in agriculture. Zn, Cu, and Pb speciation was performed according to the modified methodology of Tessier et al. (Anal Chem 51:844–851, 1979) in two different (sandy and clay) soils with background HM amounts and in soil samples amended with aerobically digested SSC to find out the predominant species of the investigated HM and to predict their potential availability. The modified method of sequential extraction initially proposed by Tessier et al. (Anal Chem 51:844–851, 1979) is designed for HM speciation into five species where HM mobility decreases in the order: F1—exchangeable HM (extracted with 1 M MgCl2 at an initial pH of 7 and room temperature), F2—carbonate-bound HM (extracted with 1 M CH3COONa buffered to pH 5 at room temperature), F3—Fe/Mn oxide-bound HM (extracted with 0.04 M NH2OH·HCl at an initial pH of 2 at 96°C), F4—organic matter-complexed or sulfide-bound HM (extracted with 0.02 M HNO3 and 30% (v/v) H2O2 at a ratio of 1:1 and an initial pH of 2 at 85°C), and F5—the residual HM (digested with HNO3, HF, and HCl mixture). After digestion, HM amounts in solution were determined by atomic absorption spectrometry (AAS ‘Hitachi’). Mixtures of uncontaminated soils of different textures (clay and sandy) with SSC in ratios 20:1, 10:1, and 5:1 were used to simulate the land application with SSC. During a period of 7 weeks, changes in Zn, Cu, and Pb content within species were investigated and compared weekly in soil–SSC mixtures with their speciation in pure soil and in the SSC. Results in the SSC showed that more HM were found as mobile species compared to the soils, and in sandy soil, more were found in the mobile species than in clay soil. But the HM speciation strongly depended on the metal chemical origin. According to the potential availability, HM ranked in the following order: Zn>Pb>Cu. Zinc generally occurred in the mobile species (F1 and F3), especially in sandy soils amended with SSC, and changes of the Zn speciation were insignificant at the end of the experiment. Pb transfer to insoluble compounds (F5) was evident in the SSC–soil mixtures. This confirms that Pb is extremely immobile in the soil. However, the observed increase of Pb amounts in the mobile species (F1 and F2) during the course of experiment shows a critical trend of Pb mobilization under anthropogenic influence. Copper in the soil–SSC mixtures had a trend to form compounds of low mobility, such as organic complexes and sulfides (F4) and nonsoluble compounds (residual fraction F5). Initially, the amounts of mobile Cu species (F1 and F2) increased in the soils amended with SSC, probably due to the influence of SSC of anthropogenic origin with lower pH and high organic matter content, but Cu mobility decreased nearly to the initial level again after 3–4 weeks. Hence, the soil has a great specific adsorption capacity to immobilize Cu of anthropogenic origin. Zn mobility and environmental impact was greater than that seen for Cu and Pb, while mobility of both Cu and Pb was similar, but variable depending on soil texture and contamination level. The effect on the shift of HM mobility and potential availability was greater in sandy SSC-amended soils than in clay soils and increased with an increasing amount of SSC. Usage of SSC for land fertilization should be strictly regulated, especially regarding Pb amounts. The influence of SSC on Cu and Zn mobility and potential availability was more significant only in the case of sandy soil with a higher SSC ratio. Nevertheless, this waste product of anthropogenic origin increased Pb mobility in all cases in spite of only moderate Pb mobility in SSC itself. Therefore, aerobic processing of sewage sludge must be strictly regulated, especially regarding Pb amounts, and SSC ratios must be in control regarding HM amounts when using it for on-land application.

The application of pH stat leaching tests to assess the pH-dependent release of trace metals from soils, sediments and waste materials

pH is one of the key parameters that determines heavy metal mobility in soils, sediments and waste materials. In many respects leaching behaviour as reflected by the pH stat leaching tests provide a better means of assessing environmental impact than analysis of total elemental composition. This paper discusses the use of pH stat leaching tests as a tool to assess the potential mobilisation of trace metals from soils, sediments and waste materials. The possibilities of pH stat leaching tests are illustrated by means of different examples. The mathematical fitting of metal leaching behaviour from soils and sediments enabled a distinction between 5 groups of elements with a different leaching behaviour, which could be related to ‘pools’ with different reactivity. Contrary to single and sequential extractions, where pH is difficult to control, the reactivity and mobility of metals at a user-defined pH can be investigated. Moreover, the potential buffering capacity of the sample and its sensitivity to pH changes as a result of external stresses (e.g. soil acidification, liming) can be estimated. A multidisciplinary approach combining mineralogical analysis (X-ray diffraction) with chemical analysis, pH stat leaching tests and geochemical modelling (MINTEQA2) can provide information on the solid-phase speciation and reactivity of heavy metals in soils, sediments and waste materials. Besides the influence of pH on heavy metal leaching behaviour, additional information on heavy metal leachability and retention by the solid matrix was obtained from the kinetics of metal release during a pH stat test.

Mobilisation of Cu from soils by dissolved natural and processed humic substances

Dissolved humic substances (HS) may increase the dissolution of heavy metals (HM) and hence augment HM mobility in soils by forming dissolved HM–HS complexes, but the role of HS composition, which depends on the origin of HS, is uncertain. In order to determine the infl uence of HS composition / origin on HM dissolution, two HM-polluted soil samples were extracted in the batch mode by three diff erent HS solutions containing ~25 mM dissolved organic carbon (DOC) in 0.05 mol/l KNO 3 at pH = 6 for totally 10 weeks with weekly replacements of HS solutions. Two natural HS solutions (MEMO(beech)-HS and MEMO(spruce)-HS) were obtained from litter layers under beech and Norway spruce. Processed HS (Bio-HS) is cow slurry, which has been treated by oxidative, hydrolytic destruction in order to dissolve organic compounds and remove inorganic compounds such as HM. DOC, Cu concentrations and pH were determined in clear extracts obtained each week by centrifugation. Th e investigation showed that natural as well as processed HS possess a high capacity to dissolve HM in polluted soils. In fact, up to 50% of total Cu was extracted aft er 10 weeks from strongly contaminated soil (CRC), indicating that HS has a substantial potential as a cleaning agent for remediation of HM-polluted soils. Th e origin of HS infl uenced the extracted amounts, which decreased in the order MEMO(spru ce)-HS > ME MO(beech)-HS > Bio-HS, but only in the extraction of the CRC soil, while the three HSs extracted similar percentages from moderately Cu-polluted agricultural soil (Cu-P). Accordingly, HM nature, maybe HS origin and soil composition aff ect HM mobility and must be taken into consideration if HS is to be used as a cleaning agent in the remediation of HM-polluted soils.

Influence of red mud, zeolite and lime on heavy metal immobilization, culturable heterotrophic microbial populations and enzyme activities in a contaminated soil

In this study we compared the efficiency of different amendments, notably red mud (a bauxite residue), natural zeolite and lime, to immobilize the heavy metals present in a polluted acidic soil [Pb (3266 mg kg − 1 d.m.), Cd (35.4 mg kg − 1 d.m.) and Zn (1495 mg kg − 1 d.m.)] and to influence several microbiological properties. The addition of all the amendments decreased significantly ( P < 0.05) the solubility of Pb, Cd and Zn and the increase of soil pH was identified as a common mechanism of action for both red mud and lime. Despite reducing the heavy metal solubility, the addition of zeolite and lime did not affect the number of culturable fast-growing heterotrophic bacteria whereas the red mud caused a significant increase ( P < 0.05) of this soil microbial component. All the amendments reduced the number of heterotrophic fungi ( P < 0.05) while only the lime addition influenced negatively the number of free-living N 2-fixing bacteria. Furthermore, the addition of red mud and lime caused a significant change of the dominant culturable bacterial community. Partial sequencing of the 16S rDNA gene of randomly selected bacterial isolates revealed that dominant strains from the lime and red mud-soils were mostly belonging to β-Proteobacteria and Bacteroidetes/Chlorobi group whilst only Actinobacteria and Firmicutes were identified in control and zeolite soils. These latter were largely colonized by Arthrobacter and Bacillus while Ralstonia and Pedobacter prevailed in soils treated with lime and red mud. Moreover, the Biolog Ecoplate assay revealed that the number of substrates utilized (OD 590 > 0.15) by the different microbial communities (richness) was following the order: red mud-soil > lime-soil > zeolite-soil = control-soil. The same trend was observed for the urease activity but not for dehydrogenase and β-glucosidase. It is concluded that all the amendments considered influenced with a different extent the heavy metal mobility in soil as well as the structure and function of the resident culturable microbial communities. Red mud was the most effective at reducing the “mobile” form of the metals considered and at promoting bacterial abundance and soil enzyme activity. Nevertheless, red mud and lime addition caused a dramatic shift of the culturable bacterial population from Gram positive to Gram negative forms. The poor catabolic activity detected with the Biolog assay for zeolite and control-soil suggested the inability of Arthrobacter and Bacillus strains to oxidize the substrates in the Ecoplate rather than reflect the actual catabolic versatility of the microbial communities.

Single‐Element and Competitive Metal Mobility Measured with Column Infiltration and Batch Tests

The distribution coefficient, Kd, is often used to quantify heavy metal mobility in soils. Batch sorption or column infiltration tests may be used to measure Kd. The latter are closer to natural soil conditions, but are difficult to conduct in clays. This difficulty can be overcome by using a laboratory centrifuge. An acceleration of 2600 gravities was applied to columns of London Clay, an Eocene clay sub-stratum, and Cu, Ni, and Zn mobility was measured in centrifuge infiltration tests, both as single elements and in dual competition. Single-element Kd values were also obtained from batch sorption tests, and the results from the two techniques were compared. It was found that Kd values obtained by batch tests vary considerably depending on the metal concentration, while infiltration tests provided a single Kd value for each metal. This was typically in the lower end of the range of the batch test Kd values. For both tests, the order of mobility was Ni>Zn>Cu. Metals became more mobile in competition than when in single-element systems: Ni Kd decreased 3.3 times and Zn Kd 3.4 times when they competed with Cu, while Cu decreased only 1.2 times when in competition with either Ni or Zn. Our study showed that competitive sorption between metals increases the mobility of those metals less strongly bound more than it increases the mobility of more strongly bound metals.

Crop contamination by selected trace elements

Goal and Background The regulatory limit for the allowable concentration of heavy metals (HM) in agricultural soils should be based both on HM status and on soil parameters that influence HM mobility. In this paper, a soil categorization scheme is proposed which is based on the main factors that influence HM mobility in soils. The scheme also makes use of the existing regulatory limits for total concentrations of trace elements in Slovak soils but additionally takes into account the potential ability of the soils to mobilize trace elements. A map of the Slovak Republic showing the soil categorization using this scheme is presented.

Significance of aqueous cation composition on heavy metal mobility in a natural clay.

Heavy metal mobility in soils is influenced by various soil variables and environmental factors, including the composition of the soil-aqueous phase. This study used the sequential extraction technique to study how major cations could affect heavy metal sorption and speciation in a natural clay. The sorption of Zn, Pb, and Cd by the soil in the presence of Na+ and Ca2+ and the resulting metal speciation in the sorbed phases were examined. Sorption experiments were performed at pH levels of 3 to 8. Sorptions occurring in both single and multiple heavy metal systems were investigated. The results show that Na+ and Ca2+ significantly inhibited Zn, Pb, and Cd sorption in the acidic pH range only. The reduction in the exchangeable sorption was responsible for a large part of the reduction in the total Zn, Pb, and Cd sorption in the presence of Na+ and Ca2+. Specific adsorptions of heavy metals in other fractions of sorbed phases were only marginally affected by the composition of cations. The reduction in the exchangeable sorption increased with increasing concentration of Na+ and Ca2+. In the presence of a major cation, the competitive adsorption among the heavy metals seemed to have only a minor effect on individual heavy metal sorption.

Determination of mobile heavy metal fraction in soil: Results of a pot experiment with sewage sludge

The development of a method using a chelating resin to assess heavy metal mobility in soil and the first results obtained from a pot experiment with sewage sludge additions were studied. The resin was Chelex 100 with the calcium (Ca)‐form of the resin proving to be best suited for the extraction. The efficiency of recovery of the heavy metals from an aqueous solution ranged from 81.2% for cadmium (Cd) to 102% for copper (Cu) within 24 hours. For heavy metal extractions from a soil sample, a 96 hour extraction period was found to be optimum. The extracted heavy metal portion was comparable with the results obtained with an ammonium acetate (NH4AOc) extraction. Total heavy metal contents in the substrate of the pot experiment did not show a significant influence due to the sewage sludge treatments, although considerable amounts of heavy metals were added by the sewage sludge. This effect can be both due to the incomplete recovery of heavy metals by an aqua regia extraction and leaching losses of these elements from the pots. Rape (Raphanus sativus L.) plants did not have any heavy metal contents which might indicate a high availability in soil, with the Cd and Cr contents in the rape biomass being partly lower in the sewage sludge‐treated pots than in the control plants; however, zinc (Zn) uptake slightly increased with increasing sewage sludge treatments. The Chelex 100 extraction procedure was correlated with Cd plant uptake, while the NH4AOc extraction procedure was better related to the Zn uptake by rape plants.