Lead Immobilization In Soil Research Articles

Lead immobilization in soil using new hydroxyapatite-like compounds derived from oyster shell and its uptake by plant

Protecting the natural environment and ecological systems from the inorganic pollutants such as lead (Pb) has highlighted the urgent need to develop new and effective approaches for this substance’s immobilization in soil. In this study, new, low-cost, and eco-friendly hydroxyapatite (HAp)-like compounds were prepared by reacting oyster shell (Oys) with diammonium phosphate ((NH4)2HPO4) (DAP) and calcium hydroxide (Ca(OH)2) at 25–28 °C (OyOHr) and 100 °C (OyOHh). Furthermore, OyOHr and OyOHh were assessed for their effectiveness to immobilize Pb in soil and suppress Pb uptake by Indian spinach (Basella Alba L.). Application of 0.5% OyOHr and OyOHh to soil (by weight) reduced Pb concentration in the shoots by 76.9–78.0% compared to control (CK), to a level that was slightly higher (by 15.5–21.5%) than the recommended food safety level (2 mg kg−1) suggested by WHO. The changes in Pb fractions revealed that the total contents of oxidizable and residual forms in OyOHr or OyOHh after harvest was >415.0 mg kg−1, which indicated that >92% of Pb when added to the soil, was immobilized and not able to be taken up by plants. The proposed Pb immobilization mechanism might be the dissolution of OyOHr or OyOHh followed by hydroxypyromorphite (Pb10(PO4)6(OH)2) (HP) formation. Due to their facile preparation and eco-friendly and excellent Pb immobilizing characteristics, OyOHr or OyOHh could be readily integrated into current farming systems to mitigate the risk of Pb transferring to plants. However, OyOHr seemed a better immobilizing agent correspond to OyOHh in terms of cost and efficiency.

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.

Isolation and Characterization of Phosphorus Solubilizing Bacteria With Multiple Phosphorus Sources Utilizing Capability and Their Potential for Lead Immobilization in Soil

Phosphorus solubilizing bacteria (PSB) can promote the level of plant-absorbable phosphorus (P) in agro-ecosystems. However, little attention has been paid to PSB harboring abilities in utilizing multiple phosphorus sources and their potentials for heavy metal immobilization. In this study, we applied the strategy of stepwise acclimation by using Ca3(PO4)2, phytate, FePO4, and AlPO4 as sole P source. We gained 18 PSB possessing abilities of multiple P sources utilization, and these bacteria belonged to eight genera (Acinetobacter, Pseudomonas, Massilia, Bacillus, Arthrobacter, Stenotrophomonas, Ochrobactrum, and Cupriavidus), and clustered to two apparent parts: Gram-positive bacteria and Gram-negative bacteria. The isolate of Acinetobacter pittii gp-1 presented good performance for utilizing Ca3(PO4)2, FePO4, AlPO4, and phytate, with corresponding P solubilizing levels were 250.77, 46.10, 81.99, and 7.91 mg/L PO43–-P, respectively. The PSB A. pittii gp-1 exhibited good performance for solubilizing tricalcium phosphate in soil incubation experiments, with the highest values of water soluble P and available P were 0.80 and 1.64 mg/L, respectively. Additionally, the addition of A. pittii gp-1 could promote the immobilization of lead (Pb), and the highest Pb immobilization efficiency reached 23%. Simultaneously, we found the increases in abundances of both alkaline phosphatase gene (phoD) and β-propeller phytase gene (bpp) in strain gp-1 added soils. Besides, we observed the expression up-regulation of both pyrroloquinoline quinone gene (pqq) and polyphosphate kinases gene (ppk), with the highest relative expression levels of 18.18 and 5.23, respectively. We also found the polyphosphate particles using granule staining. To our knowledge, our findings first suggest that the solubilizing of tricalcium phosphate by phosphorus solubilizing bacterium belonging to Acinetobacter is coupled with the synthesis of polyphosphate. Taken together, A. pittii gp-1 could be a good candidate in improving soil fertility and quality.

Synergistic construction of green tea biochar supported nZVI for immobilization of lead in soil: A mechanistic investigation

Biochar-based nanocomposites with functional materials provide an excellent prospect in reactivity and stability. Most biochar reported have no reusability upon aging and offer the risk of release of immobilized components after short-term immobilization. To overcome this, we developed nano zero-valent iron (nZVI) impregnated magnetic green tea biochar (nZVI@GTBC) and studied its performance in immobilizing Pb and long-term effectiveness in the soil. The reactive nZVI units were obtained from iron oxide solution by reducing with polyphenol solution (green tea extract) and were successively stabilized by impregnation onto the remaining green tea waste matrix through co-precipitation technique. Finally, the magnetic biochar was developed from the above nZVI impregnated green tea waste through oven drying and slow pyrolysis technique in different temperature range (150–650 °C). The synthesized nZVI@GTBC biochar was characterized and studied by XRD, FTIR, Raman, UV–Vis, TG/DSC, XPS, SEM, and TEM. The nZVI@GTBC obtained with a particle size of 130 nm and surface charge of +2.8 C/m2 at 450 °C. Moreover, colloidal stability and mobility experiments were considered to explain the transport behavior and stability of bare nZVI and magnetic nZVI@GTBC in the soil. The immobilization of Pb by pristine nZVI, GTBC, and nZVI@GTBC was compared and explained under different soil pH conditions. The bioavailability of Pb content before and after immobilization was investigated through leaching experiments. Further, thirty days of soil incubation were carried out to examine different species of Pb according to the Tessier sequential extraction scheme. The study suggested that nZVI@GTBC enhanced the immobilization efficiency by 19.38% in comparison with pristine nZVI and 57.14% in comparison with bare GTBC biochar.

Effectiveness of Biochar Obtained from Corncob for Immobilization of Lead in Contaminated Soil.

Background.Recent studies have explored the potential for using biochar as a soil amendment in agriculture. However, it can also be used as a gentle remediation option for contaminant reduction. Biochar is a by-product obtained from the pyrolysis of biomass (organic matter). It is known for its long-lasting chemical properties, wide surface area values, and carbon-richness, which make it an efficient method for the immobilization of organic and inorganic contaminants such as heavy metals.Objective.The aim of the present study was to analyze the efficiency of biochar, obtained from the gasification of corncob, for the immobilization of lead in contaminated soils.Methods.In the present study, biochar from corncob was used as an amendment for soil contaminated with lead (extracted from the municipality of Malambo, Colombia) in order to estimate its ability to immobilize leaching lead. A comparison laboratory test applied a modified biochar produced with a 10% hydrogen peroxide chemical treatment. In addition, a pot experiment was done with both biochar by sowing seeds of Pennisetum clandestinum for 33 days. During this period, plant growth was measured for the different amendments of biochar concentrations.Results.Laboratory tests indicated that unmodified biochar obtained a maximum retention of 61.46% of lead, while the modified biochar obtained only 44.53% retention. In the pot experiments, the modified biochar indicated high germination and growth of seeds (up to 89.8%).Conclusions.Although the lead immobilization in soil was positive for both cases, the use of soil with high concentrations of lead (167.62 g/kg) does not indicate biochar's effectiveness for purposes of comparison with the current United States Environmental Protection Agency (USEPA) limit value (400 ppm for bare soil in urban play areas). Therefore, further studies are recommended using soil with lower lead concentration levels.Competing Interests.The authors declare no competing financial interests. One author is an employee of Pure Earth.

Effect of SRB-zeolite technology on immobilization of lead in soil

Effect of SRB-zeolite technology on immobilization of lead in soil

Impact of phosphorus and water-soluble organic carbon in cattle and swine manure composts on lead immobilization in soil

In the present study, we aimed to understand how amelioration of animal manure compost (AMC) with high phosphorus and low water-soluble organic carbon (WSOC) contents can simultaneously immobilize lead and reduce lead mobility and bioavailability in soil irrespective of the animal source. The amount of water-soluble lead in the soil amended with swine compost (SC) was not suppressed as compared with that in the soil without compost, whereas it was suppressed in the case of the soil amended with cattle compost (CC). The lead phases in the soil amended with SC became less soluble; however, those in the soil amended with CC were equivalent to those in the soil without compost. The ameliorated cattle and SCs with high phosphorus and low WSOC contents simultaneously induced a significant reduction in the concentration of water-soluble lead and ensured the formation of higher concentrations of insoluble lead phases. The microbial enzyme activities in the soil amended with the ameliorated compost were lower than those in the soil amended with the SC. This study suggests that ameliorated AMC can alter lead phases to insoluble forms and suppress the level of water-soluble lead, simultaneously. Therefore, such ameliorated AMC with high phosphorus and low WSOC contents would be suitable as a lead immobilization material.

Immobilization of lead in soil influenced by soluble phosphate and calcium: lead speciation evidence.

We investigated the effect of soluble Ca on the speciation of Pb in phosphate-amended soils. A calcareous soil was amended in sequence with soluble phosphate (0 and 299 mg kg P), calcium nitrate (0, 200, and 400 mg kg Ca), and/or lead nitrate (0 and 1000 mg kg Pb) and incubated for 50 d. Extractable Ca was relatively similar across all samples, with a minor reduction in Ca release for treatments amended with P possibly from the formation of Ca-phosphate minerals. Olsen-P extractability from P-added treatments was highest in the non-Pb-amended soils and was about 40% lower when Pb was added as a result of Pb-phosphate formation. In the absence of P, diethylene triamine pentaacetic acid (DTPA)-Pb extractability increased with increasing Ca amendment; however, in the P-amended treatments, DTPA-Pb decreased with increasing Ca addition. X-ray absorption spectroscopy results of the Pb spiked soils indicate that adsorbed Pb is the primary phase (up to 92%) in non-P-amended soils with minor distribution to hydrocerussite and Pb-phosphate phases. In the P-amended treatments, Pb speciation shifted to Pb-phosphate [chloropyromorphite and Pb(PO)] (42-48%) and adsorbed Pb (44-50%). As Ca concentration increased in the P-amended soils, Pb-phosphate speciation moved from combined chloropyromorphite and Pb(PO) (0 mg kg Ca) to exclusively chloropyromorphite. The study demonstrates that soluble Ca enhances Pb immobilization with P amendments.

Coupled Dissolution and Precipitation at the Cerussite-Phosphate Solution Interface: Implications for Immobilization of Lead in Soils

In situ atomic force microscopy (AFM) has been used to study the interaction of phosphate-bearing solutions with cerussite, PbCO3, (010) surfaces. During the dissolution of cerussite we observed simultaneous growth of needle-shaped or spherical pyromorphite phases. This occurred at two different pH values and ionic strengths relevant to soil solution conditions. The initial dissolution processes occurring at the cerussite solid-phosphate solution interface were clearly distinguished, and heterogeneous nucleation and growth rates of pyromorphites at phosphate concentrations ranging from 0.1 μM to 10 mM were quantitatively defined. Enhanced cerussite dissolution in the presence of high salt (NaCl or NaF) concentrations leads to an increase in pyromorphite nucleation and growth rates. The newly formed pyromorphites were found to be stable upon contact with water or citrate-bearing solutions under acidic or alkaline conditions in the pH range 4-8. These in situ observations may improve the mechanistic understanding of processes resulting in lead immobilization in diverse soil systems as well as to enhance the effectiveness of phosphate-based treatments for remediation of lead-polluted soils.

The role of organic acids in the mobilization of heavy metals from soil

Batch laboratory experiments were performed to determine the effectiveness of organic acids in mobilizing heavy metals (Cu, Pb, Zn) from contaminated soils. Because the direct measurement of all of the species that are extracted by an organic acid is not possible, we calculated the speciation of Cu, Pb, and Zn in the presence of oxalate with regard to the primary distribution of metals and oxalate in solution using GEOCHEM-PC. Significant amounts of copper and zinc were removed from contaminated soil at higher initial concentrations of oxalic and succinic acids in solution. For the viewpoint of lead immobilization in soil, citric acid was the most effective among organic acids. Our speciation calculations by GEOCHEM-PC for metal-oxalate complex imply that significant amounts of the Cu, Pb and Zn that was extracted from the soil existed as oxalate complexes and free metal ionic form.

Isolation of phosphate solubilizing bacteria and their potential for lead immobilization in soil

Lead (Pb), a highly toxic heavy metal forms stable compounds with phosphate (P). The potential of phosphate solubilizing bacteria (PSB) to immobilize Pb by enhancing solubilization of insoluble P compounds was tested in this research. Eighteen different PSB strains isolated from P amended and Pb contaminated soils were screened for their efficiency in P solubilization. The PSB isolated from P amended soils solubilized 217–479 mg/L of P while the PSB from Pb contaminated soil solubilized 31–293 mg/L of P. Stepwise multiple regression analysis and P solubility kinetics indicated that the major mechanism of P solubilization by PSB is the pH reduction through the release of organic acids. From the isolated bacteria, two PSB were chosen for Pb immobilization and these bacteria were identified as Pantoea sp. and Enterobacter sp., respectively. The PSB significantly increased P solubilization by 25.0% and 49.9% in the case of Pantoea sp., and 63.3% and 88.6% in the case of Enterobacter sp. for 200 and 800 mg/kg of rock phosphate (RP) addition, respectively, thereby enhancing the immobilization of Pb by 8.25–13.7% in the case of Pantoea sp. and 14.7–26.4% in the case of Enterobacter sp. The ability of PSB to solubilize P, promote plant growth, and immobilize Pb can be used for phytostabilization of Pb contaminated soils.

Estudo do comportamento do chumbo em latossolos brasileiros tratados com fosfatos: contribuições para a remediação de sítios contaminados

Phosphates have been used for lead immobilization in soils but the influence of soil type is not fully understood. In this work, lead chemical behaviour in two Brazilian latosoils (LA and LV) was studied via treatment with phosphates. The Pb concentration in Toxicity Characteristic Leaching Procedure (TCLP) solutions was decreased in all treatments. After treatment with H3PO4 the Pb concentration in the LA remained within the regulatory limit established by EPA. The ecotoxicological results with Daphnia pulex showed that this treatment reduced the lead bioavailability. Sequential extraction analyses showed that the lead was transferred from the most available to the residual fraction. Relevant decrease of soluble lead was observed in all phosphate treatments.

Selected bioavailability assays to test the efficacy of amendment-induced immobilization of lead in soils

Lead immobilization in 10 soils contaminated with Pb from different origin was examined using lime (CaCO3), a mix of cyclonic ash and steelshots (CA+ST), and a North Carolina phosphate rock. The immobilization efficacy of the three amendments was evaluated using single (CaCl2solution) and sequential (BCR method) chemical extractions in tandem with a microbiological Pb biosensor (BIOMET), a Pb phytotoxicity test, Pb plant uptake, and a Physiologically Based Extraction Test (PBET) mimicking Pb bioavailability in the human gastro-intestinal tract. The results demonstrated the necessity of using a diverse suite of bioavailability methodology when in situ metal immobilization is assessed. Sequential (BCR) extractions and PBET analysis indicated that PR was the most effective amendment. PR however, proved ineffective in totally preventing Pb phytotoxicity and Pb uptake on all soils tested. On the contrary, CA+ST and lime decreased BIOMET Pb, Pb phytotoxicity, and Pb uptake to a far greater extent than did PR. BIOMET detectable Pb and Pb uptake, however, were strongly related to Pb in soluble or exchangeable soil fractions (i.e., CaCl2 extractable). By combining these fractions with the acid-extractable Pb, accomplished by using acetic acid extractant, the recently developed BCR sequential extraction scheme appeared to have lost some valuable information on judging Pb bioavailability. The data show that different amendments do not behave consistently across different soils with different sources of contamination. Different indices for measuring Pb bioavailability are also not necessarily consistent within particular soil and amendment combinations.

Modelling the Role of Active Biomass on the Fate and Transport of a Heavy Metal in the Presence of Root Exudates

The influence of active biomass in immobilizing heavy metals in the soil rhizosphere is investigated through mechanistic models. The movement of water in the soil is modeled using Richards equation. An advection-dispersion equation, with a sink term for metal uptake by biomass, is used for modeling the fate and transport of lead. This sink term represents the nonlinear kinetics of metal adsorption to the biomass that is partitioned into mobile and stationary fractions within the soil. Transport of the mobile biomass fraction is modeled by an advection-dispersion equation, with a source term that is based on Monod growth kinetics, and a linear sink term for endogenous decay. The movement of metal in association with mobile biomass is also included as a transport mechanism for lead. Root exudates serve as carbon substrate for the biomass growth, and their transport is modeled in a similar way as that of the biomass. A hypothetical one-dimensional vertical soil column containing metal, biomass and a carbon substrate is used for analyzing lead movement. Model simulations demonstrate the influence of water content, growth rate of biomass, partitioning coefficient of biomass between soil and aqueous phase, and partitioning coefficient of metal between biomass and aqueous phase of the soil on fate and transport of lead. The extent of immobilization of lead in soil is found to be dependent on the growth of biomass, which in turn depends on the availability of root exudates in the rhizosphere. Apart from analyzing different scenarios, such a model can be used for designing future experiments.