DTPA Extraction Research Articles

TOTAL AND PLANT AVAILABLE TOXIC TRACE ELEMENTS (Cd, Cr, Co AND Pb) AT FARMS OF EASTERN CROATIA

UDK 631.453(497.5)
 It is well known that soil properties, metal speciation and plant species, especially soil- plant interactions, determine the availability of metals in soils. Therefore, various one- step extraction methods such as EDTA and DTPA have been used to represent the available fraction. In present study we observed the total (aqua regia) and available fraction (EDTA and DTPA) of toxic trace elements (Co, Cd, Cr and Pb) from soil on two farms (Berak and Vinogradci) in eastern Croatia that have different soil properties. The study included 106 soil samples from soil depth 0-30 cm that were collected during 2013- 2014. Samples were analyzed for standard soil properties (pH, organic matter, AL-P, AL- K) as well as for total and available fractions of toxic trace elements. Analyses of main soil properties show vide variety of soils. Soil pH (in H2O) was in range 4.4-8.6 (avg: 6.5), thus sampling sites included range from very acid to alkaline soils. Farm in Berak (average pH was 7.2) had more alkaline soils while farm in Vinogradci was acidic (average pH was 5.9). Organic matter varied from 1.1-2.8% (avg: 1.9), average phosphorous was 17.4 mg/100g and potassium 20.9 mg/100g. Total concentration of trace elements extracted by aqua regia show satisfactory results as not one sample had elevated levels of toxic trace elements (Co, Cd, Cr and Pb). In that regard all sites satisfy Croatian regulation on pollutants in agricultural fields. However, EDTA and DTPA extractions show higher availability of Cr, Co and Pb for both extractions (EDTA and DTPA) at farm in Vinogradci where soils are more acidic compared to farm Berak. Only available Cd was shown to be higher in Berak than in Vinogradci.

The effect of municipal sludge compost on the mobility and bioavailability of Cd in a sierozem-wheat system in an arid region northwest of China

The effect of sewage sludge on the mobility and the bioavailability of trace metals in plant-soil systems have aroused wide interested and been widely explored. Based on a wheat-cultivating experiment, the effect of municipal sludge compost (MSC) on the mobility and bioavailability of Cd in a soil-wheat system was studied. With the application of MSC, soil organic matter (SOM), total nitrogen (TN), and total phosphorus (TP) in the soil increased significantly, while concentrations of trace metals (Cu, Zn, Ni, Pb, Cd) were below the China's minimum thresholds. The application of MSC could improve wheat growth. The application of MSC at the rate of 0.5% had no significant effect on the chemical fraction distribution of Cd in soil. In two soil treatments, Cd mainly existed in the labile chemical fractions (exchangeable chemical fraction (EXCF) and carbonate chemical fraction (CABF)). However, the application of MSC could reduce accumulation of Cd by wheat. Cd contents in each part of the MSC-applied wheat were significantly less than that of non-MSC-applied wheat. In the tested soils, the extractable concentrations decreased in the order: EDTA > MgCl2 ≈ NH4OAc > DTPA. There were no significant differences between soil treatments in the amounts of extractable Cd when the extraction was done under neutral conditions, although significant differences were observed when the extraction was done under alkaline conditions. In this study, the DTPA extraction procedure provided a good indication of Cd bioavailability. Our results suggest that, in the short term at least, amending soils with MSC may benefit crop dry matter production while not increasing the risk of human exposure to Cd through consumption of wheat grown on MSC-amended soils.

Analysing spatio-temporal patterns of archaeological soils and sediments by comparing pXRF and different ICP-OES extraction methods

In this paper we compare six different multi-element sediment analyses for archaeological purposes. Two different sets of samples from archaeological excavations in Germany and Turkey representing feature, mixed-debris and offsite samples are extracted with HNO3, HCl, Aqua Regia (AR), DTPA and NH4NO3, and measured using ICP-OES techniques. The results are compared to each other and the total elemental content obtained by a portable X-ray fluorescence spectrometer (pXRF). DTPA and NH4NO3 extraction were found not to be suitable for multi-element analysis in the archaeological context, as they displayed poor correlations with all other methods. NH4NO3 showed values not reflecting the known settlement activities. AR, HNO3, HCL and pXRF results do reflect the settlement history and are highly correlated. A separation into different sample categories (feature, mixed-debris and offsite) was achieved for all those methods by using multivariate statistics (PCA). pXRF is a cheap and quick procedure which can be easily performed at an excavation site and can thus eliminate cumbersome sample transport. We provide evidence that pXRF is highly suitable for multi-element analysis in the archaeological context.

Ecological restoration of an acidic Cd contaminated soil using bamboo biochar application

Biochar is an organic amendment with good effects on soil properties but its influence on Cd fractionation and growth of vegetable crops (e.g. Chinese cabbage) and field crops (e.g. maize) is still restricted. A pot experiment was conducted to investigate the effect of biochar derived from bamboo residues (pyrolyzed at temperature of 400°C) at four levels (0%, 0.5%, 1% and 1.5%) on Cd solubility and bioavailability, and plant growth in a loamy soil artificially contaminated with Cd at three rates (0, 5 and 50mgkg−1). The soil was strongly acidic (pH=4.63) with low organic carbon content (1.064gkg−1). Chinese cabbage and maize were used as indicator plants in this investigation. Addition of babmboo biochar significantly increased soil pH, electrical conductivity (EC), organic carbon (SOC), and cation exchange capacity (CEC). Concentrations of Cd in CaCl2 and DTPA extractions decreased due to the increase of biochar rates but there were no alterations noticed in total concentrations of Cd in the soil. The acid soluble/exchangeable Cd decreased by 3.35–3.88 times, but the reducible and oxidizable fractions of Cd increased by 1.95–1.96 times and 1.91–2.14 times, respectively, after harvesting cabbage and maize plants in the presence of 1.5% biochar. Changes of soil properties, especially pH could be used as a good reason to illustrate the immobilization of Cd in biochar treated soils. The increase of biochar rates from 0% to 1.5% enhanced the growth of cabbage by 64.23%, 47.31% and 34.93%, and maize by 50.78%, 32.83% and 29.68% in soils treated with Cd at 0, 5 and 50mgkg−1, respectively. Using biochar at a dose of 1.5% diminished concentrations of Cd in cabbage shoots by 4.71–2.29 times and in maize shoots by 5.17–2.68 times, respectively. Our results suggested that bamboo biochar had positive residual effects on maize after the harvest of cabbage. Finally, bamboo biochar, especially at its highest rate (1.5%) could be recommended as a safe amendment in the immobilization of Cd in contaminated agricultural soils and then reduced its threat on the food chain and human health.

Cadmium, lead, and zinc mobility and plant uptake in a mine soil amended with sugarcane straw biochar.

Accumulation of heavy metals in unconsolidated soils can prove toxic to proximal environments, if measures are not taken to stabilize soils. One way to minimize the toxicity of metals in soils is the use of materials capable of immobilizing these contaminants by sorption. Biochar (BC) can retain large amounts of heavy metals due to, among other characteristics, its large surface area. In the current experiment, sugarcane-straw-derived biochar, produced at 700 °C, was applied to a heavy-metal-contaminated mine soil at 1.5, 3.0, and 5.0% (w/w). Jack bean and Mucuna aterrima were grown in pots containing a mine contaminated soil and soil mixed with BC. Pore water was sampled to assess the effects of biochar on zinc solubility, while soils were analyzed by DTPA extraction to confirm available metal concentrations. The application of BC decreased the available concentrations of Cd, Pb, and Zn in the mine contaminated soil leading to a consistent reduction in the concentration of Zn in the pore water. Amendment with BC reduced plant uptake of Cd, Pb, and Zn with the jack bean uptaking higher amounts of Cd and Pb than M. aterrima. This study indicates that biochar application during mine soil remediation could reduce plant concentrations of heavy metals. Coupled with this, symptoms of heavy metal toxicity were absent only in plants growing in pots amended with biochar. The reduction in metal bioavailability and other modifications to the substrate induced by the application of biochar may be beneficial to the establishment of a green cover on top of mine soil to aid remediation and reduce risks.

Biochar application to a contaminated soil reduces the availability and plant uptake of zinc, lead and cadmium

Heavy metals in soil are naturally occurring but may be enhanced by anthropogenic activities such as mining. Bio-accumulation of heavy metals in the food chain, following their uptake to plants can increase the ecotoxicological risks associated with remediation of contaminated soils using plants. In the current experiment sugar cane straw-derived biochar (BC), produced at 700 °C, was applied to a heavy metal contaminated mine soil at 1.5%, 3.0% and 5.0% (w/w). Jack bean (Canavalia ensiformis) and Mucuna aterrima were grown in pots containing soil and biochar mixtures, and control pots without biochar. Pore water was sampled from each pot to confirm the effects of biochar on metal solubility, whilst soils were analyzed by DTPA extraction to confirm available metal concentrations. Leaves were sampled for SEM analysis to detect possible morphological and anatomical changes. The application of BC decreased the available concentrations of Cd, Pb and Zn in 56, 50 and 54% respectively, in the mine contaminated soil leading to a consistent reduction in the concentration of Zn in the pore water (1st collect: 99 to 39 μg L−1, 2nd: 97 to 57 μg L−1 and 3rd: 71 to 12 μg L−1). The application of BC reduced the uptake of Cd, Pb and Zn by plants with the jack bean translocating high proportions of metals (especially Cd) to shoots. Metals were also taken up by Mucuna aterrima but translocation to shoot was more limited than for jack bean. There were no differences in the internal structures of leaves observed by scanning electron microscopy. This study indicates that biochar application during mine soil remediation reduce plant concentrations of potential toxic metals.

Methods to Quantify Nickel in Soils and Plant Tissues

In comparison with other micronutrients, the levels of nickel (Ni) available in soils and plant tissues are very low, making quantification very difficult. The objective of this paper is to present optimized determination methods of Ni availability in soils by extractants and total content in plant tissues for routine commercial laboratory analyses. Samples of natural and agricultural soils were processed and analyzed by Mehlich-1 extraction and by DTPA. To quantify Ni in the plant tissues, samples were digested with nitric acid in a closed system in a microwave oven. The measurement was performed by inductively coupled plasma/optical emission spectrometry (ICP-OES). There was a positive and significant correlation between the levels of available Ni in the soils subjected to Mehlich-1 and DTPA extraction, while for plant tissue samples the Ni levels recovered were high and similar to the reference materials. The availability of Ni in some of the natural soil and plant tissue samples were lower than the limits of quantification. Concentrations of this micronutrient were higher in the soil samples in which Ni had been applied. Nickel concentration differed in the plant parts analyzed, with highest levels in the grains of soybean. The grain, in comparison with the shoot and leaf concentrations, were better correlated with the soil available levels for both extractants. The methods described in this article were efficient in quantifying Ni and can be used for routine laboratory analysis of soils and plant tissues.

Erratum to: Predicting zinc bioavailability to wheat improves by integrating pH dependent nonlinear root surface adsorption

Aim Our aim was to improve the prediction of Zn bioavailability to wheat grown on low-Zn soils. The classical approach that directly relates Zn in a certain soil extract to Zn uptake has been shown to be inadequate in many cases. We tested a stepwise approach where the steps of the uptake process are characterized with, respectively, Zn solid-solution distribution, adsorption of Zn to root surface, Zn uptake into root and Zn translocation to shoot. Methods Two pot experiments were done with wheat grown on nine low-Zn soils varying widely in pH, clay and organic matter content. Soluble Zn concentrations in two soil extracts (DTPA and CaCl2) were measured. Free Zn ion concentrations in CaCl2 soil extracts were determined with the Donnan Membrane Technique. These Zn concentrations were then related to plant Zn uptake following both the direct and the stepwise approach. Results In the direct approach, Zn in the DTPA extract was a better predictor for shoot Zn uptake than Zn in the CaCl2 extract. In the stepwise approach, the relationship between Zn in CaCl2 extracts and the root surface adsorbed Zn was pH-dependent and nonlinear. Root surface adsorbed Zn was linearly related to root Zn uptake, and the latter was linearly related to the shoot Zn uptake. The stepwise approach improved the Zn uptake prediction compared to the direct approach and was also validated for different wheat cultivars. Conclusions The adsorption of Zn on the root surface is pH dependent and nonlinear with respect to the soil Zn concentration, and a useful proxy for bioavailable Zn over a wide range of soils.

Pedogenesis and nickel biogeochemistry in a typical Albanian ultramafic toposequence

This study aimed at relating the variability of Ni biogeochemistry along the ultramafic toposequence to pedogenesis and soil mineralogy. Hypereutric Cambisols dominate upslope; Cambic Vertisols and Fluvic Cambisols occur downslope. The soil mineralogy showed abundance of primary serpentine all over the sequence. It is predominant upslope but secondary smectites dominate in the Vertisols. Free Fe-oxides are abundant in all soils but slightly more abundant in the upslope soils. Whereas serpentines hold Ni in a similar and restricted range in every soil (approx. 0.3%), Ni contents in smectites may vary a lot and Mg-rich and Al-poor smectites in the Vertisol could hold up to 4.9% Ni. Ni was probably adsorbed onto amorphous Fe-oxides and was also exchangeable in secondary smectites. High availability of Ni in soils was confirmed by DTPA extractions. However, it varied significantly along the toposequence, being higher in upslope soils, where Ni-bearing amorphous Fe-oxides were abundant and total organic carbon higher and sensibly lower downslope on the Vertisols: NiDTPA varied from 285mgkg(-1) in the surface of soil I (upslope) to 95.9mgkg(-1) in the surface of Fluvic Cambisols. Concentration of Ni in Alyssum murale shoots varied from 0.7% (Hypereutric Cambisols) to 1.4% (Hypereutric Vertisol). Amazingly, Ni uptake by A. murale was not correlated to NiDTPA, suggesting the existence of specific edaphic conditions that affect the ecophysiology of A. murale upslope.

In situ stabilization of As and Sb with naturally occurring Mn, Al and Fe oxides in a calcareous soil: Bioaccessibility, bioavailability and speciation studies

This study investigated the effectiveness of 6 different types of naturally occurring manganese, aluminum and iron oxides for stabilization of As and Sb in a calcareous soil spiked with 50mgkg−1 of As or Sb and two dosages of treatments (2% and 5%). The resulting contaminated soils were subjected to a series of chemical extraction studies including sequential extraction, single step extraction with DTPA and Simplified Bioaccessibility Extraction Test (SBET) for estimation of bioaccessible fraction of As and Sb in soil and a greenhouse experiment using barley as the test crop. The results showed that Fe-associated and carbonate-bound fraction of As and Sb were predominant fractions. However, the amounts of labile fractions were higher in As contaminated soils, whereas the percentage of Sb associated with crystalline Fe-oxide and residual fractions were higher. The results revealed that application of natural metal oxides reduced DTPA and SBET extractable amounts and plant uptake of As and Sb. After application of amendments, the exchangeable fraction of As decreased dramatically by up to 82% while Sb exchangeable fraction decreased by up to 60% depending upon the additive. The results of chemical extractions and plant uptake confirmed that Sb had lower bioavailability, compared with As.

Total and available heavy metal concentrations in soils of the Thriassio plain (Greece) and assessment of soil pollution indexes

The Thriassio plain is located 25km west of Athens city, the capital of Greece. Two major towns (Elefsina and Aspropyrgos), heavy industry plants, medium to large-scale manufacturing, logistics plants, and agriculture comprise the main land uses of the studied area. The aim of the present study was to measure the total and available concentrations of Cr, Zn, Ni, Pb, Co, Mn, Ba, Cu, and Fe in the top soils of the plain, and to asses soil contamination by these metals by using the geoaccumulation index (I geo), the enrichment factor (EF), and the availability ratio (AR) as soil pollution indexes. Soil samples were collected from 90 sampling sites, and aqua regia and DTPA extractions were carried out to determine total and available metal forms, respectively. Median total Cr, Zn, Ni, Pb, Co, Mn, Ba, Cu, and Fe concentrations were 78, 155, 81, 112, 24, 321, 834, 38, and 16 × 10(3)mg kg(-1), respectively. The available fractions showed much lower values with medians of 0.4, 5.6, 1.7, 6.9, 0.8, 5.7, 19.8, 2.1, and 2.9mg kg(-1). Though median total metal concentrations are not considered as particularly high, the I geo and the EF values indicate moderate to heavy soil enrichment. For certain metals such as Cr, Ni, Cu, and Ba, the different distribution patterns between the EFs and the ARs suggest different origin of the total and the available metal forms. The evaluation of the EF and AR data sets for the soils of the two towns further supports the argument that the EFs can well demonstrate the long-term history of soil pollution and that the ARs can adequately portray the recent history of soil pollution.

Single and Sequential Extraction of Cadmium in Some Highly Calcareous Soils of Southwestern Iran

Thirty-two surface soil samples with different physical and chemical properties were collected from calcareous soils of arid regions of Khuzestan Province, Southwestern Iran. Actual and potential cadmium (Cd) bioavailability was assessed by means of a greenhouse study, two different single extractions: 0.005 DTPA and 0.05 EDTA and two sequential extraction procedures: modified five-step Tessier method and the three-step BCR method. Extraction results were correlated with grain Cd uptake by Durum wheat (Triticum durum L. ) grown under greenhouse conditions. Cadmium in the durum grain ranged from 0.064 to 0.273 mg kg -1 . The results showed better suitability of DTPA extraction in these highly carbonated soils than EDTA extraction for predicting Cd phytoavailability. DTPA –extractable Cd was positively related to soil electrical conductivity (p < 0.01, r = 0.65). Cadmium was predominantly associated with carbonate fraction in these soils (Tessier procedure 40% and BCR 44%).1 M NH 4 OAc which extracted the soluble + exchangeable fraction in the Tessier scheme may also provide useful information on Cd availability in studied soils.

Availability of heavy metals in contaminated soil evidenced by chemical extractants

Heavy metals have been accumulating in Brazilian soils, due to natural processes, such as atmospheric deposition, or human industrial activities. For certain heavy metals, when in high concentrations in the soil, there is no specific extractant to determine the availability of these elements in the soil. The objective of the present study was to evaluate the availability of Cd, Cu, Fe, Mn, Pb and Zn for rice and soybeans, using different chemical extractants. In this study we used seven soil samples with different levels of contamination, in completely randomized experimental design with four replications. We determined the available concentrations of Cd, Cu, Fe, Mn, Pb and Zn extracted by Mehlich-1, HCl 0.1 mol L-1, DTPA, and organic acid extractants and the contents in rice and soybeans, which extracts were analyzed by ICP-OES. It was observed that Mehlich-1, HCl 0.1 mol L-1 and DTPA extractants were effective to assess the availability of Cd, Cu, Pb and Zn for rice and soybeans. However, the same was not observed for the organic acid extractant.

Acúmulo e disponibilidade de cromo, cádmio e chumbo em solos tratados com lodo de esgoto por onze anos consecutivos

The sewage sludge used for agricultural purposes provides many benefits to soil, but it contain harmful elements to environment, that infers in a great attention on its use. The aim of this work was to evaluate the effects of successive applications of sewage sludge on heavy metals accumulation (cadmium, chromium and lead) in samples of soils and corn plants, as well as evaluate the chemicals extractants efficiency in estimate the phyto disponibility of those elements. The experiment was conducted in randomized blocks design in the 2007/08 season, with 4 treatments (0, 5, 10 and 20 Mg ha-1 of sewage sludge) and 5 replicates. It was evaluated: the quantities available of Cd, Cr and Pb in soil by Melich-1, Melich-3 and DTPA extractants; the quantities extracted by corn plants; and the correlation between the disposition and quantities of those metals on whole plants, diagnosis leaves and corn grains. The application of sewage sludge for eleven consecutive years has not showed increase in total quantity nor availability of Cr, Cd and Pb in the evaluated soils. The extractor Melich-1 was the only one that showed significant correlation for availability of Cd, Cr and Pb in soil and corn plants. The correlation of metal availability in soil x leaf diagnosis was significant only for Pb with the Melich-3 and DTPA extractants.

Assessment of single extraction methods for evaluating the immobilization effect of amendments on cadmium in contaminated acidic paddy soil

Various single extractants (EDTA, DTPA, CaCl&lt;sub&gt;2&lt;/sub&gt;, NaNO&lt;sub&gt;3&lt;/sub&gt; and NH&lt;sub&gt;4&lt;/sub&gt;NO&lt;sub&gt;3&lt;/sub&gt;) and the first step of Community Bureau of Reference (BCR1) method were used to evaluate the immobilization of Cd in contaminated acidic paddy soil by different amendments. The extractability of Cd in amended soil changed in the following order: EDTA &amp;asymp; BCR1 &amp;gt; DTPA &amp;gt; NH&lt;sub&gt;4&lt;/sub&gt;NO&lt;sub&gt;3&lt;/sub&gt; &amp;asymp; CaCl&lt;sub&gt;2&lt;/sub&gt; &amp;gt; NaNO&lt;sub&gt;3&lt;/sub&gt;. A simple correlation analysis indicated that the BCR1, CaCl&lt;sub&gt;2&lt;/sub&gt;, NH&lt;sub&gt;4&lt;/sub&gt;NO&lt;sub&gt;3&lt;/sub&gt;, and NaNO&lt;sub&gt;3&lt;/sub&gt; methods are the best suited methods for predicting changes in the phytoavailability to rice of Cd in soil (r = 0.680 to 0.828, P &amp;lt; 0.001), followed by the DTPA extraction procedure (r = 0.543 to 0.666, P &amp;lt; 0.01). However, non-significant correlations were observed between soil EDTA-extractable Cd and Cd accumulated in rice. Accordingly, the BCR1, CaCl&lt;sub&gt;2&lt;/sub&gt;, NH&lt;sub&gt;4&lt;/sub&gt;NO&lt;sub&gt;3&lt;/sub&gt;, and NaNO&lt;sub&gt;3&lt;/sub&gt; extraction procedures are recommended for evaluating the immobilization of Cd in contaminated acidic paddy soil. &amp;nbsp;

Comparison of two sequential extraction procedures for the fractionation of zinc in agricultural calcareous soils

Twenty soil samples with a wide range of chemical and physical properties were collected from typical uncontaminated soils of south-west Iran, characterised by their high calcium carbonate contents (mean value of 321 g kg−1) and zinc deficiency (mean value of 0.2 mg kg−1 for DTPA-extractable Zn). The extractability and solid-phase fractionation of Zn in the soils was determined by the single extraction procedure (DTPA extractability) and two different sequential extraction procedures: a seven-step Singh method (procedure A) and the modification of three-step BCR (Community Bureau of Reference) method (procedure B). The DTPA extractable zinc levels were low (on average 3.34%). Zinc was mainly contained in the residual fraction (91.43% for procedure A and 75.25% for procedure B). In comparison with procedure B, few relationships were established between the zinc fractions isolated by procedure A and the soil properties. The Singh scheme provided better information than the BCR scheme about Zn distribution in the soils studied.

Removal of Heavy Metals from Aqueous Solution by Zeolite in Competitive Sorption System

In this study, the sorption behaviour of natural (clinoptilolite) zeolites with respect to cadmium (Cd), copper (Cu), nickel (Ni), lead (Pb) and zinc (Zn) has been studied in order to consider its application to purity metal finishing wastewaters. The batch method has been employed, using competitive sorption system with metal concentrations in solution ranging from 50 to 300 mg/l. The percentage sorption and distribution coefficients (Kd) were determined for the sorption system as a function of metal concentration. In addition lability of the sorbed metals was estimated by DTPA extraction following their sorption. The results showed that Freundlich model described satisfactorily sorption of all metals. Zeolite sorbed around 32, 75, 28, 99, and 59 % of the added Cd, Cu, Ni, Pb and Zn metal concentrations respectively. According to the percentage sorption and distribution coefficients values, the selectivity sequence of studied metals by zeolite can be given as Pb > Cu > Zn > Cd > Ni. About 57, 47, 78, 22, and 29 % from the total sorbed Cd, Cu, Ni, Pb and Zn recovered by DTPA indicating that lability of the adsorbed Ni was higher than, Cd, Cu, Zn, and Pb respectively. These results show that natural zeolites hold great potential to remove cationic heavy metal species from industrial wastewater.

Functioning and toxicity of artificial soil mixtures with metal-bearing sewage sludge

Various artificial soil mixtures were prepared by mixing two different toxic metals containing sewage sludge from Ljubljana and Maribor wastewater treatment plants with natural mineral soil. The plots with mixtures were exposed to field environmental conditions for a period of 1 year, after which we assessed soil toxicity (germination test with Lactuca sativa), potential metal phyto-accessibility (diethylenetriamine pentaacetic acid – DTPA extraction test), soil functioning (by soil enzymes activity) and conducted a field growth test with Lollium perenne L. as a metal bio-indicator plant. The metal phyto-accessibility extraction test (DTPA) showed lower values than the metal accumulation test with L. perenne L., which also showed higher metal concentrations in roots compared to leaves. With the exception of the mixture containing 30% (w/w) of sludge from the Ljubljana wastewater treatment plant, all mixtures containing more than 20% of sludge negatively affected root elongation of L. sativa seeds, indicating an increase in artificial soils toxicity. Increasing the ratio of sludge from the Ljubljana plant increased dehydrogenase and decreased phosphomonoesterase, while the addition of sludge from the Maribor plant increased phosphomonoesterase activity. Overall, the effect of sludge addition on artificial soil properties, toxicity and functioning not only depended on dosage but was also sensitive to the source and pre-treatment of the sewage sludge.

Cadmium availability and accumulation by lettuce and rice

Among the toxic elements, Cd has received considerable attention in view of its association with a number of human health problems. The objectives of this study were to evaluate the Cd availability and accumulation in soil, transfer rate and toxicity in lettuce and rice plants grown in a Cd-contaminated Typic Hapludox. Two simultaneous greenhouse experiments with lettuce and rice test plants were conducted in a randomized complete block design with four replications. The treatments consisted of four Cd rates (CdCl2), 0.0; 1.3; 3.0 and 6.0 mg kg-1, based on the guidelines recommended by the Environmental Agency of the State of São Paulo, Brazil (Cetesb). Higher Cd rates increased extractable Cd (using Mehlich-3, Mehlich-1 and DTPA chemical extractants) and decreased lettuce and rice dry matter yields. However, no visual toxicity symptoms were observed in plants. Mehlich-1, Mehlich-3 and DTPA extractants were effective in predicting soil Cd availability as well as the Cd concentration and accumulation in plant parts. Cadmium concentration in rice remained below the threshold for human consumption established by Brazilian legislation. On the other hand, lettuce Cd concentration in edible parts exceeded the acceptable limit.

Immobilization of heavy metals in a contaminated soil in Iran using di-ammonium phosphate, vermicompost and zeolite

Fractionation of heavy metals (HMs) in amended soils is needed to predict elemental mobility in soil and phytoavailability to plants. A study was conducted to determine the effects of different amendments on HMs availability and their redistribution among soil fractions. A contaminated soil was selected from around a Zn mine and amended with 0, 2, 4, and 6 g kg−1 of vermicompost (VC), zeolite (ZE), and di-ammonium phosphate (DP) and incubated at field moisture. The amounts of Cd, Pb, Zn, and Cu were determined from the soil after 6 months of incubation time using DTPA and sequential extraction procedures. The total concentrations of Cd, Pb, Zn, and Cu were 41, 3,099, 1,997, and 83 mg kg−1 of soil, respectively. All amendments decreased significantly [probability (p) ≤ 0.05] DTPA-extractable Cd, Pb, and Cu, but not Zn, in the soil. For instance, DTPA-extractable Cd, Pb, and Cu decreased by 40, 290, and 20%, respectively, and that of Zn increased by 18% with DP1 (2 g kg−1 of di-ammonium phosphate) application. The concentrations of Pb and Cd decreased mainly in the specifically sorbed (SS) but increased in the amorphous Fe oxide (AFeO) fraction with DP application, indicating redistribution of Pb and Cd in the fractions with less mobility. Lead immobilization by DP was mainly attributed to the P-induced formation of chloropyromorphite, which was identified in the DP treatment using X-ray diffraction technique. It was concluded that DP was the most effective amendment in immobilizing Pb and Cd, though it increased Zn mobility.