Immobilization Of Pb In Soil Research Articles

Pb-resistant Pantoea rwandensis promotes maize's growth by altering Pb accumulation in biomass and soil Pb immobilization.

In lead (Pb)-contaminated soil, inoculating phosphate-solubilizing bacteria (PSB) to reduce the phytoavailability of Pb and to change the soil nutrients is an important way to inhibit the Pb uptake by plants. In this study, we isolated the native Pb-resistant Pantoea rwandensis from a tailings site. We employed broth culture and pot experiments to investigate the effect of the inoculation of P. rwandensis on Pb immobilization in the soil, the soil nutrients, the microbial community, and Pb accumulation in the biomass of maize (Zea mays L.). The results showed that P. rwandensis not only tolerated Pb2+ but also dissolved Ca3(PO4)2 by secreting oxalic acid, tartaric acid, lactic acid, and acetic acid, which significantly increased the amount of dissolved P, up to 567.50 mg.L-1. In the pot experiment, the application of culture filtrate, an inoculation with P. rwandensis, or a mixture of culture filtrate and P. rwandensis increased the soil residual Pb by 49.57%, 89.81%, and 41.69%, respectively, compared to the control. Consequently, the increase in the residual Pb in the soil inhibited its uptake by maize, and an inoculation of P. rwandensis or a mixture of culture filtrate and P. rwandensis decreased the accumulation of Pb in the shoot biomass of maize by 61.65% and 72.48% and in the roots of maize by 26.00% and 39.59%, respectively. Meanwhile, P. rwandensis and the mixture of culture filtrate and P. rwandensis increased the shoot biomass of maize by 54.39% and 17.86% and the root biomass of maize by 108.77% and 17.86%, respectively. A P. rwandensis inoculation increased the biodiversity of the fungal community and the abundance of Proteobacteria, Mortierella, and Sphingomonas. Our results demonstrate that an inoculation with P. rwandensis could promote the transformation of Pb fractions and a functional change in the soil bacterial community, ultimately decreasing Pb accumulation in the biomass and promoting the development of maize.

Natural ageing of biochar improves its benefits to soil Pb immobilization and reduction in soil phytotoxicity.

Amendments are good tools for immobilizing metal(loid) and improving phytoremediation success. However, the amendment effect is variable and depends on multiple parameters, including amendment type and ageing. Such an ageing effect is rarely studied. Our study is one of the first focusing on how biochar storage affects its effect on soil properties and metal(loid) immobilization, when biochar was applied alone or in combination with green manure. To answer this, a 33-day pot incubation experiment was set up using contaminated soil, amended with two biochars (differing in ages: old (Bo) and new (Bn)) and/or two green manures (leaves of clover or poplar) and sown with Phaseolus vulgaris (bioindicator plant). Soil pore waters, plant growth and metal(loid) accumulation were evaluated. Biochar reduced soil acidity (Bn: + 0.75 pH unit, Bo: + 0.72 unit) and Pb mobility (Bn: - 42%, Bo: - 50%), while green manures acidified the soil (- 0.30 pH unit) and immobilized Pb only after 10days (- 44%). All amendments reduced soil phytotoxicity. Moreover, the biochar stored at room temperature for a few years demonstrated better abilities to improve soil properties, particularly for Pb immobilization, than the biochar freshly prepared. Finally, as mixtures maturated, soil parameters changed until about ten days, then tended to stabilize. Therefore, it can be concluded that (1) biochar storage will affect its chemical properties and ameliorate its effects, (2) biochar can ameliorate soil properties and immobilize metal(loid)s, while green manures tended to have adverse effects at first, and (3) soil/amendment mixtures should be left to mature about two weeks before potential plant implementation.

Phosphorus release characterization of biochar loaded with inherent and exogenous phosphorus and impact on soil Pb immobilization

Phosphorus release characterization of biochar loaded with inherent and exogenous phosphorus and impact on soil Pb immobilization

Optimization strategies for Cd and Pb immobilization in soil using meta-analysis combined with numerical modeling

Chemical immobilization is one of the most effective technologies for remediating sites with heavy metals, but the selection of proper immobilization material and determination of its dose ratio is a challenge that limits the remediation efficiency. In this study, we conducted a meta-analysis of 489 independent observations on the immobilization of heavy metals, in which the immobilization materials were divided into biochar, phosphate, lime, metal oxides, and clay minerals. The statistical analysis of these observations revealed that the material dose ratio was the most important parameter that controlled immobilization efficiency, and the Freundlich adsorption model was successfully applied to calculate the bioavailable heavy metal (BHM) concentration after immobilization. Based on the calculation results, phosphate was the most effective material for Pb immobilization. Lime was the most effective when the initial bioavailable Cd content was 0.1–1 mg kg–1, whereas the immobilization effects of lime and phosphate were similar when the initial bioavailable Cd content was 10 mg kg–1 .In addition to the material dose ratio, initial soil pH (pH) and organic matter (OM) content were negatively correlated, whereas the fraction of initial BHMs before immobilization (FB) and immobilization time were positively correlated with immobilization efficiency. A numerical model that considered the material dose ratio, pH, OM, FB, and immobilization time was established to calculate the residual BHM concentration after immobilization. However, these factors only explained less than 45% of the immobilization effect, indicating that other factors, such as the sub-type of the material and modification methods, also affect the immobilization effect. These results could help to optimize the type of immobilization material of heavy metals and its dose ratio in practical engineering applications.

Lead stabilization in a polluted calcareous soil using cost-effective biochar and zeolite amendments after spinach cultivation

Biochar has been shown to be an effective organic soil amendment for the in situ immobilization of Pb. Little research has been done on the effects of biochar and zeolite interactions on Pb immobilization in contaminated calcareous soils. Therefore, the aim of this study was to investigate the effect of different levels of zeolite (2% and 4% w/w) and biochar (3% w/w) prepared from compost and poultry manure on the concentration of Pb in spinach shoots and Pb stabilization in contaminated calcareous soil after spinach cultivation using sequential extraction and release kinetics procedures. The results of this study show that the application of biochars derived from compost and poultry manure significantly decreased the Pb mobility factor (MF) (2.8% to 4.6%) and the release of cumulative diethylenetriamine pentaacetate (DTPA)-extractable Pb (16.8% to 20.1%) in calcareous soil. This benefit was further enhanced by the combined addition of zeolite (MF reduction of 4.4% to 8.4%; cumulative Pb release reduction of 24.8% to 28.6%). The enhancement of soil Pb immobilization is attributed to the properties of the amendments, such as high pH (10.0 to 11.0), ash content (39.0% to 43.5%), and P content (0.25% to 0.43%). The results of the soil Pb sequential extraction and Pb release kinetics were highly and significantly correlated with spinach shoot Pb concentration. Soil chemical data showed that the application of municipal waste biochar with 4% zeolite (MB+Z 2 ) was the most effective treatment for immobilizing Pb (8.4% reduction in MF, 28.6% reduction in cumulative DTPA-extractable Pb), which is in agreement with the results of the spinach shoot Pb concentration (89.0% reduction in uptake).

Quantitative evaluation of the synergistic effect of biochar and plants on immobilization of Pb

Biochar and plant cooperation in remediation of heavy metal contaminated soil is effective and important, but there still have knowledge gaps of synergistic effect between the two and the synergistic pathway has not been clarified. We prepared the Enteromorpha prolifera biochar at 400 °C and 600 °C (denoted as BC400 and BC600). The Pb fractions changes in soil and Pb toxicity in Brassica juncea were investigated by adding 30 g kg−1 biochar to soil containing 1200 mg kg−1 Pb in a pot experiment. There was a significant synergistic effect between biochar and plants on Pb immobilization in soil, according to the “E > 0” of Pb fractions in the interaction equation. Pb immobilization rates of biochar-plant treatments (BJBC4 and BJBC6) were 12.47% and 11.38% higher than biochar treatment (BC4, BC6), and 17.66% and 16.28% plant treatment (BJ). BJBC4 had a better immobilization effect than BJBC6. Biochar alleviated the phytotoxicity of Pb by increasing the antioxidant enzymes activities of plants. These results indicated two synergistic pathways: (1) The high pH and oxygen-containing functional groups of biochar could immobilize Pb through ion exchange, precipitation, or complexation. (2) Biochar enhanced the activity of the antioxidant enzyme system in plants thus improving the Pb tolerance of plants. Statistical analysis methods such as the partial least squares path modeling (PLS-PM) also confirmed the pathways. In a word, clear synergistic effects and pathways could guide the application of biochar and plants in Pb-contaminated soil.

Three types of passivators on the stabilization of exogenous lead-contaminated soil with different particle sizes

Study on the form partitioning and content of heavy metals in soil particles with different sizes is crucial for preventing and controlling heavy metals pollution, but few studies regard soil contaminated by heavy metals as a homogeneous body. In this study (Fig. 1), goat manure, lime and phosphate were used to stabilize exogenous lead (Pb). These soil passivators’ differential effects on total Pb and Pb with different chemical forms in soil particles of different sizes as well as Pb immobilization in soil were investigated. By passivation experiment in laboratory for 45 days, the passivation effect of the single and combined application treatments on exogenous Pb and partitioning characteristics were analyzed and compared. The characterization method of fine sand microstructure and mineral composition analysis was used. The results showed that the single application of P5 and combined application of LP5 had optimum passivation efficiency. The content of DTPA-Pb was reduced with P5 by 65.27% and the percentage of available Pb decreased significantly in soil particles of the four sizes. The content of TCLP-Pb and available Pb (weak acid extraction and reducible Pb) significantly decreased by 71.60 and 25.12% respectively after the application of LP5 in the original soil. Furthermore, most of the total Pb was enriched in coarse sand and clay, while its content was lower in fine sand and silt. The combined application treatment of GL5 significantly increased the content of weak acid extractable and reducible Pb in fine sand, silty sand and clay. Through SEM and XRD analysis, it was found that the diffraction peak of P5 treatment groups might be related to the formation of insoluble Pb that contained compounds, which were mainly mineral components, including quartz, feldspar and mica, and LP showed a big potential in the study on passivation of heavy metal Pb-contaminated soil in the natural environment. In conclusion, further studies on the different dosage and metal-contamination levels as well as different combination forms of passivators should be considered under natural conditions, the selection of suitable passivators according to soil texture is of great significance for remediation of Pb-contaminated soil.

Phosphorus solubilizing bacteria Bacillus thuringiensis and Pantoea ananatis simultaneously promote soil inorganic phosphate dissolution and soil Pb immobilization

The phytoavailability of lead (Pb) can be greatly reduced when Pb forms stable phosphate compounds in soil. This study employed broth culture, soil incubation, and pot experiments to investigate whether phosphate solubilizing bacteria (PSB) could effectively immobilize soil Pb through dissolution of insoluble inorganic P compounds. The results showed that both Bacillus thuringiensis GL-1 (GL-1) and Pantoea ananatis HCR2 (HCR2) could use Ca3(PO4)2, FePO4, and AlPO4 as the sole P resource and significantly increase water-soluble phosphate concentrations, which reached 555.84 and 392.66 mg/L, 13.82 and 72.06 mg/L, and 93.29 and 92.87 mg/L, respectively. The minimum pH of these culture media was reduced to 3.93 and 4.02, 3.37 and 3.40, and 2.86 and 2.89, respectively. Compared with the control, inoculation of GL-1 to artificially Pb-contaminated soil significantly reduced Fe–P, Al–P, Olsen-P, and NH4NO3-extractable Pb concentrations by 13.70%, 15.84%, 13.29%, and 33.61%, respectively, while reduced those by 23.75%, 53.43%, 11.66%, and 47.54% in the case of HCR2. Similarly, inoculation of GL-1 or HCR2 significantly reduced Fe–P concentrations of the historically metal-contaminated acidic soil by 50.00% and 46.73%, respectively. The NH4NO3-extractable soil Pb concentrations also decreased, which was only significant in soil inoculated with GL-1. Pot experiment found that inoculation of GL-1 and HCR2 decreased soil Pb phytoavailability and consequently inhibited its uptake by lettuce (Lactuca sativa L.). Meanwhile, the inoculation of HCR2 significantly promoted plant growth and reduced shoot Pb concentrations when grown in artificially Pb-contaminated soil. The results suggest that inoculation of GL-1 and HCR2 could be applied for remediating Pb-contaminated soils.

Effect of organosilicone and mineral silicon fertilizers on chemical forms of cadmium and lead in soil and their accumulation in rice

Cadmium (Cd) and lead (Pb) pollution in soil and their accumulation in edible parts possess a worldwide eco-environmental and health risk, especially in developing countries. Recently, organosilicone fertilizer (OSiF) has been reported to reduce uptake of heavy metals, but the effectiveness has not been verified and its associated mechanisms are not fully understood. This work investigated whether and how OSiF and mineral silicon fertilizer (MSiF) affect mitigation of Cd and Pb stress in rice (Oryza sativa). Both soil incubation and pot experiments were conducted to assess the effect of OSiF and MSiF on bioavailability of Cd and Pb in soil and their accumulation in rice. Additionally, a hydroponic experiment was conducted to study whether Si in rice can alleviate Cd stress. We found that both Si fertilizers could increase soil pH, induce the transformation of the acid soluble and reducible fractions of Cd and Pb to the oxidizable and residual fractions in soil, decreasing their bioavailability and the uptake of Cd and Pb in rice. However, Si in OSiF was not phyto-available, but Si in MSiF was available since available Si in soil and Si in plant increased in MSiF treatments but not in OSiF treatments. Meanwhile, rice grain yields significantly increased and the Cd and Pb content of brown rice reduced in MSiF treatments but not in OSiF treatments. In addition, Si was found to be able to alleviate Cd stress by improving the antioxidant capacity of rice. These results suggested that the decreased Cd and Pb accumulation in OSiF-treated rice was due to Cd and Pb immobilization in soil simply with pH increase, but in MSiF-treated rice Cd and Pb immobilization in soil (ex planta effect) and Si-conferred inhibitory effect of root-to-shoot Cd and Pb transport (in planta effect) contribute to the lower accumulation in rice.

Field assessment of carboxymethyl cellulose bridged chlorapatite microparticles for immobilization of lead in soil: Effectiveness, long-term stability, and mechanism

Lead (Pb) contamination in soil has been a major concern. Yet, cost-effective remediation technologies have been lacking. This study pilot-tested a new type of carboxymethyl cellulose (CMC) bridged chlorapatite microparticles (CMC-CAP) for immobilization of Pb at an abandoned chemical plant site, and monitored long-term (1 year) stability of Pb under the field conditions. Concentrated CMC-CAP (18 g L−1) was prepared at the pilot scale and then used for amending the soil on the site. CMC-CAP appeared as interwoven flocks of CAP microparticles with a hydrodynamic diameter of 2442 nm, which is 2.2 times smaller than that for bare CAP. CMC-CAP at a dosage of 0.5 wt% resulted in the highest immobilization of Pb, and decreased the acid-leachable Pb in the soil from 1.46 mg L−1 to 0.008 mg L−1 after 1 day of reaction, and further to 0.005–0.006 mg L−1 when aged for 180 and 365 days under the field conditions. The long-term aging consolidated the Pb immobilization, securing the compliance with the Chinese regulatory limit (0.010 mg L−1 for Pb). CMC-CAP served as a long-term sink for leachable Pb in soil and a pH buffer to maintain an alkaline soil pH. Sequential extraction data confirmed that the CMC-CAP amendment converted the more leachable Pb fractions into the less available Pb species. The soil amendment reduced the risk assessment code from “High risk” for the untreated soil to “Low risk” after 120 days of aging. XRD and FTIR results revealed the immobilization of Pb by CMC-CAP was achieved through the formation of the highly stable pyromorphite, surface complexation, and/or ion exchange reactions. Based on the field data, the remediation cost of the CMC-CAP based technology was estimated to be $36.2/m3. This study provides important field data on the effectiveness of CMC-CAP for cost-effective immobilization of Pb in soil.

Phosphate recycled as struvite immobilizes bioaccessible soil lead while minimizing environmental risk

Phosphorus (P) usage and water quality concerns are associated with using phosphate-based amendments to remediate lead (Pb) contaminated soils in urban areas. Struvite has gained increasing attention in the last decade to recover P from point sources while being used as a novel P fertilizer with reduced P loss risk, but its potential for serving as a P amendment for Pb immobilization has not yet been evaluated. This study evaluated the potential of using struvite to maximize Pb immobilization in alkaline urban soils while minimizing P loss risk by comparing the influences of three P amendments (triple superphosphate [TSP], struvite, phosphate rock [PR]) and two particle sizes (0.5 vs 2–4 mm) on Pb immobilization efficacy (relative change in Pb concentrations of in vitro physiologically based extraction test [PBET] test, PbPBET), P loss risk (water extractable P, Pw) and the translocation of Pb from soil to plant. The P amendments were added to two Pb-contaminated soils under urban agricultural use with contrasting clay contents (280 mg kg−1 with 4% clay versus 727 mg kg−1 with 14% clay) at a rate commonly used for Pb immobilization based on the soil elemental molar ratio of 4:1 (P/[Cd + Zn + Pb]). Greater immobilization efficacy of Pb (up to 19%) occured for granular (2-4 mm diameter) than ground (<0.5 mm) struvite. For a given particle size, Pb immobilization and plant tissue Pb decreased in the order of PR ≥ struvite > TSP, but the order reversed for P loss risk, with up to 177-fold greater Pw for TSP than PR and struvite. Greater immobilization for granular PR and struvite could be caused by lower dissolution rates which may better synchronize P dissolution and desorption of Pb. In addition to avoiding secondary contamination compared to conventional P amendments (e.g., Cd content), granular struvite can optimize trade-offs among soil Pb immobilization, crop Pb health risk, and P loss risk.

A new low-cost hydroxyapatite for efficient immobilization of lead

Distiller waste (DW), a common by-product of soda ash plants, was used as the unique calcium source to produce low-cost hydroxyapatites (HAPs) for the first time. The DW-derived HAPs were characterized by SEM, TEM, XRD and BET methods and investigated as amendments for soil Pb immobilization. The DW-derived HAPs displayed relatively smaller particle size (30–80 nm) and larger BET specific surface areas (60.00–64.06 m2/g) compared with two selected commercial HAPs (technical grade HAP and biological reagent HAP designated as HAP-TG and HAP-BR, respectively). The maximum sorption capacity of Pb on the DW-derived HAPs predicted from Langmuir sorption isotherm model was 726–734 mg/g higher than the commercial HAPs and even other well-designed sorbents. TCLP leaching experiments and BCR sequential extraction experiments were conducted to determine the effectiveness of HAP additions on Pb immobilization in soil. A lower addition ratio is required for the DW-derived HAPs than commercial HAPs to reduce Pb leachability to below the harmless level. Meanwhile, the DW-derived HAPs were found to be superior to commercial HAPs in transformation of readily bioavailable forms of Pb to stable speciation in soil, with residual fraction of Pb increased from 6.7% in non-amended soil to 60.7–61.4% in DW-derived HAPs amended soils, 58.3% in HAP-TG amended soil and 42.6% in HAP-BR amended soil, respectively. This study strongly demonstrated the feasibility and low-cost of HAPs derived from the distiller waste for reducing the environmental risks and bioavailability of Pb in soil.

Responses of soil aggregates and bacterial communities to soil-Pb immobilization induced by biofertilizer

The objective of this study was to investigate how soil aggregates and bacterial communities responded to soil-lead (Pb) immobilization induced by biofertilizer. Wheat (Triticum spp.) was planted in Pb-polluted soil. The re-distribution of Pb in soil aggregates and change of soil microbial communities due to biofertilizers were believed to be responsible for immobilizing soil Pb and alleviating its phytotoxicity. Adding biofertilizer promoted the formation of large aggregates (0.20–2.0 mm) with more mass loading of Pb, and increased soil bacterial diversity and the abundance of beneficial taxa such as those from the phyla Bacteroidetes, Actinobacteria, and Proteobacteria. In addition, there was significant alleviation of Pb availability as indicated by decreases in the values of bioconcentration factors (BCF) (up to 35.7% and 42.3% for roots and shoots, respectively) of wheat and DTPA-extractable Pb in soil (up to 34.4%) receiving fertilizer treatments compared with the CK (no treatment). Similar bacterial community structures and alpha diversities for the biofertilizer treatments and their autoclaved controls were observed, suggesting that physicochemical properties drove the structure of the soil bacterial community. This study introduced a new idea for development of effective strategies to control or reduce soil Pb risks.

Metal(loid) immobilization in soils with biochars pyrolyzed in N2 and CO2 environments

Previous studies indicated that using CO2 as a reaction agent in the pyrolysis of biomass led to an enhanced generation of syngas via direct reaction between volatile organic carbons (VOCs) evolved from the thermal degradation of biomass and CO2. In addition, the physico-chemical properties of biochar in CO2 were modified. In this current study, biochars generated from red pepper stalks in N2 and CO2 (RPS-N and RPS-C, respectively) were tested for their effects on the immobilization of Pb, Cd, Zn, and As in contaminated soils. Soils were incubated for one month with 2.5% of RPS, and two biochars (i.e., RPS-N and RPS-C) at 25°C. After the incubation period soils were analyzed to determine the amendment effects on the behavior of metal(loid)s. The potential availability and mobility kinetics of metal(loid)s were assessed by single extraction of ammonium acetate and consecutive extraction of calcium chloride, respectively. Sequential extraction was used to further examine potential changes in geochemical fractions of metal(loid)s. The increased soil pH induced by application of the biochars reduced the potentially available Pb, Cd, and Zn, while RPS-C significantly reduced Pb due to the high surface area and aromaticity of RPS-C. However, RPS-C mobilized potentially available As compared to RPS-N due to the increased soil pH. Biochars reduced the mobility kinetics of Pb, Cd, and Zn, and RPS-N effectuated the greatest reduction of As mobility. The RPS-C increased the Fe and Mn oxides, hydroxide, and organically bound Pb, while both biochars and RPS-N increased residual Cd and Zn, and organically bound As, respectively. When considering the two biochars, RPS-C was highly effective for immobilization of Pb in soils, but it had no effect on Cd and Zn and a negative effect on As. In addition, RPS-C significantly increased the total exchangeable cations in soils.

Characterization and low-cost treatment of an industrial arid soil polluted with lead sulfide in northern Chile

Lead (Pb) dust exposure can have detrimental environmental and human health effects. Improperly enclosed stockpiles of Pb concentrates can cause dust emissions, subsequent pollution of the soil and environmental risk. The aim of this work was to study Pb form, distribution and immobilization (by using eggshell and seashell) in an industrial arid soil near a storage area of Pb mineral concentrates in northern Chile. High amounts of sulfur (S; 9900 mg kg−1) and Pb (6530 mg kg−1) were found in the polluted soil. The energy-dispersive X-ray spectroscopy analysis revealed a lead sulfide (PbS: galena). Metallic Pb particles, which were between 41 and 46 µm, were identified in the soil. After eggshell and seashell (20%) were applied, the soil pH increased from 6.0 to 7.84 and 8.07, respectively. In the studied soil, the leaching test showed a 59 mg L−1 average Pb extractable concentration. After 240 days, extractable Pb by toxicity characteristics leaching procedure decreased to 4.79 mg L−1 (93.3%) with the application of seashell at 20% compared with a decrease of 33.33 mg L−1 (53.6%) using eggshell. Pb in the polluted soil was mainly found in the exchangeable fraction (66%), followed by the reducible (24%), residual (7%) and oxidizable (6%) fractions. According to the risk assessment code, the contaminated soil before treatment was classified as very high risk. Adding eggshell (20%) and seashell (20%) decreased the exchangeable fractions to 39 and 35%, respectively. Applying these liming materials achieved Pb immobilization in the soil, but the soil remained in the high environmental risk category. We conclude that the application of seashell waste, resulting from high aquaculture activity, opens an interesting window to the treatment of contaminated arid soils.

Influence of organic and inorganic amendments on the bioavailability of lead and micronutrient composition of Indian mustard (Brassica juncea (L.) Czern) in a lead-contaminated soil

Irrigation with untreated sewage water in periurban areas and other anthropogenic activities have resulted in accumulation of lead (Pb) in soils. To prevent its movement to deeper soil layers and groundwater aquifers, identification of some viable remedial measures is necessary for chemical and biological immobilization of Pb in soil. The objective of this study was to evaluate the impact of organic and inorganic amendments on Pb bioavailability, immobilization and on their effectiveness in enhancing micronutrients and growth of Indian mustard (Brassica juncea (L.) Czern). A loamy sand soil spiked with five levels of Pb varying from 0 to 400 mg kg−1 soil was used for the screen house study. Amendments used were lime (CaCO3), farm yard manure (FYM) and press mud (PM) applied at 2.5 and 5.0 % (w/w) and silt + clay applied at 20 and 40 % (w/w). Indian mustard was grown for 60 days with adequate application of nitrogen, phosphorus and potassium. All amendments reduced the extraction of Pb and the magnitude of reduction was highest with the addition of silt + clay. Addition of amendments increased plant dry matter yield as compared to unamended soil. All amendments significantly reduced Pb accumulation by Indian mustard and the magnitude of reduction increased with increasing the rate of amendment application. The addition of amendments also increased the concentration of micronutrients in Indian mustard as compared to unamended soils. The ameliorative efficiency of amendments in terms of reducing Pb content in plants followed the order silt + clay > lime > FYM > PM.

Utilization of phosphorus loaded alkaline residue to immobilize lead in a shooting range soil

The alkaline residue generated from the production of soda ash using the ammonia-soda method has been successfully used in removing phosphorus (P) from aqueous solution. But the accumulation of P-containing solid after P removal is an undesirable menace to the environment. To achieve the goal of recycling, this study explored the feasibility of reusing the P loaded alkaline residue as an amendment for immobilization of lead (Pb) in a shooting range soil. The main crystalline phase and micromorphology of amendments were determined using X-ray diffraction (XRD) and scanning electron microscopy-electron dispersion spectroscopy (SEM-EDS) methods. The toxicity characteristic leaching procedure (TCLP), sequential extraction procedure, and physiologically based extraction test (PBET) were employed to evaluate the effectiveness of Pb immobilization in soil after 45 d incubation. Treatment with P loaded alkaline residue was significantly effective in reducing the TCLP and PBET extractable Pb concentrations in contrast to the untreated soil. Moreover, a positive change in the distribution of Pb fractions was observed in the treated soil, i.e., more than 60% of soil-Pb was transformed to the residual fraction compared to the original soil. On the other hand, P loaded amendments also resulted in a drastic reduction in phytoavailable Pb to the winter wheat and a mild release of P as a nutrient in treated soil, which also confirmed the improvement of soil quality.

Recovery of nutrients from wastewater by a MgCl2 modified zeolite and their reuse as an amendment for Cu and Pb immobilization in soil

In this study, nutrients in wastewater were simultaneously removed by magnesium modified zeolite, and the precipitates of the nutrient recovery process were applied as a kind of amendment to achieve copper and lead immobilization in contaminated soil.

Biosorption mechanisms involved in immobilization of soil Pb by Bacillus subtilis DBM in a multi-metal-contaminated soil

Mechanisms of soil Pb immobilization by Bacillus subtilis DBM, a bacterial strain isolated from a heavy-metal-contaminated soil, were investigated. Adsorption and desorption experiments with living bacterial cells as well as dead cells revealed that both extracellular adsorption and intracellular accumulation were involved in the Pb2+ removal from the liquid phase. Of the sequestered Pb(II), 8.5% was held by physical entrapment within the cell wall, 43.3% was held by ion-exchange, 9.7% was complexed with cell surface functional groups or precipitated on the cell surface, and 38.5% was intracellularly accumulated. Complexation of Pb2+ with carboxyl, hydroxyl, carbonyl, amido, and phosphate groups was demonstrated by Fourier transform infrared spectroscopic analysis. Precipitates of Pb5(PO4)3OH, Pb5(PO4)3Cl and Pb10(PO4)6(OH)2 that formed on the cell surface during the biosorption process were identified by X-ray diffraction analysis. Transmission electron microscopy–energy dispersive spectroscopic analysis confirmed the presence of the Pb(II) precipitates and that Pb(II) could be sequestered both extracellularly and intracellularly. Incubation with B. subtilis DBM significantly decreased the amount of the weak-acid-soluble Pb fraction in a heavy-metal-contaminated soil, resulting in a reduction in Pb bioavailability, but increased the amount of its organic-matter-bound fraction by 71%. The ability of B. subtilis DBM to reduce the bioavailability of soil Pb makes it potentially useful for bacteria-assisted phytostabilization of multi-heavy-metal-contaminated soil.

Suitable Chemical Properties of Animal Manure Compost to Facilitate Pb Immobilization in Soil

Chemical immobilization using animal manure compost is one of the most useful for low-cost, in-situ soil remediation techniques. The present study aimed to determine suitable chemical properties of animal manure compost to facilitate lead (Pb) immobilization in soil. The level of mobile Pb in soil amended with swine compost was higher than that amended with cattle compost during the early stage of incubation. However, the level of mobile Pb was almost the same in soil amended with both types of compost on day 184 of incubation. The ratio of the residual fraction after sequential extraction was enhanced in soil amended with both types of compost, particularly swine compost. X-ray diffractometer (XRD) results demonstrated the precipitation of Pb phosphate minerals, such as pyromorphite, in Pb-sorbed composts, particularly swine compost. Amendment using swine compost could reduce Pb solubility even when it had a high content of water-soluble organic matter because it significantly lowered Pb phase solubility. The amendment with swine compost improved plant growth and microbial activity. This study suggests that composts with high phosphorus (P) content are suitable for Pb immobilization amendment even if they have a high water-soluble organic matter content.