Initial results from a long-term, multi-site field study of the effects on soil fertility and microbial activity of sludge cakes containing heavy metals

In a long‐term study of the effects on soil fertility and microbial activity of heavy metals contained in sewage sludges, metal‐rich sludge cakes each with high Zn, Cu or Cd concentrations were applied annually for 4 years (1994–1997) to nine sites throughout Britain. These sites were selected to represent agricultural soils with a range of physical and chemical properties, typical of those likely to be amended with sewage sludge. The aim was to establish individual total Zn (approx. 60–450 mg kg^?1), total Cu (approx. 15–200 mg kg^?1) and total Cd (approx. 0.2–4 mg kg^?1) metal dose–response treatments at each site. Sludges with low metal concentrations were added to all treatments to achieve as constant an addition of organic matter as possible. Across the nine sites, soil pH was the single most important factor controlling Zn (P < 0.001; r² = 92%) and Cd extracted with 1 m NH₄NO₃ (P < 0.001; r² = 72%), and total iron content the most important factor controlling Cu extracted with 1 m NH₄NO₃ (P < 0.001; r² = 64%). There were also positive relationships (P < 0.001) between soil organic carbon (C) concentrations and soil biomass C and respiration rates across the nine sites. Oxidation of sludge C following land application resulted in approximately 45% of the digested sludge cake C and approximately 64% of the ‘raw’ sludge cake C being lost by the end of the 4‐year application period. The sludge cake applications generally increased soil microbial biomass C and soil respiration rates, whilst most probable numbers of clover Rhizobium were generally unchanged. Overall, there was no evidence that the metal applications were damaging soil microbial activity in the short term after the cessation of sludge cake addition.     

Redistribution of cadmium,copper, lead,nickel, and zinc among soil fractions in a contaminated calcareous soil after application of nitrogen fertilizers

This study was conducted to evaluate the redistribution of the heavy metals Cd, Cu, Pb, Ni, and Zn among different soil fractions by N fertilizers. In a lab experiment, soil columns were leached with distilled water, KNO₃, NaNO₃, NH₄NO₃, or Ca(NO₃)₂ · 4H₂O. After leaching, soil samples were sequentially extracted for exchangeable (EXCH), carbonate (CARB), organic‐matter (OM), Mn oxide (MNO), Fe oxide (FEO), and residual (RES) fractions. Distilled water significantly increased the concentrations of Cd and Ni in EXCH fraction, while concentration of Cu and Zn did not change significantly. Application of KNO₃, NaNO₃, NH₄NO₃, or Ca(NO₃)₂ · 4H₂O significantly increased the concentrations of Cd and Zn in EXCH fraction, while concentration of Pb and Ni was decreased. Application of all fertilizers caused an increase of Cu in the OM fraction. Moreover, leaching with these solutions significantly increased Cd [except in Ca(NO₃)₂ · 4H₂O], Cu, and Zn concentrations in the CARB fraction, while Pb and Ni concentrations were decreased. With application of all leaching solutions, Zn in the EXCH, CARB, FEO, and MNO fractions was significantly increased, while Zn in the OM fraction did not change. The mobility index indicated that Ca(NO₃)₂ · 4H₂O increased the mobility of Cd, Cu, and Zn in the soil, whereas NaNO₃ decreased the mobility of Pb and Ni in the soil. The mobility index of Pb decreased by all leaching solutions. Thus, these results suggest that applying N fertilizers may change heavy‐metal fractions in contaminated calcareous soil and possibly enhance metal mobility and that N‐fertilization management therefore may need modification.     

Use of Drinking Water Treatment Residuals in Reducing Bioavailability of Metals in Biosolid-Amended Alkaline Soils

This greenhouse study evaluated the use of drinking-water-treatment residuals (WTRs) to reduce the bioavailability of metals in the biosolid-amended agricultural alkaline soils. Results showed that increasing the application rate of biosolids increased the accumulation of lead (Pb), nickel (Ni), copper (Cu), and cadmium (Cd) in corn (Zea mays cv. single hybride 10), with greater metal concentrations in roots than in shoots. However, the addition of WTRs (1–4%, w/w) to the soil amended with 3% biosolids significantly (P < 0.05) decreased the concentrations of soil diethylenetriaminepentaacetic acid (DTPA)–extractable metals. The accumulation of Pb, Ni, Cu, and Cd in corn significantly correlated with the DTPA-extractable metal concentrations in the soils. Plant metal concentrations were significantly affected by the soil type, application rates of biosolids and WTRs, and the ratio of WTRs to biosolids in the soils. The 1:1 application ratio of WTRs to biosolids at the 3% application rate effectively reduced the accumulation of metals in corn tissues.     

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.     

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

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

Impacts of Municipal Wastewater on The Transport Characteristics of Reactive Solutes Through Agricultural Soils

Reliable transport parameters of agrochemicals and soluble pollutants are crucial for modeling and management of soil and groundwater quality. This study investigated impacts of municipal wastewater on the transport parameters of five heavy metal/metalloid compounds (NaAsO₂, Cd(NO₃)₂, Pb(NO₃)₂, Ni(NO₃)₂ & ZnCl₂), two pesticides (cartap & carbendazim) and an inert salt (CaCl₂) in four agricultural soils of Bangladesh. Solute-breakthrough concentrations were measured in repacked soil columns with time-domain reflectometry (TDR) both before and after wastewater treatment. Transport velocity (V), dispersion coefficient (D), dispersivity (λ) and retardation factor (R) of the solutes, and pertinent soil properties were determined. Wastewater reduced bulk density (γ) of the soils (from 1.32–1.37 g/cm³ to 1.26–1.35 g/cm³) by increasing organic carbon (OC) (from 0.37%–0.84% to 0.40–0.93%), increased pore-size distribution index (n) (by 0.02 unit) and reduced soil pH (from 6.32–7.45 to 5.92–6.46). D and λ decreased while V and R increased after wastewater treatment; D decreased and R increased linearly with decreasing bulk density. The correlations of V, D, and R with n improved significantly (p < 0.05) after wastewater treatment. The correlation between λ and OC improved markedly for Ca, Pb, Ni, and cartap. The observed indicative results have practical implications in developing pedo-transfer functions for solute-transport parameters using basic soil properties, which are subject to progressive modification due to agrochemicals application and wastewater irrigation.     

Chelating resin method for estimation of sludge‐cadmium bioavailability

Abstract

A chelating resin procedure was developed to predict the plant uptake of Cd by municipal sewage sludges applied to land. Seventeen anaerobically digested sludges were sampled to give a range of total Cd content of 0.07 to 2.02 mmol/kg. Sludge suspensions [20 g in 100 mL 0.05 M Ca(NO₃)₂] were equilibrated with 1 g Chelex 100 resin placed in dialysis tubing and shaken at 200 rpm for 16 h. Resin‐extractable Cd was compared with sludge solution Cd (CdT and Cd²⁺) in equilibrium with 0.05 M Ca(NO₃)₂, and 0.05 M Ca(NO₃)₂ containing 50 (μM Na‐EDTA (ethylenediaminetetraacetate). Resin extractable Cd was correlated with Cd uptake by sudax, a sorghum/sudangrass hybrid (Sorghum bicolar), grown in Spinks loamy sand (Typic Udipsamment) amended with each of the sludges to give a constant Cd concentration of 22 μmol/kg soil.

Resin extractable Cd ranged from < 0.1 to 48 μmol/kg. Resin extracted between zero and 5.3% of total sludge Cd. Resin extractable Cd was highly correlated with CdT and Cd²⁺ in 0.05 M Ca(NO₃)₂ (R² = 0.97 and 0.98, respectively), and with 0.05 M Ca(NO₃)₂ containing 50 μM NaEDTA (R² = 0.97 and 0.98, respectively). There was a lower correlation with total sludge Cd and soil solution Cd (R² = 0.53 and 0.63, respectively). Cadmium concentration in sudax was highly correlated with resin extractable sludge Cd (R² = 0.92). When the two sludges with highest total sludge Cd were dropped, the correlation dropped (R² = 0.57), but resin extractable Cd predicted Cd uptake as effectively as CdT and Cd²⁺ in Ca(NO₃)₂ or Ca(NO₃)₂/EDTA. Resin extraction appears to be a promising method of assessing the potential bioavailability of sludge Cd.     

Reduction of soil heavy metal bioavailability by nanoparticles and cellulosic wastes improved the biomass of tree seedlings

The purpose of this study was to use zero‐valent iron nanoparticles (nZVI) and cellulosic wastes to reduce bioavailability of lead (Pb) and cadmium (Cd), and to establish Persian maple seedlings (Acer velutinum Bioss.) in contaminated soil. One‐year‐old seedlings were planted in pots filled with unpolluted soil. Lead [Pb(NO₃)₂] and Cd [Cd(NO₃)₂] were added with concentrations of 0 (Control), 100 (Pb100), 200 (Pb200), and 300 (Pb300) mg kg⁻¹ and 10 (Cd10), 20 (Cd20), and 30 (Cd30) mg kg⁻¹. Cellulosic wastes were mixed with soil at the same time of planting [four levels: 0, 10 (W1), 20 (W2), 30 (W3) g 100 g⁻¹ soil]. The nZVI was prepared by reducing Fe³⁺ to Fe⁰ and injected to pots [four levels: 0, 1 (N1), 2 (N2), and 3 (N3) mg kg⁻¹]. Height, diameter, biomass, tolerance index of seedlings, bioavailability of heavy metals in soil, and removal efficiency of amendments were measured. The highest values of seedling characteristics were observed in N3. The highest removal efficiency of Pb (Pb100: 81.95%, Pb200: 75.5%, Pb300: 69.9%) and Cd (Cd10: 92%, Cd20: 73.7%, Cd30: 68.5%) was also observed in N3. The use of nZVI and cellulosic waste could be a proper approach for seedling establishment in forests contaminated with heavy metals.     

Influence of phosphorus application on growth and cadmium uptake of spinach in two cadmium‐contaminated soils

A pot experiment was conducted to investigate the influence of phosphate (P) application on diethylene triamine pentaacetic acid (DTPA)–extractable cadmium (Cd) in soil and on growth and uptake of Cd by spinach (Spinacia oleracea L.). Two soils varying in texture were contaminated by application of five levels of Cd (NO₃)₂ (0, 20, 30, 40, and 60 mg Cd kg^–1). Three levels of KH₂PO₄ (0, 12, and 24 mg P kg^–1) were applied to determine immobilization of Cd by P. Spinach was grown for 60 d after seeding. Progressive contamination of soils through application of Cd affected dry‐matter yield (DMY) of spinach shoot differently in the two soils, with 67% reduction of DMY in the sandy soil and 34% in the silty‐loam soil. The application of P increased DMY of spinach from 4.53 to 6.06 g pot^–1 (34%) in silty‐loam soil and from 3.54 to 5.12 g pot^–1 (45%) in sandy soil. The contamination of soils increased Cd concentration in spinach shoots by 34 times in the sandy soil and 18 times in the silty‐loam soil. The application of P decreased Cd concentration in shoot. The decrease of Cd concentration was higher in the sandy soil in comparison to the silty‐loam soil. Phosphorus application enhanced DMY of spinach by decreasing Cd concentration in soil as well as in plants. The results indicate that Cd toxicity in soil can be alleviated by P application.     

After effects of metals derived from a highly metal-polluted sludge on maize (Zea mays L.)

High Cd and Ni concentrations in sandy soils were built up in a field experiment, receiving an unusually metal-polluted sewage sludge between 1976 and 1980, at Bordeaux, France. The study evaluates the availability of metals and their after effects on maize at one point in time, the 8th year following termination of sludge application (1988). Plant parts (leaves, stalks, roots, grains) and soil samples were collected from plots which received 0 (Control), 50 (S1) and 300 Mg sludge DW ha^?1 (S2) as cumulative inputs. Dry-matter yield, plant metal concentrations, total, and extractable metals in soils were determined. Metal inputs resulted in a marked increase in total and extractable metals in soils, except for extractable Mn and Cu with either 0.1 N Ca(NO₃)₂ or 0.1 N CaCl₂. Total metal contents in the metal-loaded topsoils (0–20 cm depth) were very often lower, especially for Cd, Zn, and Ni, than the expected values. Explanation was partly given by the increases of metal contents below the plow layer, particularly for Cd at the low metal loading rate, and for Cd, Ni, and Cu at the high one (Gomez et al., 1992). In a control plot beside a highly metal- polluted plot, Cd, Zn, and Ni concentration in soil increased whereas the concentration of other metals was unchanged; lateral movement, especially with soil water, is plausible. Yield of leaves for plants from the S2 plot was reduced by 27%, but no toxicity symptoms developed on shoots. Yields of stalks for plants in both sludge-treated plots numerically were less than the controls but the decrease was not statistically significant. Cd and Ni concentrations increased in all plant parts with metal loading rate while Mn concentrations decreased. Leaf Cd concentration in plants from sludge-treated plots (i.e. 44 and 69 mg Cd kg^?1 DM for S1 and S2) was above its upper critical level (i.e. dry matter yield reduced by 10%: 25μg Cd g^?1 DM in corn leaves, Macnicol and Beckett, 1985). Yield reduction at the high metal-loading rate was probably due to 3 main factors: Mn deficiency in leaves, the accumulation of Ni especially in roots, and the increase of Cd in leaves. The amount of metal taken up by plants from the control plot ranked in the following order (mole ha^?1): Fe(22)? Mn(7)>Zn (5.6)?Cu (0.7), Ni (0.6), Cd (0.4). For sludge-treated plots, the order was (values for S1 and S2 in mole ha ^?1): Fe (16, 15)>Zn (7.9, 7.7)>Ni (4.3, 4.7)>Cd (1.9, 2.1)>Cu (1.0,1.2), Mn (1.5, 1.1). Zn and Cd had the greatest offtake percent from the soil to the above ground plant parts. Cd or Ni uptake by maize were correlated with extractable metals by unbuffered salts (i.e. 0.1 N Ca(NO₃)₂ and 0.1 N CaCl₂). It is concluded that part of the sludge-borne Cd and Ni can remain bioavailable in this sandy soil for a long period of time (e.g. 8 yr) after the termination of metal-polluted sludge application.     

Methods for determining labile cadmium and zinc in soil

Isotopically exchangeable cadmium and zinc (‘E values’) were measured on soils historically contaminated by sewage sludge and ones on zinc‐rich mine spoil. The E‐value assay involves determining the distribution of an added metal isotope, e.g. ¹⁰⁹Cd, between the solid and solution phases of a soil suspension. The E values for both metals were found to be robust to changes in the position of the metal solid?solution equilibrium, even though the concentration of dissolved metal varied substantially with electrolyte composition and soil:solution ratio. Concentration of labile metal was also invariant over isotope equilibration times of 2–6 days. The use of a submicron filtration procedure, in addition to centrifuging at 2200 g , proved unnecessary if 0.1 m Ca electrolyte was used to suspend the soils. The proportion of ‘fixed’ metal, in non‐labile forms, apparently increased with increasing pH, although there was considerable variation in both sets of contaminated soil. Zinc and cadmium in the sludged soils were similarly labile. Several possible methods for the measurement of chemically reactive metal were explored for comparison with E values, including single extraction with 1 m CaCl₂ and a ‘pool depletion’ (PD) method. The latter involves comparing solid?solution metal equilibria in two electrolytes with differing degrees of (solution) complex formation, 0.1 m Ca(NO₃)₂ and CaCl₂. Both the single extraction and the PD method gave good estimates of E value for Cd, although the single extraction was more consistent. Neither technique was a useful substitute for determining labile Zn, because of weak chloro‐complexation of Zn^2+. We therefore suggest that 1 m CaCl₂ extraction of Cd alone be used as an alternative to E values to avoid the inconvenience of isotopic dilution procedures.     

Parameterization and regionalization of Cd sorption characteristics of sandy soils. I. Freundlich type parameters

Cd sorption isotherms (n = 24) were established for arable, sandy soils of the ‘Fuhrberger Feld’ catchment area northeast of Hannover (Germany) using 0.01 M_c Ca(NO₃)₂ solution with Cd additions ranging from 0 to 44 μM_c Cd. Alternative fractions of initially (prior to analysis) sorbed Cd (S₀) were added to the amount sorbed during the experiments. The Freundlich equation was fitted to the resulting isotherms. The obtained retention parameters k and M varied with respect to the different S₀ fractions. Isotherms corrected with Cd_EDTA as S₀ fraction were nonlinear in their log-form. The highest degree of log-linearity is obtained if S₀ is characterized by 40% of the agua regia extractable Cd. The corresponding k values ranged from 36 to 1275 g^1-M L^M kg^?1 (mean 338 g^1-M L^M kg^?1, cv = 92%). The Freundlich exponent M showed less variation (0.7 to 1.1, cv = 12%) with a mean of 0.88. Functions based on these parameters predicted Cd concentrations in Ca(NO₃)₂?soil suspensions well (r² = 0.96) but were hardly related to Cd concentrations of ‘fresh’ soil solutions (r² = 0.20).     

Sources and Ecological Risks of Heavy Metals in Soils Under Different Land Uses in Bangladesh

Soil heavy metal pollution, influenced by both natural and anthropogenic factors, significantly reduces environmental quality. In this study, Cr, Ni, Cu, As, Cd, and Pb in eight different land-use soils from Patuakhali District in Bangladesh were assessed. Concentrations of Cr, Ni, Cu, As, Cd, and Pb in soils were 1-87, 5-271, 4-181, 0-80, 0.2-24.0, and 5-276 mg kg^-1, respectively, measured using an inductively coupled plasma-mass spectrometer. The enrichment factor, pollution load index (PLI), and contamination factor (C_fⁱ) of metal i were used to assess the ecological risk posed by metals in soils. The PLI ranged from 0.78 to 2.66, indicating baseline levels to progressive deterioration of soil due to metal contamination. However, C_fⁱ of Cd ranged from 1.8 to 12.0, which showed that the studied soils were strongly impacted by Cd. Considering the severity of the potential ecological risk of a single metal, the descending order was Cd > As > Pb > Cu > Ni > Cr. Soils under all land uses showed moderate to very high potential ecological risk.     

Effect of biosolid application to Mollisol Chilean soils on the bioavailability of heavy metals (Cu,Cr, Ni,and Zn) as assessed by bioassays with sunflower (Helianthus annuus) and DGT measurements

Purpose

This study assessed the effect of biosolid application on the bioavailable fraction of some trace elements (Cu, Cr, Ni, and Zn) using a bioassay with sunflower (Helianthus annuus) and a chemical assay, diffusion gradient in thin films (DGT).

Materials and methods

Five surface soil samples (0–20 cm) were collected from an agricultural zone in Central Chile where biosolids are likely to be applied. Municipal biosolids were mixed with the soil at concentrations of 0, 30, 90, and 200 Mg ha^?1. The experiment to determine the bioavailability of metals in the soil using the bioassay was performed using sunflower. The DGT technique and Community Bureau of Reference (BCR) sequential extraction were used to determine the bioavailable fractions of the metals.

Results and discussion

The application of biosolids increased the phytoavailability of Zn, Ni, and Cr in most of the soils, as indicated by the increasing concentrations in sunflower plants as the biosolid application rate increased. In two of the soils, Codigua and Pelvín, this increase peaked at an application rate of 90 Mg ha^?1. Decreases in the bioavailable fractions of Zn, Ni, and Cr were observed with higher biosolid application rates. The bioavailability of metals was estimated through multiple linear regression models between the metals in the sunflower plants and the different chemical fractions of metals in the soils treated with different biosolid rates, which displayed a positive contribution of the labile (water soluble, carbonate, and exchangeable), oxide, and organic metal forms in the soil, particularly with respect to Ni and Zn at application rates of 30 and 90 Mg ha^?1. The bioavailable fraction of metals was determined in soils using the DGT technique. The effective concentration (C _E) results were compared with those in sunflower plants. The DGT technique could effectively predict the bioavailable fractions of Cr, Ni, and Zn in the Taqueral soil but only that of Zn in the Polpaico soil.

Conclusions

The application of biosolids significantly increased the labile fraction of most of the metals in the studied soils, particularly at the highest biosolid application rate. C _E increased as the concentration of biosolids increased for most of the metals. The effectiveness of the DGT technique for predicting the bioavailability of metals was dependent on the soil type and the metal. However, the C _E for soil Cu was not related to plant Cu for all soils studied.     

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.     

贵州铅锌冶炼区农田土壤镉铅有效性评价与预测模型研究

农田土壤重金属的不同活性库分布和土壤-溶液分配模型能够提供重金属的生物有效性和浸出能力等信息,因而在风险评价和修复实践中非常重要。本研究采集毕节铅锌冶炼区30个历史污染农田土壤,同时在贵州省范围内采集5种类型背景土壤制成不同浓度Pb/Cd单一污染土壤;经3个月老化,分别测定由0.43 mol/L HNO_3、0.1 mol/L HCl和0.005 mol/L DTPA提取态表征的重金属反应活性库以及由0.01 mol/L CaCl_2提取态表征的直接有效库;分析铅锌冶炼区农田土壤Cd、Pb不同有效库的分布特征,建立土壤-溶液分配模型,并讨论土壤理化性质的影响。结果表明:历史污染土壤中Cd和Pb的直接有效库占全量比例分别比人工污染土壤低4倍和223倍,然而历史污染土壤Cd和Pb的反应活性库(0.43 mol/L HNO_3提取态)占全量比例要高于相应人工污染土壤中的比例。拓展Freundlich形式吸附方程能够准确描述各提取态表征的Cd和Pb活性库与土壤全量Cd和Pb的关系,尤其0.43 mol/L HNO_3提取方法能够克服土壤理化性质对土壤Cd和Pb提取的影响而与总量建立极显著的相关关系。pH依附性Freundlich吸附方程准确描述了Cd和Pb的总反应活性库分别与土壤溶液Cd和Pb的关系,对于Pb而言,还要考虑土壤有机质和有效磷的影响。本研究可为矿区农田土壤重金属污染评价、修复以及农田有效态标准的推导提供参考。     

Immobilization of heavy metals in soils using inorganic amendments in a greenhouse study

The effect of red mud (10 g kg^–1), a by‐product of the alumina industry, zeolite (20 g kg^–1), a naturally‐occurring hydrous aluminosilicate, and lime (3 g kg^–1) on metal lability in soil and uptake by fescue (Festuca rubra L.) (FEST) and amaranthus (Amaranthus hybridus L.) (AMA) was investigated in four different soils from Austria. The soil collection locations were Untertiefenbach (UNT), Weyersdorf (WEY), Reisenberg (REI), and Arnoldstein (ARN). The latter was collected in the vicinity of a former Pb‐Zn smelter and was highly polluted with Pb (12300 mg kg^–1), Zn (2713 mg kg^–1), and Cd (19.7 mg kg^–1) by long‐term deposition. The other soils were spiked with Zn (700 mg kg^–1), Cu (250 mg kg^–1), Ni (100 mg kg^–1), V (100 mg kg^–1), and Cd (7 mg kg^–1) salts in 1987. The two plant species were cultivated for 15 months. Ammonium nitrate (1 M) extraction was used in a soil : solution ratio of 1:2.5 to assess the influence of the amendments on the labile metal pools. The reduction of metal extractability due to red mud was 70 % (Cd), 89 % (Zn), and 74 % (Ni) in the sandy soil (WEY). Plant uptake in this treatment was reduced by 38 to 87 % (Cd), 50 to 81 % (Zn), and 66 to 87 % (Ni) when compared to the control. Sequential extraction revealed relative enrichments of Fe‐oxide‐associated metal fractions at the expense of exchangeable metal fractions. Red mud was the only amendment that decreased lability in soil and plant uptake of Zn, Cd, and Ni consistently. Possible drawbacks of red mud application (e.g., As and Cr concentration) remain to be evaluated.     

Remediation of a soil contaminated with heavy metals by immobilizing compounds

The labile fraction of heavy metals (HM) in soils is the most important for toxicity for plants and microorganisms. Thus, it is crucial to reduce this fraction in contaminated soils to decrease the negative effect of HM. In a greenhouse experiment, the effects of several additives on the labile fractions of Zn, Cd, Cu, Ni, and Pb were investigated in a soil contaminated during long‐term sewage‐sludge application. The accumulation of HM was studied in the aboveground biomass of wheat (Triticum aestivum L.). The additives used were the clay minerals Na‐bentonite, Ca‐bentonite, and zeolite; the Fe oxides hematite and goethite; the phosphate fertilizers superphosphate and Novaphos. Wheat was planted three times during 5 months, allowed to grow for 7 w, and harvested. Dry matter and HM content of shoots were determined after each harvest. Soil samples were taken after the first and third harvest, and the NH₄NO₃‐extractable HM contents were determined. After the addition of 2% Na‐bentonite as well as 2% Ca‐bentonite, a strong reduction of the labile HM soil fraction and shoot HM concentration was observed. At the end of the experiment, the labile fraction was reduced due to the addition of Na‐bentonite and Ca‐bentonite by 24% and 31% for Zn, by 37% and 36% for Cd, by 41% and 43% for Cu, by 54% and 61% for Ni, and by 48% and 41% for Pb, respectively. Furthermore, the shoot HM concentrations with the exception of Zn were reduced below the phytotoxicity range. Accordingly, the shoot dry‐matter production was significantly increased. The addition of phosphate fertilizers (notably Novaphos) strongly reduced the bioavailability of Pb for wheat plants. By addition of 0.05% Novaphos, the labile fraction and the shoot concentration of Pb were lowered by 39% and 64%, respectively. However, the addition of Fe oxides and zeolite resulted only in a small reduction in HM bioavailability to wheat plants. Among the studied additives, Na‐bentonite and Ca‐bentonite have the most promising potential to reduce the bioavailability for the studied HM.     

Evaluation of certain Ni soil tests for an initial estimation of Ni sufficiency critical levels

Although Ni is officially recognized as an essential micronutrient for all higher plants, the majority of the published research on soil availability of Ni focuses on its hazardous role as a heavy metal. The objective of the study was to evaluate certain Ni soil tests in uncontaminated soils for an initial estimation of its sufficiency critical levels. Nickel was extracted from 30 cultivated soils employing the following extraction methods: DTPA, AB‐DTPA, AAAc‐EDTA, Mehlich‐3, 0.1 M HCl, and 0.1 M HNO₃. Ryegrass (Lolium perenne L.) was grown in pots containing the soils, harvested five times, certain plant parameters were determined, and the Cate–Nelson procedures were used for Ni critical levels determination. Among the six methods, HCl was the least reliable extractant for the evaluation of soil available Ni, whereas the most significant (p ≤ 5%) relationships between Ni concentration or Ni uptake by ryegrass and Ni soil tests were consistently obtained for AAAc‐EDTA or Mehlich‐3 extractable Ni. In many cases, > 80% of the variability of Ni concentration or uptake by ryegrass was explained by these two soil tests without the inclusion of other soil properties that affect Ni bioavailability. Sufficiency critical levels of Ni in soil were ≈ 2 mg kg^–1 for both methods. Consequently, as an initial approach, concentrations of AAAc‐EDTA or Mehlich‐3 extractable Ni < 2 mg kg^–1 are probably a good guide to indicate soils that will respond to Ni fertilization.     

Crop uptake and extractability of cadmium in soils naturally high in metals at different pH levels

Abstract

A greenhouse experiment was conducted for three years to study the effect of different pH levels on metal concentrations in plants and the cadmium (Cd) extractability by DTPA and NH₄NO₃. The soils used were an alum shale (clay loam) and a moraine (loam), which were adjusted to pH levels of 5.5, 6.5, 7.0, and 7.5. Wheat (Triticum aestivum), carrot (Daucus carota L.), and lettuce (Lactuca sativa) were grown as test crops. Crop yields were not consistently affected at increasing soil pH levels. The concentration of Cd in plant species decreased with increasing soil pH in both soils and in all three years. Significant concentration differences between soil pH levels were only seen in wheat and carrot crops. Increasing soil pH also decreased the nickel (Ni) and zinc (Zn) concentrations in plants in the first year crop but the copper (Cu) concentration was not consistently affected by soil pH. The effect of pH was more pronounced in the moraine then the alum shale soil. The DTPA‐and NH₄NO₃‐extractable Cd was decreased with the increasing soil pH and the pH effect was more pronounced with NH₄NO₃ extractable Cd. Both extractants were found equally effective in relation to the Cd concentration in plants in this study.