Bean Plant Production of Dry Matter and Grain Related to Soil Citric Acid–Extractable Copper,Zinc, Cadmium,and Lead

Some knowledge concerning soil heavy‐metal content and its availability to plants is essential to evaluate the risk of potentially toxic elements in the alimentary chain. Assessment of heavy‐metal availability to plants was achieved by a simple extraction method. The goal of this work was to determine the contents of copper (Cu), zinc (Zn), cadmium (Cd), and lead (Pb), soluble in 2% citric acid solution (chelating agent), in dystrophic red latosol soil (RL_d) and humic red‐yellow latosol soil (RYL_h). We focused on relating the contents of Cu, Zn, Cd, and Pb to the production of dry matter and grains by bean plants cultivated in a glasshouse. Heavy‐metal contents extracted by citric acid increased with increasing dosage increments, mainly in RL_d; production of dry matter by bean plant was negatively affected by the studied metals. However, in some cases, grain production was increased.     

Effect of Olive‐Derived Organic Amendments on Lead,Zinc, and Biochemical Parameters of an Artificially Contaminated Soil

Abstract

An incubation experiment was conducted to ascertain the effects of three olive‐derived organic amendments (fresh, compost, and vermicompost olive cake) on the soluble and diethylenetriamine pentaacetic acid (DTPA)–extractable lead (Pb) and zinc (Zn) and on different enzymatic activities in an artificially contaminated calcareous soil. Application of the compost and vermicompost, which increased amounts of humic acids in soil, initially stimulated dehydrogenase, ß‐glucosidase, and urease activities, which tended to decline afterward. In contrast, dehydrogenase and ß‐glucosidase activities were lower after application of the fresh olive cake. Amounts of soluble Pb and Zn increased when fresh olive cake was added to the soil, due to the high content of water‐soluble carbon in this amendment. On the contrary, application of the compost and vermicompost decreased the concentration of soluble Zn and did not change the soluble Pb levels in the soil. The DTPA‐Pb and DTPA‐Zn were scarcely affected by the application of the three olive‐derived amendments.     

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.     

Availability of Lead and Cadmium in Farmland Soil and Its Distribution in Individual Plants of Dry‐Seeded Rice

Abstract

Availability of lead (Pb) and cadmium (Cd) in farmland soils and its distribution in individual plants of dry‐seeded rice were investigated utilizing graphite furnace atomic absorption spectrometry (GFAAS) with a matrix modification technique. Five extractants were compared, and the operating conditions for GFAAS were optimized. The detection limits were 4.2 ng for Pb with the precision of 1.54% and 0.1 ng for Cd with the precision of 2.38%. The contents of the extractable Pb and Cd in soils were determined with the five extractants, and availability of Pb and Cd in farmland soil was discussed. The contents of Pb and Cd in different parts of dry‐seeded rice were lower than those in dry‐seeded rice soil. The contents of Pb and Cd in rice were lower than in other parts. The end top leaves accumulated the highest amounts of Pb and Cd.     

Determination of Uranium and Thorium in Soil and Plant Parts around Abandoned Lead–Zinc–Copper Mining Area

This study reports distribution of uranium (U) and thorium (Th) in soil samples and the roots and shoots of some plants grown around an abandoned lead (Pb)–zinc (Zn)–copper (Cu) mining area. The plants Euphorbia macroclada, Verbascum cheiranthifolium Boiss, and Astragalus gummifer were examined. The determinations of U and Th were carried out by inductively coupled plasma‐mass spectrometry (ICP‐MS). Uranium and Th levels of the studied soil samples were found to be in the range of 1.1–70.3 mg kg^?1 and 2.1–62.1 mg kg^?1, respectively. Some results obtained from this study were higher than the mean U and Th concentrations of soils reported around the world. Uranium and thorium concentrations in studied plant roots were in the range of 0.04–16 and 0.08–14.57 mg kg^?1, whereas in plant shoots they were 0.02–2.76 and 0.07–12.3 mg kg^?1, respectively. It was concluded that the shoots of Astragalus and roots of Euphorbia and Verbascum can be used as both a biomonitor for environmental pollution and biogeochemical indicator because of their higher U and Th concentrations.     

Effect of Flooding Lead Arsenate–Contaminated Orchard Soil on Growth and Arsenic and Lead Accumulation in Rice

Lead arsenate has been used as pesticide. Flooding soils contaminated by lead arsenate could increase plant arsenic and lead and become a human health risk. The objective was to determine the effects of flooding of lead‐arsenate soils on rice grain yield and arsenic and lead accumulation. Bagstown and Chashmont soils with high levels of arsenic and lead were planted with rice in the greenhouse under flooded and nonflooded conditions. Flooding reduced grain yield and increased grain arsenic concentration on both soils. Grain lead decreased with flooding for the Bagstown soil but increased for the Chashmont. Arsenic and lead concentrations in the straw were more than in grain. Grain arsenic and lead levels observed would not be expected to become a human health risk. However, bioavailability studies are needed. The high arsenic and lead in the straw may indirectly become a human health risk because rice straw is used for livestock feed and bedding.     

Heavy‐Metal Concentration of Sewage‐Contaminated Water and Its Impact on Underground Water,Soil, and Crop Plants in Alluvial Soils of Northwestern India

Abstract

Heavy‐metal concentration in underground and surface water, soil, and crop plants growing in farmers' fields near the industrial city of Ludhiana, Punjab, India, that receive irrigation with water contaminated with sewer and untreated industrial effluents was studied. The concentrations of lead (Pb), chromium (Cr), cadmium (Cd), and nickel (Ni) in sewage‐contaminated water were 18, 80, 88, and 210 times higher than in shallow handpump water, and 21, 133, 700, and 2200 times higher than in deep tube‐well water, respectively. The concentrations of Cd and Ni in shallow handpump underground water were significantly higher than in deep tube‐well underground water. The concentrations of Pb, Cr, Cd, and Ni in deep tube‐well water were 0.017, 0.003, 0.0002, and 0.0002 mg L^?1, respectively. Soils irrigated with sewage‐contaminated water had higher electrical conductivity, cation exchange capacity, organic carbon (C), and clay content but had lower pH and calcium carbonate content compared to soils irrigated with deep underground water. The concentrations of diethylenetriamine pentaacetic acid (DTPA)–extractable Pb, Cr, Cd, and Ni in soils irrigated with sewage‐contaminated water were 1.8, 35.5, 3.6, and 14.3 times higher, and total concentrations of these heavy metals were 1.5, 3.0, 3.7, and 2.2 times higher than that in soils irrigated with deep underground water. The mean concentrations of Pb, Cr, Cd, and Ni in crop plants growing on soils irrigated with sewage‐contaminated water were 4.88, 4.20, 0.29, and 3.99 mg kg^?1, which were 1.2, 2.1, 8.7, and 1.9 times higher than in plants irrigated with deep tube‐well water, respectively. The amounts of potentially toxic metals were significantly and positively correlated with cation exchange capacity and organic C content and negatively correlated with soil pH. In conclusion, long‐term accumulation of toxic metals in soils and their uptake by crop plants has a high potential for phytotoxicity as well as for entering into the food chain. The findings also suggest contamination of underground shallow drinking water through leaching of some highly mobile metals.     

Distribution of Forms of Zinc and Their Association with Soil Properties and Uptake in Different Soil Orders in Semi‐arid Soils of Punjab,India

Abstract

Profiles of semi‐arid–zone soils in Punjab, northwest India, were investigated for different forms of zinc (Zn), including total, diethylenetriamine penta‐acetic acid (DTPA)-extractable, soil solution plus exchangeable (Zn), Zn adsorbed onto inorganic sites, Zn bound by organic sites, and Zn adsorbed onto oxide surfaces. Irrespective of the different fractions of Zn present, its content was higher in fine‐textured Alfisols and Inceptisols than in coarse‐textured Entisols. In general, the higher content of Zn was observed in the surface horizon and then decreased in the subsurface horizons. However, none of the forms of Zn exhibited any consistent pattern of distribution. Organic matter and size fractions (clay and silt) had a strong influence on the distribution of different forms of Zn. Based upon the linear coefficient of correlation, the soil solution plus exchangeable Zn, adsorbed onto inorganic sites, and DTPA‐Zn increased with increase in organic carbon but decreased with increase in pH and calcium carbonate content. Total Zn increased with increase in clay and silt content. Among the different forms, Zn bound by organic sites, water soluble plus exchangeable Zn and Zn adsorb onto oxide (amorphous surfaces) were all correlated with DTPA extractable Zn. The uptake of Zn was more in recent floodplain Entisols than very fine textured Alfisols and Inceptisols. Among the different forms soil solution +exchangeable and DTPA‐extractable Zn was positively correlated with total uptake of Zn.     

Distribution and Accumulation of Copper and Cadmium in Soil–Rice System as Affected by Soil Amendments

The effects of seven amendments on the distribution and accumulation of copper and cadmium in a soil–rice system were investigated using a pot experiment. Results showed that application of limestone, calcium magnesium phosphate (Ca–Mg–P fertilizer), calcium silicate (silicon fertilizer), Chinese milk vetch, pig manure, and peat significantly decreased the concentrations of Cu and Cd in rice roots by 24.8–75.3% and 9.7–49.9%, respectively. However, no significant difference was observed between zinc sulfate (zinc fertilizer) and the control treatment. The concentrations of Cu and Cd in different parts of rice followed the order: root > straw > grain, and all amendments restrained the transfer of Cu and Cd from rice root to stem. Copper and Cd concentrations in rice stems at the tillering stage were the highest, and then decreased from the tillering stage to the heading stage. However, they increased again at the ripening stage. The results also showed that application of amendments changed Cu and Cd solubility in soil and decreased their bioavailability, which resulted in the reduction of Cu and Cd uptake by rice. Significant correlations between the concentrations of Cu and Cd in soil solutions and in rice stems were found. The result demonstrated that limestone has the best efficiency among all the amendments used in reducing Cu and Cd contamination to rice production.     

Effect of Selenium on Magnesium,Iron, Manganese,Copper, and Zinc Accumulation in Corn Treated by Indole‐3‐acetic Acid

In this work, the relationship among accumulation of selenium, auxin, and some nutrient elements [magnesium (Mg²⁺), iron (Fe³⁺), manganese (Mn²⁺), copper (Cu²⁺), zinc (Zn²⁺)] in tissues of roots, mesocotyls, and leaves of Zea mays L. plants was studied. Seeds of maize were cultivated for 4 days in the darkness at 27 °C on moist filter paper, then the individual seedlings were transferred into an aerated solution containing the macro‐ and microelements and were cultivated in a greenhouse for 12 h in the light and 12 h (12‐h photoperiod) in the dark at 25 °C. The seedlings were exposed to the solution containing sodium hydrogen selenite (NaHSeO₃), indole‐3 acetic acid (IAA), or IAA+NaHSeO₃ for approximately 96 h before chemical analysis. The concentration of IAA in the external medium was 10^?4 mol dm^?3, concentration of selenite (NaHSeO₃) was 10^?6 mol dm^?3, and the pH of the medium was 6.5.

The accumulation of the probed elements in seedlings of maize was measured by inductively coupled plasma optical emission spectroscopy (ICP‐OES). It was determined that the selenite and IAA, present in the external medium of growing plants, changed the uptake and accumulation of some cations in tissues of leaves, mesocotyls, and roots. The change of transport conditions of these nutrient elements is probably one of the first observed symptoms of selenium effects on plants.     

Effect of Zinc Humate on Growth of Soybean and Wheat in Zinc‐Deficient Calcareous Soil

Abstract

Humic acids have many benefits for plant growth and development, and these effects may be maximized if these materials are combined with micronutrient applications. In the present study, pot experiments were conducted to evaluate the effects of zinc (Zn) humate and ZnSO₄ on growth of wheat and soybean in a severely Zn‐deficient calcareous soil (DTPA‐Zn: 0.10 mg kg^?1 soil). Plants were grown for 24 (wheat) and 28 days (soybean) with 0 or 5 mg kg^?1 of Zn as either ZnSO₄ or Zn humate. Zinc humate used in the experiments was obtained from Humintech GmbH, Germany, and contained 5% of Zn. When Zn was not supplied, plants rapidly developed visible symptoms of Zn deficiency (e.g., chlorosis and brown patches on young leaves in soybean and necrotic patches on middle‐aged leaves in wheat). Adding Zn humate eliminated Zn‐deficiency symptoms and enhanced dry matter production by 50% in soybean and 120% in wheat. Zinc‐humate and ZnSO₄ were similarly effective in increasing dry matter production in wheat; but Zn humate increased soybean dry matter more than ZnSO₄. When Zn was not supplied, Zn concentrations were 6 mg kg^?1 for wheat and 8 mg kg^?1 for soybean. Application of Zn humate and ZnSO₄ increased shoot Zn concentration of plants to 36 and 34 mg kg^?1 in wheat and to 13 and 18 mg kg^?1 in soybean, respectively. The results indicate that soybean and wheat plants can efficiently utilize Zn chelated to humic acid in calcareous soils, and this utilization is comparable to the utilization of Zn from ZnSO₄. Under Zn‐deficient soil conditions, plant growth and yield can be maximized by the combined positive effects of Zn and humic acids.     

Heavy‐Metal Contamination of Soil and Vegetables in Wastewater‐Irrigated Agricultural Soil in a Suburban Area of Hanoi,Vietnam

The To Lich and Kim Nguu Rivers, laden with untreated waste from industrial sources, serve as sources of water for irrigating vegetable farms. The purposes of this study were to identify the impact of wastewater irrigation on the level of heavy metals in the soils and vegetables and to predict their potential mobility and bioavailability. Soil samples were collected from different distances from the canal. The average concentrations of the heavy metals in the soil were in the order zinc (Zn; 204 mg kg^?1) > copper (Cu; 196 mg kg^?1) > chromium (Cr; 175 mg kg^?1) > lead (Pb; 131 mg kg^?1) > nickel (Ni; 60 mg kg^?1) > cadmium (Cd; 4 mg kg^?1). The concentrations of all heavy metals in the study site were much greater than the background level in that area and exceeded the permissible levels of the Vietnamese standards for Cd, Cu, and Pb. The concentrations of Zn, Ni, and Pb in the surface soil decreased with distance from the canal. The results of selective sequential extraction indicated that dominant fractions were oxide, organic, and residual for Ni, Pb, and Zn; organic and oxide for Cr; oxide for Cd; and organic for Cu. Leaching tests for water and acid indicated that the ratio of leached metal concentration to total metal concentration in the soil decreased in the order of Cd > Ni > Cr > Pb > Cu > Zn and in the order of Cd > Ni > Cr > Zn > Cu > Pb for the ethylenediaminetetraaceitc acid (EDTA) treatment. The EDTA treatment gave greater leachability than other treatments for most metal types. By leaching with water and acid, all heavy metals were fully released from the exchangeable fraction, and some heavy metals were fully released from carbonate and oxide fractions. The concentrations of Cd, Cr, Cu, Ni, Pb, and Zn in the vegetables exceeded the Vietnamese standards. The transfer coefficients for the metals were in the order of Zn > Ni > Cu > Cd = Cr > Pb.     

Distribution of Total and DTPA‐Extractable Zinc,Copper, Manganese,and Iron in Vertisols of India

Abstract

Vertisols of India are developed over isohyets of 600 to 1500 mm, and their chemical cycles are set by drainage, landforms, and particle size, which results in variable pedogenic development within the otherwise homogeneous soils. The purpose of this study was to identify pedogenic processes in the distribution of total and DTPA‐extractable zinc (Zn), copper (Cu), manganese (Mn), and iron (Fe). The soils are developed over basaltic parent material of Cretaceous age. Soil samples were drawn from genetic horizons of the 13 benchmark profiles and analyzed by using HF–HClO₄ acid for total and DTPA extraction. Correlation coefficients were calculated taking all samples together. The total concentration varied from 24 to 102 mg kg^?1 for Zn, 21 to 148 mg kg^?1 for Cu, 387 to 1396 mg kg^?1 for Mn, and 2.36 to 9.50% for Fe. Their variability was proisotropic and haplodized, and their concentrations increased with advancing isohyets. Within the isohyets, hindrance in drainage caused retention of Zn and Cu but loss of Fe. The piedmont soils had more Fe than alluvium soils. The spatial distribution of total contents of Zn, Cu, and Fe was influenced by the pedogenic processes associated with Haplusterts but not with provenance materials. Surface concentrations of the elements by biotic lifting and/or harvest removal were negated by the pedoturbation that further contributed to the irregular distribution of the elements in the profiles. Total Zn and total Cu had positive coefficients of correlations with coarse clay, whereas total Mn and total Fe were positively correlated with fine clay. The DTPA‐extractable forms were functions of isohyets and drainage and showed association with organic carbon content and coarse clay.     

Integration of Soil pH with Soil‐Test Values of Zinc for Prediction of Yield Response in Rice Grown in Mollisols

Seventeen Mollisols having pH_(1:2) in the range of 6.00 to 8.42 were analyzed with five extractants, and the extractable zinc (Zn) ranges were 0.84 to 2.75 mg Zn kg^?1 soil for diethylenetriaminepentaacetic acid (DTPA) (pH 7.3), 0.91 to 2.72 mg Zn kg^?1 soil for DTPA + ammonium bicarbonate (pH 7.6), 1.82 to 7.18 mg Zn kg^?1 soil for Mehlich 3, 1.22 to 3.83 mg Zn kg^?1 soil for ethylenediaminetetraacetic acid (EDTA) + ammonium carbonate, and 0.88 to 1.18 mg Zn kg^?1 soil for 1 mol L^?1 magnesium chloride (MgCl₂) (pH 6.0). Zinc extracted by DTPA (pH 7.3) and Mehlich 3 showed significant positive correlation with sand content, whereas only Mehlich 3 showed negative correlation with soil pH. All extractants showed significant positive correlation with each other except for 1 mol L^?1 MgCl₂‐extractable Zn, which had significant positive correlation with only Mehlich 3– and EDTA + ammonium carbonate–extractable Zn. A greenhouse experiment showed that Bray's percentage yield of rice was poorly correlated to extractable soil Zn but had a significant and negative linear correlation with soil pH (r = ?0.662, significant at p = 0.01). Total Zn uptake by rice had a significant positive correlation with 1 mol L^?1 MgCl₂– and Mehlich 3–extractable Zn. A proposed parameter (p extractable Zn + p OH^?) involving both soil extractable Zn and pH terms together showed significant and positive correlation with Bray's percentage yield and total Zn uptake of rice. The calculated values of critical limits of soil Zn in terms of the proposed parameter were 14.1699 for DTPA (pH 7.3), 13.9587 for DTPA + ammonium bicarbonate, 13.7016 for Mehlich 3, 13.9402 for EDTA + ammonium carbonate, and 14.1810 for 1 mol L^?1 MgCl₂ (pH 6.0). The critical limits of Zn in rice grain and straw were 17.32 and 22.95 mg Zn kg^?1 plant tissue, respectively.     

Cadmium,Nickel, Chromium,and Lead Levels in Soils and Vegetables under Long‐Term Irrigation with Industrial Wastewater

Abstract: The industrial activity areas, rivers, and water sources in neighboring areas are influenced by wastewater of manufacturers. Utilizing water influenced by wastewater increased heavy metals in soils and plants. In 2004, to investigate the effects of wastewater on cadmium (Cd), nickel (Ni), chromium (Cr), and lead (Pb) content in soil and plants, wastewaters of three manufactures (chrome chemical, wood and paper, and textiles) were examined. At harvest time roots, whole shoots (rice, spinach, clover, grass), and rice grain in industrial wastewater–influenced areas and uninfluenced areas were sampled. Soil samples were also taken (0–15, 15–30 cm). Results indicated that when wastewater was discharged into the river water, the concentrations of Cd, Ni, Cr, and Pb increased in river water. Application of river water influenced by industrial wastewater for irrigation of rice and another plants enhanced, the amounts of available Cd, Ni, Cr and Pb in soil. In subsurface horizons (15–30 cm), the concentrations of heavy metals were more than in the surface horizon (0–15 cm). With increasing cation exchange capacity in the soil, the amount of available Cr increased. When the calcium carbonate content in soils was raised, the available Cd and Pb increased in the soil, but Ni and Cr decreased. Meanwhile, organic matter enhanced the concentrations of heavy metals in soil. Accumulations of heavy metals were higher in the roots of rice (control and treatment) than in shoot and rice grain. Cadmium accumulation in rice root was three times that in whole shoot, and grain was two times more than control. The concentrations of Ni, Cr, and Pb in root, whole shoot, and grain of rice were two times higher in industrial wastewater–treated areas. The concentrations of heavy metals in root and whole shoot of spinach, clover, and grass in industrial wastewater area increased about 100%, but not to a toxic level. Cadmium translocated more than other heavy metals from soil to root, whole shoot, and grain of rice, and whole shoot of spinach, clover, and grass.     

Adsorption of Copper,Zinc, and Cadmium on Goethite,Aluminum‐Substituted Goethite,and a System of Kaolinite–Goethite: Surface Complexation Modeling

Abstract

Goethite, aluminum‐(Al)‐substituted goethite (GA2), and a system of kaolinite–goethite were examined for their ability to adsorb copper (Cu), zinc (Zn), and cadmium (Cd) as a function of pH, in two ionic strengths and two different metal concentrations. Specific surface area was determined by BET‐N₂, whereas the charge development on the solid surface was studied in the pH range ～3.5 to ～10.0 by potentiometric titration under continuous flow of argon.

Constant capacitance (CCM) and the double‐layer model (DLM) were used to fit the titration and adsorption data with the help of the least‐square optimization program FITEQL32. In both models, surface site density was fixed at Ns=2.31 sites nm^?2, whereas for CCM capacitance density was set at C=1.06. Alternatively, bibliographic suggestions for these two parameters were examined.

Aluminum‐substituted goethite exhibited higher specific surface area and adsorbed all three metals in lower pH values than the other solids. Moreover, GA2 exhibited point of zero salt effect (PZSE) higher than goethite, approaching that corresponding to Al₂O₃, possibly due to Al‐substitution, and the system exhibited PZSE values much higher than kaolinite, approaching that corresponding to goethite. The adsorption order for all three solids was Cu>Zn>Cd in any case, thus more Cu is adsorbed at a certain pH than Zn and even more than Cd, whereas the increase of metal concentration shifts the adsorption curve toward higher pH values.

Constant capacitance described the titration data satisfactorily, but by altering the Ns and C values, the fit became worse. Adsorption data are described by CCM, by emphasizing the formation of monodentate surface complex. Bidentate complex, in most of the cases, was of no importance in describing the data despite the evidence of its presence in recent spectroscopic studies for Cu and Cd on goethite. Alteration of Ns and C values worsened the fit in any case, and bidentate complex vanished. The DLM exhibited the worse fit in any case.     

Distribution and Transport of Residual Lead and Copper Along Soil Pro?les in a Mining Region of North China

Residual heavy metals are commonly considered to be immobile in soils,leading to an underestimation of their environmental risk.This study investigated the distribution and transport of residual heavy metals along soil pro?les,using the Xiaoqinling gold mining region in North China as a case study.Soil samples were collected at three depths from three locations near the tailing heap.The speciation of copper(Cu) and lead(Pb)(exchangeable,carbonate-bound,Fe-Mn oxide-bound,organic matter-bound,and residual fractions) was determined using a sequential extraction procedure.The residual fraction's morphology was observed using scanning electron microscopy(SEM).Results showed that metal fraction distributions along the soil pro?les were in?uenced by each fraction's mobility.Residual fraction with high chemical stability can not be transformed from or into other fractions.This led to the conclusion that the high concentration of residual metals in soils mainly resulted from residual fraction transport.The SEM analysis showed that ?ne particles(submicrons) were mainly attached to large particles and were likely released and transported by water?ow.The more sorptive fractions(non-residual fractions) were mainly retained in the top soil,and the more mobile fractions(residual fraction) were mainly leached to the deep soil.Cu and Pb concentrations in the residual fraction decreased slightly and those in the non-residual fractions decreased signi?cantly with soil depth.These suggest a relatively higher residual metal mobility along the soil pro?les.Therefore,residual metals can be transported in soils and their environmental risk can not be ignored in assessing soil contamination.     

Forms of Iron and Their Association with Soil Properties in Four Soil Taxonomic Orders of Arid and Semi‐arid Soils of Punjab,India

Profiles of arid and semi‐arid zones soils of Punjab, northwestern India, were investigated for different forms of iron (Fe): total Fe, diethylenetriamine penta‐acetic acid (DTPA)–extractable Fe, soil solution plus exchangeable Fe, Fe adsorbed onto inorganic sites and oxide surfaces, and Fe bound by organic sites. Irrespective of the different fractions of Fe present, its content was higher in the fine‐textured Alfisols and Inceptisols than in the coarse‐textured Entisols and Aridisols. Lower content of total Fe was observed in the surface horizon and then increased in the subsurface horizons, whereas no set pattern was observed in Entisols. Also, irrespective of the soil orders, the contents of different forms of Fe were higher in the surface horizon and then decreased by depth. None of the forms of Fe exhibited any consistent pattern of distribution.

Organic matter and the content of clay and silt fractions had a strong bearing on the distribution of forms of Fe. Based on a linear coefficient of correlation, the soil solution plus exchangeable Fe adsorbed onto inorganic sites and DTPA‐extractable Fe increased with increase in soil organic carbon but decreased with increase in soil pH and calcium carbonate content. Total Fe increased with increase in cation exchange capacity (CEC) and clay and silt content. The results also revealed that there was equilibrium in different fractions of this element. Among the different Fe forms, Fe bound by organic sites, water‐soluble plus exchangeable Fe, and Fe adsorbed onto oxides (amorphous surfaces) were positively correlated with the DTPA‐extractable Fe. Though some forms are interrelated, none of the forms had any relationship with the total Fe.     

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.