Article

A Comparison of Tests for Extractable Copper and Zinc in Metal-Spiked and Field-Contaminated Soil

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Abstract

Common soil test methods were compared with 0.01 M CaCl2 extraction to determine their relative abilities to extract and estimate phytoavailability of Cu and Zn. In aged metal-spiked soils, all soil tests evaluated (Mehlich 3, diethylenetriaminepentaacetic acid [DTPA], Morgan, modified Morgan, CaCl2) showed a linear relationship of extractable to total Cu and Zn for both soil types studied. The fraction of total Cu and Zn extracted by aggressive tests (Mehlich 3, DTPA) was much higher than the fraction extracted by CaCl2, with the Morgan tests being intermediate. Although all extraction methods revealed Cu and Zn to be more available in the coarse-textured soil than the fine-textured soil, this texture effect was greatest for the least aggressive test (CaCl2) and least for Mehlich 3. The texture effect on soil test Cu and Zn was also reflected in bioavailability, with greater plant tissue concentrations of both metals from the coarse-textured soil in a soybean assay. Although all soil test methods provided similarly strong correlations to plant tissue concentrations of Zn for soybeans grown in the two soils, the less aggressive soil tests seemed more reliable as predictors of Cu uptake. The efficiency of Cu and Zn extraction from field-contaminated soils was much lower than that from laboratory-spiked aged soils. For Mehlich 3 and DTPA tests, Cu and Zn in field-contaminated soils were less extractable by a factor of about 2 compared with the spiked soils. For less aggressive tests, the difference in extractability was even greater. This study suggests that soil extraction methods removing smaller pools of Cu and Zn are more responsive to soil properties affecting chemical lability of the metals. Therefore, chemically nonaggressive neutral salts may be the most appropriate extractants where phytotoxicity is the concern in metal-contaminated soils.

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... Many studies have been focused on chemical agents to extract water-soluble, acid-extractable, exchangeable, and surface-complexed fractions of PTEs (Menzies et al. 2007;McBride et al. 2009;Luo et al. 2019;Jalali and Hurseresht 2020). The soil tests have been used to investigate the bioavailability of PTEs over the past few decades and include single-stage extraction, multi-stage extraction, kinetics, fractionation, dynamic modeling, and index determination (McLaughlin et al. 2000). ...
... Therefore, they are suitable for evaluating ecological relationships of PTEs (Sparks et al. 1996). In contaminated soils where the available content of PTEs is a concern, neutral salt solutions such as 0.01 M calcium chloride (CaCl 2 ) are the most appropriate method to extract the available part of these PTEs (McBride et al. 2009). The ionic strength of this extractant is similar to the soil solution and also contains calcium which is the predominant cation in most neutral and calcareous soils. ...
... Diethylene-tri-amine-penta-acetic acid (DTPA) is also used extensively to investigate the bioavailability of PTEs and a positive significant correlation between plant uptake and the amount of DTPA-extractable Zn, nickel (Ni), and cadmium (Cd) has been reported (Massas et al. 2009). However, it has been found that the content of PTEs extracted by EDTA or DTPA changes due to the environmental conditions and soil properties (McBride et al. 2009;Behera et al. 2011). Jalali and Khanlari (2007) indicated that the presence of carbonates in soils affected the efficiency of PTEs extraction by EDTA. ...
Article
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Single-extraction methods are one of the common ways to study the mobility of potentially toxic elements (PTEs) in artificially contaminated soils. The present study was aimed to evaluate the power of eight chemical agents to mobilize five PTEs including cadmium (Cd), cobalt (Co), copper (Cu), nickel (Ni), and zinc (Zn) in 25 soils spiked with two contamination levels (T1 and T2) and the effect of soil properties on PTEs extractable by different extractants using statistical analysis and multivariable regression. Regarding average values of the relative percentage of PTEs extracted of their total amounts in contaminated soils, EDTA was the strongest reagent except for Co, while NaNO3 was the weakest one. pH showed a negative correlation with CaCl2-extractable Cd, Co, Ni, and Zn, DTPA- and EDTA-extractable Ni, HNO3-extractable Cd, Co, Cu, and Zn, MgCl2-, NaNO3-, and NH4NO3-extractable Co, Ni, and Zn, and NH4OAc-extractable Cd, Co, and Zn. Cation exchange capacity (CEC) was negatively significantly correlated with HNO3-extractable Cd, while it had a positive significant correlation with MgCl2-extractable Cd. Organic matter (OM) showed a negative correlation with HNO3-extractable Cd and Zn, whereas it had a positive correlation with NH4NO3-extractable Cu. Equivalent calcium carbonate (ECC) was negatively significantly correlated with CaCl2-extractable Cd, Co, and Ni, EDTA-extractable Co, Cu, Ni, and Zn, HNO3-extractable Cd, Co, Cu, Ni, and Zn, MgCl2- and NaNO3-extractable Zn, NH4NO3-extractable Cd, Co, Ni, and Zn, and NH4OAc-extractable Cd and Co. According to the results, pH and ECC were the most effective parameters among soil properties in multivariable regression equations.
... Weak and neutral salt extractants such as CaCl 2 , Ca(NO 3 ) 2 and NaNO 3 have been evaluated in a number of recent studies (Datta and Young, 2005;Ettler et al., 2007;McBride et al., 2009;Meers et al., 2009;Menzies et al., 2007;Nolan et al., 2005) with promising results. The use of neutral salts as a method to predict bioavailability is based on the hypothesis that plant available metals are mostly sourced on soil mineral surfaces and can be easily displaced by other cations such as Ca and Na (Andrews et al., 1996;Houba et al., 2000;McBride et al., 2003;McLaughlin et al., 1999). ...
... The success of these tests were not influenced by biosolids amendments which was evident in the examination of the relationship between Ca(NO 3 ) 2 , the C E of metals and shoot concentrations (Figure 4.15 and 4.16). This result concurs with some recent studies (McBride et al., 2009;Menzies et al., 2007), which provides evidence to the hypothesis that the bioavailable metals, especially Ni are located on mineral surfaces (Andrews et al., 1996;McLaughlin et al., 1999). ...
... Numerous studies and several reviews on concepts and methods to accurately assess metal bioavailability and toxicity in soils have attempted, with some success, to link assays of metal extractability and solubility to plant tissue concentrations (Andrews et al., 1996;Basar, 2009;Degryse et al., 2009a;Lehto et al., 2006c;Lofts et al., 2007;McBride et al., 2009;McLaughlin et al., 2000;Meers et al., 2008;Menzies et al., 2007). A few studies have met with some success but in general results from these predictions have been largely inconclusive (Hamon et al. 1997;Hooda 2007;Zhang and Young 2005;. ...
... With regards to chemical methods, it is generally considered that metal soluble fractions⎯extracted by chemically-nonaggressive neutral salts⎯are useful for assessing metal toxicity in contaminated soils ( Kabata-Pendias, 2004;McBride et al., 2009). An alternative approach for assessing toxicity of metals to organisms is to use the soil solution free metal activities (Sauvé et al., 1996;Sauvé et al., 1998). ...
... With regards to biological methods for assessing metal phytotoxicity in contaminated soils, ISO and OECD protocols propose the use of artificial soils (composed of a mixture of peat, clay, and sand) or natural noncontaminated soils spiked with solutions of metals at increasing concentrations. However, it is well known that the solubility of metals, and thus their potential phytotoxicity, is greater in artificially-contaminated soils in comparison to field-collected soils (Hamels et al., 2014;McBride et al., 2009;Smolders et al., 2009;Spurgeon and Hopkin, 1995). This difference in solubility is explained by aging processes in soils, which are very slow and occur during several years ( Ma et al., 2006;Martínez and McBride, 2000). ...
... Generally, it is considered that total metal content is not a good indicator of soil metal toxicity (Adriano, 2001;McBride, 1994), while metal soluble fractions are more useful for assessing metal phytotoxicity in contaminated soils ( Kabata-Pendias, 2004;McBride et al., 2009). Furthermore, the free Cu 2+ ion is considered the main bioavailable form of copper in soils and the best indicator of copper phytotoxicity (Oliver et al., 2004;Sauvé et al., 1998). ...
... Chemical immobilization is one of the promising remediation technologies to minimize the mobility of heavy metals in soils and availability of these for plant uptake [1]. Several studies have observed that Cd immobilization in soils and reducing phytoavailability of this metal could be attributed mainly to the following reactions: (1) formation of Cd in a variety of insoluble Cd minerals, such as CdCO 3 and Cd 3 (OH) 2 [2][3][4]; (2) pHinduced Cd 2? adsorption to soil particles and humus [4][5][6]; and (3) the formation of Cd-organic complex [4]. Therefore, the phytoavailability of Cd in soils is likely to be affected by change of soil pH, amending counter anions including CO 3 2and OH -, and application of organic amendments. ...
... Chemical immobilization is one of the promising remediation technologies to minimize the mobility of heavy metals in soils and availability of these for plant uptake [1]. Several studies have observed that Cd immobilization in soils and reducing phytoavailability of this metal could be attributed mainly to the following reactions: (1) formation of Cd in a variety of insoluble Cd minerals, such as CdCO 3 and Cd 3 (OH) 2 [2][3][4]; (2) pHinduced Cd 2? adsorption to soil particles and humus [4][5][6]; and (3) the formation of Cd-organic complex [4]. Therefore, the phytoavailability of Cd in soils is likely to be affected by change of soil pH, amending counter anions including CO 3 2and OH -, and application of organic amendments. ...
... Several studies have observed that Cd immobilization in soils and reducing phytoavailability of this metal could be attributed mainly to the following reactions: (1) formation of Cd in a variety of insoluble Cd minerals, such as CdCO 3 and Cd 3 (OH) 2 [2][3][4]; (2) pHinduced Cd 2? adsorption to soil particles and humus [4][5][6]; and (3) the formation of Cd-organic complex [4]. Therefore, the phytoavailability of Cd in soils is likely to be affected by change of soil pH, amending counter anions including CO 3 2and OH -, and application of organic amendments. ...
Article
There have been few studies evaluating the effect of bottom ash (BA) on immobilization of heavy metals and reducing their phytoavailability. Further, work has not been conducted to evaluate the effect of BA along with mature animal manure compost (CP) on immobilization of cadmium (Cd) in soil and phytoavailability of this metal in contaminated soil. Therefore, this study was conducted to determine the effect of application of BA and CP on Cd phytoextractability. To elucidate the mechanism of Cd immobilization with BA and CP, soil was mixed without BA and CP, with BA only, with CP only, and with BA and CP together in the incubation. Bottom ash was applied at rates of 0 and 30 Mg/ha under different application rates of CP (0 and 30 Mg/ha) 2 weeks before sowing lettuce (Lactuca sativa). Our first experiment clearly demonstrated that reduced extractability of Cd with addition of BA, CP, and BA + CP was mainly the result of Cd adsorption by an increase in pH and negative charge of soil. Concentration of bioavailable Cd fraction (F1) effectively decreased with BA, CP, and BA + CP from 1.33 mg Cd/kg in control to 0.98, 0.29, and 0.26 mg Cd/kg, respectively. Applying BA and CP alone or together effectively reduced Cd uptake by lettuce. Concentration of Cd in lettuce decreased from 13.9 mg Cd/kg in control to 10.3 and 7.6 mg Cd/kg with application of BA and CP alone, respectively. However, applying BA with CP increased fresh lettuce yields more than BA applied alone. Therefore, combined application of BA and CP might be a good management practice in Cd contaminated arable soil from the view point of Cd phytoavailability and crop productivity.
... With regards to chemical methods, it is generally considered that metal soluble fractions-extracted by chemically-nonaggressive neutral salts-are useful for assessing metal phytotoxicity in contaminated soils (Kabata-Pendias, 2004;McBride et al., 2009). An alternative approach for assessing toxicity of metals to plants is to use the soil solution free metal activities (Sauvé et al., 1996,1998). ...
... With regards to biological methods for assessing metal phytotoxicity in contaminated soils, ISO 11269-2 (2005) andOECD 208 (2006) propose the use of artificial soils (composed of a mixture of peat, clay, and sand) or natural non-contaminated soils spiked with solutions of metals at increasing concentrations. However, it is well known that the solubility of metals, and thus their potential phytotoxicity, is greater in artificially-contaminated soils in comparison to field-collected soils (Hamels et al., 2014;McBride et al., 2009;Smolders et al., 2009). This difference in solubility is explained by aging processes in soils, which are very slow and occur during several years (Ma et al., 2006;Martínez and McBride, 2000). ...
... Generally, it is considered that total metal content is not a good indicator of soil metal toxicity (Adriano, 2001;McBride, 1994), while metal soluble fractions are more useful for assessing metal phytotoxicity in contaminated soils (Kabata-Pendias, 2004;McBride et al., 2009). Furthermore, the free Cu 2 þ ion is considered the main bioavailable form of copper in soils and the best indicator of copper phytotoxicity (Oliver et al., 2004;Sauvé et al., 1998). ...
Article
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It has been argued that the identification of the phytotoxic metal thresholds in soil should be based on field-collected soil rather than on artificially-contaminated soils. However, the use of field-collected soils presents several difficulties for interpretation because of mixed contamination and unavoidable covariance of metal contamination with other soil properties that affect plant growth. The objective of this study was to estimate thresholds of copper phytotoxicity in topsoils of 27 agricultural areas historically contaminated by mining activities in Chile. We performed emergence and early growth (21 days) tests (OECD 208 and ISO 11269-2) with perennial ryegrass (Lolium perenne L.). The total Cu content in soils was the best predictor of plant growth and shoot Cu concentrations, while soluble Cu and pCu(2+) did not well correlate with these biological responses. The effects of Pb, Zn, and As on plant responses were not significant, suggesting that Cu is a metal of prime concern for plant growth in soils exposed to copper mining activities in Chile. The effects of soil nutrient availability and shoot nutrient concentrations on ryegrass response were not significant. It was possible to determine EC10, EC25 and EC50 of total Cu in the soil of 327mgkg(-1), 735mgkg(-1) and 1144mgkg(-1), respectively, using the shoot length as a response variable. However, the derived 95% confidence intervals for EC10, EC25 and EC50 values of total soil Cu were wide, and thus not allowing a robust assessment of metal toxicity for agricultural crops, based on total soil Cu concentrations. Thus, plant tests might need to be performed for metal toxicity assessment. This study suggests shoot length of ryegrass as a robust response variable for metal toxicity assessment in contaminated soils with different nutrient availability. Copyright © 2015 Elsevier Inc. All rights reserved.
... A consistent relationship between Mehlich 3 and total metals would provide a low-cost approach for quickly screening wetland soils (e.g., Minca et al., 2013). Morse et al. (2016) simply applied a conversion factor to calculate total metals from the Mehlich 3 results based on the very high correlation between the two tests reported by McBride et al. (2009). However, the support for this approach outside of highly contaminated areas appears to be very limited (Franklin et al., 2007). ...
... These mean values were lower than previous studies from contaminated upland soils. McBride et al. (2009) reported mean Mehlich 3 to total metal ratios of approximately 0.3 for both Cu and Zn. For another comparison, combining the background total metal concentrations for upland soils from US EPA (2007c) (56 and 34 mg/kg for Zn and Cu, respectively) with the average Mehlich 3 concentrations from Hardy et al. (2008) (27.2 mg/kg for Zn and 9.2 mg/kg for Cu) results in ratios of Mehlich 3 extractable to total metal of 0.27 and 0.49 for Cu and Zn, respectively. ...
... While there was clear, positive correlation between total and Mehlich 3 Cu and Zn, a simple, accurate predictive relationship that would provide reasonable estimates of total metals from Mehlich 3 values was not obtained. McBride et al. (2009) reported substantially higher r 2 values of 0.98 for Zn and 0.82 for Cu for contaminated soils, potentially indicating this relationship may be stronger for more contaminated soils. ...
Article
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Wetlands are often located in landscape positions where they receive runoff or floodwaters, which may contain toxic trace metals and other pollutants from anthropogenic sources. Over time, this can lead to the accumulation of potentially harmful levels of metals in wetlands soils. To assess the potential risk of Cu and Zn buildup in wetland soils in North Carolina, soil data from 88 wetlands were analyzed. In a subset of 16 wetlands, more intensive sampling was conducted. Samples were analyzed for Mehlich 3 Cu and Zn, and a subset of the samples was analyzed for total Cu and Zn. Overall, Mehlich 3 Cu and Zn were low, with mean values of 0.9 mg/kg for Cu and 3.2 mg/kg for Zn. Warning levels for Mehlich 3 Zn were only exceeded in three of the 88 sites; elevated Mehlich Cu was not observed. Total Cu and Zn were also low, with only a few sites having elevated levels; however, there was not a strong linear relationship between Mehlich 3 and total metals. Mean levels of Mehlich 3 Cu and Zn in wetlands were much lower than for human-impacted upland soils and background threshold concentrations that might be indicative of disturbance were much lower than warning levels for agricultural soils. The very low mobile Zn and Cu in most of these wetlands indicated that these metals do not pose a risk to the biota in most North Carolina wetlands, but wetlands with a direct and significant anthropogenic source of metal contamination could be exceptions.
... ISO 11269-2, 2005;OECD-208, 2006). However, it is well known that the potential phytotoxicity is greater in metal-spiked soils in comparison to fieldcontaminated soils (Hamels et al., 2014;McBride et al., 2009). Thus, phytotoxicity thresholds established for sensitive species and/or for metal-spiked soils can be overprotective and can lead to unnecessary efforts to clean up the soils. ...
... Here and in Verdejo et al. (2015), soluble Cu and pCu 2þ did not correlate well with the biological responses. These results are contrary to the widely knowledge that soluble metal and free Cu 2þ ion activity are considered bioavailable extractions of Cu and more useful than total metal concentration for assessing metal phytotoxicity in contaminated soils (Kabata-Pendias, 2011;McBride et al., 2009;Oliver et al., 2005;Sauv e et al., 1998). However, Zhao et al. (2006) reported that solubility and speciation of Cu are not able to explain the variation in Cu toxicity by themselves, and that bioavailability of Cu in the soil toward the plant depends on Cu speciation, interactions with protective ions, and the resupply from the solid phase. ...
... Zinc and Cu results (mg dm À3 ) were divided by the specific soil density (g cm À3 ) to yield metal concentrations mg kg À1 . For comparisons to previous studies that reported total Zn or Cu concentrations based on complete metal removal (e.g., microwave-assisted digestion via EPA Method 3052), results herein were also transformed with the extraction efficiencies reported by McBride et al. (2009McBride et al. ( , 2009 reported that the Mehlich III extraction removed approximately 30% and 29% of total Zn and Cu, respectively, from contaminated agricultural soils. Consequently, each Zn and Cu sample result was divided by 0.30 and 0.29, respectively, to obtain an estimate of "total" metal concentrations. ...
... Zinc and Cu results (mg dm À3 ) were divided by the specific soil density (g cm À3 ) to yield metal concentrations mg kg À1 . For comparisons to previous studies that reported total Zn or Cu concentrations based on complete metal removal (e.g., microwave-assisted digestion via EPA Method 3052), results herein were also transformed with the extraction efficiencies reported by McBride et al. (2009McBride et al. ( , 2009 reported that the Mehlich III extraction removed approximately 30% and 29% of total Zn and Cu, respectively, from contaminated agricultural soils. Consequently, each Zn and Cu sample result was divided by 0.30 and 0.29, respectively, to obtain an estimate of "total" metal concentrations. ...
... Total metal(loid) concentrations in a contaminated soil are frequently not sufficient to predict its potential phytotoxicity (McBride, 1994;Sauv e et al., 1998;Ginocchio et al., 2002;ISO 17402, 2008). Metal fractions extracted by chemically nonaggressive neutral salts can be useful for assessing potential root exposure to metal excess in contaminated soils (Ginocchio et al., 2002;Kabata-Pendias, 2004;McBride et al., 2009). An alternative option for assessing metal availability to roots and predicting its potential phytotoxic effect is to use the soil solution free metal activities (Sauv e et al., 1998;Ginocchio et al., 2009;Kader et al., 2016). ...
... It is well known that the solubility of metals, and thus their potential phytotoxicity, is higher in artificially contaminated soils, i.e., soils spiked with metal solutions in gradually increasing concentration, in comparison to field-collected soils (Ginocchio et al., 2006;McBride et al., 2009;Smolders et al., 2009;Hamels et al., 2014;Senkondo et al., 2015). This discrepancy is attributed to the metal residence time in soils. ...
... Stronger correlations between pH and CaCl 2 extracted metals for metal oxides and spinel minerals were observed compared to metal salts (Fig. 4). This was because metals are readily available when spiked as metal salts making surface complexation reactions with ligands a major determinant of availability (McBride et al., 2009). This is the probable reason why metal salts were comparatively more toxic. ...
... As a result, higher concentrations of Cu and Pb with high affinities for ligands were extracted in DTPA in all soils (Fig. 5). The strong correlations between enzyme activities in oxide spiked soils and CaCl 2 and DTPA extractable metals suggests that both DTPA and CaCl 2 are reliable methods for assessing metal availability of field contaminated soils, but toxicity of the metals may be dependent on the biological endpoint as observed in our study (McBride et al., 2009). ...
Article
Metals are present as mixtures in the environment, yet testing such complex mixture poses design and technical challenges. One possible solution is the use of fixed ratios, i.e. rays of increasing metal concentrations. But fixed ratios rays are compromised when soils dosed with metal salts are leached due to metal-soil selectivity rules. Two alternative metal forms, metal oxides and spinel minerals of quinary metal mixtures (Pb, Cu, Co, Ni, Zn), were evaluated for their toxicity to soil microorganisms measured by the activity of ammonia monooxygenases and acid-phosphatases in three soils. Leaching, a required step for salts, had a larger effect on ammonia monooxygenases than metals. Generally, metal salts were the most toxic form, while the spinel minerals were the least toxic form. Two extractants, CaCl2 and DTPA, were evaluated for their ability to link toxicity to metals across all three metal forms. Salt toxicity was closely linked to CaCl2 extractable concentrations but DTPA was the most appropriate for oxides. We strongly recommend combining fixed ratio rays with metal oxides for metal mixture studies, since soil ratios created using oxides were more precise and required less experimental effort compared to salts and spinel minerals. Furthermore, because DTPA and CaCl2 closely tracked the toxicity of more realistic metal forms (i.e. oxides), we recommend that field studies investigating metal mixtures use both DTPA and CaCl2.
... These procedures, however, are complicated, time consuming, and quite costly (McBride et al. 2011). Moreover, many authors have reported that the total concentration does not reflect the real risk of contamination (McLaughlin et al. 2000;McBride et al. 2009;Menzies et al. 2007;Rao et al. 2008). Measuring the availability of heavy metals for plants is essential for the evaluation of the environmental risk associated with their excess in the soil. ...
... It is commonly known that there is a strong barrier of the Cu transfer from the roots to the shoots, much stronger than for other metals (McBride 2001;McBride et al. 2009). Therefore, the assessment of Cu phytoavailability requires testing the roots, not the shoots. ...
Article
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The aim of the study was to compare the usefulness of 1 M HCl with aqua regia, EDTA, and CaCl2 for the extraction of phytoavailable forms of Cu, Ni, and Zn on coarse-textured soils contaminated with these metals. Two microplot experiments were used for the studies. Reed canary grass (Phalaris arundinacea), maize (Zea mays), willow (Salix viminalis), spartina (Spartina pectinata), and miscanthus (Miscanthus × giganteus) were used as test plants. They were grown on soil artificially spiked with Cu, Ni, and Zn. The experimental design included a control and three increasing doses of metals. Microplots (1 m² × 1 m deep) were filled with sandy soil (clay—6%, pH 5.5, Corg—0.8%). Metals in the form of sulfates were dissolved in water and applied to the plot using a hand liquid sprayer. During the harvest, samples were collected from aboveground parts, roots, and the soil and then tested for their Cu, Zn, and Ni contents. The metal content of the soil was determined using four tested extractants. It was found that Cu and Ni were accumulated in roots in bigger amounts than Zn. The usefulness of the extractants was evaluated based on the correlation between the content of metals in the soil and the plant (n = 32). This study demonstrated that 1 M HCl, aqua regia, and EDTA were more efficient or equally useful for the assessment of the phytoavailability of Cu, Ni, and Zn as CaCl2. Due to the ease of performing determinations and their low cost, 1 M HCl can be recommended to assess the excess of Cu, Ni, and Zn in the coarse-textured soils.
... This method was chosen to extract the fraction of heavy metals that is less strongly adsorbed to soil and more mobile and therefore of an interest from an environmental water quality standpoint. In contrast, a substantial fraction of the heavy metals extracted using chemically aggressive reagents may not be bioavailable [39], especially under natural environmental conditions. A 10 g subsample of air-dried soils from the unvegetated pots was taken, combined with 25 mL of 0.01 M CaCl 2 solution, and the suspension was shaken for 24 h on a mechanical shaker at room temperature [39]. ...
... In contrast, a substantial fraction of the heavy metals extracted using chemically aggressive reagents may not be bioavailable [39], especially under natural environmental conditions. A 10 g subsample of air-dried soils from the unvegetated pots was taken, combined with 25 mL of 0.01 M CaCl 2 solution, and the suspension was shaken for 24 h on a mechanical shaker at room temperature [39]. Solution was filtered through Ahlstrom filter paper 642 (particle retention of 2 µm), and filtrate was analyzed in triplicates using the inductively coupled plasma optical emission spectrometry (ICP-OES/AES, Optima 3000DV, Perkin Elmer Corp, Norwalk, CT, USA). ...
Article
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We investigated the effects of organic amendments (thermophilic compost, vermicompost, and coconut coir) on the bioavailability of trace heavy metals of Zn, Cd, Pb, Co, and Ni from heavy metal-spiked soils under laboratory conditions. To test switchgrass (Panicum virgatum) as a potential crop for phytoremediation of heavy metal from soil, we investigated whether the addition of organic amendments promoted switchgrass growth, and consequently, uptake of metals. Compost is a valuable soil amendment that supplies nutrients for plant establishment and growth, which is beneficial for phytoremediation. However, excess application of compost can result in nutrient leaching, which has adverse effects on water quality. We tested the nutrient leaching potential of the different organic amendments to identify trade-offs between phytoremediation and water quality. Results showed that the amendments decreased the amount of bioavailable metals in the soils. Organic amendments increased soil pH, electrical conductivity (EC), and soil nutrient status. Switchgrass shoot and root biomass was significantly greater in the amended soils compared to the non-amended control. Amended treatments showed detectable levels of heavy metal uptake in switchgrass shoots, while the control treatment did not produce enough switchgrass biomass to measure uptake. Switchgrass uptake of certain heavy metals, and concentrations of some leachate nutrients significantly differed among the amended treatments. By improving soil properties and plant productivity and reducing heavy metal solubility that can otherwise hamper plant survival, organic amendments can greatly enhance phytoremediation in heavy metal-contaminated soils.
... This model is quite similar to the one obtained for H 2 O Zn, but according to a previous study, extraction carried out with non-aggressive extractants, such as CaCl 2 , better represents the bioavailable Zn and is most sensitive to the effects of soil properties, such as pH, texture and organic matter [35]. CaCl 2 Zn is more retained in clayey soils; therefore, the relationship we obtained between the CaCl 2 Zn and the amount of clay has a negative slope [35]. ...
... This model is quite similar to the one obtained for H 2 O Zn, but according to a previous study, extraction carried out with non-aggressive extractants, such as CaCl 2 , better represents the bioavailable Zn and is most sensitive to the effects of soil properties, such as pH, texture and organic matter [35]. CaCl 2 Zn is more retained in clayey soils; therefore, the relationship we obtained between the CaCl 2 Zn and the amount of clay has a negative slope [35]. Since CaCl 2 zinc also includes H 2 O zinc, parameters such as pH and K will have some weight in its modelling. ...
Article
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Different fractions of Ni, Zn, Cu and Pb were determined in metal-spiked forest soils derived from four parent materials using three extractants (H2O, CaCl2 and diethylenetriaminepentaacetic acid (DTPA)). It is important to determine how parent materials and soil properties affect the retention of these metals in order to predict their behavior and act accordingly in the event of accidental spillage, for example. The extraction of fractions was not sequential (before carrying out the extractions, the soil samples were divided into three parts), so the CaCl2 fraction also included the H2O one, and the DTPA fraction contained the other two. With the results, we developed models to predict the extraction of each fraction employing the physicochemical characteristics of the soil (e.g., pH, organic matter content and texture values) and the amount of metal added. The objective of this work was to determine how the properties of the soil would influence the fractioning of the metals considered, and through these characteristics create models to predict the behavior of each metal fraction. We found correlations between the different fractions of Ni and Zn, suggesting that there are soil properties that condition the retention of both metals. Pb and Cu showed different behavior than Zn or Ni, since the proportions extracted by H2O and CaCl2 were much lower. Regarding the DTPA fraction, unlike the case of Ni or Zn, the extraction of Cu and Pb was more homogeneous; they did not show great variation in different soils, even when considering the results of extraction in limestone soils. This may be due to the fact that the soil properties do not exert an important effect on their availability, or these two metals are considerably sensitive to the effect of pH, and no differences were observed because the extraction of the DTPA fraction was conducted with a buffered solution. For each fraction of metal used, we obtained a model with R2 always greater than 0.65. Considering these results, we can conclude that it is possible to predict Zn, Ni, Cu and Pb availability in soils developed on different parent materials. This can be achieved by identifying some basic soil characteristics and applying the developed equations.
... A range of chemical extractants including mineral acids (e.g., 1 N HCl), salt solutions (e.g., 0.01 M CaCl 2 ), buffer solutions (e.g., 1 M NH 4 OAc), and chelating agents [e.g., diethylene triamine pentaacetic acid (DTPA)] have been used to predict the bioavailability of metal(loid)s in soils [104][105][106]. Chelating agents, such as ethylenediamine tetraacetic acid (EDTA -0.05 M) and 0.05 M DTPA, have often been found to be more reliable in predicting the plant availability of metal(loid)s [107,108], since they are more effective in removing soluble metal(loid)-organic complexes that are potentially bioavailable. ...
... Methods used to determine soil metal bioavailability vary from measuring concentrations of the immediately bioavailable metal pool, for example, water-soluble metals and weak salt extractions (Andrews et al., 1996;McLaughlin et al., 2000;Almas et al., 2007;McBride et al., 2009), to techniques that quantitatively measure the supply of labile trace metals in soils, for example, diffusive gradient in thin films technique (DGT) (Hamon et al., 1997;Zhang et al., 2001;Zhang & Young, 2005;Hooda, 2007;Menzies et al., 2007). Although success has been demonstrated using weak salt extractions (Menzies et al., 2007;Black et al., 2011), there has been no assessment made to determine what effects biosolids amendments may have on the reliability of such assays, particularly in the context of a mixed metal matrix where the potential exists for synergistic or antagonistic responses. ...
Article
This paper questions whether the presence of biosolids amendment in metal-spiked soils alters the outcome of soil-based assays of metal bioavailability. The effects of biosolids amendment on the efficacies of six soil metal bioavailability assays (total recoverable, EDTA, Ca(NO3)2, soil solution, diffusive gradient in thin films and free ion activity) were assessed against metal concentrations in wheat shoots (Triticum aestivum) germinated in three contrasting soils, each previously incubated for either 2 weeks or 6 months following treatment with Cd, Cu, Ni and Zn +/− biosolids amendment. Overall, Ca(NO3)2 was the most accurate method to predict Cd (r2 = 0.62), Ni (r2 = 0.73) and Zn (r2 = 0.55) bioavailability in soils and therefore was used to compare variations in responses between biosolids and nonbiosolids-amended soils. Comparisons between these two groups revealed no significant differences in linear relationships for all four metals and soil types assessed. These findings not only support Ca(NO3)2 as a robust and valid method for determining soil metal bioavailability across metal matrices and soil types, but also that the presence of biosolids does not compromise the predictive power of this assay or any of the others examined.
... Thus, metals such as Zn and Cu in historically field-contaminated soils are less labile and less toxic than the same metals spiked into soils. [6,7,9,10] Cadmium, conversely, shows a lower tendency to be immobilised or 'fixed' into biologically unavailable forms than Zn or Cu. [2] The question is then raised: how long should metal-spiked soils be aged before bioassays or other tests of availability can be considered to be realistic? ...
Article
To assess long-term effects of field aging on Cu and Zn availability and phytotoxicity in soils, soils were spiked in the field using metal sulfate salts, and tested over 10 years for changes in total metals, salt-extractable (0.01M CaCl2) metals, Cu ion activity and phytoavailable metals using a soybean assay. Metal losses from the soils were generally small, with the coarse-textured (Arkport) soil having greater losses than the fine-textured (Hudson) soil. However, large reductions in salt-extractable metals occurred over the 10-year period, with most of this decline observed in the first several years following spiking. Copper ion activities decreased after 10 years of aging in all of the Cu-spiked soils, but remained high enough to be phytotoxic at metal loadings of 200 and 400mgkg-1. The soybean assay showed that Zn phytoavailability was significantly elevated in both soils at the loadings of 200 and 400mgkg-1 Zn. Higher plant tissue Cu was evident at additions of 200 and 400mgkg-1 Cu in the Arkport soil, but only at the 400mgkg-1 additions in the Hudson soil. Plant growth was significantly reduced at the 400mgkg-1 additions for both metals in both soils; growth inhibition at the 200mgkg-1 addition was also observed for both metals in both soils, but was not statistically significant for Zn. In summary, soils spiked with 200mgkg-1 (or more) of Cu or Zn salts express significant phytotoxicity after 10 years of field aging despite a shift of the metals into less labile forms.
... Early versions of the protocols of soil quality tests with earthworms proposed the use of artificial soils (composed of peat, clay, and sand) or natural non-contaminated soils spiked with solutions of metals at increasing concentrations (ISO 11268-2, 1998;OECD 222, 2004). However, it is well known that the solubility of metals, and thus their potential toxicity, is greater in artificially-contaminated soils in comparison to field-collected soils (McBride et al., 2009;Smolders et al., 2009;Spurgeon and Hopkin, 1995). This difference in solubility is explained by aging processes in soils, which are very slow and occur during several years (Ma et al., 2006;Martínez and McBride, 2000). ...
... When chemical methods are used, it is assumed that the potential TE bioavailability correlates to its solubility/chemical speciation and mobility, estimated by leaching tests and chemical extractions (Prueβ, 1992;Lebourg et al., 1998;McBride et al., 2009;Soriano-Disla et al., 2010). Some chemical methods have been standardized and are currently used in the legislation of several Countries, like protocols for quantifying soluble and exchangeable TE fraction using 0.1 M NaNO 3 in Switzerland (Osol, 1998) and TE extraction using 1 M NH 4 NO 3 in Germany (DIN ISO 19730, 2008;Prueß, 1998). ...
... When chemical methods are used, it is assumed that the potential TE bioavailability correlates to its solubility/chemical speciation and mobility, estimated by leaching tests and chemical extractions (Prueβ, 1992;Lebourg et al., 1998;McBride et al., 2009;Soriano-Disla et al., 2010). Some chemical methods have been standardized and are currently used in the legislation of several Countries, like protocols for quantifying soluble and exchangeable TE fraction using 0.1 M NaNO 3 in Switzerland (Osol, 1998) and TE extraction using 1 M NH 4 NO 3 in Germany (DIN ISO 19730, 2008;Prueß, 1998). ...
Article
Full-text available
Phytoextraction is a promising technology to remediate soils contaminated with trace elements (TE). One phytoextraction strategy is based on cultivation of high biomass herbaceous species, e.g. sunflower and tobacco, with or without addition of TE mobilizing agents to the soil. The second one is based on cultivation of rapidly growing trees, e.g. willow and poplar, with high TE accumulation ability in short rotation coppice (SRC) and the third one is based on the cultivation of TE-hyperaccumulators. After the cultivation of appropriate plant species on the contaminated soil, TE enriched harvestable plant parts are removed from the site. Problems associated with the treatment and disposal of the metal-enriched biomass produced during phytoextraction limit the development of commercially viable phytoextraction while ensuring that environmental parameters do not infringe current regulation. In the ongoing project GREENLAND (FP7, KBBE-2010-4, 266124) project, one work package aims at testing different various conventional and innovative technologies of biomass valorization, such as combustion, anaerobic digestion, solvolysis and microwave thermal treatment, and determining the fate of the TE in the resulting products of each conversion process. A first round of assays was carried out on a wide range of plant species cultivated at the field trials of the GREENLAND partners. The results will be presented and discussed. Keywords: bioenergy, phytoremediation, Salix, poplar, environmental impact
... Studies on Zn toxicity to plants (McBride et al., 2009), invertebrates (Lock and Janssen, 2001) and microorganisms (Broos et al., 2007;Smolders et al., 2004) predominantly focus on total concentrations. Toxicity end points have been reported using dose-response studies in the laboratory (Warne et al., 2008b) and in short-term field studies (Heemsbergen et al., 2009; 2008a). ...
... Plants essentially take up heavy metals from the soil via soil solutions (Schindler and Sposito 1991), and phytotoxicity of a metal is related to its free ion activity in the solution to which the plant root is exposed (Parker and Pedler 1997) and also to soluble metal-organic complexes and metal-inorganic ligand complexes (Huang et al. 1997;Jones 1998). Recent studies have also shown that less aggressive reagents that extract predominantly soluble and exchangeable fractions are frequently better at predicting plant availability of excess heavy metals in soils than the traditional more aggressive tests involving the use of reagents such as hydrochloric acid, diethylenetriamine pentaacetic acid and ethylenediamine tetraacetic acid (McBride et al. 2009;Menzies et al. 2007;Meers et al. 2007). ...
Chapter
Soil quality is severely affected due to contamination with salts, toxic metals, non-metals and organic pollutants generated from mainly urban and industrial activities and therefore needs to be managed appropriately for sustaining agricultural productivity. Deterioration in soil quality in the polluted agricultural land can be ascertained through measurement of different physical, chemical and biological indicators. While salts affect crop productivity by degrading rhizosphere environment, heavy metals express toxicity on plant growth and on activities of agriculturally important microflora and fauna and also contaminate food. Although adverse effect of organic pollutants in soil on plant growth and produce quality has not been found significant, these are reported to affect soil microbe activity and therefore are required to be decontaminated. The role of different agricultural operations on countering the adverse effects of soil pollution has been discussed, and different soil and crop management, tillage, nutrient management, water management and soil conservation measures have been suggested for improving productivity of crops, quality of food and environment.
... Salt solutions (0.01 mol L −1 CaCl 2 ), mineral acids (1 mol L −1 HCl), chelating agents (diethylene triamine pentaacetic acid (DTPA)), and buffer solutions (1 mol L −1 NH 4 OA c ) are chemical extractants used in single extraction procedure for assessing bioavailability in Pb-and Cd-contaminated soils (McBride et al., 2009;Bakircioglu et al., 2011). Chelating agents (0.05 mol L −1 DTPA and 0.05 mol L −1 ethylenediamine tetraacetic acid (EDTA)) have been documented as more trustworthy in predicting the Pb and Cd availability in plants and are more impressive in eliminating soluble metal-organic complexes (Sims and Johnson, 1991;Zhu et al., 2012). ...
Article
Since the inception of industrial revolution, metal refining plants using pyrometallurgical processes have generated the prodigious emissions of lead (Pb) and cadmium (Cd). As the core target of such pollutants, a large number of soils are nowadays contaminated over widespread areas, posing a great threat to public health worldwide. Unlike organic pollutants, Pb and Cd do not undergo chemical or microbial breakdown and stay likely in site for longer duration after their release. Immobilization is an in-situ remediation technique that uses cost-effective soil amendments to reduce Pb and Cd availability in the contaminated soils. The Pb and Cd contamination in the soil environment is reviewed with focus on source enrichment, speciation and associated health risks, and immobilization options using various soil amendments. Commonly applied and emerging cost-effective soil amendments for Pb and Cd immobilization include phosphate compounds, liming, animal manure, biosolids, metal oxides, and biochar. These immobilizing agents could reduce the transfer of metal pollutants or residues to food web (plant uptake and leaching to subsurface water) and their long-term sustainability in heavy metal fixation needs further assessment.
... Soil testing has usually been done to determine if soil nutrients are deficient or adequate. However, traditional soil tests are being extended to evaluate excess or even toxic levels of nutrients and trace elements (McBride, Pitiranggon, and Kim 2009). ...
Article
Full-text available
The aim of this study was to compare four micronutrient soil-test extractants currently in common use in Poland, Rinkis, Mehlich 3, modified Lindsay and Norvell, and Yanai, for ability to determine the plant-available concentration of copper (Cu) and manganese (Mn) in two acidic soils (pH 4.8?4.9) that had been amended with different doses of Cu and Mn fertilizers. The comparison was based on two pot experiments (each with a different soil) with corn (Zea mays), barley (Hordeum vulgare), spring wheat (Triticum aestivum), rape (Brassica napus), red clover (Trifolium pratense), and English ryegrass (Lolium perenne). The extractants were evaluated based on a correlation analysis of the microelement concentrations in plants at the end of the vegetative phase and micronutrient concentration in the fertilized soil determined by each extractant at the end of the experimental period. The largest extractable concentrations of Cu and Mn in soils were obtained with Rinkis. The modified Lindsay and Norvell soil test extracted the lowest amount of both microelements. For soil Cu, the results with the Mehlich 3 and Yanai extractants were highly correlated with the Rinkis procedure results (r = 0.98). The modified Lindsay and Norvell results were not as well correlated with Rinkis (r = 0.84). For soil Mn, the correlation of results of Yanai, Mehlich 3, and modified Lindsay and Norvell to Rinkis ranged from r = 0.80 to r = 0.86. Levels of Mn and Cu measured with each of the extractants were highly correlated with plant tissue concentrations of Mn and Cu in most of the six plant species. The exceptions to this were the following: The modified Lindsay and Norvell soil Cu levels were not correlated with ryegrass and wheat plant Cu levels; Mehlich 3 Cu was not correlated with red clover Cu; and the Rinkis-extractable Mn was not correlated with the wheat Mn. It is concluded that the Yanai and Mehlich 3 procedures are suitable alternatives to the Rinkis for Cu but not for Mn.
... When chemical methods are used, it is assumed that the potential TE bioavailability correlates to its solubility/chemical speciation and mobility. Consequently, various leaching tests and chemical extractions are used to predict risks related to the contaminant behavior under specific environmental conditions (Prueβ, 1992;Lebourg et al., 1998;McBride et al., 2009;Soriano-Disla et al., 2010). Several methods have been standardized, e.g. the protocol for quantifying soluble and exchangeable TE fraction using 0.1 M NaNO 3 in Switzerland (Osol, 1998) and TE extraction using 1 M NH 4 NO 3 in Germany (DIN ISO, 19730, 2008;Prueß, 1998). ...
... When chemical methods are used, it is assumed that the potential TE bioavailability correlates to its solubility/chemical speciation and mobility. Consequently, various leaching tests and chemical extractions are used to predict risks related to the contaminant behavior under specific environmental conditions (Prueβ, 1992;Lebourg et al., 1998;McBride et al., 2009;Soriano-Disla et al., 2010). Several methods have been standardized, e.g. the protocol for quantifying soluble and exchangeable TE fraction using 0.1 M NaNO 3 in Switzerland ( Osol, 1998) and TE extraction using 1 M NH 4 NO 3 in Germany ( DIN ISO, 19730, 2008;Prueß, 1998). ...
... Several previous studies highlighted the importance of using field-collected soils -and not artificiallycontaminated soils -for phytotoxicity tests for assessment of soil quality of metal-contaminated soils (Hamels et al., 2014;McBride et al., 2009;Smolders et al., 2009 Ginocchio et al., 2004). In this case, it might be difficult to distinguish between the effects of different metals on plant responses. ...
Article
Full-text available
Several previous studies highlighted the importance of using field-collected soils instead of artificially spiked contaminated soils for phytotoxicity tests. However, the use of field-collected soils presents several difficulties for interpretation of results, due to presence of various contaminants in the soil and unavoidable differences in the physicochemical properties of the tested soils. The objective of this study was to estimate thresholds of copper phytotoxicity in topsoils of 27 agricultural areas historically contaminated by mining activities in Chile. We performed standard emergence and early growth (21 days) tests (OECD 208 and ISO 11269-2) with lettuce. The response of lettuce was best explained by Cu toxicity and P deficiency. Growth of lettuce was related to soil total Cu concentration and Olsen-P and was not affected by soluble Cu (extractable by 0.1 M KNO3) or Cu2+ free ion activity of the soil solution. Thus, lettuce has a limited applicability for metal toxicity assessment in metalcontaminated soils, due to sensitivity of its response to P deficiency. However, it was possible to determine toxic thresholds for shoot concentrations of Cu in lettuce for responses of shoot and root length, suggesting that shoot concentrations of Cu in lettuce can be useful as indicators of Cu toxicity even in soils with a wide range of nutrient concentrations. © 2016, Sociedad Chilena de la Ciencia del Suelo. All rights reserved.
... Dilute salt reagents (e.g., 0.01 M NaCl 2 , 0.01 M KNO 3 , 0.01 M CaCl 2 ) are generally used to mimic the electrolytic properties of in situ soil pore water and have been commonly used to extract fractions of bioavailable trace metals. 24,25 KNO 3 has traditionally been used to extract electrostatically bound trace metals (i.e., ionic metal forms) and a recent study demonstrated how 0.01 M KNO 3 could be used to extract and analyze both Ag + and AgNP forms within the same extract. 26 While this scenario was advantageous from a mass balance perspective, the extracts showed only moderate soil dispersion and resulted in large dissolved-to-particulate Ag ratios, which is not ideal for SP-ICP-MS analysis. ...
... This extractant is widely used for the extraction of exchangeable metals from metal-polluted soils (e.g., Almas et al. 2000, Luo et al. 2006, Moreno-Caselles et al. 2000, Perez-Esteban et al. 2013. Although chemically aggressive extractants, such as ammonium acetate buffer and 0.1 N HNO 3 , are widely used (e.g., Slukovskaya et al. 2020), metal fractions extracted with chemically non-aggressive neutral salts are preferrable for assessing potential exposure of roots to metals in contaminated soils (e.g., Altimira et al. 2012, Kabata-Pendias 2004, McBride et al. 2009). The resulting suspension was shaken for 60 minutes and then filtered through ashless filter paper. ...
Article
Full-text available
Lime is one of the effective agents for reducing the phytoavailability of metals in contaminated acidic soils. However, previous studies have shown that lime alone cannot reduce metal phytotoxicity to the desired extent in such soils. The goal of this study was to evaluate the effect of different amendment combinations (lime with and without Feand/or Mn-based amendments) on plant growth. A sample of Histosol (0-5 cm) was collected around a Cu/Ni smelter near Monchegorsk, Murmansk region, exhibiting total Cu and Ni concentrations in the soil of 6418 and 2293 mg kg-1, respectively. Likewise, a sample of forest litter (0-15 cm) was collected around a Cu smelter near Revda, Sverdlovsk region, exhibiting total Cu concentration in the soil of 5704 mg kg-1. Fe-Mn oxides were sourced from ferromanganese nodules in the Gulf of Finland, and iron powder was used as a precursor for iron oxides. Perennial ryegrass was grown in pots for 21 days under controlled laboratory conditions. Two dolomite doses were tested: 5% w/w (giving a soil pH of 6.5) and 20% w/w (giving a soil pH of 7.4). Over-liming stunted plant growth; therefore, the dolomite dose was set at 5% in the further experiments of the study. Importantly, the addition of 0.5% and 1% of Fe-Mn-oxides or iron powder did not improve the efficacy of the lime amendment in promoting plant growth in the soils. Therefore, the issue of reducing plant exposure to metals remained unresolved in the soils under study.
... These statistical tests were conducted using the Statview software 196 (SAS Institute, Cary, NC). The Modified Morgan extractable metals and nutrients were used for these 197 regression tests because this extraction method is considered to provide a good estimate of 198 bioavailable trace metals and essential nutrients, whereas the 0.01 M CaCl 2 and DTPA tests 199 respectively underestimate and overestimate bioavailable fractions of these elements in soils200 (O'Connor, 1988;McBride et al., 2009).201 Microbial O 2 Consumption: Redox Assay 202 Indigo carmine (3,3′-dioxo-2,2′-bisindolyden-5,5′-disulfonic acid disodium salt) was used as a redox 203 indicator (Tratnyek et al., 2001) to determine the rate at which soils reached a low redox potential 204 following submergence in water, an indirect measure of O 2 consumption by microbial respiration. ...
Article
Soils contaminated historically by refinery Ni emissions were subjected to laboratory assays evaluating soil health, including microbial function, biomass and community diversity based on high- throughput DNA sequencing. The assays showed that soils with greater than 500 mg kg-1 total Ni had lower microbial biomass and respiration rates as well as reduced microbial diversity and shifts in prevalent phyla compared to most soils with lower Ni. Soil testing for nutrient status suggested additional limitations due to factors other than Ni contamination, including deficiencies of Mn and other essential elements that could possibly explain reduced microbial function even in relatively uncontaminated soils. A greenhouse soybean assay showed greater Ni uptake from soils with the highest total and 0.01 M CaCl2-extractable Ni, with one of the high-Ni soils (1900 mg kg-1 total Ni) having a level of CaCl2-extractable Ni predicted to reduce soybean growth by more than 25%. The study revealed that conventional macroscopic measures of soil health were reflected at the microscopic scale by differences in microbial community composition and diversity as evidenced by DNA analysis. Although soil health indicators were affected by high Ni bioavailability, other factors attributable to local differences in fertility status and organic matter content appeared to have strong influences on these indicators
... The quantities of elements extracted from soils using the Modified Morgan method are considered to represent a bioavailable fraction of the total elements [33,34]. For many trace elements and macronutrients, this extractable quantity is a small fraction of the total and better predicts the leachability and potential for plant uptake than total quantities [35,36]. Table 4 presents the Modified Morgan-extractable elements of interest in the present study, which were determined to be Ca, Cd, Cu, Zn, P, and S because of the observed effect of biosolids amendment in increasing these extractable elements compared to the unamended control soils. ...
Article
Full-text available
The impact of repeated application of alkaline biosolids (sewage sludge) products over more than a decade on soil concentrations of nutrients and trace metals, and potential for uptake of these elements by crops was investigated by analyzing soils from farm fields near Oklahoma City. Total, extractable (by the Modified Morgan test), and water-soluble elements, including macronutrients and trace metals, were measured in biosolids-amended soils and, for comparison, in soils that had received little or no biosolids. Soil testing showed that the biosolids-amended soils had higher pH and contained greater concentrations of organic carbon, N, S, P, and Ca than the control soils. Soil extractable P concentrations in the biosolids-amended soils averaged at least 10 times the recommended upper limit for agricultural soils, with P in the amended soils more labile and soluble than the P in control soils. Several trace elements (most notably Zn, Cu, and Mo) had higher total and extractable concentrations in the amended soils compared to the controls. A radish plant assay revealed greater phytoavailability of Zn, P, Mo, and S (but not Cu) in the amended soils. The excess extractable and soluble P in these biosolids-amended soils has created a long-term source of slow-release P that may contribute to the eutrophication of adjacent surface waters and contamination of groundwater. While the beneficial effects of increased soil organic carbon on measures of “soil health” have been emphasized in past studies of long-term biosolids application, the present study reveals that these benefits may be offset by negative impacts on soils, crops, and the environment from excessive nutrient loading.
... Numerous studies have focused on the effects of short-term metal toxicity on earthworms in freshly spiked soil (OECD, 1984;Martikainen, 1996;Lowe and Butt, 2007). Furthermore, information collected from laboratory studies may be impractical (OECD 222, 2004;McBride et al., 2009). Alterations in earthworm community structure and abundance can accurately re ect the metal toxicity in elds Huang et al., 2020), where metal contamination often comprises a mixture of contaminants (Pascaud et al., 2014). ...
Preprint
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In this study, we examined the influence of soil properties (pH, total potassium (TK), available potassium (AK), total nitrogen (TN), total phosphorus (TP), available potassium (AP), cation exchange capacity (CEC), and soil organic carbon (SOC)), and metals (Cd, Pb, Cu, and Zn) on the density, diversity, and species composition of earthworms in the Hebei Province, North China. In total, 535 earthworms were collected from 20 sites in the study area, and belonged to three families, six genera, and ten species. Amynthas hupeiensis (39.4%) and Drawida gisti (37.8%) were the dominant species. The correlations between soil variables and earthworm composition determined using redundancy analysis indicated that SOC, TK, and AK enhanced earthworm density (total, adult, and juvenile) and species ( A. hupeiensis and D. gisti ) abundances. Earthworm composition remained unaffected by the metals (Cd and Pb) in the uncontaminated sites; in contrast, species were absent in areas with high metal concentrations (S19 and S20). Soil TN content was negatively and positively related to Shannon and Peilou indexes ( p <0.05), respectively, indicating that TN may be pivotal in influencing earthworm diversity and species evenness. Overall, the soil properties such as K, SOC, and TN were the key variables affecting earthworm density, diversity, and species dominance.
... The fate and bioavailability of heavy metals in soil are dependent on the physicochemical properties of soil, organic matter content, metal speciation, plant type, and the potential measures of heavy metals (Olaniran et al., 2013). Numerous methods, including chemical extractants such as chelating agents (DTPA-TEA, EDTA) and acid solutions (HNO 3 ,HCl), have been used to assess the efficiency of metals availability measurements (McBride et al., 2009). ...
Article
Full-text available
The purpose of this study was to assess and validate measures of cadmium (Cd), lead (Pb), and zinc (Zn) bioavailability in a contaminated calcareous soil treated with sewage sludge (0, 10, and 30 g kg ⁻¹) under peppermint (Mentha pipertia L.) cultivation using new allylagarose-assembled diffusive gradients in thin-films technique (DGT). To achieve the best gel composition, various diffusive hydrogels were made from different amounts of acrylamide monomer (15, 20, and 25%) and allylagarose cross-linker (0.3, 0.4, and 0.6%). The DGT assembled with 15% acrylamide and 0.3% allylagarose was the best hydrogel based on the obtained swelling rate (3.2) and diffusion coefficients of Cd (5.81 ×10 cm ² s⁻¹), Pb (8.07 cm ² s⁻¹), and Zn (6.13 cm ² s⁻¹). Sewage sludge application increased resupply (R-value) and effective concentration (CE) of Cd, Pb, and Zn. The highest amounts of CE-Zn (2202 μg l⁻¹), Cd (982.5 μg l⁻¹), and Pb (1847 μg l⁻¹) were observed in soil treated with 30 g kg ⁻¹ sewage sludge. Comparison of correlation revealed that 0.3% allylagarose-measured CE-Zn and Pb had a significant logarithmic correlation with the corresponding plant metals concentrations, while CE-Cd was linearly correlated with the plant Cd concentration. These results support the conclusion that the combination of 15% acrylamide and 0.3% allylagarose as a diffusive gel in DGT is a robust gel to predict metal bioavailability and can be reliably used to replace the patented gel cross-linked with agarose.
... In recent decades, several studies attempted to predict the so-called phytoavailable metal fraction by correlating plant responses with various soil metal pools. It is generally thought that metal soluble fractions-extracted by chemically nonaggressive neutral salts-are useful for assessing metal phytotoxicity in contaminated soils (Kabata-Pendias 2004;McBride et al. 2009). Indeed, our recent study with soils near a Cu smelter in central Chile (Lillo-Robles et al. 2020) suggests that salt-extractable (i.e., exchangeable) Cu was the best indicator of metal phytotoxicity in soil, whereas total soil Cu was not a good predictor of plant responses. ...
Article
Root elongation method may be implemented using two internationally accepted protocols: exposing plants to either soil-water extract or whole soil. But which of the two protocols is more suitable for root elongation analysis undertaken for the quality assessment of metal-polluted soils? Soils were sampled at various distances from the site of the Middle Urals Copper Smelter located in Russia. White mustard was used as a bioindicator. We observed considerable differences in root elongation under the two protocols. In plants grown in whole soil, root length inversely correlated with pollution index, but in soil-water extract, metal concentrations had no effect on root length. Nutrient and metal concentrations in the soil-water extract were not buffered, due to the absence of the solid soil phase. It is for this reason that in highly polluted soils, root growth was greater in soil-water extracts rather than in whole soils, whereas in background soils (in the absence of toxicity), root growth was greater in whole soils compared with soil-water extracts. The quantity, intensity, and capacity factors are a plausible explanation for the differences in root length between the two protocols. The soil-water extract does not represent actual soil with respect to the desorption-dissolution reactions that take place between the soil solid phase and the soil solution. For this reason, whole soil protocol should be used for measuring root elongation given that only under this protocol, direct contact between metal-polluted soil and test organisms correctly replicates the risks inherent in the actual soil habitat.
... In general, soil total metal concentration is of little use of assessing metal bioavailability and plant uptake (Ciadamidaro et al., 2017;McBride et al., 2009) whereas concentration or activity in the soil so lution, regarded as an 'intensity' factor, provide the best predictors for plant uptake and toxicity (Black et al., 2011;Zhang et al., 2015). However, in the present study, as seen in Fig. 6 (and Fig. S2-S5), there was hardly any difference amongst the contrasting estimates of soil metal availability. ...
Article
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Biosolids application to arable land is a common, and cost-effective, practice but the impact of prolonged disposal remains uncertain. We evaluated the dynamics of potentially toxic elements (PTEs) at a long-established 'dedicated' sewage treatment farm. Soil metal concentrations exceeded regulations governing application of biosolids to non-dedicated arable land. However, measurement of isotopic exchangeability of Ni, Cu, Zn, Cd and Pb demonstrated support for the 'protection hypothesis' in which biosolids constituents help immobilise potential toxic metals (PTMs). Metal concentrations in a maize crop were strongly, and almost equally, correlated with all 'capacity-based' and 'intensity-based' estimates of soil metal bioavailability. This was attributable to high correlations between soil factors controlling bioavailability (organic matter, phosphate etc.) on a site receiving a single source of PTMs. Isotopic analysis of the maize crop suggested contributions to foliar Pb from soil dust originating from neighbouring fields. There was also clear evidence of metal-specific effects of biosolids on soil metal lability. With increasing metal concentrations there was both decreasing lability of Cd and Pb, due to interaction with increasing phosphate concentrations, and increasing lability of Ni, Cu and Zn due to weaker soil binding. Such different responses to prolonged biosolids disposal to arable soil should be considered when setting regulatory limits.
... Bioavailability of heavy metals in soils can be analyzed using chemical extraction including single extraction and sequential fractionation (Basta and Gradwohl, 2000). Chemical extractants include acids, salt solutions, buffer solutions, and chelating agents (McBride et al., 2009;Hodson et al., 2011). Sequential fractionation such as BCR and Tessier sequential extraction is often used to examine the redistribution or partitioning of heavy metals in various chemical forms, including soluble, adsorbed, precipitated, and organic forms. ...
Article
Heavy metal contamination of agricultural soils poses risks and hazards to humans. The remediation of heavy metal-polluted soils has become a hot topic in environmental science and engineering. In this review, the application of clay minerals for the remediation of heavy metal-polluted agricultural soils is summarized, in terms of their remediation effects and mechanisms, influencing factors, and future focus. Typical clay minerals, natural sepiolite, palygorskite, and bentonite, have been widely utilized for the in-situ immobilization of heavy metals in soils, especially Cd-polluted paddy soils and wastewater-irrigated farmland soils. Clay minerals are able to increase soil pH, decrease the chemical-extractable fractions and bioavailability of heavy metals in soils, and reduce the heavy metal contents in edible parts of plants. The immobilization effects have been confirmed in field-scale demonstrations and pot trials. Clay minerals can improve the environmental quality of soils and alleviate the hazards of heavy metals to plants. As main factors affecting the immobilization effects, the pH and water condition of soils have drawn academic attention. The remediation mechanisms mainly include liming, precipitation, and sorption effects. However, the molecular mechanisms of microscopic immobilization are unclear. Future studies should focus on the long-term stability and improvement of clay minerals in order to obtain a better remediation effect.
... However, it is well known that total metal concentration in soil is not sufficient to predict its potential phytotoxicity (McBride, 1994;Sauvé et al., 1998;Ginocchio et al., 2002;ISO 17402, 2008). It is generally considered that metal soluble fractions, extracted by chemically nonaggressive neutral salts, are more useful for assessing metal phytotoxicity in contaminated soils (Ginocchio et al., 2002;Kabata-Pendias, 2004;McBride et al., 2009). Indeed, our recent study (Lillo, 2019) demonstrated that exchangeable Cu was a good indicator of phytotoxicity, whereas the effect of total Cu was not significant, in the soils of the Puchuncaví valley. ...
Article
The townships of Puchuncaví and Quintero, on the coast of central Chile, have soils contaminated by atmospheric deposition of sulfur dioxide and trace elements from the nearby Ventanas Industrial Complex. The purpose of this study was to evaluate potential human health and ecological risks, by determining the spatial distribution of soil total concentrations arsenic (As), copper (Cu), lead (Pb), and zinc (Zn) in these townships. Total concentrations of these elements were determined in 245 topsoil samples, used to generate continuous distribution maps. The background concentrations of Cu, As, Pb, and Zn in the studied soils were 100, 16, 35, and 122 mg kg-1, respectively. The concentrations of Cu, As, and Pb were positively correlated with each other, suggesting that their source is the Ventanas copper smelter. On the other hand, correlations for Zn were weaker than for other trace elements, suggesting low impact of the Ventanas copper smelter on spatial distribution of Zn. Indeed, only 6% of the study area exhibited Zn concentrations above the background level. In contrast, 77, 32 and 35% of the study area presented Cu, As, and Pb concentrations, respectively, above the background level. The carcinogenic risk due to exposure to As was above the threshold value of 10-04 in the population of young children (1-5 years old) on 27% of the study area. These risk values are classified as unacceptable, which require specific intervention by the Chilean government. Based on the estimated concentrations of exchangeable Cu, 10, 15, and 75% of the study area exhibited high, medium, and low phytotoxicity risk, respectively.
... Cd bioavailability and its fraction can be determined by using several chemical extraction and bioassay procedures to assess the bioaccessible fraction. Single chemical extraction by (0.01 M CaCl 2 ) (Fig. 2), glacial acetic acid extraction, mineral acids (1 M HCl), NH 4 NO 3 extraction, chelating agents (EDTA), and buffer solutions (1 M NH 4 OAc) are chemical extractants used in the single extraction procedure for assessing bioavailability in Cd-contaminated soils (McBride et al., 2009;Bakircioglu et al., 2011). ...
... Nowadays, it still remains the question about which is the most adequate extractant for soil metal phytotoxicity estimation. Currently, some extractants such as DTPA and Mehlich 3 can efficiently be used to diagnose nutrient deficiency, but they are not so efficient for the identification of phytotoxicity (McBride et al., 2009;Chang et al., 2014). Nagajyoti et al. (2010) concluded that there is a lot of emphasis on experimental research concerning metals in soils fertilized with municipal residues. ...
... It is generally considered that metal exchangeable frac- tionsdextracted by chemically-nonaggressive neutral saltsdare useful for assessing metal phytotoxicity in contaminated soils ( Kabata-Pendias, 2004;McBride et al., 2009). In this study, Fig. 1. ...
... Most common single extraction reagents include weak salt solutions of calcium chloride, sodium nitrate, and ammonium nitrate, which are also known as unbuffered mild extractants or neutral salt solutions, and have been recommended as the best "general purpose" soil extractants for the estimation of phytoavailability (McBride et al., 2009;Menzies et al., 2007;Rao et al., 2008). Also, Melich3, rhizosphere-based methods (mixture of low-molecular weight organic acids), and passive sampling devices (such as diffusive gradients in thin films and "rhizon" pore water samplers) have been widely used to determine trace element bioavailability in contaminated soils (Davidson, 2013;Moreno-Jiménez et al., 2011). ...
Chapter
There are a number of strategies employed for mine site rehabilitation that, in opposition to conventional remedial approaches, which involve the removal of contaminated soil or its capping with an impermeable layer, are based on in situ technologies of soil remediation. The main aim of these in situ technologies is to reduce trace element mobility, which can be achieved by raising soil pH, adding amendments and/or establishing a sustainable plant cover. Because of that, the soil retention function is usually monitored using conventional chemical tests and extraction procedures. However, strategies to monitor mine soil rehabilitation should take into account the soil´s physical, chemical and biological properties. In this respect, the benefits and risks from their application must be evaluated not only in terms of soil physicochemical characteristics but also regarding relevant bioassays that can assess soil health and the restoration of soil processes and ecosystem services. This chapter describes different tests for the assessment of mine site rehabilitation, from traditional chemical and physical tests, to more recently proposed toxicological and biological assays that include a range of ecological receptors, endpoints and relevant exposure pathways, which are recommended to be used in a complete soil health assessment. For the improvement of ecological risk assessment as the most suitable decision-making tool, we should address two challenges: (i) to take into account not only the total concentration of contaminants but also the bioavailable fractions and (ii) to incorporate ecological data from ecological receptors as well as the more traditional toxicological data.
... It has been generally accepted that phytotoxicity of a metal is related to its free ion activity in the solution to which the plant root is exposed (Lund 1990;Parker and Pedler 1997) and also to soluble metal-organic complexes and metal-inorganic ligand complexes (Smolders and McLaughlin 1996;Huang et al. 1997;Jones 1998). Recent studies have also shown that less aggressive reagents that extract predominantly soluble and exchangeable fractions, most notably, dilute salt solutions such as 0.01 M CaCl 2 , are frequently better at predicting plant availability of excess heavy metals in soils than the traditional, more aggressive tests involving the use of reagents such as hydrochloric acid, diethylene triaminepentaacetic acid, and ethylene diamine tetraacetic acid (Houba et al. 2000;McBride et al. 2003McBride et al. , 2009Menzies et al. 2007;Meers et al. 2007). After a comprehensive review of literature, McLaughlin et al. (2000) concluded that soil tests based on the determination of the most easily extractable metal pools (like the neutral dilute salt-extractable fraction) appear to reflect the current toxicity better than total metal concentrations or the amounts of metals removed by strong extractants. ...
Chapter
Impact assessment of pollution is important step towards initiating appropriate remedial measures. However impact of soil pollution may not necessarily be uniform across the agro-ecological regions due to complex relationship among soil types, climate, crop types, nature and level of contamination as well as soil and crop management methodologies adopted. Moreover land resources are habitat of numerous organisms having varying degree of sensitivity towards contaminants. Hence, choosing right approach for assessing impact of pollution becomes important for satisfying various stakeholders affected by soil pollution. This chapter covers different types of impact of pollution on soil quality, economic yield of crop, food quality, biodiversity, fertilizer nutrient use efficiency, economy of the country etc. Pollution has already made adverse impacts on environment including soil in different countries. Widely cited instances of different types of pollution across the world and their impacts on soil and crop has also been discussed in this chapter.
... It can also form soluble chelation complexes with amino acids and multidentate organic acids such as ethylenediaminetetraacetic acid. Zinc is essential to maintain a good health but increased concentrations may cause skin irritations, vomiting, nausea and stomach cramps [65]. Even higher concentrations cause liver damage, respiratory disorders and disturb protein metabolism [66]. ...
Chapter
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Mining, manufacturing, industrialization and the use of synthetic products have resulted in heavy metal contamination of all the segments of environment. Due to their non-biodegradability, it is very difficult to eliminate metals from the environment. Their sources can be categorized as natural and anthropogenic activities. Natural sources are seepage and weathering from rocks, volcanic activity and forest fires. Some of the heavy metals like Cr, Cd, Se, Pb, As, Hg, Cu, Co, Ni and Zn are of severe concern for the researchers in terms of their environmental load and health effects. Several scientific groups, chemical engineers, and environmentalists are making several attempts for minimizing the effects caused by excessive release of heavy metals in the environment and on human being. Therefore, different remediation technologies such as phytoremediation, adsorption, ion-exchange, coagulation, precipitation, flocculation, ultra-filtration and electrochemical methods have been developed and applied for the scavenging of the toxic metals. In the present chapter, a thorough discussion about the sources, adverse impacts on living beings as well as on environment and the remediation technologies of heavy metals have been systematically compiled.
Chapter
This chapter explores the analytical methods currently available for the measurement of heavy metal content in soils, ranging from well-established techniques routinely applied in laboratories worldwide, to newly emerging approaches, and with emphasis on the need to select strategies that are ‘fit-for-purpose’ in terms of the information required. Included are guidelines for field sampling and for the storage of samples and avoidance of contamination. Brief information is provided on analytical techniques directly applicable to solid samples including neutron activation analysis, laser-induced breakdown spectrometry and X-ray-based methods. Suitable approaches to sample extraction for different situations are summarised (total digestion, pseudototal digestion, single and sequential extraction) together with examples of procedures involving hot-plate, block, bomb, and microwave apparatus. The use of extractants to assess (plant) bioavailability or (human) bioaccessibility of heavy metals in soils is discussed. Details are provided of the various types of atomic spectrometry that nowadays serve as ‘workhorses’ for trace metal determination in environmental chemistry, with particular emphasis on their principles, strengths, limitations and applicability. Included are flame and electrothermal atomic absorption spectrometry, inductively coupled plasma atomic emission spectrometry and inductively coupled plasma mass spectrometry. The chapter also provides a brief introduction to the vast topic of speciation analysis, an area of particular interest for metals that can occur in different oxidation states e.g. Cr, or that have environmentally important organometallic forms e.g. Hg. Finally, some recommendations are given on strategies that researchers should adopt whenever possible to improve the quality of their analytical data.
Article
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Toxic metalliferous mine-tailings pose a significant health risk to ecosystems and neighboring communities from wind and water dispersion of particulates containing high concentrations of toxic metal(loid)s (e.g., Pb, As, Zn). Tailings are particularly vulnerable to erosion before vegetative cover can be reestablished, i.e., decades or longer in semi-arid environments without intervention. Metal(loid) speciation, linked directly to bioaccessibility and lability, is controlled by mineral weathering and is a key consideration when assessing human and environmental health risks associated with mine sites. At the semi-arid Iron King Mine and Humboldt Smelter Superfund site in central Arizona, the mineral assemblage of the top 2 m of tailings has been previously characterized. A distinct redox gradient was observed in the top 0.5 m of the tailings and the mineral assemblage indicates progressive transformation of ferrous iron sulfides to ferrihydrite and gypsum, which, in turn weather to form schwertmannite and then jarosite accompanied by a progressive decrease in pH (7.3 to 2.3). Within the geochemical context of this reaction front, we examined enriched toxic metal(loid)s As, Pb, and Zn with surficial concentrations 41.1, 10.7, 39.3 mM kg⁻¹ (3080, 2200, and 2570 mg kg⁻¹), respectively. The highest bulk concentrations of As and Zn occur at the redox boundary representing a 1.7 and 4.2 fold enrichment relative to surficial concentrations, respectively, indicating the translocation of toxic elements from the gossan zone to either the underlying redox boundary or the surface crust. Metal speciation was also examined as a function of depth using X-ray absorption spectroscopy (XAS). The deepest sample (180 cm) contains sulfides (e.g., pyrite, arsenopyrite, galena, and sphalerite). Samples from the redox transition zone (25-54 cm) contain a mixture of sulfides, carbonates (siderite, ankerite, cerrusite, and smithsonite) and metal(loid)s sorbed to neoformed secondary Fe phases, principally ferrihydrite. In surface samples (0-35 cm), metal(loid)s are found as sorbed species or incorporated into secondary Fe hydroxysulfate phases, such as schwertmannite and jarosites. Metal-bearing efflorescent salts (e.g., ZnSO4·nH2O) were detected in the surficial sample. Taken together, these data suggest the bioaccessibility and lability of metal(loid)s are altered by mineral weathering, which results in both the downward migration of metal(loid)s to the redox boundary, as well as the precipitation of metal salts at the surface.
Article
Soil trace metal ecotoxicity testing requires a set of soil samples with increasing metal concentrations that are otherwise chemically similar. Leaching samples amended with soluble metal salts has been proposed as a means to reduce chemical artefacts of the spiking procedure (i.e., salt effect), thereby improving their environmental relevance. Demonstrating with copper (Cu), we proposed a spike/leach procedure whereby metal solutions were added to test soils over 5 days and subsequently leached with dilute nutrient solutions until the electrical conductivity in leachates stabilized. During the 5 days of Cu additions, pH in leachates from Cu-spiked samples decreased by up to 0.90 pH units and showed up to 30- and 25-fold increases in calcium (Ca) and magnesium (Mg) concentrations, indicative of the salt effect. Leaching removed the excess acidity and dissolved cations and minimized the differences in leachate pH, Ca, Mg, aluminum (Al), iron (Fe), manganese (Mn), and dissolved organic carbon (DOC) concentrations between control and Cu-spiked samples. Leaching also reduced dissolved Cu concentrations in spiked samples by up to an order of magnitude, resulting in more environmentally relevant concentrations than were achieved prior to leaching.
Article
In the present study, a laboratory experiment was designed to compare the 0.01 mM calcium chloride (CaCl2) and diethylenetrinitrilopentaacetic 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 multi systems. Different order of metals extractability was found in binary and multi systems for both extraction methods. Solid/solution distribution coefficient (Kd), 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 multi systems, the average Kd (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 Kd, implying a relative higher mobility in these calcareous soils. The Visual Minteq indicated that 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.
Article
Soil leaching has been proposed as a way to reduce soil-spiking artefacts (i.e., increased acidity, metal solubility) that occur in soils amended with trace metal salts. Leaching metal-spiked samples prior to ecotoxicity testing is therefore expected to reduce toxicity, however, leaching not only removes excess amounts of the trace metal being tested, but also reduces the concentrations of cations that could decrease the toxic effects of the metal of interest. To clarify these conflicting processes, the effects of leaching on toxicity and bioaccumulation of Cu, Ca and Al, were investigated using 14-d plant assays conducted on leached and non-leached, Cu-spiked soils. The median inhibitive concentration (EC50) to root elongation ranged from 78 to 589 µg/g. Leaching was found to reduce toxicity by 1.2- to 2.1-fold. The Cu(2+) activity predicted toxicity better than root or shoot Cu concentrations which were generally not affected by leaching. Plant uptake of Ca increased with increasing Cu dose in non-leached samples, which likely contributed to the hormesis-like response observed in these samples, whereas Ca uptake in the leached samples was more consistent with that of the control except at the largest Cu doses for which Ca uptake decreased. Surprisingly, Al uptake in the most acidic soil was greater in leached than non-leached samples, which may have contributed to the greater toxicity exhibited in this soil than was predicted by Cu(2+) activity. These findings have implications for predicting trace metal toxicity in nutrient-stressed, acidic soils. Environ. Toxicol. Chem. © 2013 SETAC.
Article
Solubilizing experiments were carried out to evaluate the ability of biodiesel to remove polycyclic aromatic hydrocarbons (PAHs) from highly contaminated manufactured gas plant (MGP) and PAHs spiked soils with hydroxypropyl-β-cyclodextrin (HPCD) and tween 80 as comparisons. Biodiesel displayed the highest solubilities of phenanthrene (420.7 mg·L−1), pyrene (541.0 mg·L−1), and benzo(a)pyrene (436.3 mg·L−1). These corresponded to several fold increases relative to 10% HPCD and tween 80. Biodiesel showed a good efficiency for PAH removal from the spiked and MGP soils for both low molecular weight and high molecular weight PAHs at high concentrations. Biodiesel was the best agent for PAH removal from the spiked soils as compared with HPCD and tween 80; as over 77.9% of individual PAH were removed by biodiesel. Tween 80 also showed comparable capability with biodiesel for PAH solubilization at a concentration of 10% for the spiked soils. Biodiesel solubilized a wider range of PAHs as compared to HPCD and tween 80 for the MPG soils. At PAH concentrations of 229.6 and 996.9 mg·kg−1, biodiesel showed obvious advantage over the 10% HPCD and tween 80, because it removed higher than 80% of total PAH. In this study, a significant difference between PAH removals from the spiked and field MGP soils was observed; PAH removals from the MGP soil by HPCD and tween 80 were much lower than those from the spiked soil. These results demonstrate that the potential for utilizing biodiesel for remediation of highly PAH-contaminated soil has been established. Keywordspolycyclic aromatic hydrocarbons (PAHs)-biodiesel-soil-removal-solubilization
Article
Leaching metal-spiked samples has been proposed as a means to reduce the artifacts of the spiking procedure (e.g., salt effect, increased metal solubility) that can artificially increase metal bioaccessibility and toxicity in laboratory ecotoxicity tests. The effects on soil chemistry from leaching Cu-spiked samples were investigated by comparing chemistries of freshly spiked samples to samples that underwent the spike/leach procedure. Chemical parameters investigated included electrical conductivity (EC), pH, ethylenediaminetetraacetic acid- and CaCl(2) -extractable Cu, soil-solution Cu, Cu(2+) activity (estimated using Visual MINTEQ), and other solution parameters (dissolved organic carbon [DOC], Ca, Mg, Al). In leached samples, the electrical conductivity values of the spiked samples did not vary significantly from those of the control samples (p > 0.05), confirming that the leaching procedure had sufficiently minimized the salt effect. In the range of soil Cu concentrations where Cu ecotoxicity is expected, the pH in freshly spiked samples was as much as 0.52 units lower than the pH from leached samples at the same total-soil Cu concentration. The CaCl(2) -extractable fraction was up to 2.3-fold smaller in leached samples and inversely related to the pH of the spiked soil. Despite little to no difference in soil-solution Cu, up to 100-fold less Cu(2+) activity was observed in leached samples. Reduced Cu(2+) activity was related to less Al(3+) competition for DOC. Leaching resulted in solution chemistries that were more consistent with those of the control samples and reduced the artifacts of traditional soil-spiking procedures. Environ. Toxicol. Chem. 2012; 31: 2253-2260. © 2012 SETAC.
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This study attempts to identify the soil properties controlling the fractionation of copper into various soil pools and determine the influence of pH and metal loading on soil-solution free copper activity (pCu2+). The pCu2+ was determined in 0.01 M CaCl2 soil extracts using a copper ion selective electrode. We analyzed a wide variety of soils: urban, agricultural and forest soils from the Province of Qubec, New York State and Denmark. The pCu2+ ranged from 12.21 to 6.18. The relationships among pCu2+, total soil copper, total dissolved copper and soil pH are studied for their variability within and between sites as well as for the whole data set. Regression equations are presented for predicting soluble copper as a function of total soil copper and also for predicting pCu2+ as a function of total soil copper and soil pH.
Article
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L'évaluation de la biodisponibilité des métaux en traces du sol intéresse deux grands domaines d'application : d'une part, le diagnostic de fertilité chimique basé sur l'établissement de seuils de carence, employé depuis plusieurs décennies dans différents pays ; d'autre part, l'estimation du risque de phytotoxicité ou de contamination de la chaîne alimentaire qu'entraîne la pollution du sol par les éléments en traces. Dans ce cas, très peu de pays sont allés jusqu'à l'élaboration de références de diagnostic. Afin de guider le choix d'une méthode d'extraction chimique pour permettre l'ébauche de telles références en France, une synthèse bibliographique a été entreprise. Elle reprend les principaux résultats obtenus depuis les vingt dernières années concernant l'évaluation de la biodisponibilité de Cd, Cu, Zn, Pb, Cr et Ni. De cette étude, il ressort que les solutions salines non tamponnées semblent les mieux adaptées à l'estimation rapide du transfert des éléments du sol aux végétaux et à la mise au point de valeurs guides permettant de statuer quant aux risques de toxicité susceptibles d'être engendrés par des sites pollués. Suitability of chemical extraction to assess risks of toxicity induced by soil trace metal bioavailability. The prediction of soil trace metal bioavailability using extractions has two direct applications: i) evaluation of soil chemical fertility and nutrient deficiency, as has been used widely in different countries for many years; and ii) risk assessment of phytotoxicity and contamination of the food chain induced by polluted soils. In this latter case, few countries have defined guide values. In order to choose one of the extraction methods proposed in the literature, and then define such references for France, a review of research concerning the chemical estimation of Cd, Cu, Zn, Ni, Cr and Pb plant uptake in the last twenty years was undertaken. In conclusion, the use of unbuffered salt solutions seems to be the most suitable way to i) estimate trace element transfert from polluted soil to plant and ii) define guide values for risk assessment.
Article
The DTPA soil test was originally developed to identify near-neutral and calcareous soils with insufficient available Zn, Fe, Mn, and Cu for maximum yields of crops. It apparently draws on labile pools it was designed to extract and correlates well with plant micronutrient concentrations when the soil metal levels are neither too high nor too low. The soil test reliably reflects metal loadings to soils supplied in a variety of forms, but may not reliably predict plant metal concentrations expected from increased soil loadings. The successes or failures of the soil test noted in the literature can be explained as correct uses or misuses, respectively, of the test. The soil test is best used to identify micronutrient deficient, near-neutral, and calcareous soils. Whenever one strays from the original design of the test, one should be aware of the possible consequences and pass that awareness on to others.
Article
Soil testing for metal contaminants is a continually evolving process aimed at improving the assessment of environmental and human health hazards associated with heavy metals in soils and plants. A number of challenges present themselves before accurate, reliable and precise contaminant hazard assessment criteria for soils and plants can be made. These include: sampling, extraction and analytical obstacles associated with the determination of trace levels of metals in environmental media; quality assurance and quality control issues associated with both extraction and analytical procedures (especially for metals where non‐compliance with regulatory standards may be penalised); and confounding environmental effects (e.g. rooting depth, soil salinity, Eh, pH, plant species, metal species) which limit the usefulness of the relationship between the current tests and actual hazards. These difficulties have combined to produce soil tests for heavy metals often poorly correlated with hazardwhether this be crop uptake of a contaminant (e.g. Cd), or the adverse effects of metals or metalloids on human or environmental health (e.g. As, Cr, Cu, Hg, Ni, Se, Pb, Zn). Assessment of an “available” fraction of a particular soil nutrient is the accepted norm of soil testing for crop nutrition. In many countries, assessment of metal hazard is still inappropriately based on the total soil metal concentration, despite increasing recognition that the concept of elemental availability is just as relevant for environmental hazard as for crop nutrition. Tests that aim to assess metal “bioavailability” are now gaining widespread acceptance by regulators as a means to characterise hazards from contaminants in soil. While a significant advance on the use of total metal concentrations, the concept raises difficulties in providing an adequate assessment of potential risk, due to changes in environmental conditions which affect bioavailability, e.g. soil pH, soil organic matter content. This chapter summarises current soil testing methodologies for metal contaminants and examines new concepts and procedures for assessing hazards from metal contamination of soils.
Article
With the availability of sensitive multielement analytical capability, it is no longer essential to use chemically aggressive soil tests to extract measurable levels of most trace elements. However, the relative abilities of mild and aggressive extractants to assess metal bioavailability in soils have rarely been compared. A greenhouse experiment was carried out to compare a mild soil extractant (hot 0.01 M CaCl2) with an aggressive one (Mehlich 3) for predicting accumulation of trace metals by red clover (Trifolium pratense L.). Clover was grown on large columns of nonacid fine-textured and acid coarse-textured soils that had been amended several years earlier by a heavy application of sewage sludge products, and pH was subsequently adjusted using CaCO3 or H2SO4. The soil extractants (CaCl2 and Mehlich 3) and clover tissue were analyzed for trace metals (As, Cd, Mo, Cu, Ni, Mn, Pb, and Zn) by axial-view ICP spectrophotometry. Linear regression analyses were performed to relate the concentration of each trace element in the red clover tissue to the concentration extracted from the soil. The results indicate that CaCl2 extraction is more reliable than Mehlich 3 extraction when evaluating plant availability of trace elements in soils with a wide range of properties (especially pH). The strongly acidic nature of the Mehlich 3 extractant caused large quantities of metals such as Zn, Cd, Cu, and Ni to be extracted from metal-contaminated soils even when the plant availability of these metals was low because of near-neutral soil pH or high clay and organic matter content. Conversely, in coarse-textured and acid soils containing lower total concentrations of metals, plant-available metals were often relatively high, yet Mehlich 3 frequently extracted smaller quantities of metals from these soils than from the near-neutral soils. We conclude that dilute CaCl2 is preferable to Mehlich 3 as a universal soil extractant for estimating short-term trace metal availability to crops.
Article
Environmental risk assessment of metals depends to a great extent on modeling the fate and the mobility of metals based on soil−liquid partitioning coefficients. A large variability is observed among the reported values that could be used to predict metal mobility and bioavailability. To evaluate this, soil−liquid partitioning coefficients (Kd) for many elements but especially for the metals cadmium, copper, lead, nickel, and zinc were compiled from over 70 studies of various origins collected from the literature. The relationships between the reported values are explored relative to variations in soil solution pH, soil organic matter (SOM), and concentrations of total soil metal. The results of multiple linear regressions show that Kd values are best predicted using empirical linear regressions with pH (with R 2 values of 0.29−0.58) or with pH and either the log of SOM or the log of total metal and with resulting R 2 values of 0.42−0.76. A semi-mechanistic model based on the competitive adsorption of metal and H+ [dependent on solution pH, total metal content, and log(SOM)] was a better tool to predict dissolved metal concentrations (with R 2 values of 0.61−0.88), with the exception of Pb (at 0.35).
Article
In Western Europe, policy makers are currently moving towards a more integrated risk-based approach of soil contamination assessment. As part of this approach, selective single extraction procedures have been proposed to add complementary insights regarding heavy metal behaviour and phytoavailability in soils and sediments. However, there is currently a wide range of such procedures available in literature, hampering standardisation and harmonisation of phytoavailability research of heavy metals. The current study examines shoot accumulation of Cd, Cu, Ni, Pb and Zn by the test plant Phaseolus vulgaris in 21 soils, differing in soil composition and level of contamination. On these soils, 12 different commonly used extraction procedures have been compared: soil solution extraction by Rhizon soil moisture samplers, 0.01 M CaCl2, 0.1 M NaNO3, 1 M NH4NO3, 1 M NH4NOAc, 1 M MgCl2, 0.11 M HOAc, 0.5 M HNO3, 0.1 M HCl, DTPA–TEA–CaCl2, EDTA-NH4OAc and aqua regia. The plant species used in this study has previously been proposed as a test plant in a bioassay for assessing heavy metal induced oxidative stress in contaminated soils [Van Assche, F., Clijsters, H., 1990. A biological test system for the evaluation of the phytotoxicity of metal-contaminated soils. Environ. Pollut., 66, 157–172]. Cadmium shoot accumulation correlated best with soil solution concentrations, unbuffered nitrate solutions and the dilute CaCl2 extraction procedure. The same was observed for Zn, yet for this element NH4OAc and MgCl2 also provided significant interactions. The best prediction for Ni was observed in the cluster containing CaCl2 and NH4NO3. For Cd, Zn and Ni, the pseudo-total content and the aggressive chelate based and/or acidic extractants did not correlate well with shoot accumulation. Cu and Pb uptake on the other hand was found to correlate significantly (p = 0.01) with total content as well as with all aggressive extraction procedures over the range of soils used in this experiment. In general, the 0.01 M CaCl2 extraction procedure proved to be the most versatile as it provided a good indication of phytoavailability for all five metals under evaluation.
Article
This publication gives details of laboratory procedures for the determinations of bioavailable (e.g., plants) quantities of nutritional and polluting inorganic elements in 0.01 M CaCl2 extracts of air‐dry soil samples. Air‐day soil samples are extracted for two hours with a 0.01 M CaCl2 solution of 20°C in a 1:10 extraction ratio (W/V). After measuring the pH in the settling suspension, the concentrations of nutritional and polluting elements are measured in the clear centrifugate or filtrate. The procedure is simple, easy to perform, and cheap (labor, chemicals) in daily use in routine soil laboratories. The method receives internationally more and more attention as an alternative for the many extraction procedures for a single nutrient or pollutant that are still in use nowadays. The soil is extracted with a solution what has more or less the same ionic strength as the average salt concentration in many soil solutions. Various nutrients and metals can be measured in a single extract that allows considering relationships between them during interpretation of the data. For most elements, different detection techniques are described in detail in this publication. Detailed laboratory procedures are described for the determination of pH, total dissolved organic carbon, nitrate, ammonium, total dissolved nitrogen, sulphate, total dissolved sulfur, ortho‐phosphate, total dissolved phosphate, sodium, potassium, magnesium, cadmium, copper, nickel, lead, aluminum, iron, arsenic, boron, and phenols. Since only one extract of soil samples is used, profitable use can be made of multi‐element detection techniques like segmented‐flow analysis spectrometry, ICP‐OES, and ICP‐MS.
Article
Copper phytotoxicity in soils is difficult to assess because Cu accumulates at and damages roots, and is not readily transferred to shoots. Soil chemical properties strongly influence Cu speciation, so that total soil Cu alone is not a broadly useful indicator of potential toxicity to plants. The present study measured free Cu2+ activity in Cu-enriched peat soils using the ion selective electrode. The soil Cu2+ activity was related to the severity of phytotoxicity as measured by several indicators in a maize (Zea mays L.) bioassay, including leaf chlorosis, root stunting, and reduced shoot growth and Fe concentration. A soil Cu2+ activity of 10(-7.0) to 10(-7.5), corresponding to total Cu of about 275 mg/kg in the peat soil, caused phytotoxicity in maize seedlings. It is proposed that Cu2+ activity is more directly related to phytotoxic effects than other soil tests, such as extractions with strong acids or chelating agents, because it is the free Cu2+ in soil solution that has the most direct toxic effects on roots. There was very limited uptake of Cu into maize shoots, and even when Cu2+ activity and total soil Cu were raised into the extreme toxicity range of 10(-5) and 4,000 mg/ kg, respectively, shoot Cu remained less than 35 mg/kg. These results indicate the inadequacy of the USEPA risk assessment of potential for Cu toxicity to crops amended with sewage sludge, which assumed a no-effect level of maize shoot Cu of 40 mg/kg.
Article
Virtually all photomultiplier-based inductively coupled plasma spectrometers (ICPS) use the lead (Pb) 220.3-nm analytical line, even though it has severe background continuum and interelement interference from the aluminium (Al) 220.4-nm line, and background shift due iron (Fe). Many Pb analytical lines above 220 nm are unsuitable due to poor detection limits. There are no reports in the literature on the use of Pb analytical lines below 220 nm, especially the 168.2-nm line recommended by Spectro Analytical (Kleve, Germany). The Pb 168-nm analytical line has a superior detection limit and is less prone to matrix, background continuum radiation and inter-element interference from high concentrations of Al and Fe compared to the Pb 220-nm analytical line. This has been demonstrated by the better precision and accuracy of analysis of soils containing high levels of Al and Fe.
Article
Sequential extraction procedures are widely used to estimate the quantity of trace metals bound to different solid fractions in contaminated soils. However, reliability of speciation of trace metals by these procedures remains largely unexamined. In the present study, the selectivity of each extraction step was tested by observing the effect of reversing the extraction order in the procedure. Two different sequential extraction methods and their reversed modes were used for metal fractionation in sewage sludge-amended soils. Significantly increased amounts of extractable metals (Cd, Cu, Pb and Zn) were evident in the sludge-amended soils compared to control soil by all extraction schemes; however, the amounts of metals extracted by each step were strongly dependent on the order of extraction, the type of reagents and the nature of the individual metals. Caution is advised in deducing the forms of soil metals from sequential extraction results from metal-contaminated soils.
Article
Despite its environmental (and financial) importance, there is no agreement in the literature as to which extractant most accurately estimates the phytoavailability of trace metals in soils. A large data set was taken from the literature, and the effectiveness of various extractants to predict the phytoavailability of Cd, Zn, Ni, Cu, and Pb examined across a range of soil types and contamination levels. The data suggest that generally, the total soil trace metal content, and trace metal concentrations determined by complexing agents (such as the widely used DTPA and EDTA extractants) or acid extractants (such as 0.1M HCl and the Mehlich 1 extractant) are only poorly correlated to plant phytoavailability. Whilst there is no consensus, it would appear that neutral salt extractants (such as 0.01 M CaCl(2) and 0.1 M NaNO(3)) provide the most useful indication of metal phytoavailability across a range of metals of interest, although further research is required.
Soil analysis procedures using 0.01 M calcium chloride as extraction reagent A test of sequential extractions for determining metal speciation in sewage sludge-amended soils
  • V J G Houba
  • E J M Temminghoff
  • G A Gaikhorst
  • W Van
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