Speciation Of Metals In Soils Research Articles

Predicting chemical speciation of metals in soil using Visual Minteq

• Soil processes affect metal chemical speciation and their biogeochemical activity. • The current study predicted chemical speciation of eight metals in two soil layers. • Divalent forms of metals predominated in both soil layers (79.9%). • Chromium showed a chemical speciation that varied from that of the other metals (95.8% as CrOH+). • Mean percentage ages of all metal ions were similar for all 15 field locations investigated. From soil contamination and risk assessment perspectives, it is imperative to understand the ecological processes occurring in soils. Certain soil processes greatly affect chemical speciation of potentially toxic metals (PTMs), and thus also influence their biogeochemical activity. The current study analyzed chemical speciation of eight PTMs (Cd, Cr, Fe, Cu, Mn, Ni, Zn, and Pb) in upper and lower soil layers for 15 agronomic fields of Vehari-Pakistan using Visual Minteq software. The divalent forms of most PTMs (PTM2+) generally predominated in both soil layers (79.9% overall occurrence). However, chromium revealed a different pattern of chemical speciation (95.8% as CrOH+) compared to other PTMs. The mean percentage of all the PTMs2+ was slightly higher for the lower soil layer (81.3%) than in the upper layer (78.4%), the trend being same for all the PTMs, except Cr. This higher PTMs2+ percentage in lower soil layers than upper layers was due to lower content of organic matter and other anions such as Cl− and HCO 3 − . The mean percentage ages of all the PTMs2+ was similar among all the 15 agronomic fields, which was confirmed by strong Pearson correlation values (R2 > 0.95). The PCA graph grouped all the agronomic fields and PTM2+ closely, except Cr2+ and Cu2+. This grouping confirmed the similar chemical speciation of PTMs, except Cu and Cr in studied fields.

Speciation of metals in soils of steppe landscapes affected by mining (Southern Urals)

Speciation of ore and accompanying elements (Cu, Zn, Fe, Ni, Pb, Cd, Cr, V, Ba, Sr) in steppe soils of the Transurals (vicinity of city of Sibay, Bashkortostan) was studied with sequential extraction method. Attention was given to change of elements’ speciation in area affected by mining (Cu-Zn deposit). The results are supplemented by chemical analysis of humic acids (isolated by alkaline extraction) and granulometric fractions. It was revealed that the soils of background areas are characterized by low mobility of studied elements and a relatively uniform distribution over soil profile. Residual fraction percentage (fraction’s share in element’s total content) is the highest. Percentage of exchangeable and carbonate fractions is insignificant (Sr and Ba are exceptions). Percentage of fraction of crystalline Fe hydroxides, reduceable and oxidizable fractions varies from shares of a percent to 15%. Cd stands out for a high percentage of oxidizable fraction (up to 30% of Cd total content) and relatively low percentage of residual fraction (up to 50%). Comparison of obtained results allows us to suggest that near objects of mining industry dust enriched with Cu, Zn, Cd, Pb and Sb comes to the surface. This leads to shard increase of Cu, Zn, Cd content in the upper layer of chernic horizon, change of these elements’ speciation and distribution among granulometric fractions. Increase of elements content is not only due to prevailing residual fraction; Cu, Zn, Cd of oxidizable fraction, reducible fraction and Fe hydroxides fraction significantly increase. Sharp increase of oxidizable fraction percentage (largely due to sulfides) is noted.

Biochar derived from hydrolysis of sewage sludge influences soil properties and heavy metals distributed in the soil.

Sewage sludge contains a large number of nutrients and dangerous substances, when sludge was processed into sludge hydrochar that was added to the soil, which not only solve the problem of sludge disposal, but also amend the soil and fix pollutants in the soil. However, it was lack of report on the effect of the sludge hydrochar on soil compositions and soil microorganism community structures until now. In the present study, the hydrothermal carbonization method is used to prepare hydrochar from sewage sludge at temperatures of 180℃ and 240℃ at durations of 6h and 15h in this paper. The effects of the prepared sludge hydrochar on soil-derived dissolved organic matter (DOM), the content of total dissolved nitrogen (TDN) and NO3--N in soil, and the community structure of soil bacteria and fungi were evaluated. Furthermore, the change rules in heavy metal speciation in soils treated with sludge hydrochar were investigated. With the increase in the preparation temperature and dosage of sludge hydrochar, the main components of DOM changed from soluble microbial byproducts to fulvic acid-like and humic acid-like fractions through UV and fluorescence characterization. The sludge hydrochar prepared at low temperature could significantly increase the contents of TDN and NO3--N in the soil. Affected by sludge hydrochar, the dominant phylum of the bacterial community changed from Proteobacteria to Actinobacteria, and the dominant phylum in the fungal community did not change, but its relative abundance increased. Finally, the sludge hydrochar obtained when the carbonization time was 15h was more beneficial to reduce the total amount and available content of heavy metals in the soil. The study provides a basis for sludge hydrochar application for the soil amendment.

A bibliometric analysis and assessment of priorities for heavy metal bioavailability research and risk management in contaminated land.

Risk assessment has been recognized as an important tool for evaluating heavy metal pollution and providing risk-based information for decision makers. In order to accurately assess the risk of heavy metals in contaminated soil to human health, it is necessary to conduct bioavailability studies on heavy metals in soil. Bioavailability of heavy metals in soils and the implications for risk assessment and land management/remediation has evolved over the decades and now has considerable practical and economic implications internationally. This article aims to explore its evolution by undertaking a bibliometric analysis of the research fields which have addressed heavy metal bioavailability in soils, with a focus on the risk assessment of contaminated land and human exposure to soil-borne metals. Bibliometric analysis techniques are applied to monitor and assess the changing research literature on the bioavailability of heavy metals in contaminated soils. Over 5000 articles were found for the period 1979-2020. The purpose was not to perform an exhaustive literature review, but to draw out trends and patterns in the literature, and to make observations on past and current priorities. Key words were extracted from the analysis and the roles of different countries in driving the research literature identified. Three phases in literature/subject development were identified. Between 1979 and 2000 (initial phase, 213 articles), studies used extraction procedures and solubility studies to investigate the roles of soil properties on metal form/speciation and focused on bioavailability to (crop) plants in agricultural soils. Between 2001 and 2010 (slow development phase, 1105 articles), attention switched to metals introduced in soil amendments and wastes, metal impacts on soil microbial processes, and incorporating bioavailability in risk assessment. More rigorous techniques were being used, such as the diffusive gradients in thin films technique, to better understand kinetic and metal speciation in soils and the quantitative relationship to bioavailability. By 2011-2020 (rapid development phase, 3137 articles), research was being conducted in many countries (site specific, often industrially contaminated and urban sites), with a focus shift to health risk assessment, remediation, and bioavailability to various ecological receptors (e.g., humans and animals), with the development of many methods of bioavailability (e.g., simulated gastrointestinal tract enzymolysis methods). Some priorities for research on soil heavy metal bioavailability are identified.

POSSMs: a parsimonious speciation model for metals in soils

Environmental context Predicting the chemistry of metals is important for understanding their movement and impacts in the environment. Metal chemistry models are generally complex and difficult to apply, but a simpler model, which does not need large amounts of input data, can also provide good results. A simpler model can be more easily included in large-scale models of metal transport and impacts in the environment. Abstract Mechanistic geochemical models are useful for detailed study of the speciation of metals in well-characterised soils, but can be challenging to apply when driving soil compositional data are sparse, for example, at large scales. Empirical models, using minimal driving data, have been developed either for prediction of solid–solution partitioning or for the computation of the free metal ion from the total or geochemically active metal. This work presents an empirical speciation model, POSSMs (ParsimOniouS Speciation of Metals in soils), which predicts the free, solution-bound and sorbed metal in a soil in a single calculation, using a minimal set of soil parameters. The model has been parameterised for Ni, Cu, Zn, Cd and Pb using datasets of geochemically active soil metal and solution phase composition. The parameterised model can also be used to compute the free metal ion from the solution metal. The model was tested by applying it to literature datasets on the speciation of metals in soil solutions and extracts, and on the metal solid–solution partitioning. The performance of the model was comparable to other empirical models of similar complexity. Some test datasets produced biased predictions, particularly in the underestimation of measured free ion at circumneutral and alkaline pH, where the model predicted low free ion concentrations. The model is not a replacement for mechanistic geochemical models, but is a useful tool for soil metal speciation where comprehensive driving data are not available.

Assessing the Influence of Compost and Biochar Amendments on the Mobility and Uptake of Heavy Metals by Green Leafy Vegetables.

Municipal green-waste compost and wheat straw biochar amendments were assessed for their assistance in regulating the mobility of Cu, Pb, Zn, Cd, Cr and Ni and the uptake of these metals by five commonly grown green leafy vegetables (radish, lettuce, dill, spinach and parsley). The amendments were applied alone or combination of both in 5% and 10% (v/w) doses to soil contaminated with heavy metals. Vegetables were grown for eight weeks under greenhouse conditions, and in collected samples plant uptake and metal speciation in soil after sequential extraction procedure (BCR) were analyzed by Microwave Plasma Atomic Emission Spectrometer (MP-AES). The results of our study show that organic amendments noticeably reduced the uptake of heavy metals by various leafy vegetables, with the best result of reduced leaf accumulation for single biochar and biochar–compost mix application at higher dose. Single application of green-waste municipal compost may have adverse effects on heavy metal uptake, increasing the risk of vegetable contamination with Zn, Pb and Cr. This study recommends careful selection of vegetables for cultivation when organic fertilizers are applied to soil with elevated contents of trace elements or co-application of compost in mix with biochar to mitigate possible negative effects and human health risk.

Metal type and aggregate microenvironment govern the response sequence of speciation transformation of different heavy metals to microplastics in soil

Microplastics change the physical, chemical, and biological processes in soil, and these changes further affect the transformations of heavy metal speciation in soil. Whether this influence mechanism differs between heavy metals is unknown on the soil aggregates level. In this study, 5 months incubation experiments and soil fractionation were conducted to evaluate the effect of microplastic addition on the chemical speciation of seven heavy metals (Zn, Cu, Ni, Cd, Cr, As, and Pb) in the three soil aggregate fractions. The results show that 28% concentration of polyethylene microplastics with size 100 μm reduces and increases the heavy metal content in the bioavailable and organic-bound fractions, respectively, indicating that microplastics promote the transformation from bioavailable to organic-bound species. The transformation in the larger-sized aggregate fractions is more dramatic than that of smaller-sized aggregate fractions within the incubation period. This indicates that the extent of the response of the different heavy metals to microplastics is significantly different in the three aggregate-size fractions. Soil physicochemical factors affected different heavy metals in different pathways, and microplastics have different adsorption or complexation effects on different heavy metals. These processes result in heterogeneous responses of different heavy metals to microplastic addition. In addition, the microplastics have different extents of influence on the different chemical speciation of the heavy metals, having the greatest influence on the exchangeable and carbonate-bound of Cu and Zn, FeMn oxide-bound of As, and organic-bound of Cr, Ni, Cd, and Pb. This phenomenon is relatively consistent among the three aggregate-size fractions. Our findings provide more accurate management information for soil environmental quality management with different heavy metal pollution and different soil types.

Acid buffering capacity of four contrasting metal-contaminated calcareous soil types: Changes in soil metals and relevance to phytoextraction

Four different metal-contaminated calcareous soil types, Carbonati-Perudic Cambosols (CPC), Fe-accumuli-Stagnic Anthrosols (FSA), Ochri-Aquic Cambosols (OAC) and Calci-Orthic Aridosols (COA), were investigated. The acid buffering capacity and metal-releasing behaviors of the soils were explored using an acid extraction method. Soil incubation and pot experiments were conducted to investigate changes in soil metal speciation and the enhancement of phytoextraction by soil acidification. There were several to tens of times differences in acid buffering capacities between soils. Soil calcium content may represent the major buffering system as indicated by significant linear correlations between the amount of Ca2+ released and H+ addition, and metal release into solution with H+ addition showed three stages, i.e. little release, slow release and rapid release stages. Soil carbonate-bound and Fe/Mn oxide-bound Cd and Zn decreased with the addition of H+ to all four soils, but organic matter-bound and residual metals remained unchanged. Based on the intensity of acidification, the efficiency Cd and Zn phytoextraction increased substantially with the addition of H+ in the case of the CPC but not the FSA which had a higher acid buffering capacity than the CPC. Hence, it may be concluded that the acid buffering capacity and changes in soil metal fractions with acidification of contaminated calcareous soil types should be determined before phytoextraction of these soils is attempted.

Effect of Soil Washing Using Oxalic Acid on Arsenic Speciation and Bioaccessibility in Soils

Objectives : Soil washing process has been widely applied for remediation of contaminated soil with arsenic and heavy metals in Korea. The application of soil washing could change physical and chemical properties of soils and metal speciation in soil, which could affect the risk to the environment and human health. Thus, it is necessary to evaluate metal and arsenic speciation and their mobility in soil after soil remediation in order to evaluate effectiveness of soil remediation process and manage soil quality effectively. The purpose of this study is to evaluate the risk of arsenic in soil after remediation of arsenic contaminated soil via soil washing.Methods : Arsenic contaminated soil collected at the abandoned mine site was washing with oxalic acid. The arsenic contaminated soil was divided into 2,000-500 µm, 500-250 µm, 250-150 µm, 150-75 µm, 75-38 µm, < 38 µm particle size fractions. After soil washing for each soil particle size fraction, arsenic speciation via sequential extraction and bioaccessibility in the soils were evaluated. Results and Discussion : Generally, arsenic and metal concentrations were higher in the soil fractions with smaller particle sizes. But high arsenic concentration was observed at the large particle size fractions (>250 µm), which might be due to the presence of mineral phases containing arsenic such as arsenolite or pyrite in the large particle size fraction soils. Sequential extraction showed that arsenic in mine soils was majorly present as associated with amorphous oxides. After soil washing with oxalic acid, arsenic in soils associated with amorphous oxides was greatly decreased, whereas the arsenic fraction associated sulfide and organic matter was increased. Soil washing decreased the bioaccessible arsenic concentration (mg/kg) in soil, but increased the bioaccessibility (%) depending on the soil characteristics. Conclusions : Soil washing changed arsenic species in soils, which affected mobility and risk of arsenic in soil.

Study on heavy metals’ influence on buried cultural relics in soil of an archaeological site

ABSTRACT The protection of cultural relics in a chariot pit in the ancient ruins has become an important issue. In order to study the spatial distribution, speciation of heavy metals in soil at a cemetery where an ancient chariot was buried and the influence heavy metals have had on the cultural relics. Heavy metals in soil samples surrounding the cultural relic were analyzed via atomic absorption spectrometry (AAS) using a wet digestion method combined with a three-step sequential extraction procedure. Results for seven heavy metals (Cu, Pb, Zn, Cr, Fe, Mn and Sn) and the speciation of six heavy metals (Cu, Pb, Zn, Cr, Fe and Mn) indicated that their contents exceeded local soil background values, indicating that the soil around the site had been contaminated to a certain degree. Analysis of their speciation showed that Mn mainly existed in the form of a reducible fraction in the soil, while the other elements were mainly in the form of a residual fraction. Correlation analysis showed that, except for the HOAc soluble fraction, a significant positive correlation existed between the content of the different forms and their total amounts. Heavy metals present in the soil surrounding the ancient relic predominantly influence the relic due to their related chemical reactions. In particular, copper and iron have a significant influence on corrosion of the cultural relics in this chariot pit.

Heavy Metal Speciation and Health Risk Assessment of Soil and Jute Mallow (Corchorus Olitorus) Collected From a Farm Settlement in Ikorodu, Lagos, Nigeria

There is an increasing global concern for adverse effects of inorganic fertilizer and pesticides applied to agricultural soils. This study investigated metal speciation in soil and health risk assessment of Jute mallow (Corchorus olitoriuos) from a farm settlement in Ikorodu, Lagos State. Soil samples were collected according to the set standard procedure, sequentially extracted and analyzed for selected heavy metals using standard methods. Results showed that chromium (Cr) was associated with reducible fraction (Fe-Mn) for top soil, while cadmium (Cd), manganese (Mn), and copper (Cu); lead (Pb) and nickel (Ni); and Cr were predominantly bound to carbonate, reducible and residual mineral components respectively for sub-soil. The results of Contamination Factor (CF), Contamination Degree (CD), Pollution Load Index (PLI) and Geoaccumulation Index (Igeo) showed that the soil samples were not polluted for all the investigated metals. The Cd level in the soil (13.54 ± 1.21 mg·kg﹣1) and vegetables (0.83 ± 0.05 mg·kg﹣1) were above the USEPA critical permissible limit of 3.0 mg·kg﹣1 and 0.1 - 1.2 mg·kg﹣1 respectively. The daily intake of estimated selected heavy metals from the vegetable ranged from 8.8 × 10﹣03 to 1.4 × 10﹣02 for adult and 3.8 × 10﹣03 to 1.1 × 10﹣02 for children while the Hazard Quotient (HQ) for adults ranged from 5.4 × 10﹣05 to 1.1 × 10﹣01 and that of children ranged from 8.3 × 10﹣03 to 1.4 × 10﹣02. The cancer risk (CR) values of heavy metals in the soil ranged from 1.02 × 10﹣11 to 9.90 ×

Speciation of Metals in Soils and Water: Risk Assessment

Scarce management of solid wastes, excessive wastewater discharge and irrigation with noxious water are among the main causes of heavy metal contamination in agricultural soils. The soils of upper Litani basin in Lebanon are subjected to these sources, beside soil irrigation by Litani river water, contaminated by wastewater. However, the metal mobility, bioavailability, or potential risk can be elucidated by metal soil and water chemical speciation. This study involved the metal speciation in soils of the upper Litani basin, and computation of pollution indices for risk assessment. A modified BCR sequential extraction technique was implemented to soil samples that operationally extract metals sequentially from fractions termed as acid soluble, reducible, oxidizing, and residual. Beside, soil pH, Eh and TOC, macro-water parameters, and metal water content were measured. The geochemical computer model PHREEQC was used to predict water metal species. Data indicated that Mn, Zn, Cr, and As had their highest average percentage from total metal in the reducible and acid soluble soil fractions, while Cu, Ni, Cd, Hg were in the oxidizing and acid soluble soil fractions. Metal speciation was related to TOC, Eh and water BOD. The average values for the indices indicated: enrichment factor and geo-accumulation of severe enrichment and very strong contamination for Cd and Hg; risk assessment high risk for Cr, Ni, and Cd; and 50% of sites suffered from considerable contamination according to the global contamination factor. The highest percentage of water species were for Mn, Zn, Ni, and Cd, the free metal aqua ion.

Establishing a health risk assessment for metal speciation in soil—A case study in an industrial area in China

An improved method was proposed which integrates the distribution of metal speciation simulated by chemical equilibrium model, different exposure models and average daily intake dose modified by analytic hierarchy process for human health risk assessment of metal species (MS). With the rapid development of economic and urbanization, the metals pollution had become more serious in industrial areas. Adverse effects of soil contaminants on human health in typical industrial area should be assessed to evaluate the risks of soils in these areas. The method was applied to study nickel (Ni) species health risks in soil of industrial areas. The pH possessed significant impact to determine distribution/existence and solubility of Ni species, followed by DOC. The non-carcinogenic risk (HQ) of Ni species were less than 1 in each sampling points, except Ni2+. In addition, the carcinogenic risk (CR) of different Ni species were less than 10−6, except for FANi and Ni2+.

Regionalized Terrestrial Ecotoxicity Assessment of Copper-Based Fungicides Applied in Viticulture

Life cycle assessment has been recognized as an important decision-making tool to improve the environmental performance of agricultural systems. Still, there are certain modelling issues related to the assessment of their impacts. The first is linked to the assessment of the metal terrestrial ecotoxicity impact, for which metal speciation in soil is disregarded. In fact, emissions of metals in agricultural systems contribute significantly to the ecotoxic impact, as do copper-based fungicides applied in viticulture to combat downy mildew. Another issue is linked to the ways in which the intrinsic geographical variability of agriculture resulting from the variation of management practices, soil properties, and climate is addressed. The aim of this study is to assess the spatial variability of the terrestrial ecotoxicity impact of copper-based fungicides applied in European vineyards, accounting for both geographical variability in terms of agricultural practice and copper speciation in soil. This first entails the development of regionalized characterization factors (CFs) for the copper used in viticulture and then the application of these CFs to a regionalized life-cycle inventory that considers different management practices, soil properties, and climates in different regions, namely Languedoc-Roussillon (France), Minho (Portugal), Tuscany (Italy), and Galicia (Spain). There are two modelling alternatives to determine metal speciation in terrestrial ecotoxicity: (a) empirical regression models; and (b) WHAM 6.0, the geochemical speciation model applied according to the soil properties of the Harmonized World Soil Database (HWSD). Both approaches were used to compute and compare regionalized CFs with each other and with current IMPACT 2002+ CF. The CFs were then aggregated at different spatial resolutions—global, Europe, country, and wine-growing region—to assess the uncertainty related to spatial variability at the different scales and applied in the regionalized case study. The global CF computed for copper terrestrial ecotoxicity is around 3.5 orders of magnitude lower than the one from IMPACT 2002+, demonstrating the impact of including metal speciation. For both methods, an increase in the spatial resolution of the CFs translated into a decrease in the spatial variability of the CFs. With the exception of the aggregated CF for Portugal (Minho) at the country level, all the aggregated CFs derived from empirical regression models are greater than the ones derived from the method based on WHAM 6.0 within a range of 0.2 to 1.2 orders of magnitude. Furthermore, CFs calculated with empirical regression models exhibited a greater spatial variability with respect to the CFs derived from WHAM 6.0. The ranking of the impact scores of the analyzed scenarios was mainly determined by the amount of copper applied in each wine-growing region. However, finer spatial resolutions led to an impact score with lower uncertainty.

Towards the Use of Software Modelling for Determination of Heavy Metal Speciation in Soils in Zambia

The toxicity of heavy metals in water is typically related to the concentration of the metals in water. However, it is known that apart from the concentration the speciation of the heavy metals is also a critical factor. In this study, the concentration and type of species (ionic form) of Cu, Co, and Pb from two different soil samples on the Copperbelt Province in Zambia were investigated by modeling using Visual MINTEQ software. The concentration and the conductivity of the sample from ore-dump site were higher than that of the second site further away owing to the higher mineral content in the waste ore-dump site. Modeling by Visual MINTEQ uses defined parameters such as concentration, ionic conductivity and pH of the sample solutions to analyze the free metal ion and bound-metal distribution as a function of pH. The results of the model showed that Cu2 , Pb2 and Co2 ions thrive in aqueous acidic solutions up to pH 6.5. At higher pH, formation of the hydroxo and bicarbonate species leads to a decline in the concentration of the divalent ions. Interestingly, the Co2 ion persists in solution up to pH 8.5 with little formation of the hydroxo or carbonate forms. Finally, the results show that without elaborate analytical tools, speciation modeling can be used to ascertain the availability of metal ions in soils/aqueous solutions when chelating and competing metal ions are taken in consideration.

Chemical Speciation of Heavy Metals in Soils of Jeju Island, Korea

Chemical Speciation of Heavy Metals in Soils of Jeju Island, Korea

A Comprehensive Evaluation of Environmental Pollution Characteristics of the Greenhouse Soils (A Case Study in Kaş-Antalya)

A study was carried out in intensive greenhouse areas of Kas district, Antalya to determine the relation among soil properties and metal characteristics, ground water properties and metal contents and greenhouse plant metal contents. Additional to routine water and soil analysis, a sequential extraction procedure was used to estimate the availability of heavy metals (Zn, Cd, Ni and Pb) in greenhouse soils and several environmental pollution indexes were used to evaluate the size of pollution and risks. Groundwaters of greenhouse area have high conductivity and nitrate content, but heavy metal contents were below the permissible levels. Average total Cd, Ni, Pb and As contents of groundwaters were below the pollutant limits, but Zn concentrations were exceeded. However, the average heavy metal evaluation index (HEI) values for all metals in groundwaters were below the critical value. The concentrations of heavy metals with the exception of Ni in soils of greenhouses were generally below the referenced limits. Soil metal speciation showed that the greatest percentage of all metals was present in the residual form, and the mobility of metals declined in the following order: As>Zn>Cd>Pb>Ni. Single factor and composite pollution coefficient values of all metals with the exception of Ni were not exceeded critical limit. Anthropogenic and enrichment factor indexes of greenhouse soils indicate that both two parameters showed similar trends and 1 to 9 fold metal enrichments by anthropogenic inputs compared to uncontaminated soil. Potential ecological risk indexes of soil metals except Ni were found below the threshold value that indicates these metals have a low risk to surrounding environment. All heavy metal concentrations with the exception of Cd in tomato fruits were found below the permissible heavy metal limits. Although soil Ni concentration was excessed the pollutant limits, possibly due to low soil mobility factor of Ni, concentration of Ni in tomato fruit was found very low. However, target hazard quotient (THQ) of tomato fruits was found below the critical value and thus it can be presumable no health risk for Cd metal in short or medium terms. In a comprehensive manner, in addition to total concentrations referenced, environmental risk evaluation methods and soil speciation studies may provide useful information for assessing metal bioavailability and environmental risks.

Metal speciation in soil at a contaminated glassworks site in southeastern Sweden

Risk assessments of metal contaminated land are often based on total metal concentrations of the soil material, although it is well known that the potential for leaching is determined by the fractionation between labile metal forms and forms that are not to be assessed as geochemically active. In the present study, a 4-step sequential leaching procedure was applied to solid material from five subareas of a glass waste site in southeastern Sweden (including, for example, landfill areas and natural till material). The aim was to assess whether the major fraction of the total Cd and Pb content should be considered labile (easily mobilizable) or relatively stably sorbed, which is a question that is motivated by the fact that previous site-specific investigations have shown strongly elevated metal concentrations in soil, but very little impact on local groundwater. Although the total metal concentrations as well as the amount of visable glass particles differed between the subareas, the fractions extracted in the different steps of the sequential leach were similar for all areas. Only a minor part of the total content of both Cd and Pb was released in the final strong acid residual leach (9-19 %), which indicates that there has been a significant release of metal ions from the glass waste material in the past, followed by a transition to secondary phases. Of the two metals, Cd was assessed to be the most labile one. The first extraction, targeting the exchangeable and carbonate bound fraction, released 43-59 % of the total Cd content. So, although the relatively small effect seen on groundwater quality indicates an effective retention of these metal cations by the soil solid matrix, the relatively high fraction of potentially mobile forms highlights the need of further assessments of the stability in major retention mechanisms.

The Effect of Liming and Sewage Sludge Application on Heavy Metal Speciation in Soil

The aim of this paper is to assess the effect of liming and low doses of municipal sewage sludge (5%, 10%, 15% of the soil mass) on lead, chromium and nickel speciation in soil. The 420-day experiment was carried out in laboratory conditions. In all the samples lead, chromium and nickel concentration was determined with the ICP-AES method, while the content of those metals in different fractions was measured with the seven-step Zeien and Brümmer method, on the 30th and 420th days of the experiment. Sewage sludge doses significantly diversified lead, chromium and nickel amounts in the soil. The highest dose of sludge caused a significant increase, compared to the control, in the content of those metals. In the sludge the dominant forms of metals tested in the experiment were lead and chromium bound to organic matter (F4) as well as nickel bound to amorphous iron oxides (F5). Liming decreased the mobility of the metals in the soil.

Modelling the concentrations of dissolved contaminants (Cd, Cu, Ni, Pb, Zn) in floodplain soils.

Central European floodplain soils are often contaminated with potentially toxic metals. The prediction of their aqueous concentrations is a prerequisite for an assessment of environmental concerns. We tested the aqueous concentrations of cadmium (Cd), copper (Cu), nickel (Ni), lead (Pb) and zinc (Zn) derived from multi-surface adsorption modelling (on hydrous iron, aluminum and manganese oxides, clay and soil organic matter) against those analyzed in situ in the soil solution of four horizons of floodplain soils at the Elbe River, Germany. The input data for the reactive metals were derived from a seven-step sequential extraction scheme or from extraction with 0.43M nitric acid (HNO3) and evaluated in four modelling scenarios. In all scenarios, measured and modelled concentrations were positively related, except partially for Pb. Close reproduction of the measured data was obtained using measured data of accompanying cations and anions together with amounts of reactive metals from both the sequential extraction or from 0.43M HNO3 extraction, except for Cu, which was often strongly overestimated, and partially Cd. We recommend extraction with 0.43M HNO3 to quantify reactive metals in soil because the modelling results were metal-specific with better or equal results using the single extractant, the application of which is also less laborious. Approximations of ion concentrations and water contents yielded similar results. Modelled solid-phase speciation of metals varied with pH and differed from that from sequential extraction. Multi-surface modelling may be an effective tool to predict both aqueous concentrations and solid-phase speciation of metals in soil.