Influence of Redox Potential and Plant Species on the Uptake of Nickel and Cadmium from Soils

The influence of soil redox potential on the uptake of nickel and cadmium from three soils was studied in a pot experiment with oat (Avena sativa L. cv. Pirol) and rye-grass (Lolium multiflorum L. cv. Lema). The soils used were a Luvisol (naturally low in Ni and Cd), a sewage-sludge amended Luvisol (anthropogenic enrichment of Ni and Cd) and a Cambisol (naturally high in Ni and Cd). Nickel and Cd supplied in sewage-sludge amendments were several times more available for plant uptake than those present naturally in the soil. Short term decreases in soil redox potential, as a result of soil flooding, had little effect on the availability of Ni and Cd from sludge amended soils, but resulted in a substantial increase in Ni and Cd availability in the soil naturally high in Ni and Cd. In general, increases in soil solution concentrations of Ni and Cd, due to sludge amendment or changes in soil redox potential, resulted in increased Ni and Cd concentrations in the aerial parts of plants. Nickel concentrations in the grain of oat increased with increasing Ni concentration in the soil solution, whereas grain Cd concentrations did not. In contrast, Cd concentrations in vegetative parts of both oat and rye-grass were strongly affected by soil type and sludge-amendment. In all treatments Ni concentrations in the grain were much higher than in the vegetative parts, whereas Cd concentrations were always higher in vegetative parts than in the grain. Tissue Ni concentrations correlated well with DTPA extractable soil Ni but only poorly with total soil Ni. Differences in the availability and uptake of Ni and Cd in response to soil type, environmental conditions and plant species suggest that the use of total soil-metal content to regulate the use of sewage sludge on agricultural land is inappropriate.     

The effect of EDTA on the extractability of Zinc (Zn), Cadmium (Cd) and Nickel (Ni) in Vertisol and Alluvial soils

Ethylendiamintetraacetic acid (EDTA) is persistent in the environment. The presence of EDTA in soil may alter the mobility and transport of Zn, Cd and Ni in soils because of the formation of water soluble chelates, thus increasing the potential for metal pollution of natural waters. Mobility of metals is related to their extractability. To investigate metal extractability affected by EDTA, Zn, Cd and Ni were added to Vertisol and Alluvial soil at rates of 50, 2 and 5 mg kg^-1, respectively. Both natural and metal amended soils were treated with Na₂EDTA at rates of 0; 0.2 and 0.5 mg kg^-1. After five months of incubation soil samples were extracted with 0.1 N HCl, 0.005 M DTPA + 0.01 M CaCl₂ + 0.1 M TEA (0.005 M Diethylenetriaminepentaacetic acid + 0.01 M Calcium cloride + 0.1 M Triethanolamine) and 1 M Mg(NO₃)₂, the latter of which extracts the exchangeable from of metald (Zn, Cd and Ni).

According to experiment results, Zn, Cd and Ni in all extraction increased with increasing rates of EDTA in the natural and metal amended soils.     

Persistence of glyphosate in a sandy loam

Glyphosale was added to samples of a sandy loam at rates of 0, 2, 5 and 10μg g^?1soil. After 120 days, soil was transferred to pots which were planted with subterranean clover. Plants were inoculated with Rhizohium trifolii and N₂ fixation (C₂H₂-reduction) was recorded after 9, 13, 15 and 19 weeks of growth. Nodule numbers and root weights were determined after the final C₂H₂-reduction assays had been performed. Decreased C₂H₂-reduction, nodule numbers and root weights associated with plants growing in glyphosate-treated soil indicated that this herbicide was not inactivated during the 120-days before planting.     

Changes in tolerance of soil microbial communities in Zn and Cd contaminated soils

Trace metals are present in the soil matrix in different forms, and this obscures the relationship between the amounts of metals, their biological availability and effects. Chemical methods have been devised to directly measure the biological available pools of trace metals, but such methods need to be validated against measured exposure of organisms in the soil. We studied acquired Zn- and Cd tolerance of the soil microbial community as a reporter of its exposure, and compared it with chemical determination of Zn and Cd in 10 soils differing in pH, organic matter content, texture, vegetation-/cultivation history and metal contamination. The tolerance was measured as LC₅₀ (i.e. the metal concentration which inhibits 50% of the activity) in suspensions of extracted soil bacteria, by measuring the incorporation rate of [³H] thymidine at different metal concentrations. Chemical determination of Cd and Zn in soils included total concentrations by aqua regia extractions (AR), and total concentrations in extracted pore water (PW). In addition was the ‘effective concentration’ (C_E) determined using the Diffusion Gradients in Thins films method (DGT). The LC₅₀ values correlated better with PW (r²=0.90 for Cd and r²=0.97 for Zn) and C_E (0.90 for Cd and 0.98 for Zn) compared to the correlation with AR (0.72 for Cd and 0.82 for Zn). After excluding a single extremely contaminated soil from the analysis, the correlation of LC₅₀ with AR was much poorer (r²=0.03 (ns) for Cd and r²=0.48 for Zn), whereas correlations remained significant for both PW (0.90 for Cd and 0.87 for Zn) and C_E (0.54 for Cd and 0.84 for Zn). In conclusion, PW fraction of Cd and Zn appear to be the best predictor of trace metal exposure of the soil microorganisms.     

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.     

Arylesterase activity in trace element contaminated soils

Arylesterase activity was measured along with microbial biomass C (B_C) and respiration, and H₂O‐soluble and NH₄NO₃‐exchangeable trace elements (TE), in contaminated soils (TECS) from three long‐term field trials. The AGIR (AG) soils were contaminated only by inorganic Cd, whereas the Ambarès (AM) and Louis Fargue (LF) soils were contaminated mainly by Mn and Zn, and Cd and Ni, respectively, from past sludge application at different rates. In the AG soils, the arylesterase activity decreased with increasing Cd total concentration and solubility. In the AM soils, the arylesterase activity decreased with increased contamination, whereas in the LF soils the arylesterase activity was increased by sludge additions, with the higher values detected in soils with lower sludge incorporation rates. In the AG and AM soils, arylesterase activity was significantly and negatively correlated with H₂O‐soluble and NH₄NO₃‐exchangeable TE, whereas in the LF soils it showed a ‘hump’‐shaped trend with sludge additions and could not be modelled. Multiple regression analysis showed significant interactions between TE, soil pH value and TOC with this enzyme activity. Respiration values of the AG soils generally increased while the B_C generally decreased with Cd contamination, while different trends were observed in the AM and LF soils. No trends in the enzyme activity‐to‐B_C ratios were found in relation to soil contamination. Information regarding the inhibition of arylesterase activity in TECS can be important for the management of soils co‐contaminated by TE and organic pollutants, in which the detoxification action of arylesterase may be reduced.     

Metal Extractability in Binary and Multi-metals Spiked Calcareous Soils

In the present study, a laboratory experiment was designed to compare the 0.01 M calcium chloride (CaCl₂) and diethylenetriaminepentaacetic acid (DTPA) extraction methods for their ability to predict cadmium (Cd), copper (Cu), iron (Fe), Manganese (Mn), nickel (Ni), and zinc (Zn) availability and mobility in five calcareous soils. The soils were spiked with different amounts of metals (0, 50, 100, 200, and 400 mg kg^?1) both in binary (Cu and Zn; Ni and Cd; Fe and Mn) and in multi-systems (Cd, Cu, Fe, Mn, Ni, and Zn) and incubated for 1 months at field capacity. In metal-spiked soils, both extraction methods showed a linear relationship of extractable to total metals for all soils. The fraction of total metals extracted by DTPA was much higher than the fraction extracted by CaCl₂, which was attributed to the formation of soluble metal-complexes in the complexing extracts calculated by the Visual Minteq program. DTPA extraction method showed higher selectivity for Cu over other metals both in binary and in multi-systems. Different order of metals extractability was found in binary and multi-systems for both extraction methods. Solid/solution distribution coefficient (K_d) was calculated by the ratio of the solid phase to soil solution concentration of metals extracted by CaCl₂ or DTPA extraction methods. Both in binary and in multi-systems, the average K_d (l kg^?1) of metals by soils were in the order of Mn (5398) > Fe (4413) > Zn (3376) > Cu (2520) > Ni (969) > Cd (350) in the CaCl₂-extractable metals and Fe (35) ≥ Ni (34) > Zn (18) > Mn (11.2) > Cu (6.3) > Cd (4) in the DTPA-extractable metals. Results showed that among the six studied metals, Cd had the lowest K_d, implying a relative higher mobility in these calcareous soils. The Visual Minteq indicated that in the CaCl₂-extraction method and in both binary and multi-systems the dominant species for Cu, Mn, Ni, and Zn were Cu²⁺, Mn²⁺, Ni²⁺ and Zn²⁺, respectively, while for Cd and Fe, the dominant species were CdCl⁺ and Fe(OH)²⁺, respectively.     

Cadmium-tolerant plant growth-promoting bacteria associated with the roots of Indian mustard (Brassica juncea L. Czern.)

Eleven cadmium-tolerant bacterial strains were isolated from the root zone of Indian mustard (Brassica juncea L. Czern.) seedlings grown in Cd-supplemented soils as well as sewage sludge and mining waste highly contaminated with Cd. The bacteria also showed increased tolerance to other metals including Zn, Cu, Ni and Co. The isolated strains included Variovorax paradoxus, Rhodococcus sp. and Flavobacterium sp., and were capable of stimulating root elongation of B. juncea seedlings either in the presence or absence of toxic Cd concentrations. Some of the strains produced indoles or siderophores, but none possessed C₂H₂-reduction activity. All the strains, except Flavobacterium sp. strain 5P-3, contained the enzyme 1-aminocyclopropane-1-carboxylate (ACC) deaminase, which hydrolyses ACC (the immediate precursor of plant hormone ethylene) to NH₃ and α-ketobutyrate. V. paradoxus utilized ACC as a sole source of N or energy. A positive correlation between the in vitro ACC deaminase activity of the bacteria and their stimulating effect on root elongation suggested that utilization of ACC is an important bacterial trait determining root growth promotion. The isolated bacteria offer promise as inoculants to improve growth of the metal accumulating plant B. juncea in the presence of toxic Cd concentrations and for the development of plant-inoculant systems useful for phytoremediation of polluted soils.     

Digestion Methods for Total Heavy Metals in Sediments and Soils

The objectives of this study were to analyze the total contents of Cd, Cr, Cu, Ni, Pb, and Zn in the freshwater sediments and the arable and non-arable soils of Taiwan, and to compare the different digestion methods for their determination. Two hundred and thirty-nine freshwater sediments were collected from the Fei-Tsui Reservoir Watershed (FTRW) in northern Taiwan. Forty-two surface (0–15 cm) and subsurface (15–30 cm) soil samples were likewise collected from 21 representative arable soils derived from various parent materials and with varying weathered degrees in different regions of Taiwan. In addition, one hundred and ninety-four non-arable soils were collected from the different forest regions, industrial parks, resident areas, and commercial areas. Several digestion methods including the aquaregia and different combinations of concentrated acids (HClO₄, HNO₃, H₂SO₄, or HF) were compared. All samples were digested both by the aqua regia method and the Baker and Amacher method for Cd, Cr, Cu, Ni, Pb, and Zn. The Reisenauer method was used for Cr and the Burau method for Pb further. The results indicate that the best digestion methods to analyze the total contents of heavy metals in the sediments and soils were recommended as follows: the Baker and Amacher method for Cd, Cr,Cu, Ni, and Zn; the Reisenauer method for Cr, but for simplicity the Baker and Amacher method is also recommended as the flexible method for the total analysis of Cr; the aqua regia method for Cu, Ni, and Zn; and the Burau method for Pb.     

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.     

Cadmium speciation as influenced by soil water content and zinc and the studies of kinetic modeling in two soils textural classes

Background and aimsSince few studies have existed in the literature about the effect of zinc (Zn) on cadmium (Cd) chemical forms in soils. Therefore, this study has been performed to determine the impact of Zn on cadmium Cd chemical forms in two soil textural classes in Fars province-Iran at two soil water content (SWC) (flooded soil water content (FSWC) and field capacity soil water content (FCSWC)) and study the kinetic modeling of Cd.Methods and materialsVariables were three levels of Cd (0, 30 and 60 mg kg^-1 of soil as CdSO₄·8H₂O), three levels of Zn (0, 5 and 10 mg kg^-1 of soil as Zn-EDTA) three level Incubation times (2, 4 and eight weeks), two soil textural classes (clay and sandy clay loam) and two SWC. The randomized completed block design (RCBD) was used for this experiment. The Tessier sequential extraction method was used to determine the Cd concentration in (WsEx), (Fe-MnOx), (Car), (Om) and (Res) chemical forms.ResultsIn the FSWC, Zn reduced the Cd concentration in Fe-MnOx, Car and Om forms and increased the WsEx but had no significant effect on the Res form. Changes in the Cd chemical forms under the influence of Zn in both soils followed a similar trend. In the FCSWC, Zn reduced the Cd concentration Car and Om forms and increased the Cd concentration in the Fe-MnOx and WsEx forms while had no significant effect on Res form in the sandy clay loam soil. In the clay soil adding Zn reduced the Cd concentration in Car and Om fractions and increased the Fe-MnOx and Res forms while has no significant effect on WsEx form. The competitive transport and adsorption Interactions between these two ions caused the changing in the Cd concentration in its chemical forms. Zn reduces the Cd concentration in the forms which are easily released into the soil solution from where they can be absorbed by plants. The power function kinetic mode is the best fitted model which can describe the Cd adsorption in our soil samples. The clay and organic compounds control the Cd adsorption in soils. The higher rate of Cd adsorption in almost all shaking times shows that Cd has more ability to occupy the adsorption sites in soils.     

Responses of wheat to zinc sulfate fertilizer and plant growth‐promoting rhizobacteria under cadmium stress in soil

Cadmium (Cd) is a major pollutant in soils as a result of extensive use of fertilizers, mining and industrial discharges. Zinc (Zn) and certain bacterial species have been known to alleviate Cd toxicity in plants. In this study, the individual and combined effects of the application of Zn and Pseudomonas species with the aim of reducing Cd stress in wheat cultivars were investigated. Plants (durum wheat and bread wheat) were exposed to different concentrations of Cd and Zn, and either P. putida or P. fluorescens in a growth chamber. Concentrations of Zn, Cd, chlorophyll (Chl), carotenoid, hydrogen peroxide (H₂O₂), and malondialdehyde (MDA), as well as antioxidant enzyme activities were assayed. The addition of Zn in soils reduced the toxicity of Cd in durum wheat more than in bread wheat even though there was more uptake of Zn in bread wheat. Analysis of variance showed that by using Zn fertilizer and Pseudomonas species the amounts of peroxidase (POD), polyphenoloxidase (PPO), MDA, and H₂O₂ were reduced at three growth stages. Surprisingly, with increasing Zn concentration, Cd concentration in plant tissue was slightly increased, which suggests that adding Zn to soil could facilitate Cd desorption from soil particles. Application of Pseudomonas and Zn could be a promising solution to reduce detrimental effects of Cd, especially in durum wheat.     

Chemical pools of cadmium, nickel and zinc in polluted soils and some preliminary indications of their availability to plants

This study was conducted to determine the chemical distribution and plant availability of Cd, Zn and Ni in eight metal-polluted soils in southern Ontario, Canada. There were altogether 30 different soil samples because two of the soils had received various sewage sludge treatments. The soils were sequentially extracted with 1 m ammonium acetate to remove soluble plus exchangeable metals, with 0.125 m Cu(II) acetate to remove complexed metals, and with 1 m HNO₃ to dissolve chemisorbed or occluded metals and precipitates such as oxides and carbonates. Expressed as a percentage of the metal so extracted, exchangeable Cd and Zn and Ni; complexed Cd and Zn>Ni and Ni>Zn>Cd in the acid-soluble pool. With a few exceptions (soils with high organic matter content or low pH) at least 50 per cent of the extracted metal was in the acid-soluble pool. The percentage of metal complexed was significantly correlated with organic matter content. The percentage of metal in the acid-soluble fraction was significantly correlated with soil pH. Preliminary findings based on the results with two soils suggested that for Cd and Zn plant availability was correlated with the concentrations of exchangeable, complexed or acid-soluble pools of Cd and Zn.     

The relative affinities of Cd,Ni and Zn for different soil clay fractions and goethite

Cadmium, Ni and Zn ions in aqueous solution were allowed to react with clay fractions (< 2 μm) separated from soils with a wide range of mineralogical composition and properties. Sorbed metals were separated into two components, termed specifically and non-specifically bound, by a controlled washing procedure using 10^?2M Ca(NO₃)₂.Sorption reactions were characterized by Δ pH₅₀ values, by shapes of adsorption curves, and by measuring separation factors and distribution coefficients under prescribed conditions. Three reaction types were identified, viz., (i) those associated with soil adsorbing surfaces dominated by iron oxides; these appear to be controlled by mechanisms which involve metal-ion hydrolysis and result accordingly in relative sorption affinities of Zn > Ni > Cd; (ii) those associated with organic surfaces for which metal-ion hydrolysis was of little significance and little difference in metal-ion affinity was evident; at lower pH-values, Cd and Ni were somewhat preferred over Zn, with the converse at higher pH-values; (iii) those associated with 2:1 layer lattice silicates which exhibit greater preference for Zn, i.e., Zn >> Ni, Cd and higher affinities for each metal at lower pH-values (< 5) than is shown by clays dominated by iron oxides. There was also evidence of greater relative affinity for Ni shown by clay fractions dominated by fine kaolinites when compared with other clays.This investigation has shown that a range of sorption processes are involved in reactions of heavy metals with soils. We caution against undue emphasis on any particular sorption process in developing theoretical sorption models as a basis of understanding and solving problems connected with pollution and plant nutrition; we also stress the need for studies with colloids separated from soils in conjunction with those using synthetic adsorbents as models for soil constituents.     

Soil algae: Effects of herbicides on growth and C2H2 reduction (nitrogenase) activity

The influence of the soil-applied herbicides chlortoluron, terbutryne, metabenzthiazuron, chloridazon, and dinosebacetate as well as the fungicide carbendazime on the growth and nitrogenase activity of soil algae was tested. The degree of algal cover on the soil surface was correlated with the measured C₂H₂-reduction (nitrogenase) activity. All the herbicides tested at recommended rates of application caused a total suppression of algal growth and C₂H₂-generation for several weeks. The fungicide had no detectable effect on algal populations or C₂H₂ reduction.     

The sorption of Cd,Zn and Ni by soil clay fractions: Procedures for partition of bound forms and their interpretation

This work is the first of several projects concerned with the study of higher-affinity reactions of Cd, Zn and Ni ions with soil clay fractions. Procedures for the separation of sorbed metals into fractions of lower and higher affinity for soil surfaces are described and evaluated.Various concentrations of Cd, Zn and Ni were allowed to react in the presence of 0.01 M Ca(NO₃)₂ with soil clays for 1 week after stabilization of suspension pH. The adsorbed metals were partitioned by a brief extraction with 0.01 M Ca(NO₃)₂ and the resultant fractions, called specifically and non-specifically sorbed metals, were measured by radioisotopic procedures.Measured separation factors showed that the fraction of sorbed metals that was desorbed by a rapid Ca(NO₃)₂ extraction still had a preference, sometimes marked, over Ca on the soil clay fraction. Separation of fractions of sorbed metals on the basis of affinity was reproducible, but the boundary conditions defined by separation factors vary appreciably between adsorbents, with values in the range 3–20 for amounts sorbed equivalent to ≦ 0.05% of cation exchange capacity and for pH values < 7.The proportions of Cd, Zn and Ni bound at high-affinity sites were strongly dependent on experimental conditions of pH, equilibrium time and surface saturation in relation to each soil clay. Hence, comparisons of affinities of trace metals for soils by reliance on measures of total sorption only, without assessing the contribution of lower-affinity forms, may prejudice conclusions and predictions arising from studies of the possible retention of metal pollutants in soils and fixation of micronutrients from fertilizers.     

Concentration Changes of Cd, Ni and Zn in Sugarcane Cultivated Soils

In the southwest of Iran over 130,000 ha of land are under sugarcane (Saccarum officinarum). In these sugarcane fields, about 400 kg ha^?1 diamonium phosphate (DAP) and 400 kg ha^?1 urea are applied annually. Four sugarcane growing sites were selected for this study: Haft-tapeh, Karoon, Shoeibieh and Ghazali with cultivation histories of 36, 20, 2 and 1 years, respectively. For each area, soil samples (0–30 cm) were taken from a transect of uncultivated, and both furrows and ridges of cultivated land. Electrical conductivity (EC), pH, clay, and calcium carbonate and organic carbon (OC) contents, Cl, Cd, Ni and Zn of 101 soil samples were measured. Cadmium profile distribution to a soil depth of 300 cm was determined, and the heavy metal concentrations in sugarcane and the associated soil samples of the three sugarcane sites were measured. The Cd and Ni contents among the sugarcane sites differed where Cd was related to clay content and Ni was related to OC content of soils. Cadmium content in sugarcane cultivated soil was lower compared to uncultivated soil even after years of application of P fertilizers. Nickel and Cd contents of sugarcane were much higher than levels in top soils but there was no significant relationship between Cd or Ni contents of sugarcane and soil chemical properties. The Zn content of soils decreased as either EC or Cl concentration of soils increased. There were no significant differences in Zn contents between different sugarcane sites and also between cultivated and uncultivated soils. Results also indicated that Cd was accumulated in bagasse and Ni was primarily accumulated in bagasse and molasses, but these heavy metals of white sugar were lower than the detectable values.     

龙游硫铁矿区农田土壤重金属污染的空间 变异及在水稻中的积累

为了解浙江龙游硫铁矿区农田重金属污染状况,采集矿区265件农田土壤样品,分析8种重金属Cu、As、Hg、Zn、Cd、Ni、Pb、Cr元素全量,利用地统计学软件GS+9.0对研究区土壤各元素指标进行半变异函数拟合,并利用普通克里格法进行插值并绘制空间分布图。采集30件水稻籽粒样品,分析重金属在研究区中水稻籽粒的累积特征,并进行了健康风险评价。结果表明:矿区土壤中8种重金属元素的变异系数从0.72到1.76,离散程度较高。8种重金属的土壤空间半变异函数Cu、As、Hg元素符合指数模型,Zn、Cd、Ni、Pb符合球状模型,Cr符合高斯模型。元素Cu、Pb、Zn、Cr、Ni的块金值与基台值的比值C0/C0+C都小于0.25,说明空间变化主要受地质背景等因素影响;元素Cd、Hg和As的块金值与基台值的比值C0/C0+C在0.25~0.75之间,说明除了地质背景因素,人为活动等随机因素也有影响。矿区水稻籽粒中重金属Ni和Cd的变异系数最高,分别为0.95和0.87,说明Ni和Cd元素可能存在异常积累。矿区水稻籽粒对重金属的富集能力由大到小依次为Cd、Zn、Cu、Ni、As、Hg、Cr、Pb。健康风险评价结果表明矿区农田水稻籽粒中元素As、Cd的风险商大于1,存在潜在健康风险;而其他6种重金属Cu、Hg、Zn、Ni、Pb和Cr基本属于安全范围。