Vergleich zwischen Total- und königswasserextrahierbaren Elementgehalten in natürlichen Böden und Sedimenten

Comparison between total- and aqua regia extractable contents of elements in natural soils and sediments Total- and aqua regia extractable contents of 19 elements from 28 soil samples with widely varying composition of the ISE ring analytical program (INTERNATIONAL SOIL-ANALYTICAL EXCHANGE) of the year 1995 to 1997 have been taken to find out the comparability between the two fractions. The relations between the two fractions and pH, organic matter and clay content were considered by means of single and multiple regressions. The correlations between the total and aqua regia extractable contents of As, Ca, Cd, Co, Cr, Cu, Fe, Hg, Mg, Mn, Ni, P, Pb and Zn are very close, whereas Al, Ba, K, Na and Sr are not or only weakly correlating. The multiple regressions show that the content of some aqua regia extractable elements and the proportion (in %) of the total contents is correlated with pH, organic matter and/or content of clay. In the same way the proportion of aqua regia extractable elements is closely related (except Fe and Hg) to the soil pH. Hereby the proportion of the aqua regia extractable content increases with increasing pH in the range 3,5—7,7. The determined equations are tested for As, Cd, Co, Cr, Cu, Hg, Mn, Ni, Pb and Zn by using the values of certified reference material. The estimated aqua regia extractable contents are being compared with values of reference material. The average proportion of the calculated to the measured aqua regia contents of an element in percent are 99 for Zn, 98 for Co, Cu and Mn, 94 for Cd, 90 for Ni, 88 for Cr, 105 for Hg, 113 for As and 114 for Pb.     

Tea Plantation–Induced Activation of Soil Heavy Metals

Abstract

The accumulation of heavy metals in tea leaves is of concern because of its impact on tea quality. This study characterized long‐term changes of soil properties and heavy‐metal fractions in tea gardens and their effect on the uptake of metals from soils by the plants. Soil and tea leaf samples were collected from five plantations with a history of 2–70 years in Jinghua, Zhejiang Province, southeast China. The six chemical fractions (water‐soluble, exchangeable, carbonate‐bound, organic‐matterbound, oxide‐bound, and residual forms) of cadmium (Cd), chromium (Cr), copper (Cu), iron (Fe), nickel (Ni), manganese (Mn), lead (Pb), and zinc (Zn) in the soils were characterized. Dissolved organic‐matter accumulation in the soils and effects of low‐molecular‐weight organic acids on solubility of soil heavy metals were also tested. Long‐term tea plantation use resulted in accumulation of dissolved organic matter, decrease of soil pH, and elevation of water‐soluble and exchangeable metal fractions, thereby increasing metal contents in leaves. The influence was more significant when soil pH was less than 4.4. The results indicated that both acidification and accumulation of dissolved organic matter induced by tea plantations were also important causes of increased accumulation of the metals in the tea leaves. This was particularly true for the soils polluted with low concentration of heavy metals, because availability of the metals in these soils was mainly controlled by pH and dissolved organic matter.     

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

Abstract

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

生物炭对不同酸化水平稻田土壤性质和重金属Cu、Cd有效性影响

针对南方稻田土壤酸化严重,导致养分流失有毒重金属活化,严重影响稻米质量安全的重大现实问题。以水稻秸秆和谷壳等农业废弃物为原料制备生物炭(分别记为RSC和RHC),研究不同原料生物炭对酸化土壤改良及其对重金属有效性的影响。设置3个生物炭用量(0,20,50 g/kg,分别记为CK、C1、C2),4种土壤酸化水平(pH 4.01,4.25,4.33,4.58,分别记为L1、L2、L3、L4),生物炭与重金属污染土壤共同培养60天后测定土壤pH、全氮、有机质、有效磷、速效钾和有效态Cu、Cd含量。结果表明:RSC对酸化土壤pH的改良效果明显优于RHC,且施炭量越高提高幅度越大,RSC的C2处理使4种酸度水平的土壤pH分别提高了0.68,0.97,1.29,1.71个单位。2种生物炭均能提高土壤的全氮、有效磷、速效钾和有机质含量,其中各施炭处理有机质显著提高,尤以速效钾的增幅最为显著,RSC对4种养分的提高均优于RHC。RHC对土壤有效态Cu含量无显著影响;RSC的C2较C1处理更能降低土壤中有效态Cu含量,使4种酸度水平的土壤分别降低了13.62%,6.57%,4.36%,7.88%。RHC处理的L3、L4土壤中有效态Cd含量显著降低,最大分别降低了13.79%,19.23%。RSC使4种酸度土壤有效态Cd含量最大分别降低了20.00%,25.81%,20.69%,19.23%。相关分析表明,土壤pH与有效态重金属含量呈显著负相关关系。水稻秸秆炭用于改良酸化土壤、降低重金属Cu和Cd有效性的效果更佳,且降低污染土壤中Cd的有效性较Cu好;生物炭对酸化程度越低的土壤pH和有效磷含量的提高以及有效态Cd含量的降低效果较好,而有效态Cu含量的降低效果则在酸化程度越高的土壤中表现更佳;土壤pH是生物炭调控重金属Cu、Cd有效性的主要影响因素。     

Extractability and plant uptake of heavy metals in alum shale soils

Abstract

Fifty soil samples (0–20 cm) with corresponding numbers of grain, potatoes, cabbage, and cauliflower crops were collected from soils developed on alum shale materials in Southeastern Norway to investigate the availability of [cadmium (Cd), copper (Cu), zinc (Zn), lead (Pb), nickel (Ni), and manganese (Mn)] in the soil and the uptake of the metals by these crops. Both total (aqua regia soluble) and extractable [ammonium nitrate (NH₄NO₃) and DTPA] concentrations of metals in the soils were studied. The total concentration of all the heavy metals in the soils were higher compared to other soils found in this region. Forty‐four percent of the soil samples had higher Cd concentration than the limit for application of sewage sludge, whereas the corresponding values for Ni, Cu, and Zn were 60%, 38%, and 16%, respectively. About 70% the soil samples had a too high concentration of one or more of the heavy metals in relation to the limit for application of sewage sludge. Cadmium was the most soluble of the heavy metals, implying that it is more bioavailable than the other non‐essential metals, Pb and Ni. The total (aqua regia soluble) concentrations of Cd, Cu, Zn, and Ni and the concentrations of DTPA‐extractable Cd and Ni were significantly higher in the loam soils than in the sandy loam soils. The amount of NH₄NCyextractable metals did not differ between the texture classes. The concentrations of DTPA‐extractable metals were positively and significantly correlated with the total concentrations of the same metals. Ammonium nitrate‐extractable metals, on the other hand, were not related to their total concentrations, but they were negatively and significantly correlated to soil pH. The average concentration of Cd (0.1 mg kg^‐1 d.w.) in the plants was relatively high compared to the concentration previously found in plants grown on the other soils. The concentrations of the other heavy metals Cu, Zn, Mn, Ni, and Pb in the plants were considered to be within the normal range, except for some samples with relatively high concentrations of Ni and Mn (0–11.1 and 3.5 to 167 mg kg‘¹ d.w., respectively). The concentrations of Cd, Cu, Zn, Ni, and Mn in grain were positively correlated to the concentrations of these respective metals in the soil extracted by NH₄NO₃. The plant concentrations were negatively correlated to pH. The DTPA‐extractable levels were not correlated with plant concentration and hence DTPA would not be a good extractant for determining plant availability in these soils.     

Residual heavy metal concentrations in sludge‐amended coastal plain soils ‐ I. Comparison of extractants

Abstract

The purposes for this research were: to examine the long‐term residual effects of farmland applications of municipal sludges from four treatment technologies on the total and extractable Zn, Cu, Mn, Fe, Pb, Ni and Cd concentrations in Coastal Plain soils; to investigate the effects of sludge sources and rates on the effectiveness of soil extractants to remove the various metals; and to determine correlation coefficients for soil extractable versus plant accumulation in tobacco. The extractants evaluated were Mehlich 1 and 3, and DTPA‐pH 7.3. Composite Ap horizon soil samples and tobacco leaf samples were obtained in 1984 from research plots at two sites in Maryland that were established in 1972 and 1976, respectively, using sludge materials from three wastewater treatment facilities in the Washington, D.C. metropolitan region. Similar application rates were used at both sites.

A wide range in soil pH values was found among treatments at each site. Significant (p ≤ 0.05) increases were observed in total Zn, Cu, Fe, Pb, Ni, and Cd for all sludge sources with increased rates; however, values for total soil Mn exhibited high variability in all cases. The rankings among the extractants varied for some elements depending on the sludge sources. For Zn, the rankings were Mehlich 1 > Mechlich 3 > DTPA‐pH 7.3 across all sources and rates. For Cu, Mehlich 3 > Mehlich 1 > DTPA‐pH 7.3 was found for soils amended with Blue Plains digested (BPD) and Piscataway limeddigested (PLD) sludges but Mehlich 1 ≥ DTPA pH 7.3 > Mehlich 3 for Blue Plains limed compost (BPLC) and Annapolis Fe and heat treated (AFH) sludges. Concerning extractable Mn, Mehlich Mehlich 1 > Mechlich 3 > DTPH pH 7.3 was the order for BPLC and AFH sludges but Mehlich 3 > Mehlich 1 > DTPA‐pH 7.3 was observed for BPD and PLD sludges. The rankings among extractants for Fe (Mehlich 3 > Mehlich 1 > DTPA‐pH7.3), Ni (Mehlich 3 ≥ Mehlich 1 > DTPA‐pH 7.3), Pb (Mehlich 3 > DTPA‐pH 7.3 > Mehlich 1) and Cd (Mehlich 1 > Mehlich 3 > DPTA‐pH7.3) were somewhat similar across all sludge sources. Significant correlation coefficients were obtained for all three extractants for soil extractable vs. plant Zn, Cu, Ni, and Cd at both sites; however, Mehlich 3 was not significant for Mn. Also, neither of the extractants produced significant coefficients for Fe and Pb.     

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

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

Sorption behavior of copper,zinc, and cadmium in response to simulated changes in soil properties

Abstract

Environmental changes and management practices which alter soil properties may affect the capacity of soils to sorb trace metals, such as copper (Cu), zinc (Zn), and cadmium (Cd), and thus influence the bioavailability and leach ability of the metals. Two agricultural soils were treated to partially oxidize organic matter and to decrease soil pH for evaluating the effects of acidification and organic matter oxidation on trace metal sorption onto soils. For the one soil with a pH value of 6.74 and organic carbon (C) content of 46.9 g‐kg^‐1, loss of 11% of its organic matter reduced by 97, 72, and 62% the original sorption capacity for Cu, Zn, and Cd, respectively, while the corresponding values caused by acidifying the soil one pH‐unit were 32, 16, and 29%. For the another soil with a pH of 4.69 and organic C content of 16.3 g‐kg^‐1, a decrease in pH by one unit resulted in a loss of 43, 21, and 52% of the sorption capacity for Cu, Zn, and Cd, respectively.     

Chemical fractions of copper and zinc in organic‐rich particles from aqueous extracts of a metal‐contaminated granite soil

Abstract

Chemical fractions of copper (Cu) and zinc (Zn) in the organic‐rich particles collected from filtered aqueous extracts (<20 μm) of an acid soil were determined. A sequential extraction procedure was used to partition the particulate Cu and Zn into four operationally defined chemical fractions: adsorbed (ADS), iron (Fe) and manganese (Mn) oxides bound (FeMnOX), organic matter bound (OM) and residual (RESD). Total extractable concentrations of Cu and Zn in the fine particles were higher than their total concentrations in the original bulk soil. The concentration of particulate Cu was usually much higher than that of particulate Zn. Addition of lime stabilized sewage sludge cake and/or inorganic metal salts markedly increased the concentrations of particulate Cu and Zn in aqueous extracts, especially from limed soil. The proportional distributions of particulate Cu and Zn were quite similar. The two particulate metals were present predominantly in the ADS and FeMnOX fractions, with less (about 20%) in the OM and RESD fractions. Some of the ADS metal fraction was associated with dissolved organic substances. The concentrations of particulate Cu and Zn in the various extractable fractions were significantly affected by the application of lime, lime stabilized sewage sludge cake, or inorganic metal salts.     

Solubility control of Cu, Zn, Cd and Pb in contaminated soils

We developed a semiempirical equation from metal complextion theory which relates the metal activity of soil solutions to the soil's pH, organic matter content (OM) and total metal content (MT). The equation has the general form: where pM is the negative logarithm (to base 10) of the metal activity, and a, b and c are constants. The equation successfully predicted free Cu²⁺ activity in soils with a wide range of properties, including soils previously treated with sewage sludge. The significant correlation of pCu to these measured soil properties in long-contaminated soils suggests that copper activity is controlled by adsorption on organic matter under steady state conditions. An attempt was made from separate published data to correlate total soluble Cu, Zn, Cd and Pb in soils to soil pH, organic matter content and total metal content. For Cu, the total Cu content of the soil was most highly correlated with total soluble Cu. Similarly, total soluble Zn and Cd were correlated with total metal content, but were more strongly related to soil pH than was soluble Cu. Smaller metal solubility in response to higher soil pH was most marked for Zn and Cd, metals that tend not to complex strongly with soluble organics. The organic matter content was often, but not always, a statistically significant variable in predicting metal solubility from soil properties. The solubility of Pb was less satisfactorily predicted from measured soil properties than solubility of the other metals. It seems that for Cu at least, solid organic matter limits free metal activity, whilst dissolved organic matter promotes metal solubility, in soils well-aged with respect to the metal pollutant. Although total metal content alone is not generally a good predictor of metal solubility or activity, it assumes great importance when comparing metal solubility in soils having similar pH and organic matter content.     

Partitioning of organic carbon, aluminium and cadmium between solid and solution in soils: application of a mineral–humic particle additivity model

The partitioning of chemical elements between the solid and solution phases in soil is fundamental in understanding processes such as leaching and bioavailability. Here I present a model in which the partitioning of Cd, Al and carbon in both mineral and organic soils can be simulated in the pH range 2–8. A two‐phase additivity approach simulates ion adsorption by the soils using a hydrous ferric oxide and humic type surface. A model for the partitioning of soil humic matter has also been developed in which the NICA–Donnan model calculates humic surface charge. Other key processes represented include mineral solubilization and solution speciation. Methods for deriving model input parameters either from analytical data or by parameter optimization were used. Acid ammonium‐oxalate‐extractable Fe was used to estimate the amount of hydrous ferric oxide, and reactive humic substances were estimated by a scaled down version of the International Humic Substances Society method for the extraction of humic and fulvic acid. For initial calculation the 0.1 m HCl‐extractable Al was used to estimate reactive Al. Optimization of reactive Al improved the fit of both the total dissolved Al data and the adsorbed Cd. The model for the solid–solution partitioning of humic substances could simulate reasonably well the release of carbon in the pH range 4–8 for both the organic and mineral soils.     

Effect of Grinding on Soil Extraction by Aqua Regia, 2 M Nitric Acid,and Mehlich 3

Abstract

The effect of grinding on soil extraction was determined for two soil fractions and three extractants. Arsenic (As), beryllium (Be), cadmium (Cd), cobalt (Co), chromium (Cr), copper (Cu), nickel (Ni), lead (Pb), vanadium (V), and zinc (Zn) were extracted by aqua regia and 2 M nitric acid. Mehlich 3 extractant was used for determination of potassium (K), magnesium (Mg), calcium (Ca), phosphorus (P), iron (Fe), and aluminum (Al). One hundred forty‐seven agricultural soil samples representing all major soil types, climatic regions, and proportions of agronomic cultures in the Czech Republic were collected for the study. Particle size fractions smaller than 2 mm and smaller than 0.150 mm were chosen for investigation. Extraction of elements by aqua regia was similar for both size fractions of soil. Cold 2 M nitric acid is a weaker extractant than aqua regia, and a statistically significant increase in extractable Be (5%), Cd (6%), Co (11%), Cu (5%), Ni (5%), and V (2%) was measured with the finely ground soils. An increase for the finer fraction for K (10%) and Mn (25%) was found for Mehlich 3. A more complex nonlinear relationship was found for Mehlich 3 extractable Al and Fe. This was probably caused by a more intensive re‐adsorption of Fe and Al to the finely ground soils.     

Association of cadmium,zinc, copper,and nickel with components in naturally heavy metal‐rich soils studied by parallel and sequential extractions

Abstract

In this study, a new parallel and sequential extraction procedure was proposed to investigate the solubility of metals [cadmium (Cd), zinc (Zn), copper (Cu), and nickel (Ni)] and their association with soil components in naturally metal‐rich soils of Norway. Two different soils, alum shale (clay loam) and moraine (loam), developed on alum shale minerals were used. Each soil had two pH levels. For parallel and successive extractions, H₂O, 0.1M NH₄OAc (soil pH), 0.3M NH₄OAc (soil pH), 1M NH₄OAc (soil pH), and 1M NH₄OAc (pH 5.0) were used. A significant amount of Cd was extracted by NH₄O Ac related to concentration of NH₄OAc in the extracting solution. The amounts of Zn, Cu, and Ni extracted by these reagents were almost negligible except with 1M NH₄OAc (pH 5.0). Thus these metals were strongly bound to soil components. A seven step sequential extraction procedure was applied to evaluate the association of metals with soil constituents. The extractions were performed sequentially by extracting the soil with reagents having an increasing dissolution strength: 1M NH₄OAc (soil pH), 1M NH₄OAc (pH 5.0), 1M NH₂OH.HCl (in 25% HOAc), 1M NH₂OH.HCl (in 0.1M HNO₃), 30% H₂O₂ (in 0.1M HNO₃), 30% H₂O₂ (1M HNO₃), and aqua regia. In both soils at both pH levels investigated, appreciable percentages of total Cd (20–50%) were found associated with the NH₄OAc extractable fraction (mobile fraction). For Zn, Cu, and Ni, the percentage of total metal extracted with NH₄OAc was low (<4%), but it increased significantly by introducing a reducing agent (NH₂OH.HCl). The NH₂OH.HCl‐extractable fraction was the greatest fraction (>60%) for all four metals examined. These results suggest that among the metals studied, only Cd was easily desorbed from soil and should be considered mobile and potentially bioavailable. Other metals (Zn, Cu, and Ni) were strongly associated with the soil components and should be considered less available to plants. Using the sequential fractionation technique as a measure of availability, mobility and potential bioavailability of these four metals in the alum shale soils were: Cd>Zn>Ni>Cu.     

Effect of Liming on the Plant Availability and Distribution of Zinc and Copper among Soil Fractions

Abstract

Information on the redistribution of applied micronutrients into different fractions as a result of lime application is important to predict plant accumulation of nutrients and to select appropriate chemical extraction procedures for evaluation of micronutrient availability. The present work was carried out to study the influence of liming on the availability and redistribution of zinc (Zn) and copper (Cu) among soil fractions. Additionally, the effect of liming was evaluated on the recovery of these micronutrients by different chemical extractants (Mehlich‐1, Mehlich‐3, and diethylenetriaminepentaacetate (DTPA), which were correlated with Zn and Cu concentrations in corn (Zea mays L.) plants and soil fractions (exchangeable, organic matter, amorphous iron oxides, and crystalline iron oxides). The results showed that Zn added to soil samples that did not receive lime was retained mainly in the exchangeable and organic matter fractions. The liming resulted in distribution of Zn into iron oxides and as a result decreased the plant accumulation of Zn. Mehlich‐3 was the most efficient extractant to predict the plant accumulation of Zn in the acid soils, whereas DTPA was the most efficient in the limed soils. The oxide crystalline fraction was the major fraction responsible for retaining Cu in the soils. However, Cu added to soil was distributed mainly into organic matter. Mehlich‐3 was the most suitable extractant for predicting the bioavailability of Cu in limed or unlimed soils.     

Speciation of cadmium,copper, lead,and zinc in contaminated soils

Abstract

To investigate the activity of free cadmium (Cd²⁺), copper (Cu²⁺), lead (Pb²⁺), and zinc (Zn²⁺) ions and analyze their dependence on pH and other soil properties, ten contaminated soils were sampled and analyzed for total contents of Cd, Cu, Pb, and Zn (Cd_T, Cu_T, Pb_T, and Zn_T, respectively), 0.43 MHNO₃‐extractable Cd, Cu, Pb, and Zn (Cd_N, Cu_N, Pb_N, and Zn_N, respectively), pH, dissolved organic matter (DOC), cation exchange capacity (CEC), ammonium oxalate extractable aluminum (Al) and iron (Fe), and dissolved calcium [Ca²⁺]. The activity of free Pb²⁺, Cd²⁺, Cu²⁺, and Zn²⁺ ions in soil solutions was determined using Donnan equilibrium/graphite furnace atomic absorption (DE/GFAA). The solubility of Cd in soils varied from 0.16 to 0.94 μg L^‐1, Cu from 3.43 to 7.42 μg L^‐1, Pb from 1.23 to 5.8 μg L^‐1, and Zn from 24.5 to 34.3 μg L^‐. In saturation soil extracts, the activity of free Cd²⁺ ions constituted 42 to 82% of the dissolved fraction, for Cu²⁺the range was 0.1 to 7.8%, for Pb²⁺ 0.1 to 5.1% and for Zn²⁺2 to 72%. The principal species of Cd, Cu, Pb, and Zn in the soil solution is free metal ions and hydrolyzed ions. Soil pH displayed a pronounced effect on the activity of free Cd²⁺, Cu^2t, Pb²⁺, and Zn²⁺ ions.     

Chemical and Mineralogical Properties of Norwegian Alum Shale Soils,with Special Emphasis on Heavy Metal Content and Availability

Abstract

Alum shale and till soils overlying alum shale bedrock were analysed for aqua regia and NH₄OAc/EDTA extractable Pb, Cu, Zn, Ni, Mn and Cd. The means of these determinations were compared with those of Norwegian, Finnish and Swedish non-alum shale soils. Alum shale soils seemed to contain higher amounts of both total and easily extractable Cu, Zn, Ni and Cd. Total Pb content also seemed to be higher in the alum shale soils. The relative availability of Cd, Ni and Mn, expressed as the ratio of NH₄OAc/EDTA to aqua regia extractable, was found to be greater than that of Pb, Cu and Zn in the alum shale and till soils.     

Modelling the effects of ageing on Cd,Zn, Ni and Cu solubility in soils using an assemblage model

Ageing reactions can reduce trace metal solubility and can explain natural attenuation of contaminated soils. We modelled ageing reactions in soil with an assemblage model that considers slow reactions in Fe‐oxyhydroxides and reversible sorption on organic matter and clay minerals. Metal adsorption kinetics on Fe‐oxyhydroxides was obtained from data with synthetic oxyhydroxides. Metal solubility and isotopic exchangeability data were obtained from 28 soils amended with Ni, Zn, Cu and Cd metal salts and monitored for 850 days. The assemblage model was constructed in WHAM 6.0 and used soil properties and dissolved organic matter as input data. The model was first validated to predict dissolved metal concentrations, based on the concentration of isotopic exchangeable metals. The model overestimated metal solubility without parameter adjustment by mean factors of 4–7, and successful fits were obtained by increasing the specific surface area of Fe‐oxyhydroxides from measured values of synthetic systems to a value of 600 m² g^?1 recommended by other authors. The effect of ageing on the isotopic exchangeable metal fraction was subsequently modelled starting from the predicted fraction of metals present on Fe‐oxyhydroxides immediately after soil spiking. The observed isotopic exchangeable metal fractions of Ni, Zn and Cd agreed reasonably well with predicted values. The model predicts that ageing reactions are more pronounced at higher pH because metal sorption is increasingly directed to oxyhydroxide surfaces with increasing soil pH. Modelling fixation of Cu requires more information on fixation of that metal in organic matter.     

Multi‐element stable isotopic dilution and multi‐surface modelling to assess the speciation and reactivity of cadmium and copper in soil

Chemical extraction, multi‐element stable isotopic dilution (ID) and multi‐surface modelling were used to investigate the lability of cadmium (Cd) and copper (Cu) in nine types of soil with different properties and contaminated or not with Cd and Cu. The chemical extraction and ID analyses both showed that Cd was more labile than Cu in all the soil types studied. From the ID results, 32.8–93.3% of total Cd and 14.7–71.8% of total Cu were isotopically exchangeable after 3 days of equilibration. A single extraction in 0.43 m HNO₃ gave similar results to the 3‐day ID assay for Cu in most of the soils and for Cd in the non‐calcareous soils. However, an eight‐step selective sequential extraction (SSE) procedure gave different results from the ID assay for both metals. Predictions of the multi‐surface model for the amounts of Cd and Cu adsorbed, based on measured metal ion activities in the soil solution and the concentrations of reactive surfaces in the soil, agreed with the ID results. The model predicted that soil organic matter was the predominant sorbent for Cd and Cu in the soils and that manganese oxide was the least important sorbent. The contributions of iron oxides to sorption were predicted to be small except in soil with a high pH and little organic matter. The predicted sorption on different soil components did not match SSE measurements.