Concentrations and forms of heavy metals in Slovak soils

The risk assessment of heavy‐metal contamination in soils requires knowledge of the controls of metal concentrations and speciation. We tested the relationship between soil properties (pH, CEC, C_org, oxide concentrations, texture) and land use (forest, grassland, arable) and the partitioning of Al, Cd, Cr, Cu, Fe, Mn, Ni, Pb, and Zn among the seven fractions of a sequential extraction procedure in 146 A horizons from Slovakia. Using a cluster analysis, we identified 92 soils as representing background metal concentrations while the remaining 54 soils showed anthropogenic contamination. Among the background soils, forest soils had the lowest heavy‐metal concentrations except for Pb (highest), because of the shielding effect of the organic layer. Arable soils had the highest Cr, Cu, and Ni concentrations suggesting metal input with agrochemicals. Grassland soils had the highest Cd and Zn concentrations probably for geogenic reasons. Besides the parent material (highest metal concentrations in soils from carbonatic rock, lowest in quartz‐rich soils with sandy texture), pedogenic eluviation processes controlled metal concentrations with podzols showing depletion of most metals in E horizons. Partitioning among the seven fractions of the sequential extraction procedure was element‐specific. The pH was the overwhelming control of the contributions of the bioavailable fractions (fractions 1–4) of all metals and even influenced the contributions of Fe oxide‐associated metals (fractions 5 and 6) to total metal concentrations. For fractions 5 and 6, Fe concentrations in oxides were the most important control of contributions to total metal concentrations. After statistically separating the pH from land use, we found that the contributions of Cu in fractions 1–4 and of NH₄NO₃‐extractable Al, Cd, Pb, and Zn to total metal concentrations were significantly higher under forest than under grassland and in some cases arable use. Our results confirm that metal speciation in soils is mainly controlled by the pH. Furthermore, land use has a significant effect.     

Heavy Metal Concentrations,Partitioning, and Storage in Slovak Forest and Arable Soils Along a Deposition Gradient

Along a heavy metal deposition gradient, caused by a Cu smelter, heavy metal concentrations, partitioning, and storage in forest and arable soils were examined. We sampled organic and mineral soil horizons (0—50 cm) at ten pairs of forest and arable sites derived from the same parent material. A-horizons were extracted with a seven-step sequence; O- and subsoil horizons were digested with strong acids (HNO₃/HClO₄). We found high concentrations of Cd (up to 17.38 mg kg^—1 in the O horizons/up to 2.44 mg kg^—1 in the A horizons), Cu (8437/415), Pb (3343/126), and Zn (1482/637) which decreased exponentially with distance from the smelter and with soil depth. The metal concentrations in the organic layers indicate that the average transport distance decreases in the order Cd > Zn > Pb > Cu. With regard to metal partitioning, NH₄NO₃- + NH₄OAc-extractable forms in the A horizons were most affected by the deposition being more pronounced under forest. In the uppermost 50 cm of the four soils nearest to the smelter two to four times higher Cd, Cu, Pb, and Zn storages were found in forest than in arable soils. At greater distance, the higher deposition onto forest soils due to the scavenging effect of the canopy obviously was compensated by stronger leaching.     

Extraction of mobile element fractions in forest soils using ammonium nitrate and ammonium chloride

The extraction of earth alkaline and alkali metals (Ca, Mg, K, Na), heavy metals (Mn, Fe, Cu, Zn, Cd, Pb) and Al by 1 M NH₄NO₃ and 0.5 M NH₄Cl was compared for soil samples (texture: silt loam, clay loam) with a wide range of pH(CaCl₂) and organic carbon (OC) from a forest area in W Germany. For each of these elements, close and highly significant correlations could be observed between the results from both methods in organic and mineral soil horizons. The contents of the base cations were almost convertible one‐to‐one. However, for all heavy metals NH₄Cl extracted clearly larger amounts, which was mainly due to their tendency to form soluble chloro complexes with chloride ions from the NH₄Cl solution. This tendency is very distinct in the case of Cd, Pb, and Fe, but also influences the results of Mn and Zn. In the case of Cd and Mn, and to a lower degree also in the case of Pb, Fe, and Zn, the effect of the chloro complexes shows a significant pH dependency. Especially for Cd, but also for Pb, Fe, Mn, Zn, the agreement between both methods increased, when pH(CaCl₂) values and/or contents of OC were taken into account. In comparison to NH₄Cl, NH₄NO₃ proved to be chemically less reactive and, thus, more suitable for the extraction of comparable fractions of mobile heavy metals. Since both methods lead to similar and closely correlated results with regard to base cations and Al, the use of NH₄NO₃ is also recommended for the extraction of mobile/exchangeable alkali, earth alkaline, and Al ions in soils and for the estimation of their contribution to the effective cation‐exchange capacity (CEC). Consequently, we suggest to determine the mobile/exchangeable fraction of all elements using the NH₄NO₃ method. However, the applicability of the NH₄NO₃ method to other soils still needs to be investigated.     

Verhalten von Schwermetallen in Böden. 2. Extraktion mobiler Schwermetalle mittels CaCl2 und NH4NO3

Behaviour of heavy metals in soils. 2. Extraction of mobile heavy metals with CaCl₂ and NH₄NO₃ 156 soil samples from arable fields, grassland and forest stands were analysed for the CaCl₂^? and NH₄NO₃^? extractable contents of Cd, Zn, Mn, Cu and Pb. The average amounts of Cd, Zn, Cu and Pb extracted with CaCl₂ are higher compared with NH₄NO₃ whereas the relation for Mn is vice versa. The proportion of the NH₄NO₃^? extractable contents in percent of the CaCl₂^? extractable contents of Cd, Zn and Pb decrease with increasing pH, whereas the contents of Mn and Cu increase. Inspite of a differing extraction behaviour of the two salt solutions the CaCl₂^? and NH₄NO₃^? extractable amounts of Cd, Mn, Zn und Pb are highly correlated and can be converted one into another. The mobile (CaCl₂, NH₄NO₃) proportion of the corresponding total, EDTA and DTPA heavy metal contents is in close relation to the pH of the soils. Using CaCl₂ solution the threshold pH values for an increasing mobility decrease in the order Cd > Mn > Zn > Cu > Pb, using NH₄NO₃ as extractant the order is Mn > Cd > Zn > Cu > Pb. In the case of CaCl₂ as extractant soluble chloro-Cd-complexes will be formed so that the Cd mobility in soils will be overestimated in most cases.     

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.     

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.     

Der Einfluß der natürlichen organischen Substanzen auf die Metallverteilung zwischen Boden und Bodenlösung in einem sauren Waldboden

The influence of organic matter in the translocation of metals between soil and soil solution of an acid forest soil Water extracts were prepared from soil samples which were collected from a soil profile showing very little variation in the texture down to a depth of 120 cm and thus only little translocation of clay in the soil profile. The aim of the study was to describe the distribution between soil and soil solution of several metals like Cu, Pb, Cd, Zn, Al and Mn as a function of humic substances, electrolyte concentration and pH. From the experimental results the following hypothesis on the reaction mechanisms involving metals and humus derived substances has been deduced. The metals Cu, Fe, Al and Pb are mobilized through complexation by soluble humus substances in addition to the usual pH dependent desorption and dissolution of hydroxides. This mobilization determines the solution concentration of Cu and Fe at pH > 3.7 and Al and Pb at pH > 4.2. Al, Fe and Pb are complexed selectively by high molecular weight humus derived substances which undergo adsorption on soil mineral surfaces. Cu interacts with low molecular weight humus derived substances which are not easily adsorbed by the mineral surfaces. Zn, Cd and Mn primarily undergo sorption and are thus controlled by pH and electrolyte concentration of solutions because their complexation with humus derived substances seems to be weak or nonexistant. It is further postulated that the humus derived substances mobilize Al³⁺ and Fe³⁺ ions. By this, other metals like Cd, Zn, Mn, Ca and Mg can occupy the free exchange sites.     

A new soil test method for the determination of plant‐available cadmium in soils

Abstract

A new soil test procedure using 1M NH₄Cl was developed for the extraction of plant‐available cadmium (Cd) from soils. Five grams of soil is weighed into a 50‐mL polyethylene vial to which 30 mL of 1M NH₄Cl solution is added. The soil suspension is then shaken on a horizontal shaker for 16 h at 25°C at 180 cycles per min. The suspension is then centrifuged at 2,500g for 5 min and the supernatant filtered through a 0.45 μm nitrocellulose filter under vacuum. Cadmium in the extract is then determined at 228.8 nm on a graphite furnace equipped atomic absorption spectrophotometer. A highly significant correlation was observed between the natural logarithm (In) of 1M NH₄Cl‐extractable Cd in soils and the Cd content in the grain of durum wheat (Triticum turgidum var. durutn L.) grown on the same soils (r = 0.974, p = 3.8 x 10^‐7). In comparison with several commonly used extradants, such as ABDTPA, CaCl₂, NH₄OAc, and NH₄NO₃, the 1M NH₄Cl‐extracted Cd from soils was found to be a better index of Cd availability.     

Plant uptake of metals,transfer factors and prediction model for two contaminated regions of Kosovo

The bioavailability and plant uptake of heavy metals (HM), as well as finding the most reliable methods for the prediction of availability, continues to be one of the most crucial problems in agricultural and environmental studies. In agricultural soils from two regions in Kosovo, known for its metal pollution, we collected 60 soil and plant samples (wheat, corn, potatoes, and grass). Heavy metals were extracted from soil with aqua regia (pseudototal concentration), NH₄OAc‐EDTA (potential bioavailable), and NH₄NO₃ (mobile fraction), plant samples were digested with HNO₃/H₂O₂ (microwave assisted extraction). The pseudo total content of Cd, Pb, and Zn showed high value in Mitrovice (mean: Cd–2.92, Pb–570.15, and Zn–522.86 mg kg^?1), whereas in Drenas region Ni and Cr showed high value with a mean 258.54 and 203.22 mg kg^?1. Also, the potential bioavailability and mobile form of these metals were increased in Mitrovice (mean: Cd–1.59, Pb–217.05, Zn–522.86 mg kg^?1, respectively Cd–0.17, Pb–0.64, and Zn–15.45 mg kg^?1), compared to Drenas. Cd and Pb were elevated in potato tubers (mean Cd–0.48 and Pb–0.85 mg kg^?1). The TF was higher for micronutrients (Zn and Cu) than for non‐essential metals (Cd and Pb). Multiple regression analysis showed a good model for prediction of Cd, Pb and Zn content in plant with significance 99.9%, whereas this model was not significant for Cu, Cr, and Ni. Soil pH played a significant role in the content of Cd and Zn in wheat and potato plants. Clay content also showed significance in Cd concentration in wheat and potato plants, while carbon content was significant for Cd in grass plants, as well as for Zn in wheat and grass plants.     

Heavy metals in the soil–plant system of the Don River estuarine region and the Taganrog Bay coast

Purpose

The aim of this work was to study the level and degree of mobility of heavy metals in the soil–plant system and to perform bioindication observations in the Don River estuarine region and the Russian sector of the Taganrog Bay coast.

Materials and methods

The objects of the study included samples of zonal soils (chernozem) and intrazonal soils (alluvial meadow and alluvial-stratified soils, Solonchak, sandy primitive soil) from monitoring stations of the Don river estuarine region and the Taganrog Bay coast, as well as their higher plants: Phragmites australis Cav., Typha angustifolia L., Carex riparia Curtis, Cichorium intybus L., Bolboschoenus maritimus L. Palla, and Rumex confertus Willd. The total concentrations of Mn, Ni, Cd, Cu, Zn, Pb, and Cr in the soils were determined by X-ray fluorescent scanning spectrometer. The concentration of heavy metal mobile forms exchangeable, complex compounds, and acid-soluble metal were extracted using the following reagents: 1 N NH₄Ac, pH 4.8; 1 % EDTA in NH₄Ac, pH 4.8; 1 N HCl, respectively. Heavy metals in plants were prepared for analysis by dry combustion at 450 °C. The heavy metal concentration in extracts from plants and soils was determined by AAS.

Results and discussion

The total contents of heavy metals in the soil may be described with a successively decreasing series: Mn?>?Cr?>?Zn?>?Ni?>?Cu?>?Pb?>?As?>?Cd. The total concentrations of As, Cd, and Zn in the soil exceed the maximum permissible concentrations levels. Contamination of alluvial soils in the estuarine zone with mobile Сu, Zn, Pb, and Cd has been revealed, which is confirmed by the high bioavailability of Cu and Zn and, to a lesser degree, Cd and Pb accumulating in the tissues of macrophytic plants. Data on the translocation of elements to plant organs have showed their predominant accumulation in the roots. Bioindication by the morphofunctional parameters of macrophytic plants (with a Typha L. species as an example) can be used for revealing the existence of impact zones with elevated contents of metals in aquatic ecosystems.

Conclusions

The results revealed that increased content of Zn, Pb, Cu, Ni, and As in soil have anthropogenic sources. The high content of Cr in the soils is related to the lithogenic factor and, hence, has a natural source.

     

Soil nitrogen and denitrification potential as affected by land use and stand age following agricultural abandonment in a headwater catchment

Changes in vegetation and soil properties because of agricultural abandonment may affect soil nitrogen (N) and associated processes. We investigated soil N (total N: TN, inorganic N: NH₄–N and NO₃–N) and denitrification potential in cropland, pine plantations and abandoned agricultural land along a secondary succession sequence (grassland→shrubland→secondary forest) in a headwater catchment in the Qinling Mountains, northwest China. The results show that the soil denitrification potential differed significantly among the five land‐use types with the highest potential in the secondary forest, followed by grassland, shrubland, cropland and plantations. The denitrification potential of the 20‐ to 40‐cm layer was significantly lower compared with the topsoil (0–20 cm) across all land‐use types. TN, soil organic matter (SOM) and NH₄–N increased significantly with stand age, whereas there was an opposite trend in soil pH. However, the denitrification potential did not relate to stand age in a linear manner. We conclude that changes in soil TN, SOM and pH during vegetation succession following agricultural abandonment are critical controls on the denitrification potential.     

Die Bedeutung von hohen Aluminiumgehalten für die Humusanreicherung in sauren Waldböden

The role of aluminium on humus accumulation in acid forest soils The impact of soil-borne aluminum on humus accumulation was investigated in a forest soil of the chestnut zone (Castanea sativa) in southern Switzerland (Ticino). Soil samples of two soils formed on bedrocks which differ mainly in their aluminum content were extracted with HNO₃, NH₄Ac.-EDTA, NH₄Cl, KCl, and NH₄F-HCl and analyzed for the most abundant elements. On gneiss which contains up to about 10% of total aluminum the common soil type in this area is a Cryptopodzol. This soil is similar to the nonallophanic Udands. It is rich in wellhumified organic matter and shows dark-colored A_h-, A(E)- and B_h-horizons. The soil samples of these horizons are extremely rich in nonexchangeable aluminum which is, however, extractable with NH₄Ac.-EDTA. It is assumed that this Al is intimately bound to the organic matter. The soil samples of these horizons contain large amounts of HNO₃-extractable phosphorus. Up to 90% of this P appears in the organic fraction. The content of NH₄F-HCl-extractable P is only 0.7 to 3.4 mg/kg. It is concluded that due to excessive Al in the organic matter the humus mineralization is inhibited compared to the Haplumbrepts of the region.     

Effects of Soil Amended with Cadmium and Lead on Growth,Yield, and Metal Accumulation and Distribution in Parsley

A greenhouse experiment was designed to determine the cadmium (Cd) and lead (Pb) distribution and accumulation in parsley plants grown on soil amended with Cd and Pb. The soil was amended with 0, 5, 10 20, 40, 60, 80, and 100 mg Cd kg^?1 in the form of cadmium nitrate [Cd(NO₃)₂] and 0, 5, 10, 50 and 100 mg Pb kg^?1 in the form of lead nitrate [Pb(NO₃)₂]. The main soil properties; concentrations of the diethylenetriaminepentaacetic acid (DTPA)–extractable metals lead (Pb), Cd, copper (Cu), iron (Fe), zinc (Zn), and manganese (Mn) in soil; plant growth; and total contents of metals in shoots and roots were measured. The DTPA-extractable Cd was increased significantly by the addition of Cd. Despite the fact that Pb was not applied, its availability was significantly greater in treatments 40–100 mg Cd kg^?1 compared with the control. Fresh biomass was increased significantly in treatments of 5 and 10 mg Cd kg^?1 as compared to the control. Further addition of Cd reduced fresh weight but not significantly, although Cd concentration in shoots reached 26.5 mg kg^?1. Although Pb was not applied with Cd, its concentration in parsley increased significantly in treatments with 60, 80, and 100 mg Cd g^?1 compared with the others. Available soil Pb was increased significantly with Pb levels; nevertheless, the increase was small compared to the additions of Pb to soil. There were no significant differences in shoot and root fresh weights between treatments, although metal contents reached 20.0 mg Pb kg^?1 and 16.4 mg Pb kg^?1 respectively. Lead accumulation was enhanced by Pb treatments, but the positive effect on its uptake was not relative to the increase of Pb rates. Cadmium was not applied, and yet considerable uptake of Cd by control plants was evident. The interactive effects of Pb and Cd on their availability in soil and plants and their relation to other metals are also discussed.     

森林土壤重金属的分布和迁移: 一种高密度采样方法的应用

The vertical distribution and migration of Cu, Zn, Pb, and Cd in two forest soil profiles near an industrial emission source were investigated using a high resolution sampling method together with reference element Ti. One-meter soil profile was sectioned horizontally at 2 cm intervals in the first 40 cm, 5 cm intervals in the next 40 cm, and 10 cm intervals in the last 20 cm. The migration distance and rate of heavy metals in the soil profiles were calculated according to their relative concentrations in the profiles, as calibrated by the reference element Ti. The enrichment of heavy metals appeared in the uppermost layer of the forest soil, and the soil heavy metal concentrations decreased down the profile until reaching their background values. The calculated average migration rates of Cd, Cu, Pb, and Zn were 0.70, 0.33, 0.37, and 0.76 cm year^-1, respectively, which were comparable to other methods. A simulation model was proposed, which could well describe the distribution of Cu, Zn, Pb, and Cd in natural forest soils.     

Soil versus plant as indicators of agroecosystem pollution by potentially toxic elements

The major route of potentially toxic elements (PTEs) to humans is the intake through food. They enter the food chain principally by plants uptake from the soil and, to a less extent, through foliar deposition. The soil‐to‐plant transfer as part of the biogeochemical cycle of these elements is a complex and hardly predictable process. In this study, we investigated the capability of soils and plants to indicate PTEs inputs in an intermingled urban‐rural landscape of south Italy affected by legal and illegal waste disposal and dumping. For this aim, 172 agricultural soil and plant (edible part) samples were collected in pairs from 47 municipalities and analyzed for 12 PTEs (As, Be, Cd, Co, Cu, Cr, Ni, Pb, Se, Tl, V, Zn). Soil extractions with 1 M NH₄NO₃ and 0.05 M EDTA pH 7 were applied to assess PTEs bioavailability. Results were examined according to plant species and main soil chemical properties. For Pb and Cd, the soil‐to‐plant transfer factors (TF) and the corresponding soil benchmark concentrations were also investigated. Zinc, Cu, Cd, and Pb were the only PTEs of anthropic origin severely polluting from 10 to 16% of the soils, but only in a very few cases exceeded physiological or EU legal critical values in the edible part of the plants. An evaluation of human risk due to the ingestion of these elements was tried; no risk for consumers for Zn, Cu, and Pb, while for Cd three values slightly exceeded the tolerable daily intake. Therefore, we conclude that crops cultivated in the studied area could represent only a moderate risk for human health. No correlation was found between soil and plant data, which likely highlights different pollution inputs. A large variability characterized the Pb and Cd TF, making it difficult to establish a unique benchmark concentration for the studied agricultural soils.     

Relative Value of Phosphate Compounds in Reducing the Bioavailability and Toxicity of Lead in Contaminated Soils

Lead forms stable compounds with phosphate and the immobilized Pb becomes less available to soil biota. In this study, we tested the bioavailabilty of Pb using earthworms (Eisenia fetida) and plants after immobilization of Pb by a soluble P compound and an insoluble rock phosphate compound in the presence of phosphate-solubilizing bacteria (Enterobacter sp.). Rock phosphate in the presence of phosphate-solubilizing bacteria and a soluble P compound enhanced Pb immobilization as measured by NH₄NO₃-extractable Pb concentration, thereby reduced its bioavailability as evaluated by earthworm Pb loading and sunflower (Helianthus annuus) Pb uptake under greenhouse conditions. However, soluble P treatment increased the concentration of Pb in soil solution thereby inhibited the root elongation of mustard (Brassica hirta) seedlings. Sunflower plants in the Pb-spiked soil without P amendments showed symptoms of necrosis and stunting because of Pb toxicity. Both soluble and insoluble P treatments significantly increased shoot and root weight and decreased Pb concentration in shoot by more than 50% compared to the control. However, high Pb concentration in soil solution was found in soluble P treatment, which can be attributed to dissolved organic carbon–Pb complex formation, thereby increasing Pb mobility. The inoculation of phosphate-solubilizing bacteria can facilitate phytostabilization of Pb-contaminated site.     

不同调理剂对农田镉污染稳定效果及水稻吸收的影响

采集浙江杭州郊区富春江沿岸镉(Cd)污染水稻土，选择前期试验筛选的对土壤Cd钝化效果良好、可显著降低稻米Cd的4种调理剂，开展室内培养试验和温室盆栽试验，探讨不同调理剂种类(袁梦YM、祝天峰ZTF、天象一号TX1、永清YQ)、用量(推荐用量、3倍推荐用量)和调理剂与生石灰配施对污染水稻土Cd的稳定效果及对水稻生长和糙米Cd含量的影响。室内培养试验结果发现，添加调理剂能使土壤pH显著升高，落干条件下土壤pH增幅较淹水条件下更为明显；施用推荐用量调理剂，土壤硝酸铵提取态Cd显著下降，调理剂推荐用量+生石灰处理较调理剂推荐用量处理下降更为显著；总体上，同一调理剂3倍推荐用量处理下硝酸铵提取态Cd降幅更大，表明硝酸铵提取态Cd受土壤pH影响显著，且YM、TX1调理剂对硝酸铵提取态Cd的降低效果较好。盆栽试验结果显示，施用石灰和商品调理剂均可实现水稻稳产或增产，并显著降低水稻糙米Cd含量，与调理剂施用后土壤Cd有效性降低相一致。含钙、能调节土壤pH并辅以有机质和养分的复合调理剂因兼具养分作用，对水稻稳产增产、糙米Cd含量降低更为有效。     

Heavy Metal Pollution by Atmospheric Transport in Natural Soils from the Northern Part of Eastern Carpathians

The present paper is a study of the heavy metal contamination ofnatural soils due to atmospheric transport in the northern partof Eastern Carpathians. The study area is located north of BaiaMare, the main Romanian centre for processing complex sulphideores. Ten undisturbed soil profiles of andosols and andic soilswere investigated. The distribution of heavy metals (Pb, Cu, Zn,Mn, Ni, Co, Cr and Cd) was studied along the soil profile and atspecific distances from the pollution sources. In addition tothe total nitric acid soluble fraction of the metals, amounts oflead, copper, zinc and manganese extractable with 0.05 Mhydrochloric acid were determined to evaluate the fraction ofeach metal potentially available to plants. Surface soils in theIgnis Mountains (10 km from Baia Mare) were more polluted withlead (200–800 ppm), with the concentration decreasing withdistance from the processing plants. Lower lead concentrationswere observed in the deeper soil horizons. The fraction of leadextractable in 0.05 M hydrochloric acid was generally higher athigh total concentrations of lead. From its geographical andsoil profile distributions it is also evident that cadmium wasalso supplied in appreciable amounts to the topsoil from thesame polution sources, whereas the trend was weaker for zincand chromium and not evident for copper, manganese, nickel, orcobalt. The fraction extractable with 0.05 M hydrochloric acidgenerally followed the order Pb > Cu > Zn > Mn.     

Immobilization of heavy metals in soils by the application of bauxite residues: pot experiments under field conditions

In previous greenhouse experiments red mud, a residue of the alumina industry, was identified as effective amendment for in situ fixation of heavy metals. In the present study, we further evaluated the efficiency and potential drawbacks of red mud in an outdoor pot experiment. Application of 5 % (w/w) red mud (RM) should reveal possible drawbacks of red mud due to indigenous pollutants such as As, Cr, and V. Three soils from arable land in Lower Austria named Untertiefenbach (U) (Eutric Cambisol), Weyersdorf (W) (Dystric Cambisol), and Reisenberg (R) (Calcic Chernozem) were spiked with Cd, Zn, Cu, Ni, and V at two concentration levels in 1987, two soils originate from long‐term industrially polluted sites, located in Carinthia (Arnoldstein – Rendzic Leptosol; Zn, Cd, and Pb) and Tyrol (Brixlegg – Dystric Fluvisol; Cu, Zn). Zea mays was cultivated in pots for three months in outdoor conditions. Extraction with 1 M NH₄NO₃ was used to assess the influence of RM on the labile metals. Lability of Cd, Zn, Ni, and Pb was reduced upon RM treatment on a sandy soil up to 91 %, 94 %, 71 %, and 83 % of the control, respectively. Metal accumulation in shoots was reduced for Cd and Zn up to 54 % and for Ni up to 75 % (soil W), but not for Pb (soil A). Addition of RM (5 % w/w) increased the total As, Cr, and V concentrations in soils by 5, 20, and 50 mg kg^–1, respectively. Whereas the lability of Cr was not affected, 1 M NH₄NO₃‐extractable As and V exceeded the trigger value for water quality according to Prüeß (1994). Lability of Cu increased upon RM application, especially on the Cu polluted industrial soil (B), while Cu toxicity appeared to be reduced as indicated by the higher corn biomass production. Red mud holds promise as soil amendment in terms of reduction Cd, Zn, and Ni bioavailability. However, at additions as high as 5 % (w/w) large As, Cr, and V concentrations of this material may limit its application.     

Characterization of soil heavy metal pools in paddy fields in Taiwan: chemical extraction and solid-solution partitioning

Background, aim, and scope  Ongoing industrialization has resulted in an accumulation of metals like Cd, Cu, Cr, Ni, Zn, and Pb in paddy fields across Southeast Asia. Risks of metals in soils depend on soil properties and the availability of metals in soil. At present, however, limited information is available on how to measure or predict the directly available fraction of metals in paddy soils. Here, the distribution of Cd, Cu, Cr, Ni, Zn, and Pb in 19 paddy fields among the total, reactive, and directly available pools was measured using recently developed concepts for aerated soils. Solid-solution partitioning models have been derived to predict the directly available metal pool. Such models are proven to be useful for risk assessment and to derive soil quality standards for aerated soils. Material and methods  Soil samples (0–25 cm) were taken from 19 paddy fields from five different communities in Taiwan in 2005 and 2006. Each field was subdivided into 60 to 108 plots resulting in a database of approximately 3,200 individual soil samples. Total (Aqua Regia (AR)), reactive (0.43 M HNO₃, 0.1 M HCl, and 0.05 M EDTA), and directly available metal pools (0.01 M CaCl₂) were determined. Solid-solution partitioning models were derived by multiple linear regressions using an extended Freundlich equation using the reactive metal pool, pH, and the cation exchange capacity (CEC). The influence of Zn on metal partitioning and differences between both sampling events (May/November) were evaluated. Results  Total metals contents range from background levels to levels in excess of current soil quality standards for arable land. Between 3% (Cr) and 30% (Cd) of all samples exceed present soil quality standards based on extraction with AR. Total metal levels decreased with an increasing distance from the irrigation water inlet. The reactive metal pool relative to the total metal content is increased in the order Cr << Ni = Zn < Pb < Cu < Cd and ranged from less than 10% for Cr to more than 70% for Cd. Despite frequent redox cycles, Cd, Pb, and Cu appear to remain rather reactive. The methods to determine the reactive metal pool in soils yield comparable results, although the 0.43 M HNO₃ extraction is slightly stronger than HCl and EDTA. The close correlation between these methods suggests that they release similar fractions from soils, probably those reversibly sorbed to soil organic matter (SOM) and clay. The average directly available pool ranged from less than 1% for Cu, Pb, and Cr to 10% for Ni, Zn, and Cd when compared to the reactive metal pool. For Cd, Ni, Zn, and to a lesser extent for Cu and Pb, solid-solution partitioning models were able to explain up to 93% (Cd) of the observed variation in the directly available metal pool. CaCl₂ extractable Zn increased the directly available pool for Ni, Cd, and Cu but not that of Pb and Cr. In the polluted soils, the directly available pool was higher in November compared to that in May. Differences in temperature, rainfall, and changes in soil properties such as pH are likely to contribute to the differences observed within the year. The solid-solution partitioning model failed to explain the variation in the directly available Cr pool, probably because Cr is present in precipitates rather than being adsorbed onto SOM and clay. Despite obvious differences in parent material, source of pollution, climate, and land use, solid-solution partitioning of Cd in paddy fields studied here was similar to that in soils from Belgium and the Netherlands. Discussion  To assess risks of metals in soils, both analytical procedures as well as models are needed. The three methods tested here to determine the reactive metal pool are highly correlated and either of these can be used. The directly available pool was predicted most accurately by the 0.43 M HNO₃ method. The similarity of metal partitioning in paddy soils compared to well-drained soils suggests that changing redox conditions in paddy fields have a limited effect on the geochemical behavior of metals like Cd, Ni, and Zn. Small but significant differences in the directly available metal pool during the year suggest that redox cycles as well as differences in rainfall and temperature affect the size of the directly available metal pool. The large observed spatial heterogeneity of contaminant levels requires ample attention in the setup of soil monitoring programs. Conclusions  The directly available pool (0.01 M CaCl₂) of Cd, Zn, and Ni in paddy fields can be described well by an extended Freundlich model. For Cu and Pb, more information on dissolved organic carbon is needed to obtain a more accurate estimate of the directly available pool. Recommendations and perspectives  Soil testing protocols and models used in risk assessment consider the availability of pollutants rather than the total metal content. Results from extensive testing indicate that approaches developed for nontropical regions can be applied in paddy fields as well for metals like Cd, Ni, and Zn. This study shows that the chemical behavior under drained conditions in paddy fields is comparable to that observed in soils across the European Union, which allows regions with large scale soil pollution including Taiwan to apply such concepts to derive meaningful experimental protocols and models to assess risks of metals in soils.