Effectiveness of amendments on the spread and phytotoxicity of contaminants in metal-arsenic polluted soil

Chemical composition of arsenic-based acid mine drainage in the downstream of a gold mine: Fuzzy regression and clustering analysis

This study employs fuzzy regression and fuzzy multivariate clustering techniques to analyze arsenic-polluted water samples originating from acid rock drainage in waste rock dumps. The research focuses on understanding the complex relationships between variables associated with arsenic contamination, such as water arsenic concentration, pH levels, and soil characteristics. To this end, fuzzy regression models were developed to estimate the relationships between water arsenic concentration and independent variables, thus, incorporating the inherent uncertainties into the analysis. Furthermore, multivariate fuzzy k-means clustering analysis facilitated the identification of fuzzy-based clusters within the dataset, providing insights into spatial patterns and potential sources of arsenic pollution. The pairwise comparisons indicated the strongest correlation of 0.62 between soil total arsenic and pH, while the weakest correlation of 0.13 was observed between soil-soluble arsenic and soil iron, providing valuable insights into their relationships and impact on water arsenic levels. The associated uncertainties in the relationships among the variables were determined based on the degree of belongingness of each data point to various fuzzy sets. Three distinct clusters emerged from the analysis: Cluster 1 comprised Points 5, 6, and 7; Cluster 2 included Points 1, 2, 3, 4, 8, and 9; and Cluster 3 consisted of Points 10, 11, 12, and 13. The findings enhance our understanding of the factors influencing arsenic contamination to provide an effective mitigation strategy in acid rock drainage scenarios. This research also demonstrates the applicability and effectiveness of fuzzy regression and fuzzy multivariate clustering in the analysis of arsenic-polluted water samples.

Arsenic immobilisation in soil using electricity-induced spreading of iron in situ

An in situ method for spreading iron amendments to arsenic (As)-contaminated soil has been investigated in the laboratory and field. This study tested the distribution of Fe from corroding electrodes through soil using a low-voltage direct current in a laboratory setting and validated the method in the field for As immobilisation in contaminated soil. Laboratory tests revealed that the corrosion of Fe electrodes in soil occurred in a way similar to that during the Fe electrocoagulation in water, which decreased the As concentrations in flow-through water from 150 μg L^-1 to undetectable levels. Method validation over one year in the field using electric current pulses with reversing polarity revealed a decrease in As concentration in groundwater by 72-97% in five of the six groundwater wells within the experimental area. This method of introducing Fe amendments to soil can reduce the need for soil excavation upon chemical immobilisation of contaminants in soil.

Combined passivators regulate the heavy metal accumulation and antioxidant response of Brassica chinensis grown in multi-metal contaminated soils

Passivation of heavy metals is one of the most efficient techniques to remediate soil pollution. However, passivators with single component are usually unsatisfactory in the case of multi-metal contaminated soils. To resolve this problem, a series of combined passivators containing different ratios of Fe-Mn ore, Fe powder, zeolite, bentonite, etc. were designed and used to study their effects on the growth, heavy metal accumulation, and the antioxidant response of Chinese cabbage (Brassica chinensis L.) as well as the soil available forms of heavy metals in a copper refinery's multi-metal (As, Cd, Pb, Cu) contaminated yellow-brown soil and an artificially contaminated (As, Cd, Pb, Cu) calcareous alluvial soil. The results showed that compared with the control, the addition of combined passivators significantly promoted cabbage growth, with the biomass increase up to 1.77 and 3.54 times in yellow-brown soil and calcareous alluvial soil, respectively. The activity of antioxidant enzymes (SOD, CAT, POD) and the content of malondialdehyde (MDA) and glutathione (GSH) decreased, while the chlorophyll content increased significantly, as compared with no passivators. In addition, passivator application decreased As, Cd, Pb, and Cu contents in shoots and roots by 34.8%, 45.6%, 34.9%, and 11.1% and 49.2%, 63.8%, 38.6%, and 46.4% in yellow-brown soil and by 29.8%, 27.3%, 26.8%, and 25.5% and 45.8%, 55.2%, 61.8%, and 5.7% in calcareous alluvial soil, respectively. Besides, the content of soil available heavy metals was reduced by 8.0-17.1% in yellow-brown soil and 3.3-19.1% in calcareous alluvial soil after the application of passivators. The results indicated that the combined passivators formulated in this experiment could efficiently reduce the content of the multi-metals in cabbage and relieve the oxidant stress and could be used as a way to remediate multi-metal polluted soils.

Evaluation of factors affecting arsenic uptake by Brassica juncea in alkali soil after biochar application using partial least squares path modeling (PLS-PM)

Biochar application to As-contaminated soil can alter various soil chemical properties, and it can affect available As, plant As uptake, and As phytotoxicity. Increased dissolved organic carbon (DOC) and P released from biochar affect As behavior in the soil system. In this study, we evaluated the effect of biochar application on the chemical properties of soil and phytotoxicity in Brassica juncea using correlation analysis and partial least squares path modeling (PLS-PM). Biochar application increased electrical conductivity (EC), DOC, available P and available As. However, the increased available As did not significantly affect As uptake by B. juncea due to the decrease in the relative ratio and effect of available As with increase in available P derived from biochar. Moreover, biochar application negatively affected soil chemical properties (pH, EC, DOC, available P, and available As) and As uptake by B. juncea. Therefore, correlation analysis and PLS-PM analysis are useful tools to interpret the interactions among influencing factors in the soil-plant system. An approach at the equivalent molecular level rather than concentration should be adopted in future studies.

Effects of Fe-loaded biochar on the bioavailability of Arsenic and cadmium to lettuce growing in a mining contaminated soil

Arsenic (As) and cadmium (Cd) are two prominent metal contaminants in mining soil, threatening food and environmental safety. The effects of Fe-loaded biochar on the accumulation and translocation of As and Cd in a soil-lettuce system were investigated to evaluate the efficiency of Fe-loaded biochar in reducing As and Cd bioavailability. Application of Fe-loaded biochar at a rate of 0.5-1.5% decreased the concentrations of porewater As and Cd by 4.2-53.0% and -0.6-21.7%, respectively. The results of sequential extraction showed that Fe-loaded biochar can promote the transfer of As and Cd in soils from the available fraction to a relatively stable fraction, thus reducing the mobility and availability of As and Cd. The concentrations of As and Cd in lettuce shoots in the Fe-loaded biochar treatment were significantly decreased by 11.4-26.0% and 4.4-12.9% compared with those in the untreated soil, respectively. Fe-loaded biochar applied at a rate of 0.5-1.0% had no obvious effect on plant biomass, and the lowest weight of lettuce shoots and roots was observed in the treatment with Fe-loaded biochar applied at a rate of 1.5%, in which they were reduced by 12.9% and 18.0%, respectively. Overall, Fe-loaded biochar as a soil amendment was effective in simultaneously reducing As and Cd bioavailability in As and Cd co-contaminated soils, and an application rate lower than 1.5% is recommended to avoid significant decreases in plant growth.

Restoring the plant productivity of heavy metal-contaminated soil using phosphate sludge, marble waste, and beneficial microorganisms

Assisted natural remediation (ANR) has been highlighted as a promising, less expensive, and environmentally friendly solution to remediate soil contaminated with heavy metals. We tested the effects of three amendments (10% compost, C; 5 or 15% phosphate sludge, PS5 and PS15; and 5 or 15% marble waste, MW5 and MW15) in combination with microorganism inoculation (rhizobacteria consortium alone, mycorrhizae alone, and the two in-combination) on alfalfa in contaminated soil. Plant concentrations of Zn, Cu, and Pb were measured, along with proline and malondialdehyde production. The microbiological and physicochemical properties of the mining soil were evaluated. Application of the amendments allowed germination and promoted growth. Inoculation with the rhizobacteria consortium and/or mycorrhizae stimulated plant growth. PS and MW stimulated the production of proline. Inoculation of alfalfa with the rhizobacteria-mycorrhizae mixture and the application of MW allowed the safe cultivation of the legume, as shown by the low concentrations of metals in plant shoots. Zn and Pb concentrations were below the limits recommended for animal grazing and accumulated essentially in roots. Soil analyses showed the positive effect of the amendments on the soil physicochemical properties. All treatments increased soil pH (around 7), total organic carbon, and assimilable phosphorus content. Notably, an important decrease in soluble heavy metals concentrations was observed. Overall, our findings revealed that the applied treatments reduced the risk of metal-polluted soils limiting plant growth. The ANR has great potential for success in the restoration of polymetallic and acidic mining soils using the interaction between alfalfa, microorganisms, and organo-mineral amendments.

Reduced Cd, Pb, and As accumulation in rice (Oryza sativa L.) by a combined amendment of calcium sulfate and ferric oxide

A combined amendment (CF) consisting of 90% calcium sulfate (CaSO₄) and 10% ferric oxide (Fe₂O₃) was used to investigate the feasibility, active principles, and possible mechanisms of the immobilization of heavy metals in paddy soil. A soil incubation experiment, two consecutive pot trials, and a field experiment were conducted to evaluate the effectiveness and persistence of CF on metal(loid) immobilization. Soil incubation experiment results indicated that the application of CF significantly decreased the concentrations of cadmium (Cd), lead (Pb), and arsenic (As) in soil solution. CF treatments simultaneously reduced the accumulation of Cd, Pb, and As in two consecutive pot trials. The total Cd, Pb, and As concentrations in the rice grains were respectively 0.02, 2.08, and 0.62 mg kg^-1 in the control treatment in the second year, which exceeded the safety limits of contaminants in food products in China. However, a high amount of CF amendment (CF-H, 0.3%) effectively decreased Cd, Pb, and As by 75.0%, 75.5%, and 46.8%, respectively. Further, with the CF amendment, the bioavailable Cd and Pb in the soil and the accumulation of Cd, Pb, and As in rice grain in the field experiment were also significantly decreased. The concentrations of Cd, Pb, and As in grains were respectively 0.02, 0.03, and 0.39 mg kg^-1 in the control treatment in the field experiment, which decreased to 0.01, 0.01, and 0.22 mg kg^-1 with CF addition, suggesting that grains produced in the field could pose less health risk. In conclusion, these results implied that CF was an effective and persistent combined amendment to immobilize heavy metals in soil and thereby can reduce the exposure risk of metal(loid)s associated with rice consumption.

Cadmium and arsenic accumulation during the rice growth period under in situ remediation

Rice (Oryza sativa L.) planted in cadmium (Cd)- and arsenic (As)-contaminated soil is considered the main source of dietary Cd and As intake for humans in Southeast Asia and thereby poses a threat to human health. Minimizing the transfer of these pollutants to rice grain is an urgent task for environmental researchers. The main objective of this study was to investigate the effects and the mechanisms of a combined amendment (hydroxyapatite + zeolite + biochar, HZB) on decreasing Cd and As accumulation in rice. In situ remediation and aqueous solution adsorption experiments were conducted. The results showed that after application of HZB, Cd and As concentrations of the exchangeable fraction and TCLP extraction in soil decreased with the growth of rice plants. Cd concentrations in rice tissues were decreased at the tillering, filling and maturing stages after in situ remediation, while As concentrations in rice tissues were decreased only at the maturing stage. When 8 kg·plot^-1 (9000 kg ha^-1) HZB was applied, concentrations of Cd and inorganic As in brown rice were decreased to 0.18 and 0.16 mg kg^-1, respectively, lower than the levels permissible for grain in China, i.e., 0.2 mg kg^-1. Application of HZB reduced Cd accumulation in rice tissues, and the suppression of Cd accumulation was significantly greater than that of As. Furthermore, HZB significantly increased rice grain yield. An aqueous solution adsorption experiment demonstrated that HZB could adsorb and covalently bind Cd and As (V) via -OH, -COOH, -Si-O-Si and CO₃^2- groups to produce carboxylates, silicates and carbonates, thereby promoting in situ immobilization of Cd and As in soil solution.

Phytostabilization of polymetallic contaminated soil using Medicago sativa L. in combination with powdered marble: Sustainable rehabilitation

This study uses an ecotoxicology approach to evaluate the effectiveness of combining powdered marble as an amendment, with phytostabilization by Medicago sativa L. on the neutralization of acidic mine tailings, and the stabilization of heavy metals. The mine tailings were collected from an abandoned polymetallic mine in Southern Morocco, and mixed with powdered marble as the following proportions, 25%, 50%, and 75%. Laboratory immobilization/stabilization tests showed that the application of powdered marble in the treatments led to a significant increase in pH, and significant reductions of Cu, Zn (99%), Pb (98%), and Fe (45%). Greenhouse experiments showed that plant growth in all treatments was significantly (p ≤ 0.05) less than growth in agricultural soil. Plant growth significantly (p ≤ 0.05) decreased as the proportion of powdered marble increased. The concentration of metals in plant roots were significantly (p ≤ 0.05) higher than those of shoots. Combining immobilization by powdered marble with phytostabilization by M. sativa L. could represent a viable method of rehabilitating acidic polymetallic mine tailings.

Effects of an additive (hydroxyapatite-biochar-zeolite) on the chemical speciation of Cd and As in paddy soils and their accumulation and translocation in rice plants

A pot experiment was carried out to investigate the remediation of paddy soils contaminated with both Cd and As. The effects of a soil additive (HZB: hydroxyapatite + zeolite + biochar) on the chemical speciation of Cd and As in the soil and on the accumulation and translocation of these two elements in rice plants were studied. The application of HZB decreased the concentration of acid-extractable Cd in the soil by 7.3-32.6% by promoting the transformation of soil Cd from soluble to insoluble species; as a result, the concentration of organically bound Cd in the soil increased by 6.8-49.5%. The application of HZB also promoted the transformation of soil As from soluble to insoluble species, thus increasing the concentration of Ca-bound As by 34.1-93.4% and reducing the concentration of soil-exchangeable As by 12.2-55.1%. However, when the application rate of HZB was greater than 4.0 g kg^-1, the concentration of soil-exchangeable As increased again. It was found that the application of HZB decreased the Cd and As bioaccumulation capacity of rice root, and among various rice organs, rice husk was the highest in Cd transferring capacity, whereas rice root was the highest in As transferring capacity. When the amount of HZB applied was 0.05-0.2%, the Cd and As concentrations in the various parts of the rice plants decreased significantly.

State of the science review: Potential for beneficial use of waste by-products for in situ remediation of metal-contaminated soil and sediment

Metal and metalloid contamination of soil and sediment is a widespread problem both in urban and rural areas throughout the United States (U.S. EPA, 2014). Beneficial use of waste by-products as amendments to remediate metal-contaminated soils and sediments can provide major economic and environmental advantages on both a site-specific and national scale. These waste by-products can also reduce our need to mine virgin materials or produce synthetic materials for amendments. Waste by-products must not be hazardous or pose unacceptable risk to human health and the environment, and should be a suitable replacement for virgin and synthetic materials. This review serves to present the state of science on in situ remediation of metal-contaminated soil and sediment and the potential for beneficial usage of waste by-product materials. Not all unintended consequences can be fully understood or predicted prior to implementing a treatment option, however some realized, and potentially unrealized, benefits and unintended consequences are explored.

Behaviors of heavy metals (Cd, Cu, Ni, Pb and Zn) in soil amended with composts

This study investigated how amendment with sewage sludge compost of different maturation times (3, 6, 12 months) affected metal (Cd, Cu, Ni, Pb, Zn) bioavailability, fractionation and redistribution in highly contaminated sandy clay soil. Metal transformations during long-term soil stabilization (35 months) were determined. In the contaminated soil, Cd, Ni and Zn were predominately in the exchangeable and reducible fractions, Pb in the reducible fraction and Cu in the reducible, exchangeable and oxidizable fractions. All composts decreased the bioavailability of Cd, Ni and Zn for up to 24 months, which indicates that cyclic amendment with compost is necessary. The bioavailability of Pb and Cu was not affected by compost amendment. Based on the reduced partition index (IR), metal stability in amended soil after 35 months of stabilization was in the following order: Cu > Ni = Pb > Zn > Cd. All composts were more effective in decreasing Cd, Ni and Zn bioavailability than in redistributing the metals, and increasing Cu redistribution more than that of Pb. Thus, sewage sludge compost of as little as 3 months maturation can be used for cyclic amendment of multi-metal-contaminated soil.

A three-year in-situ study on the persistence of a combined amendment (limestone+sepiolite) for remedying paddy soil polluted with heavy metals

In order to study the persistence of a combined amendment (LS, limestone+sepiolite) for remedying paddy soil polluted with the heavy metals Pb and Cd, a three-year in-situ experiment was conducted in a paddy soil near a mining area in southern Hunan, China. LS was applied at rates of 0, 2, 4, and 8g/kg (w/w); rice was subsequently planted for the three consecutive years of 2012 (first season), 2013 (second season), and 2014 (third season). Experimental results indicated that LS significantly increased soil pH values for all three seasons, and the enhancement ranked as follows: first season>second season>third season. Under the experimental conditions, the effect of LS on decreasing exchangeable concentrations of soil Pb and Cd was as follows: first season (97.6-99.8% for Pb and 88.3-98.9% for Cd)>second season (80.7-97.7% for Pb and 28.3-88.0% for Cd)>third season (32.6-97.7% for Pb and 8.3-71.4% for Cd); the effect of LS on reducing Pb concentrations in brown rice was: first season (73.5-81.2%)>third season (29.6-68.1%)>second season (0-9.7%), and that for reducing Cd concentrations in brown rice was third season (72.7-81.0%)>first season (56.1-66.8%)>second season (20.9-32.3%). For all three seasons, the effect of LS on reducing Cd content in brown rice was better than that for Pb. The highest translocation factors for Pb and Cd were from rice straw to husk, implying that the husk of rice plants was the main organ in which heavy metals accumulated. The effect of LS for decreasing soil exchangeable Cd content was relatively persistent, but that for Pb gradually decreased with time, implying that LS was more suitable for the long-term remediation of Cd-polluted soil than Pb-polluted soil.

Optimizing the combined application of amendments to allow plant growth in a multielement-contaminated soil

This study was aimed to 1) properly understand the dynamics of toxic elements (Al, Fe, Mn, Cu, Pb, Zn and As) in a sulphide-mine soil after combined application of compost from urban sewage sludge (SVC) and bottom ashes from biomass combustion (BA) and to 2) optimize the combination of both amendments for vegetation growth. Soil was amended following a D-optimal design and the mixtures (15 in total) were incubated during 30 d. At the end of the incubation, the effects of amendments on the assessed variables as well as the process modelling were evaluated by Response Surface Methodology (RSM). The process modelling confirmed that quadratic models were adequate to explain the behaviour of the assessed variables (R(2) ≥ 0.94 and Q(2) ≥ 0.75). Both amendments significantly increased pH and electrical conductivity, while reduced metal extractability. A different behaviour of As respect to metals was observed and high doses of BA sharply increased its extractability. The optimization process indicated that adequate conditions for vegetation growth would be reached adding the soil with 6.8% of SVC and 3.1% of BA (dry weight). After amendments application the germination and root elongation of three energy crops were significantly increased while lipid peroxidation was decreased. Therefore, the combined application of SVC and BA to a contaminated soil could improve soil conditions and might be expected to have an advantage during plant growth. Moreover, the RSM could be a powerful technique for the assessment of combined amendment effects on soil properties and their effective application in multielement-contaminated soils.

A nanoremediation strategy for the recovery of an As-polluted soil

The present study investigates the impact of the nanoremediation treatment on soil recovery as evaluated by the development of barley plants. Highly As-polluted brownfield soil was treated with nanoscale zero-valent iron (nZVI) commercial suspension at two doses (1% and 10%). Barley plants were cultivated in treated and untreated soils in a growth chamber, and the As, Fe, and nutrients uptake were determined. The efficacy of As immobilization was evaluated according to the toxicity characteristics leaching procedure (TCLP) as well as using a sequential extraction procedure. The application of nZVI reduced the amount of As in the more available fractions and increased the amount of As in the residual fraction. The best immobilization results were obtained for the highest dose of nZVI (10%). In turn, the lower availability of As in nZVI-treated soils, particularly at the dose of 10%, stimulated the development of the barley plants and decreased the As uptake. Neither an important increase of available Fe nor negative impact on soil physico-chemical and biological properties were observed. Thus, our results show that the use of nZVI could be an adequate strategy to recover the land use in As polluted soils.

Crop residue stabilization and application to agricultural and degraded soils: A review

Agricultural activities produce vast amounts of organic residues including straw, unmarketable or culled fruit and vegetables, post-harvest or post-processing wastes, clippings and residuals from forestry or pruning operations, and animal manure. Improper disposal of these materials may produce undesirable environmental (e.g. odors or insect refuges) and health impacts. On the other hand, agricultural residues are of interest to various industries and sectors of the economy due to their energy content (i.e., for combustion), their potential use as feedstock to produce biofuels and/or fine chemicals, or as a soil amendments for polluted or degraded soils when composted. Our objective is review new biotechnologies that could be used to manage these residues for land application and remediation of contaminated and eroded soils. Bibliographic information is complemented through a comprehensive review of the physico-chemical fundamental mechanisms involved in the transformation and stabilization of organic matter by biotic and abiotic soil components.

Effect of grain size and heavy metals on As immobilization by marble particles

The effect of grain size and the interaction of heavy metals on As sorption by marble waste with different particle sizes was investigated. Acidic solutions containing only arsenic and a mixture of arsenic, lead, zinc, and cadmium were put in contact with the marble waste. The amount of metal(loid)s that were immobilized was calculated using the difference between the concentration in the acidic solution and in the liquid phase of the suspensions. Approximately 420 μg As m(-2) was sorbed onto the marble grains, both nonspecifically and specifically, where ≥ 80 % of the total arsenic in the acidic solution remained soluble, which suggests that this amendment is not effective to immobilize arsenic. However, in mixed contamination, relatively stable Pb-Ca arsenates were formed on the surface of the marble particles, and the soluble arsenic was reduced by 95 %, which indicates that marble particles can effectively immobilize arsenic and lead when both appear together.

Mobility and phytoavailability of Cu, Cr, Zn, and As in a contaminated soil at a wood preservation site after 4 years of aided phytostabilization

The remediation of copper-contaminated soils by aided phytostabilisation in 16 field plots at a wood preservation site was investigated. The mobility and bioavailability of four potentially toxic trace elements (PTTE), i.e., Cu, Zn, Cr, and As, were investigated in these soils 4 years after the incorporation of compost (OM, 5 % w/w) and dolomite limestone (DL, 0.2 % w/w), singly and in combination (OMDL), and the transplantation of mycorrhizal poplar and willows. Topsoil samples were collected in all field plots and potted in the laboratory. Total PTTE concentrations were determined in soil pore water (SPW) collected by Rhizon soil moisture samplers. Soil exposure intensity was assessed by Chelex100-DGT (diffusive gradient in thin films) probes. The PTTE phytoavailability was characterized by growing dwarf beans on potted soils and analyzing their foliar PTTE concentrations. OM and DL, singly and in combination (OMDL), were effective to decrease foliar Cu, Cr, Zn, and As concentrations of beans, the lowest values being numerically for the OM plants. The soil treatments did not reduce the Cu and Zn mineral masses of the bean primary leaves, but those of Cr and As decreased for the OM and DL plants. The Cu concentration in SPW was increased in the OM soil and remained unchanged in the DL and OMDL soils. The available Cu measured by DGT used to assess the soil exposure intensity correlated with the foliar Cu concentration. The Zn concentrations in SPW were reduced in the DL soil. All amendments increased As in the SPW. Based on DGT data, Cu availability was reduced in both OM and OMDL soils, while DL was the most effective to decrease soil Zn availability.

Effects of combined amendments on heavy metal accumulation in rice (Oryza sativa L.) planted on contaminated paddy soil

Stabilization of heavy metals in situ was investigated. Two combined amendments (LS, limestone+sepiolite; HZ, hydroxyhistidine+zeolite) were applied at ratios of 0.2%, 0.4%, and 0.8% (w/w) to paddy soil with multi-metal (Pb, Cd, Cu, and Zn) contamination. The effects of these two combined amendments on heavy metal bioavailability in soil, and on uptake and accumulation of heavy metals in rice plants were investigated. Application of LS and HZ significantly increased soil pH values and cation exchange capacity contents, and resulted in a reduction in exchangeable fraction of metals and in extract metal concentrations of amended soils through toxicity characteristic leaching procedure (TCLP). LS and HZ obviously inhibited uptake and accumulation of Pb, Cd, Cu, and Zn in rice plants. Compared with the control soil, concentrations of Pb, Cd, Cu, and Zn in brown rice were decreased by 10.6-31.8%, 16.7-25.5%, 11.5-22.1%, and 11.7-16.3%, respectively, as a result of 0.2% to 0.8% addition of LS, and decreased by 5.1-40.8%, 16.7-20.0%, 8.1-16.2%, and 13.3-21.7%, respectively, as a result of 0.2-0.8% addition of HZ. Significant positive linear correlations were found between heavy metal concentrations in TCLP extracts and those in rice tissues except for Pb. Extracting heavy metals with TCLP was a more suitable method for estimating heavy metal bioavailability concentrations of amended soil than exchangeable fraction of heavy metals, because the latter underestimated heavy metal bioavailability. These results demonstrate that LS and HZ could be effective in reducing heavy metal bioavailability and accumulation in rice grown on multi-metal-contaminated soils.

When liming and revegetation contribute to the mobilisation of metals: learning lessons for the phytomanagement of metal-polluted wetlands

The aim of this study was to identify the effectiveness of liming in combination with vegetation for the recovery of slightly acidic, saline soils of eutrophic wetlands affected by mine wastes, under fluctuating flooding conditions. Simulated soil profiles were constructed and four treatments were assayed under greenhouse conditions: control, only plant, only liming, and liming and plant. The plant species was the halophyte Sarcocornia fruticosa. Three horizons were differentiated: A (never under water), C1 (alternating flooding-drying conditions), and C2 (always under water). The pH, Eh, salinity, and the concentrations of dissolved organic carbon and soluble metals were measured regularly for 18 weeks. Liming favoured the growth of S. fruticosa, an increase in pH and a fall in Eh. The amendment was effective for reducing Mn, Zn, and Cd in pore water of bare soils, but not Cu and Pb. In the treatment with liming and plant, the growth of S. fruticosa counteracted the effect of the amendment, strongly increasing the concentrations of metals in pore water and distributing them along the soil profile. Hence, the combined use of liming and plants may increase the risk of metals mobilisation.

Chemical stabilization of metals and arsenic in contaminated soils using oxides--a review

Oxides and their precursors have been extensively studied, either singly or in combination with other amendments promoting sorption, for in situ stabilization of metals and As in contaminated soils. This remediation option aims at reducing the available fraction of metal(loid)s, notably in the root zone, and thus lowering the risks associated with their leaching, ecotoxicity, plant uptake and human exposure. This review summarizes literature data on mechanisms involved in the immobilization process and presents results from laboratory and field experiments, including the subsequent influence on higher plants and aided phytostabilization. Despite the partial successes in the field, recent knowledge highlights the importance of long-term and large-scale field studies evaluating the stability of the oxide-based amendments in the treated soils and their efficiency in the long-term.