Effect of Organic Matter and Salinity on Ethylenediaminetetraacetic Acid–Extractable and Solution Species of Cadmium and Lead in Three Agricultural Soils

Abstract

A study was conducted to investigate the chemical speciation of added cadmium (Cd) and lead (Pb) and their availability as influenced by fresh organic matter (OM) and sodium chloride (NaCl) in three agricultural soils. The soils were treated with 20 mg Cd/kg as cadmium nitrate [Cd(NO₃)₂ · 4H₂O], 150 mg Pb/kg as lead nitrate [Pb(NO₃)₂], 20 g/kg alfalfa powder, and 50 mmol/kg of NaCl and then incubated for 3 months at 60% water‐holding capacity (WHC) and constant temperature (25 °C). Subsamples were taken after 1, 3, 6, and 12 weeks of incubation, and electrical conductivity (EC), pH, dissolved organic carbon (DOC), and concentrations of cations and anions were determined in the 1:2.5 soil/water extract. Available Cd and Pb were determined in 0.05 M ethylenediaminetetraacetic acid (EDTA) extract. Concentrations of organic and inorganic species of Cd and Pb in soil solution were also predicted using Visual Minteq speciation program. The most prevalent species of dissolved Pb and Cd in the soils were Pb‐DOC and Cd²⁺ species, respectively. Salinity application increased the available and soluble Cd significantly in the acid and calcareous soils. It, however, had little effect on soluble Pb and no effect on available Pb. Organic‐matter application decreased availability of added Pb significantly in all soils. In contrast, it raised soluble Pb in all soils except for the acid one and approximated gradually to the added Pb with time. Impact of OM on available Cd was somewhat similar to that of Pb. Soluble Cd increased by OM application in the calcareous soil, whereas it decreased initially and then increased with time in the other soils.     

Schwermetallanreicherungen in Salzmarschen der südlichen Nordseeküste

Heavy metal accumulations in Salic Fluvisols of the southern North Sea coast The total contents of Cd, Pb, Cu and Zn (HNO₃ bomb digestion) and their EDTA extractable fractions in Salic Fluvisols were investigated. The mean total content of Cd was 0,09 mg/kg, of Pb 44,1 mg/kg, of Cu 11,4 mg/kg and of Zn 105,6 mg/kg. Mostly the highly developed soils showed higher contents than poorly developed ones. The EDTA extractable fractions were comparatively small: they were 59% (Cd), 44% (Pb), 15% (Cu) and 10% (Zn) of the total content. The heavy metal contents of the soils in Elisabeth-Außengroden were higher than of those in Jadebusen. The vertical heavy metal distribution showed a different sedimentation pattern over the last hundred years. Compared with the geological background values Cd was 2- to 3-fold enriched, Pb 7-fold, Cu 3- to 4-fold and Zn 3-fold in soils with high sedimentation rates. Even higher values are likely in soils with smaller sedimentation rates.     

EVALUATION OF HEAVY METAL REMEDIATION USING MINERAL APATITE

The current study investigated the sorption and desorption of dissolved lead (Pb), cadmium (Cd) and zinc (Zn) from aqueous solutions and a contaminated soil by North Carolina mineral apatite. Aqueous solutions of Pb, Cd, and Zn were reacted with the apatite, followed by desorption experiments under a wide variety of pH conditions ranging from 3 to 12, including the extraction fluids used in the Toxicity Characteristic Leaching Procedure (TCLP) of the United States Environmental Protection Agency (US EPA). The sorption results showed that the apatite was very effective in retaining Pb and was moderately effective in attenuating Cd and Zn at pH 4–5. Approximately 100% of the Pb applied was removed from solutions, representing a capacity of 151 mg of Pb/g of apatite, while 49% of Cd and 29% of Zn added were attenuated, with removal capacities of 73 and 41 mg g^-1, respectively. The desorption experiments showed that the sorbed Pb stayed intact where only 14–23% and 7–14% of the sorbed Cd and Zn, respectively, were mobilized by the TCLP solutions. The apatite was also effective in removing dissolved Pb, Cd, and Zn leached from the contaminated soil using pH 3–12 solutions by 62.3–99.9, 20–97.9, and 28.6–98.7%, respectively. In particular, the apatite was able to reduce the metal concentrations in the TCLP-extracted soil leachates to below US EPA maximum allowable levels, suggesting that apatite could be used as a cost-effective option to remediating metal-contaminated soils, wastes, and/or water. The sorption mechanisms are variable in the reactions between the apatite and dissolved Pb, Cd, and Zn. The Pb removals primarily resulted from the dissolution of the apatite followed by the precipitation of hydroxyl fluoropyromorphite. Minor otavite precipitation was observed in the interaction of the apatite with aqueous Cd, but other sorption mechanisms, such as surface complexation, ion exchange, and the formation of amorphous solids, are primarily responsible for the removal of Zn and Cd.     

Differential Sorption Behavior of Cadmium,Lead, Zinc,and Copper in Some Tropical Soils and Their Environmental Implications

This study evaluated cadmium (Cd), lead (Pb), zinc (Zn), and copper (Cu) sorption characteristics of three tropical soils. Data obtained conformed to Freundlich sorption model and the S-shaped isotherm curve. Sorption efficiency of Zn and Pb were highest in alkaline soil while slightly acid soil had the highest Cd and Cu sorption efficiency for monometal sorption. In competitive sorption, metals were more sorbed in slightly acid soil while the least efficiency was recorded in acid soil. Distribution coefficient; K_d (average across soil types) in monometal sorption followed the order: Pb > Zn > Cd > Cu. For competitive sorption, the order was Zn > Pb > Cu > Cd. When in competition, Cd was preferentially sorbed in slightly acid and alkaline soils and Zn for acid soil. Conclusively, lead is more in equilibrium solution when in competition with Cd, Zn and Cu making it potential agent of soil and groundwater pollution.     

Kurzzeittests zur Abschätzung langfristiger Wirkungen potentieller anorganischer Schadstoffe auf die mikrobielle Aktivität von Böden

Short-term experiments for the estimation of long-term effects of inorganic pollutants on soil microbial activity The purpose of the present study was to develope a short-term laboratory method to predict long-term effects of inorganic pollutants on soil microbial activity. Experiments were carried out on a sandy cambisol which had been used in a long-term field plot of the Biologische Bundesanstalt in Berlin. The perfusion technique was suitable to prove long-term effects of concentrations of 50 mg Cd/kg and 1000 mg Pb/kg dry soil on dehydrogenase activity of the test soil. 200 mg Cd/kg and 4000 mg Pb/kg caused higher reductions in the perfusion experiment than in the long-term field trial. Due to the desorption of OH-ions and the dissolution of organic material, effects of NaF-additions were partly compensated in the short-term experiment. The lysimeter technique used here seems to be of minor value to simulate long-term effects of cadmium, lead, and fluorine because unadsorbed portions of these elements and their accompanying ions (e.g. Cl, NO₃) are washed out of the system too slowly. The dehydrogenase activity was more valid to indicate long-term effects on soil microbial activity than ATP-contents and nitrification measurements did.     

Gehalte an Haupt- und Nebenelementen in Konkretionen aus Oberböden von Marschen – Untersuchungen mit einer Mikrosonde

Contents of major and trace elements in concretions of surface samples from marsh soils – Electron microprobe analysis The amounts of 14 elements (Ti, Fe, Mn, Si, Al, Ca, and P, S, Co, Ni, Cu, Zn, Cd, Pb) in concretions of four A horizons of marsh soils were determined by electron microprobe analysis on thin sections. According to the major element compositions the following types of concretions can be distinguished: Ti-Fe(-Mn) concretions (31–39% Ti; 18–29% Fe; 0,3–5,5% Mn); Fe(-Mn) concretions (31–58% Fe; ≤ 1,8% Mn); Fe-Si(-Mn) concretions (6–28% Fe; 8–42% Si; ≤ 5% Mn); Mn-Fe and Mn-Fe-Si concretions (16–40% Mn; 2–9% Fe; 2–15% Si). The formation of Ti-Fe(-Mn) concretions can be explained by adsorption of Fe²⁺ ions under reducing conditions on surfaces of Ti minerals followed by oxidation to Fe(III) oxide. In this way pseudorutile may be formed. Concretions with high Fe and/or Mn content often contain occlusions of carbonates, silicates and/or SiO₂ (bioopal) which may act as nuclei for their growth. Redox processes in marsh soils result in the formation of concretions with dominating Fe or Mn accumulation. Among the group of trace elements, P and S (like Ti and Si) reach their highest concentrations in Fe rich concretions (up to 54.000 mg P/kg and 4.200 mg S/kg). The accumulation of these elements is obviously influenced by anion competition, especially of P and Si, and probably also Ti. Likewise, high amounts of Pb were found in Fe(-Mn) concretions (up to 12.000 mg/kg). Co, Ni, Zn, and Cd show the highest amounts in Mn rich concretions (Co up to 3.400; Ni 1.800; Zn 13.200; Cd 1.000 mg/kg). Cu is also accumulated in some concretions (up to 1140 mg/kg) but no clear affinity to one of the different types of concretions was found.     

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.     

Sorption of lead,copper, zinc,and cadmium by soils: effect of nitriloacetic acid on metal retention

Abstract

Laboratory experiments were carried out to evaluate lead (Pb), copper (Cu), zinc (Zn), and cadmium (Cd) sorption‐desorption by three soils of contrasting characteristics. Talamanca (silt loam, montmorillonite, Calcic Haploxeralfs), Mazowe (clay, kaolinite, Rhodic Kandiustalf), and Realejos (sandy silt loam, allophane, Typic Hapludands). A second objective was to study the effect of nitriloacetic acid (NTA) on the sorption process. The Talamanca soil, which had a native pH of 6.4 and presented the highest effective cation exchange capacity (ECEC), sorbed more of each of the metal tested than did the other two soils. When the other two soils were compared metal sorption was also related to pH and ECEC. The very low sorption capacity showed by Realejos may be attributed to the low net surface negative charge density of this soil, arising from its allophanic nature. A common feature of the three soils was the relative strong sorption of both Pb and Cu relative to Cd and Zn with Pb showing the highest sorption levels. The selectivity sequences of metals retention were Pb>Cu>Zn>Cd for Talamanca soil, Pb>Cu>Zn≈Cd for Mazowe, and Pb>Cu>Cd>Zn for Realejos. Metal desorption values were low. The order of metal desorption (Cd≈Zn>Cu>Pb) was the same for the three soils studied. Quantitative differences observed in the extractability of the sorbed metals between the soils (Realejos>Mazowe>Talamanca) indicated that soil properties which enhanced metal sorption contributed at the same time to slow down the backward reaction. The addition of NTA to the soil suspension significantly depressed metal sorption by the three soils investigated. Compared with the free ligand system Pb, Cu, Zn, and Cd sorption in the presence of NTA decreased roughly 50%.     

Not All Phosphate Fertilizers Immobilize Lead in Soils

The effects of six phosphate (P) fertilizers in mobilizing and immobilizing water-soluble lead (Pb) were determined in a contaminated soil (Alfisol from Shaoxing) from China and four Australian soils (an Oxisol from Twonsville Queensland and three South Australian soils from Cooke Plains (Typic Palexeralf)), Inman Valley (Vertisol), and Two Wells (Natric Palexeralf). The fertilizers tested were single superphosphate (SSP), triple superphosphate (TSP), monoammonium phosphate (MAP), diammonium phosphate (DAP), monocalcium phosphate (MCP), and dicalcium phosphate (DCP) to produce an initial P concentration of 1,000 mg/L. The Chinese soil contained 16,397 mg/kg total Pb, but the Australian soils were uncontaminated. The four Australian soils were each spiked with 1,000 mg Pb/kg soil (as Pb(NO₃)₂) and incubated for a month. Single superphosphate treatments decreased total soluble Pb in soil solution to 2–14 % of those of the nil-P (0P) treatment in the four Pb-spiked soils and to 48 % in the Chinese Pb-contaminated soil. The DAP treatment followed by the MAP treatment greatly increased the total soluble Pb in soil solution up to 135–500 % of the 0P treatment, except in the Two Wells soil. MCP could decrease the total soluble Pb in Cooke Plains, Inman Valley, Shaoxing, and Two Wells soils while increase it in the Queensland soil; DCP decreased the total soluble Pb in Cooke Plains and Queensland soils while increased it in the Shaoxing and Inman Valley soils. There were close relationships between the total soluble Pb, total soluble Al, and total soluble Fe in the water extracts of each. Soluble Al and Fe ions in soil solution increased soluble Pb concentrations. We conclude that not all phosphate fertilizers immobilize Pb in soils equally well. SSP and TSP are excellent Pb-immobilizing fertilizers, while MAP and DAP are strong Pb-mobilizing fertilizers. MCP and DCP are either Pb-immobilizing fertilizers or Pb-mobilizing fertilizers depending on their reactions with individual soils.     

Mikrosondenuntersuchungen an unterschiedlich stark mit Schwermetallen belasteten Böden. 2. Gehalte an Schwermetallen und anderen Elementen in Huminstoffaggregationen,Streustoffen und Holzkohlepartikeln

Electron microprobe studies on soil samples with varying heavy metal contamination. 2. Contents of heavy metals and other elements in aggregations of humic substances, litter residues and charcoal particles EMA point analysis show that the organic matter constituents of heavy metal contaminated soils are highly enriched with heavy metals. The maximal trace element accumulation were for Cu up to 13,000 mg/kg, for Zn up to 48,000 mg/kg, for Cd up to 2,100 mg/kg and for Pb up to 193,000 mg/kg. The affinity for the accumulation of the different heavy metals in aggregations of humic substances can be described by the sequence Cu > Pb ? Cd > Zn ? Ni > Co. In very strongly acidified humic top soil horizons the Pb and Cd accumulation in the organic matter constituents is in competition with the accumulation in Fe and Mn oxides. The heavy metal contents (especially of Cu) of the organic matter are often correlated with the content of organically bound calcium. The EMA results also show that high heavy metal amounts occur in combination with Ca-accumulations in the epidermis and the outer bark parenchym of decayed roots. EMA point analysis of the interior of fungus sclerotias show that sclerotias can contain high amounts of heavy metals, in particular lead (up to 49,700 mg Pb/kg). From statistical results of EMA point analysis follows that lead and other heavy metals attached to humic substances are not only bound as metal organic complexes but also as organic metal phosphate complexes. Also charcoal particles of polluted soils contain high amounts of heay metals. The accumulation affinity is quite similar to that of humic substances.     

Die Komplexierung von Cu,Pb und Cd durch heißwasserlösliche Huminstoffe II. Die Stabilität der gebildeten Komplexe

Complexation of Cu, Pb, and Cd by hot water soluble humic substances II. The stability of the complexes Soxhlet extracts of terrestrial and underwater soils were used to determine polarographically the stability of heavy metal complexes. Stability constants were calculated using the law of mass action. They were independent of concentration at levels higher than 2 mg Cd or 5 mg Pb/g humic substance, respectively. For Cu, constants increased below 8 mg Cu/g. At pH values in the polarographic medium between 4 and 8, the stability of the Pb complexes increased markedly with increasing pH. In most cases this was also valid for the copper complexes, cadmium complexes were either not influenced by pH or stability maximum was obtained at about pH 5. Drying of the samples before extraction did not alter significantly complex stabilities. Complex stabilities increased with increasing degree of humification for oligotrophic, underwater soils and nutrient poor, low moor peat, but reduced horizons of eutrophic gyttjas exhibited lower stability values.     

潮土和潮褐土中重金属形态与土壤酶活性的关系

采用大田取样 ,运用连续提取方法 ,研究了河北平原潮土、潮褐土两种土壤中Cd、Pb的化学形态特征与四种土壤酶 (脲酶、H2 O2 酶、转化酶、碱性磷酸酶 )活性间的关系。结果表明 :大田两种土壤中交换态Cd、Pb对脲酶活性有显著抑制作用。因此 ,在石灰性土壤中 ,把交换态Cd、Pb和脲酶活性共同作为评价土壤Cd、Pb污染程度的主要生化指标是可行的     

Effects of meliorative additives on the adsorption and binding forms of heavy metals in a contaminated topsoil from a former sewage farm

In a laboratory study, a heavy metal contaminated topsoil from a former sewage farm in Berlin was amended with different additives: lime, ash/gypsum, bark mulch, brown coal and combinations of these treatments. After 8 weeks of incubation, pH of the lime and ash/gypsum treatments increased to 6.2–6.3 compared to 5.2–5.3 in the control and the other treatments. Organic-C content rose from 42 g/kg in the control to 46–53 g/kg in the organic amendments. In reaction to the pH-increase the water soluble fraction of Cd, Cu and Zn was reduced by roughly 60%, 30% and 80% respectively. Cd- and Zn-binding forms as determined with NH₄-acetate- and EDTA-extracts were not affected by the treatments, while the ash/gypsum-treatment increased EDTA-extractable Pb by 17%. The exchangeable Cu-Fraction (NH₄-acetate extract) was reduced in all treatments to 82–93% of the control values, with the greatest effects in the tree bark amendment. The FREUNDLICH adsorption isotherms also show an increased sorption of heavy metals in the lime and ash/gypsum treatments. Organic amendments alone or in combination with lime had little effect on heavy metal adsorption.     

几种有机酸对可变电荷和恒电荷土壤吸附镉的影响

The objectives of this study were to illustrate the reaction processes, to identify and quantify the precipitates formed, and to estimate the porosity losses in order to eliminate drawbacks during remediating monochlorobenzene （MCB） and trichloroethylene （TCE）-contaminated aquifers using the ORC-GAC-Fe^0-CaCO3 system. The system consisted of four columns （112 cm long and 10 cm in diameter） with oxygen-releasing compound （ORC）, granular activated carbon （GAC）, zero-valent iron （Fe^0）, and calcite used sequentially as the reactive media. The concentrations of MCB in the GAC column effluent and TCE in the Fe^0 column effluent were below the detection limit. However, the concentrations of MCB and TCE in the final calcite column exceeded the maximum contaminant level （MCL） under the Safe Drinking Water Act of the US Environmental Protection Agency （US EPA） that protects human health and environment. These results suggested that partitioning of MCB and TCE into the gas phase could occur, and also that transportation of volatile organic pollutants in the gas phase was important. Three main precipitates formed in the ORC-GAC-Fe^0-CaCO3 system： CaCO3 in the ORC column along with Fe（OH）2 and FeCO3 in the Fe^0 column. The total porosity losses caused by mineral precipitation corresponded to about 0.24% porosity in the ORC column, and 1% in the Fe^0 column. The most important cause of porosity losses was anaerobic corrosion of iron. The porosity losses caused by gas because of the production and entrapment of oxygen in the ORC column and hydrogen in the Fe^0 column should not be ignored. Volatilization, precipitation and porosity losses were considered to be the main drawbacks of the ORC-GAC-Fe^0-CaCO3 system in remediating the MCB and TCE-contaminated aquifers. Thus, measurements such as using a suitable oxygen-releasing compound, weakening the increase in pH using a buffer material such as soil, stimulating biodegradation rates and minimizing the plugging caused by the relatively high dissolved oxygen levels should be taken to eliminate the drawbacks and to improve the efficiency of the ORC-GAC-Fe^0-CaCO3 system.     

Pflanzenaufnahme und Extrahierbarkeit von lithogen,pedogen und anthropogen angereichertem Cadmium in einem Parabraunerde-Ap-Horizont aus Löß

Plant uptake and solubility of lithogeneous, pedogeneous and anthropogeneous cadmium of an Ap-horizon from Orthic Luvisol In a pot trial we investigated the cadmium uptake by ryegrass (Lolium multiflorum) and spinach (Spinacea oleracea) in soil material of an Ap-horizon from Orthic Luvisol consisting of loess contaminated with Cd lithogeneously (stone powder), pedogeneously (soil from Ah- and Bv-horizon) and anthropogeneously (CdO) respectively. The concentration of Cd in the pots was adjusted to 1.5. 3 and 6 mg/kg soil. The total Cd-charge in the soil being at the same level, the tested plants (ryegrass and spinach) took up at least two times more of Cd of anthropogeneous origin (CdO) than of the Cd of geogeneous (pedogeneous and lithogeneous) origins. A remarkably higher solubility of the anthropogeneous cadmium was noticed compared with Cd of geogeneous origin. The DTPA-solution showed these differences most clearly. The relative soluble part of the anthropogeneous Cd was more than 60% of the total content, whereas it was lower by the factor of 2 to 3 in the geogeneously enriched cadmium. In the 0, 1 M CaCl₂- and the acid (O.I M HCI + 0.125 M H₂SO₄)-extraction these differences were not as obvious. The DTPA soluble cadmium fraction and the Cd taken up by the plants tested showed the closest correlations.     

Remediation of Cadmium Pollution in Soils by Different Amendments: A Column Study

Abstract

A column study was conducted to determine the effect of city compost, lime, gypsum, and phosphate on cadmium (Cd) mobility in three well‐recognized benchmark soils of India [viz., (Islamnagar) Vertisol, (Amarpur) Inceptisol, and (Khala) Alfisol]. Columns made of PVC were filled with soil treated with different treatment doses [viz., 0.5% city compost, 1% city compost, 2% city compost, 2.5 t lime/ha, 5 t lime/ha, 2.5 t lime/ha+0.5% city compost, 2.5 t gypsum/ha, 2.5 t gypsum/ha+0.5% city compost, and 100 kg P₂O₅/ha as potassium phosphate (KH₂PO₄). The columns were leached with 100 mg L^?1 Cd under saturated condition. The amount of water moving through the soils was measured as the pore volume. A delayed breakthrough curve (BTC) of Cd in the presence of lime has been observed in all the studied benchmark soil series. Among the treatments, lime application reduced the movement of Cd from surface soil to lower depth of soil to a large extent resulted in 9, 25, and 45% more retention of Cd in surface soil of the Islamnagar, Amarpur, and Khala series respectively. Explanation for reduced Cd mobility in limed soil can be derived from pH changes of soils. In comparison to control soil, phosphate application caused 6, 21, and 30% more retention of Cd in surface soil in the Islamnagar, Amarpur, and Khala series, respectively. Combined application of lime and city compost reduced the movement of Cd in the soil profile. It appears that organic matter controls the sorption of Cd in soils. The amount of Cd sorbed increased with increasing organic carbon content, but gypsum application may leach Cd beyond the root‐zone depth. A rapid breakthrough curve was observed under gypsum‐treated soils. Retardation factor revealed that a somewhat lower degree of Cd retention occurred in the Khala series, which might possibly be attributed to less clay content and low pH. Overall, the column study indicated that total Cd accumulation occurred up to depths of 5–7.5 cm, 7.5–10 cm, and 10–15 cm in soils of Islamnagar, Amarpur, and Khala series, respectively.     

海泡石对典型水稻土镉吸附能力的影响

通过吸附解吸实验研究了添加海泡石后典型水稻土对Cd的吸附解吸特性及其对吸附溶液pH值变化的响应。结果表明,Freundlich方程可以较好地拟合红黄泥、黄泥田和红沙泥3种典型水稻土对Cd的等温吸附过程（R2〉0.962）。在溶液初始Cd浓度相同的情况下,添加海泡石可使3种水稻土对Cd的吸附量增加20%以上,增强土壤对Cd的吸附强度,有效降低吸附Cd的解吸率,其效果随海泡石添加量的增大而增强。3种水稻土吸附Cd的解吸率均高于70%,而且都随吸附量的增加而上升。溶液的pH值是影响土壤吸附Cd的一个重要因素,在低pH值的条件下（pH〈4）,随着溶液pH值的降低,土壤对Cd的吸附量迅速降低,当溶液pH值高于5时,pH值的变化对吸附量的影响较小。在溶液初始pH值2-8范围内,添加海泡石均能有效提高3种水稻土对Cd的吸附能力。     

Effect of sewage sludge on some chemical properties of calcareous sandy soils

Abstract

City sewage sludge was applied to the surface layer (0–10 cm) of two sandy soils, slightly calcareous with 8.9% CaCO₃ and moderately calcareous with 26.7% CaCO₃, at the rates of 0, 25, 50, 75, and 100 Mg ha^‐1. The effects of sewage sludge and its rates on total soluble salts, pH of soils and concentration and movement of some heavy metals within soils were investigated. Soil samples were packed at bulk density of 1.5 g cm^‐3 in PVC columns and incubated for 19 weeks. The results indicated that total soluble salts (EC) of the treated layer increased with increasing sewage sludge rates. Soluble salts also increased with an increase in soil depth for both soils. The pH values of treated layers in two soils decreased with increasing sewage sludge rates. With increasing sewage sludge rates, concentrations of heavy metals [cobalt (Co), nickel (Ni), cadmium (Cd), and leaf (Pb)] increased in the treated layers compared to the untreated layers and their mobility was restricted mostly to the upper 30‐cm depth. Movement of Co and Pb in both the soils was predominately limited up to a depth of 40 cm for Co and 5 cm for Pb below the treated soil layer. Nickel and Cd movement was mostly limited to a depth of 10 cm in slightly calcareous soil and 5 cm in moderately calcareous soil. Metal movement in the respective soils is ranked as Co>Ni=Cd>Pb and Co>Ni=Cd>Pb. The low concentrations of heavy metals and the restricted mobility with soil depth, suggest that this material may be used for agricultural crop production without any toxic effect on plants.     

Metal Uptake in Plants and Health Risk Assessments in Metal‐Contaminated Smelter Soils

Metal pollution is an important concern because of its potential to affect human health. Metals such as lead and cadmium can enter soil via the food chain and exceed normal limits, producing harmful effects. In this study, six common garden and residential plant species were grown in soils from Spelter, WV, USA, contaminated with a variety of metals including lead (Pb), zinc (Zn), cadmium (Cd), and copper (Cu). Plant species included radish, carrot, chicory, spinach, lettuce, and clover. Metal concentrations in plant tissues were compared with metal concentration in soil by a multi‐step chemical extraction. The largest accumulation of Pb (126 mg kg⁻¹) and Zn (1493 mg kg⁻¹) was seen in radish roots, with Cd (40 mg kg⁻¹) having the largest accumulation in carrot roots. Comparisons of plant availability with soil chemical extractions indicated that the combined soluble and exchangeable fractions could estimate available Zn and Cd for all six plant species. For Pb and Cu, however, the comparisons indicate that these two elements were not readily available in Spelter soils. A health risk assessment was carried out for residents at Spelter on the basis of edible tissue concentrations and publicly available consumption data. Uptake of Cd by carrot roots was about five times more than the regulatory limits for men, eight times more for women, and 12 times more for children. On the basis of the results, carrot and lettuce grown in these soils have the potential to cause toxicological problems in men, women, and young children resulting from Cd and Zn accumulation. Copyright © 2013 John Wiley & Sons, Ltd.     

Using kale (Brassica oleracea var. acephala) as a phytoremediation plant species for lead (Pb) and cadmium (Cd) removal in saline soils

Ornamental kale (Brassica oleracea var. Acephala) is usually planted from early autumn until late winter. Since most of the plants used for phytoremediation cannot be grown during this time, kale can be a suitable option for phytoremediation and utilized during autumn and winter in urban landscape, especially in metropolitan areas where high levels of cadmium (Cd) and lead (Pb) pollutions exist. Kale growth in saline soil at different growth stages (germination and vegetative growth stages) was studied in this investigation. A factorial experiment based on completely randomized design (CRD) with four replications was used in this study. Treatments included three levels of sodium chloride (NaCl) (0, 30, and 60 mg/kg), four levels of Cd (0, 4, 8, and 16 mg/kg), and four levels of Pb (0, 1, 5, and 10 mg/kg). Results indicated that increase in Cd and Pb concentrations in the soil decreased fresh and dry weights of the plants. The results of the various growth stages revealed that under salinity stress, kale plants were able to absorb more Pb than Cd and effectively remediate Pb in polluted and saline lands. Cd accumulation in control treatment was 6.2% more than that in the saline treatments, whereas, Pb accumulation in the highest NaCl level, 60 mg/kg salinity treatment was 7.64% more than that of the control condition. Also, proline content of the plants was significantly increased under Cd and Pb stress. From the results of this study, it was concluded that using kale plant is recommended for phytoremediation of saline soils with 10 and 16 mg/kg Pb and Cd contents, respectively.