Remediation Of Lead-contaminated Soil Research Articles

Remediation of Lead-Contaminated Soil by Using Saponin Derived from Sapindus Mukorossi

Lead (Pb) contamination in soils is a major global concern for both humans and the environment. Saponin, a plant-based based and environment-friendly surfactant was used for remediation of Pb-spiked garden soil to test its effectiveness and suitability for Pb removal. A Box-Behnken design was designed to optimise the washing conditions using the following variables: soil type (100% topsoil; 50% topsoil/50% sand; 20% topsoil/ 80% sand); pH of the washing solution (2; 3.5; 5); and saponin concentration (1%; 3%; 5%). The results showed that optimum removal efficiency of 58.69% was achieved with saponin, while distilled water removed 3.92% Pb in a single wash. Saponin was found to be statistically more effective than distilled water (P< 0.05); an optimum pH of 3.5 significantly increased Pb removal efficiency (P<0.05). The washing process was found to cause slight surface erosion and weathering of the soil grains.

Remediation of lead-contaminated soil from artisanal mining site using natural zeolite

One of the impacts of artisanal gold mining (ASGM) activity is lead (Pb) contamination in soil. This research was conducted on the Pb contaminated soil at the ASGM sites in Banyumas and Wonogiri in Central Java and Kulon Progo in Yogyakarta. This research aims to conduct a study of Pb mobility in contaminated soil and laboratory experiment to carry out remediation of Pb contaminated soil using natural zeolite with the batch test. The results showed that the Banyumas soil sample had higher Pb mobility compared to the other two soil samples. The batch test results showed that zeolite application useful to reduce Pb in the contaminated soil samples, where the Banyumas soil sample results in optimum value results due to the highest Pb mobility. The batch test results also showed that pH was a significant factor in the remediation process. This study concluded that the zeolite application reduces the concentration and mobility of Pb in the soil and affect the sorption by plants.

Investigation on microbial community in remediation of lead-contaminated soil by Trifolium repensL.

Trifolium repensL. is a plant with strong adaptability and large biomass, which possess great potential for phytoremediation. However, little is known concerning its remediation effects and changes in rhizosphere microbial activity and community structure under heavy metal pressure. The aims of this study were to evaluate lead accumulation of Trifolium repensL., study microbial lead resistance, metabolism and community structure characteristics in rhizosphere soils. The accumulated Pb concentration of Trifolium repensL. was observed in 100 and 500 mg/kg Pb contained soil at 55.81 and 90.3 mg/kg, respectively, which cause the decrease of acid-soluble fractions in rhizosphere soil. In the progress of lead-contaminated soil phytoremediation by Trifolium repensL., Pb resistance and metabolic activities of microorganisms have been prompted gradually. In addition, the microbial community composition and abundance were investigated using Illumina sequencing and quantitative PCR. The result showed that after phytoremediation, beneficial microorganisms, such as Flavisolibacter, Kaistobacter, and Pseudomonas, increased, becoming the dominant genera. This study has provided insight into the distribution and activity of the microbial community.

Lead-resistant strain KQBT-3 inoculants of Tricholoma lobayensis Heim that enhance remediation of lead-contaminated soil

To enhance lead-detoxifying efficiency of Tricholoma lobayensis Heim, one lead-resistant strain KQBT-3 (Bacillus thuringiensis) was applied owing to its excellent ability to tolerate Pb. KQBT-3 domesticated in liquid medium with increasing lead concentrations could tolerate Pb(NO3)2 up to a concentration of 800 mg L−1. Pot experiments showed that the KQBT-3 not only could promote the growth of T. lobayensis, but also could enhance its Pb accumulation ability under heavy metal stress. Biomass and accumulation of Pb increased 47.3% and 33.2%, respectively. In addition, after inoculation of KQBT-3, the significant decrease of malondialdehyde indicated KQBT-3 could alleviate lipid peroxidation in T. lobayensis. What is interesting is that superoxide dismutase and peroxidase activities in T. lobayensis inoculated with KQBT-3 were increased, and the maximum increasing rate was 121.71% and 117.29%, respectively. However, the catalase activity increased slightly. This revealed that inoculating KQBT-3 further induced oxidative response in T. lobayensis due to Pb accumulation. Therefore, the present work showed that KQBT-3 made a major contribution to promote growth and lead uptake of T. lobayensis and alleviate the oxidative stress. This kind of auxiliary effect on macrofungi can be developed into a novel bioremediation strategy.

Remediation of lead-contaminated soil using dissolved organic carbon solutions prepared by wine-processing waste sludge

Wine-processing waste sludge and alkaline substances, including KOH, NaOH, Ca(OH)2, and Mg(OH)2, were employed to prepare various dissolved organic carbon (DOC) solutions for remediating a Pb-contaminated cropland by soil washing. The Pb concentrations were 5340 and 4920mgkg−1 in the topsoil and subsoil, respectively. Aqueous solution treatment, general DOC treatment, and enhanced DOC treatment were proposed as treatments for the reclamation and determination of the factors affecting the removal of Pb, such as pH, initial concentration of the DOC solution, temperature, and washing frequency. The aqueous solution treatment could not remove sufficient Pb and therefore failed in the reclamation. Approximately 86.5% Pb was removed from the topsoil at pH2.0 by the general DOC treatment undergoing two wash cycles. However, over 90% Pb was removed from the subsoil under the same conditions; only the final Pb concentration in the subsoil met the control standard, 500mgkg−1. About 93% Pb in the topsoil could be removed at pH3.0 by the enhanced DOC treatment, which was performed using a 2500mgL−1 DOC solution containing abundant Ca2+ and Mg2+ at an 80:1 liquid/soil ratio (v/v) at 40°C for 60min. Meanwhile, organic matter, cation exchange capacity, NH4+-N, as well as exchangeable K, Ca, and Mg contents increased by 125%, 22.6%, 107%, 577%, 55.3%, and 306%, respectively, and the pH in the topsoil decreased to 3.7. The use of Ca(OH)2 and Mg(OH)2 not only prevented washing losses of the exchangeable Ca and Mg but also increased Pb removal by 20%. However, its use decreased the availability of P in the soil.

Remediation of lead-contaminated soil with non-toxic biodegradable natural ligands extracted from soybean

Bench-scale soil washing studies were performed to evaluate the potential application of non-toxic, biodegradable extracted soybean-complexing ligands for the remediation of lead-contaminated soils. Results showed that, with extracted soybean-complexing ligands, lead solubility extensively increased when pH of the solution was higher than 6, and approximately 10% (500 mg/kg) of lead was removed from a rifle range soil. Two potential primary factors controlling the effectiveness of lead extraction from lead-contaminated soils with natural ligands are adsorption of extracted aqueous lead ions onto the ground soybean and the pH of the extraction solution. More complexing ligands were extracted from the ground soybean as the reaction pH increased. As a result, significantly higher lead extraction efficiency was observed under basic environments. In addition, less adsorption onto soybean was observed when the pH of the solution was higher than 7. Among two available Lewis base functional groups in the extracted soybean-complexing ligands such as carboxylate and the α-amino functional groups, the non-protonated α-amino functional groups may play an important role for the dissolution of lead from lead-contaminated soil through the formation of soluble lead–ligand complexes.

Selected Morphological Characteristics, Lead Uptake and Phytochelatin Synthesis by Coffeeweed (Sesbania exaltata Raf.) Grown in Elevated Levels of Lead-Contaminated Soil

Remediation of lead-contaminated soil is significant due to the inherent toxicity of lead (Pb), and the quantity of Pb discharged into the soil. One of the most cost-effective and environmentally sound technologies for the cleanup of metal-contaminated soils is through the use of plants. While much is known about the ecological evolution of metal tolerance in plants, the physiological, biochemical, and genetic mechanisms of tolerance is not well understood in the majority of resistant ecotypes such as the legume, Sesbania exaltata Raf. This study was therefore conducted to determine the morphological and physiological characteristics of Sesbania that had been grown in Pb-contaminated soil, and to assess phytochelatin synthesis as a way of elucidating its relative Pb tolerance. Sesbania plants were grown in the greenhouse and exposed to various levels of Pb: 0, 1000, and 2000 mg Pb/kg soil. Plants were harvested after 6, 8, and 10 weeks of growth and morphological characteristics (e.g., root and shoot biomass, root length, number of root nodules, shoot height, number of leaves, number of flowers, number and length of pods) were recorded. Generally, there were no statistical differences in morphological characteristics among the treatments. Further, no discernible phytotoxic symptoms, such as chlorosis, wilting, or necrotic lesions, in neither roots nor shoots were observed. We concluded that while Sesbania did not fit the model of a hyperaccumulator, the plant was, nonetheless, tolerant to elevated Pb levels. Our assessment for phytochelatin synthesis as a tolerance mechanism was inconclusive and further investigations of tolerance mechanisms are warranted.

Mathematical model development and simulation of in situ stabilization in lead-contaminated soils

Stabilization and remediation of lead-contaminated soils has received considerable attention recently. Amending Pb-contaminated soils with phosphate as an in situ remediation option has been proposed as an alternative to other remediation options, such as soil removal. Research shows that hydroxyapatite (HA) [Ca 5(PO 4) 3OH] can reduce the bioavailability of Pb efficiently and thus is considered as an ideal phosphate source for formation of lead pyromorphite. Environmental models are increasingly being relied upon to help identify the limiting factors in such kind of in situ remediation. In this work, the contaminated aggregates remediation model has been developed and simulated to describe the effects of initial contaminant concentration, diffusion coefficient, and aggregate diameter on the time of remediation which is defined as the time required to reduce the aqueous phase lead concentration to <1 ppb. Results of simulation demonstrate that the aggregate size plays a significant role in remediation. The compartments-in-series model has been used to describe the dynamics of in situ stabilization in a soil bed. Results show that for a shallow bed a single, well-mixed, one compartment model gives approximately the same remediation time as the three compartments-in-series model.