Pb-contaminated Soil Research Articles

Global Perspectives on Lead Contamination and Health Risks in Surface Water, Rice Grains, and Soils

ABSTRACTLead (Pb), a pervasive and highly toxic metal, and poses significant environmental and health risks due to its extensive biogeochemical cycling, driven by anthropogenic activities. This review evaluates the health hazards allied with Pb contamination in surface water bodies, soils, and rice grains, based on a comprehensive analysis (2015–2024) of 118, 133, and 102 literature studies, respectively. The year‐wise assessment of Pb concentration in surface water bodies and soils frequently exceeded their permissible limits in 2015, 2017, 2018, 2019, 2020, and 2022. However, the mean Pb concentration in rice grains consistently surpassed the Codex Alimentarius limit (2.5 μg/g) across the analyzed years. Geographically, Bangladesh, India, Pakistan, and China surpassed their limits for surface water bodies, rice grains and soils, emphasizing regional vulnerabilities. Health risk analysis indicated hazard quotient values exceeding one for children and adults in surface water bodies and rice grains, exhibiting significant non‐carcinogenic risks. In soils, dermal exposure identified as the predominant pathways contributing to health hazard followed by ingestion, while inhalation presented the lower risk. These findings emphasize the imperative necessitate for implementing strict regulatory frameworks and preventive measures to mitigate Pb contamination in the environment and minimize its potential health impacts. This study advances understanding of Pb exposure pathways and risks, offering valuable insights for targeted mitigation strategies and public health interventions.

Enhancing Cd and Pb tolerance of Robinia pseudoacacia (black locust) by regulating antioxidant defense system, macroelement uptake and microstructure.

Woody plants had received considerable attention for the phytoremediation of heavy metal-contaminated soil. This study aimed to investigate the changes in antioxidant enzyme activity, macroelement uptake, and microstructure of the woody plant Robinia pseudoacacia (black locust) for the phytoremediation of cadmium (Cd) and lead (Pb) co-contaminated soil based on dynamic sampling. The results showed that black locust demonstrated strong tolerance in Cd and Pb co-contaminated soil. After 30-120 d of cultivation, the activities of superoxide dismutase (SOD), peroxidase (POD), and the macroelement (K and Ca) content in plant leaves significantly declined in response to Cd and Pb. However, after 160 d of cultivation, the antioxidant enzyme activities, chlorophyll, sulfhydryl, and soluble protein contents, as well as Ca and Mg content in plant leaves were returned to normal levels under the 40mg·kg-1 Cd and 1000mg·kg-1 Pb contaminated soil (CdPb3). Meanwhile, K content in plant leaves under the CdPb3 treatment was significantly (P<0.05) increased by 68.9% compared to the control. Cd and Pb was primarily accumulated in black locust roots. Scanning electron microscope (SEM) analysis indicated that the sieve tubes in the roots and stems of plant might block the transport of Cd and Pb. Transmission electron microscope (TEM) analysis indicated that the number and volume of osmiophilic particles in plant leaves were increased and the cell walls were thickened in response to Cd and Pb stress. Path analysis further indicated that the growth of plant was related to macroelements uptake and physiological change (photosynthesis, antioxidant enzyme activity, and chelation). Thus, black locust could effectively regulate the antioxidant defense system, macroelement absorption, and microstructure to enhance plant tolerance to Cd and Pb stress. Moreover, black locust could maintain the normal urease, acid phosphatase, and sucrase activities in the Cd and Pb co-contaminated soil. These findings suggested that black locust could be considered as a useful woody plant for the phytostabilization in Cd and Pb-contaminated soil.

Mowing facilitated Pb accumulation in bermudagrass by mediating root radial transport.

Moderate mowing of the shoot is an effective strategy for improving Pb-contaminated soil remediation using bermudagrass. However, the mechanisms by which mowing facilitates Pb uptake and accumulation remain insufficiently understood. Root radial transport is critical in efficient heavy metal uptake and translocation in plants and is influenced by root physiological-biochemical characteristics. Herein, radial transport in roots and its effect on root-shoot Pb transport in bermudagrass under mowing were explored. Results revealed that mowing decreased Pb in apoplasts and increased Pb in symplasts, altering Pb radial transport pathways in roots. In the apoplastic pathway, mowing pretreatment intensified the inhibitory effects of a transpiration inhibitor on Pb uptake, resulting in a reduced contribution of the apoplastic pathway. Mowing induced lateral root endodermis thickening, early suberin lamellar development and increased suberin deposition, effectively preventing Pb from entering the stele through the apoplastic pathway. Conversely, in the symplastic pathway, mowing pretreatment alleviated the inhibitory effects of a metabolic inhibitor and ion channel inhibitor on Pb uptake and significantly increased net Pb2+influx in lateral root tips, thereby promoting the symplastic pathway. Furthermore, mowing upregulated the relative expression of CdNramp5 and CdHMA2 in roots, increasing Pb translocation to the shoot via the symplastic pathway. Overall, our study provided novel evidence mowing primarily improved Pb uptake and root-to-shoot transport by increasing the efficiency of the symplastic pathway. These findings provide a theoretical foundation for the use of mowing to improve the efficacy of bermudagrass in the remediation of Pb-contaminated soils.

Lead (Pb) Contamination in Soil and Plants at Military Shooting Ranges and Its Mitigation Strategies: A Comprehensive Review

Heavy metals, especially lead (Pb), is the major cause of pollution in the military shooting range soils. Bullets, which are primarily made of Pb, are a substantial source of this pollution. On speciation, this Pb is distributed into its different metal forms. Different physicochemical properties of the soil like pH, moisture content, cation exchange capacity (CEC), and organic matter play a very crucial role in the distribution, transformation, and bioavailability of the Pb. The concentration of Pb found in different shooting ranges is examined. Moreover, bullet weathering and the availability of contaminants in the soil are influenced by the physicochemical properties of the soil. For the management of firing range pollution, a variety of strategies have been investigated, including soil washing, phytoremediation, and chemical stabilization. This review focus on the pollution status of different shooting ranges, the impact of the physicochemical properties of soil on the distribution, speciation, and transformation of Pb, and different mitigation strategies to control Pb pollution in military shooting ranges.

Synergistic effects of allantoin and Achyranthes japonica-biochar profoundly alleviate lead toxicity during barley growth.

Lead (Pb), a toxic metal, causes severe health hazards to both humans and plants due to environmental pollution. Biochar addition has been efficiently utilized to enhance growth of plants as well as yield in the presence of Pb-induced stress. The present research introduces a novel use of biochar obtained from the weed Achyranthes japonica to enhance the growth of plants in Pb-contaminated soil. An experiment was performed with 7 treatments: Control, Pb2+ (10 mg kg-1) only, biochar (4 %) only, allantoin (4 g kg-1) only, biochar combined with Pb2+, allantoin combined with biochar, as well as a combination of allantoin and biochar with Pb2+. Lead toxicity alone markedly diminished plant growth metrics, including root and shoot length, biomass (wet and dry), chlorophyll concentration, and grain production. The application of biochar, allantoin, or their joint administration markedly enhanced the length of shoots (by 50.3 %, 29 %, and 70 %), length of roots (by 69 %, 50 %, and 69 %), and fresh biomass of shoots (by 5 %, 29 %, and 5 %), respectively. This enhancement is ascribed to improved soil characteristics and more efficient absorption of nutrients. The application of biochar, allantoin and their combination improved the tolerance against Pb2+ by increasing the total chlorophyll level by 12 %, 16 %, and 17 %, respectively, vs. the control. Likewise, these amendments significantly (p < 0.05) improved the activity of antioxidant enzymes, including SOD, POD, and CAT by 49 %, 29 %, and 49 %, respectively. The resistance towards Pb2+ was enhanced by biochar, allantoin, and their combined application, with lower Pb2+ concentrations in shoots (59.9 %, 40.1 %, and 49.8 %), roots (48.2 %, 24.1 %, and 58.3 %), and grains (60.2 %, 29.7 %, and 40.1 %) compared to solely Pb-stress, respectively. In summary, converting the weed Achyranthes japonica into biochar and integrating it with allantoin provides an eco-friendly approach to control its proliferation while efficiently alleviating Pb-induced toxicity in plants.

Evaluation of bromelia karatas as a bioindicator of lead contamination

Abstract: metals toxic contamination is a problem that has increased mainly due to anthropogenic activities. Lead (Pb) is a hightly toxic metal present in the environment due to industrial activities, such as mining, smelting, manufacturing, and burning of fossil fuels. This work studied Bromelia karatas as a bioindicator of the quality of the environment in the presence of lead. Forty 200-day-old plants (Bromelia karatas) were used, of which 30 were transplanted in a substrate (Peat moss) contaminated with Pb, using Pb(NO3)2 as a contaminating agent, at different concentrations, T1= 1000, T2=2000 and T3=3000 mg/kg (milligram of Pb/Kilogram of substrate), and 10 were used as control (Tc). At the end of the experiment, the presence of Pb was analyzed and found in the plant tissues (leaves and roots), using the ICP-OES equipment. This research revealed the potential of Bromelia karatas as a bioindicator of Pb contamination in soil, causing visible symptoms of foliar damage on its leaves with high doses of the contaminant. The low cost, easy reproduction and portability of bromeliad compared to other bioindicators make it a better option to be used as a bioindicator and/or biomonitor.

Cola beverage reduces risk of lead poisoning from accidental ingestion of contaminated soil particles in rat and swine models

Accidental ingestion of lead (Pb)-contaminated soils represents a major route of Pb exposure for both adults and children, and the development of accessible and cost-effective solutions to reduce Pb poisoning is urgently required. Here, we present an effective and straightforward technique, involving the consumption of cola beverages, for the purpose of lowering blood Pb levels following the ingestion of contaminated soils in animal models. This method facilitated the direct passage of Pb in contaminated soil through the digestive system, enhancing its elimination without absorption into systemic circulation. Our results demonstrated that cola effectively reduced Pb bioaccessibility in 22 contaminated soils by 32.6%–98.8%. In male rats and swine exposed to Pb-contaminated soils, cola treatment decreased blood Pb concentrations by 32.9%–96.0% and 31.5%–81.5%, respectively. This cola-induced reduction in Pb bioaccessibility and bioavailability was attributed to the rich phosphoric acid content in cola, which promoted the formation of insoluble Pb phosphate precipitate (pyromorphite [Pb5(PO4)3Cl]) during the gastric phase. The precipitate was directly excreted in feces, resulting in lower Pb absorption in the blood. These findings suggest that the consumption of cola beverages may be a practical strategy to mitigate the risk of Pb poisoning following the accidental ingestion of contaminated soils. However, the applicability of this approach in humans remains uncertain in the absence of population-based studies. While these findings underscore the potential for cola beverages to reduce Pb absorption following soil ingestion in animal models, further research is necessary to evaluate its safety, efficacy, and possible risks in humans before any such protocols are initiated.

Enhanced Pb immobilization by CaO/MgO-modified soybean residue (okara) in phosphate mining wasteland soil: Mechanism and microbial community structure.

Lead (Pb) contamination is an inevitable consequence of phosphate mining, necessitating the development of effective remediation strategies. This study investigated the use of CaO/MgO-modified okara (CMS) as an eco-friendly approach to remediate Pb-contaminated soils from phosphate mining wastelands. In the present study, following 30d of CMS application, the exchangeable Pb content was significantly decreased to 10.46%, with the majority of Pb transforming into more stable forms: carbonate-bound Pb (56.44%), Fe/Mn oxide-bound Pb (11.03%), and organic-bound Pb (19.58%). Additionally, the treatment led to a substantial enhancement in total phosphorus, available phosphorus, ammonium, and soil organic matter, thereby improving soil fertility. The microbial community structure was also significantly influenced by CMS, with a notable increase in Firmicutes to 45%. Key genera within the microbial community included Azospirillum, Pseudoxanthomonas, Sphingomonas, and Microvirga, with Pseudoxanthomonas and Massilia being the main differential species. These genera were significantly positively correlated, contributing to the maintenance of microbial community homeostasis and promoting the production of CO32- and PO43-, which further accelerated Pb immobilization. The results indicate that CMS is an effective amendment for Pb immobilization in contaminated soils, enhancing soil fertility and modulating the microbial community to promote Pb stabilization. This provides valuable insights into the ecological remediation of Pb-contaminated soils and water bodies, highlighting the potential of waste reuse in environmental management.

Experimental Study on the Change in Freezing Temperature During the Remediation of Pb-Contaminated Soils with Biochar

Experimental Study on the Change in Freezing Temperature During the Remediation of Pb-Contaminated Soils with Biochar

Sex dependent intergenerational effects of lead in mouse model

Lead (Pb) exposure negatively impacts fertility in both males and females, pregnancy outcomes, and child brain development. We investigated the reproductive and neurological effects of Pb exposure on male and female mice via Pb-contaminated soil for 4 weeks. Breeding was conducted after completion of exposure, in four groups; group 1 consisted of exposed dams and unexposed sires, group 2 consisted of exposed sires and unexposed dams, group 3 consisted of exposed sires and exposed dams and group 4 was the control. Generally, Pb exposure reduced observed conception rates, with a cumulative decrement observed when both males and females are exposed. Gene expression of the testes revealed oxidative stress as the cause of reduced conception rates. Neurological tests: Morris water maze and rotarod were conducted on F1 generation offspring. Maternally and paternally exposed F1 mice performed poorly in the Morris water maze when compared to the control. The severity of the neurological effects was also parent-dependent and sex-dependent. Paternal Pb exposure effects were more pronounced in female offspring. A comparison of gene expression changes of the hippocampus and prefrontal cortex showed paternal Pb-exposure resulted in more prefrontal cortex changes than in the hippocampus, a trend also recorded in the exposed sires. The pronounced effects in female offspring of paternal Pb exposure may suggest that Pb neurological effects may be X-chromosome-linked.

Effect and Mechanism of Water-soluble Chitosan Promoting Phytoremediation of Cd and/or Pb-contaminated Soils by Sedum aizoon L.

A pot experiment was conducted to investigate the growth response, concentration, and transportation characteristics of Cd and Pb in Sedum aizoon L. in four typical Cd/Pb-contaminated soils from northern and southern China with the addition of different levels of water-soluble chitosan （WSC）. The effect of WSC on physicochemical properties, Cd and Pb forms, and functional groups in contaminated soils was determined to clarify the internal mechanism of WSC promoting Cd and Pb accumulation by S. aizoon. The results showed that WSC improved the physicochemical properties of rhizosphere soil by increasing alkaline nitrogen and organic matter contents and significantly reducing pH values. In addition, WSC significantly increased the acid-extractable Cd and Pb in contaminated soils by 16.3%-34.5% and 88.9%-272.4%, respectively. Fourier transform infrared spectra analysis showed that amino （-NH2） and hydroxyl （-OH） groups in soils were significantly increased by adding WSC. Therefore, the coordination of Cd/Pb with -NH2 and -OH may play important roles in forming complexes and mobilizing Cd/Pb in soils. Moreover, the improvement in the rhizosphere environment of contaminated soils by WSC contributed to promoting Cd and Pb accumulation by S. aizoon. WSC significantly increased the total Cd and Pb accumulation by 14.5%-72.1% and 55.0%-128.5%, respectively, without obvious growth inhibition. Therefore, it is feasible to apply WSC to promote Cd/Pb accumulation using S. aizoon, while the matching of WSC addition amount, soil pollution condition, and plant materials should be further considered in practical application.

Deciphering the Driving Mechanism and Regulatory Strategies of Antibiotic Resistance Genes Transmission in Lead-Contaminated Soil Microbial Communities by Multiple Remediation Methods

Pb-contaminated soil poses inherent risks for the spread of antibiotic resistance genes (ARGs). However, few reports have investigated the distribution of lead resistance genes (LRGs), particularly their role in ARGs dynamics during Pb-contaminated soil remediation. This study explored the mechanisms driving ARGs variation under different remediation strategies. The results indicated that an increase in the total abundance of ARGs after applying montmorillonite (Imvite), the composite remediation agents of MgO and Ca(H2PO4)2 (MgO-Ca(H2PO4)2), and the composite remediation agents of montmorillonite, MgO, and Ca(H2PO4)2 (Imvite-MgO-Ca(H2PO4)2). Bioelectrochemical systems (BES) effectively reduced ARGs abundance, and when combined with Imvite-MgO-Ca(H2PO4)2, lowered the risk of ARGs proliferation linked to antibiotic deactivation. Changes in Pb concentration and pH reshaped microbial communities, impacting both LRGs and ARGs. To reduce the risk of ARGs proliferation and transmission during, various control strategies, such as modifying Pb stress, adjusting pH, and manipulating microbial community structure, have been proposed. The study provided theoretical foundation and practical strategies for controlling ARGs dissemination during the remediation of heavy metal-contaminated soil.

Deciphering the mechanisms, signaling, and applications of newly isolated Cladosporium crousii SHF to alleviate the negative effects of Pb stress in tomato plants

In the present study, lead (Pb) tolerant fungal strains were isolated from Pb-contaminated soil and examined for plant growth-promoting traits (PGP), including the production of exopolysaccharides, siderophores, and indole-3-acetic acid (IAA). The present study aimed to isolate and characterize the Pb-tolerant fungal strains and to inoculate them into tomatoes under Pb stress to evaluate their remediation potential. Three strains were selected based on these traits and were assessed for Pb tolerance. The myco-remediation potential of Cladosporium crousii was assessed by measuring its tolerance to various Pb concentrations (0–30 mM). Among the examined strains, C. crousii SHF exhibited the highest Pb tolerance and was, therefore, selected for further experimentation. The stress resilience efficiency and phyto-beneficial characteristics of C. crousii SHF strain were assessed under Pb stress. The results revealed that C. crousii SHF inoculation in tomato plants elicited a reprogramming of plant growth, reduced Pb accumulation, and enhanced metal tolerance through the reduction of abscisic acid by 24.2% in roots and 12.19% in shoots, and jasmonic acid by 19.24% in roots and 37.84% in shoots. Furthermore, salicylic acid significantly increased by 112% in roots and 243% in shoots while simultaneously modulating antioxidants (SOD, CAT, and APX) within the oxidative stress defense system. Gene expression analysis further validated these findings, demonstrating that C. crousii SHF inoculation significantly decreased the expression of SlPCS1 (32.3%) (phytochelatin synthase protein), SlMTP5 (31.3%) (metal transportation protein), and SlNCED3 (50%) (stress hormone) in tomato plants. The fungal strains were molecularly characterized using the nuclear ribosomal internal transcribed spacer region (ITS), and the amplified sequences through 18S rDNA were submitted to the GenBank NCBI database (accession number OR841280). These findings identified a new mycorrhizal strain, C. crousii SHF, with the potential to alleviate Pb contamination and regulate heavy metal metabolism in plants.

Development of polyfunctionalized biochar modified with manganese oxide and sulfur for immobilizing Hg(II) and Pb(II) in water and soil and improving soil health

Mercury (Hg) and lead (Pb) pose significant risks to human health due to their high toxicity and bioaccumulative properties. This study aimed to develop a novel biochar composite (HMB-S), polyfunctionalized with manganese dioxide (α-MnO2) and sulfur functional groups, for the effective immobilization of Hg(II) and Pb(II) from contaminated environments. HMB-S demonstrated superior adsorption capacities of 190.1 mg/g for Hg(II) and 259.9 mg/g for Pb(II), which significantly surpasses the capacities of unmodified biochar (HB) and biochar functionalized solely with Mn (HMB). Mechanistic studies revealed that the immobilization of these metals by HMB-S involved ion exchange, mineral precipitation, surface complexation, and electrostatic interactions. In soil incubation experiments, HMB-S significantly decreased the levels of extractable Hg(II) and Pb(II) compared to the control, reducing the mobility of these metals and converting 17 % of Hg(II) and 26 % of Pb(II) into less bioavailable residual forms. Pot experiments confirmed that all tested biochar materials (HB, HMB, and HMB-S) promoted spinach growth in contaminated soils, with HMB-S being the most effective at lowering Hg(II) and Pb(II) uptake by plants. Additionally, analysis of soil microbial communities indicated that HMB-S altered community composition and increased the relative abundance of metal-resistant bacteria. These findings highlight the potential of polyfunctionalized biochar HMB-S as an effective remediation strategy for Hg and Pb contamination in soil and aqueous environments.

Adaptive mechanisms of wheat cultivars to lead toxicity through enhanced oxidative defense, ionomic redistribution, and anatomical modifications

Lead (Pb) contamination is a critical environmental issue that poses a substantial threat to agricultural sustainability and crop productivity, particularly for staple crops like wheat (Triticum aestivum L.). This study investigates the differential physiological, biochemical, and anatomical responses of two wheat cultivars, SKD-1 and Borlaug-16, under Pb stress (100 mg/kg Pb for 21 days). Borlaug-16 displayed a notable tolerance to Pb toxicity, evidenced by a significant increase in total biomass, including a 41.22% rise in shoot turgid weight and a 23.37% increase in root turgid weight, alongside a 57.72% enhancement in root cortex thickness. This cultivar also showed increased antioxidant enzyme activities, such as catalase and peroxidase, and a better ionomic balance, maintaining higher levels of essential minerals like Ca in leaf tissues while effectively accumulating Pb and other trace elements in roots. In contrast, SKD-1 suffered from a more substantial reduction in essential minerals and weaker anatomical and biochemical defenses. The study's novelty lies in providing an integrated approach to understanding wheat cultivar-specific adaptations to Pb stress, suggesting Borlaug-16 as a promising candidate for cultivation in Pb-contaminated soils. These findings underscore the importance of developing Pb-tolerant cultivars to ensure sustainable wheat production in polluted environments.

Synergistic effects of tree-herb intercropping on the phytoremediation efficiency of cadmium and lead contaminated soil

Tree-herb intercropping has emerged as an effective strategy for the remediation of soil contamination. In this study, the effects of intercropping willow with herbaceous plants Lolium perenne L., Iris lactea Pall. and Bidens pilosa L. were investigated on the phytoremediation of Cd- and Pb-contaminated soil. After a 90-day of cultivation, the results showed that intercropping stimulated the phytoremediation efficiency through increased metal accumulation in plants. Intercropping caused a significant (p < 0.05) increase in willow biomass ranging from 48.07 % to 95.58 % by promoting photosynthesis activities and antioxidant responses. Metal contents in willow leaves and roots were also observably (p < 0.05) enhanced, indicating a beneficial effect in tree-herb intercropping systems. The biomass and metal accumulation of I. lactea Pall. and B. pilosa L. decreased due to competitive interactions with willow in the intercropping treatments. However, intercropping with willow (p < 0.05) significantly increased the Pb contents of L. perenne L. Intercropping improved the absorption of bioavailable fractions of Cd and Pb by willow and herbs in comparison to the monoculture. The decrease in soil Cd contents was partly due to the chemical changes induced by root exudates, which enhanced the transfer of Cd from the soil to the plants. Willow showed a tendency for Cd accumulation, whereas herbs exhibited Pb accumulation, reflecting the complementarity of metal accumulation in tree-herb intercropping patterns. Intercropping willow with B. pilosa L. was found to be an effective method for the remediation of Cd-contaminated soil, whereas the combination of willow with L. perenne L. proved suitable for the Pb-contaminated soil. These findings might support the potential of tree-herb intercropping as an effective strategy for enhancing the phytoremediation of contaminated soils.

AI-guided investigation of biochar’s efficacy in Pb immobilization for remediation of Pb contaminated agricultural land

This study evaluated the lead (Pb) immobilization efficiency of biochar in contaminated agricultural soil. The biochar was produced from a range of major biomass residues and pyrolyzed under well-controlled conditions. Ten different types of standard biochar samples were derived from five different feedstocks (i.e., softwood, miscanthus straw, rice husk, oilseed rape straw, wheat straw) and pyrolyzed at 550 ℃ and 700 ℃. Pb-contaminated soil near an abandoned mine was incubated with 2.5% (w w− 1) of biochar. Incubation was conducted for various durations at room temperature under both short-term (21 days) and long-term (214 days) conditions. This variation explicitly accounted for the simulated microplastic contamination during the long-term incubation period. A novel framework has been developed to predict the long-term immobilization effect of various biochar types using a machine-learning approach, following the successful identification of optimal biochar implementations. This prediction method utilizes a small on-field dataset by employing a data augmentation approach, showcasing an innovative approach to forecasting the effects of different biochar types over time. After the incubation period, soil samples were analyzed for their chemical properties. As a result, oil seed rape biochar was the highest in pH, EC, exchangeable Ca2+, Mg2+, and K+, total nitrogen content, soil organic matter content, and available phosphate. In return, OSR 700 treated soils showed the highest content of exchangeable cations and the lowest content of available Pb after the incubation period. The most efficient biochar for immobilizing lead (Pb) in soil appears to be OSR 700, based on the available evidence.

Magnesium polypeptide combined with microbially induced calcite precipitation for remediation of lead contamination in phosphate mining wasteland soil

Soil Pb contamination is inevitable, as a result of phosphate mining. It is essential to explore more effective Pb remediation approaches in phosphate mining wasteland soil to ensure their viability for a gradual return of soil quality for cultivation. In this study, a Pb-resistant urease-producing bacterium, Serratia marcescens W1Z1, was screened for remediation using microbially induced carbonate precipitation (MICP). Magnesium polypeptide (MP) was prepared from soybean meal residue, and the combined remediation of Pb contamination with MP and MICP in phosphate mining wasteland soil was studied. Remediation of Pb using a combination of MP with MICP strain W1Z1 (WM treatment) was the most effective, with the least exchangeable Pb at 30.37% and the most carbonate-bound Pb at 40.82%, compared to the other treatments, with a pH increase of 8.38. According to the community analysis, MP moderated the damage to microbial abundance and diversity caused by MICP. Total nitrogen (TN) was positively correlated with Firmicutes, pH, and carbonate-bound Pb. Serratia inoculated with strain W1Z1 were positively correlated with bacteria belonging to the Firmicutes phylum and negatively correlated with bacteria belonging to Proteobacteria. The available phosphate (AP) in the phosphate mining wasteland soil could encapsulate the precipitated Pb by ion exchange with carbonate, making it more stable. Combined MP-MICP remediation of Pb contamination in phosphate mining wasteland soil was effective and improved the soil microenvironment.

The potential of phosphate mine tailings in the remediation of acidic Pb-contaminated soil

We investigated the potential of tailings from phosphate mining, consisting of phlogopite, carbonate minerals calcite and dolomite, and residues of apatite, to serve as a stabilizing agent in the remediation of Pb-contaminated soil in situ or on-site. In a 2.5-year field trial, test plots located in a former shooting range area were surface-treated with the tailings and analyzed for tailings-induced changes in Pb solubility and thus potential mobility within the soil profile. The factors and mechanisms controlling tailings-induced changes in Pb solubility in various soil types, and the susceptibility of Pb to leaching down the soil profile following the treatment, were investigated in supplementary laboratory-scale experiments carried out with horizon-specific soil samples collected from the field site. In the tailings-treated soil, the dissolution of the carbonate fraction of the tailings and the subsequent increase in soil pH contributed to the displacement of shot-derived Pb2+ ions by the carbonate-derived calcium ions (Ca2+) and the adsorption of Pb2+ by soil organic matter and Al, Fe, and Mn (hydr)oxide surfaces. Moreover, the apatite fraction of the tailings formed poorly-soluble compounds with Pb, particularly in soils high in exchangeable Pb2+ with respect to their cation exchange capacity. Consequently, the Pb solubility in tailings-treated soils substantially decreased. The reduction in Pb solubility was most evident in the organic topsoil high in Pb. Despite the liming effect of the tailings, and the susceptibility of Pb to form organic complexes conducive to solubilization upon an increase in pH, we found no evidence of tailings-induced leaching of Pb down the soil profile.

Phytoremediation of Pb-polluted soil using bermudagrass: Effect of mowing frequencies

Plant lead (Pb) tolerance and accumulation are key characteristics affecting phytoremediation efficiency. Bermudagrass is an excellent candidate for the remediation of Pb-polluted soil, and it needs to be mowed regularly. Here, we explored the effect of different mowing frequencies on the remediation of Pb-contaminated soil using bermudagrass. Mowing was found to decrease the biomass and photosynthetic efficiency of bermudagrass under Pb stress, thereby inhibiting its growth. Although mowing exacerbated membrane peroxidation, successive mowing treatments alleviated peroxidation damage by regulating enzymatic and nonenzymatic systems. A comprehensive evaluation of Pb tolerance revealed that all the mowing treatments reduced the Pb tolerance of bermudagrass, and a once-per-month mowing frequency had a less negative effect on Pb tolerance than did more frequent mowing. In terms of Pb enrichment, mowing significantly increased the Pb concentration, total Pb accumulation, translocation factor (TF), and bioenrichment factor (BCF) of bermudagrass. The total Pb accumulation was greatest under the once-a-month treatment, while the TF and BCF values were greatest under the three-times-a-month mowing treatment. Additionally, the decrease in soil pH and DOC were significantly correlated with the soil available Pb content and plant Pb accumulation parameters. The results showed that changes in the rhizosphere are crucial factors regulating Pb uptake in bermudagrass during mowing. Overall, once-a-month mowing minimally affects Pb tolerance and maximizes Pb accumulation, making it the optimal mowing frequency for soil Pb remediation by bermudagrass. This study provides a novel approach for the remediation of Pb-contaminated soil with bermudagrass based on mowing.