Bioavailability Of Pb In Soil Research Articles

Ecotoxicological effects of polyethylene microplastics and lead (Pb) on the biomass, activity, and community diversity of soil microbes

Microplastics and heavy metals are ubiquitous and persistent contaminants that are widely distributed worldwide, yet little is known about the effects of their interaction on soil ecosystems. A soil incubation experiment was conducted to investigate the individual and combined effects of polyethylene microplastics (PE-MPs) and lead (Pb) on soil enzymatic activities, microbial biomass, respiration rate, and community diversity. The results indicate that the presence of PE-MPs notably reduced soil pH and elevated soil Pb bioavailability, potentially exacerbated the combined toxicity on the biogeochemical cycles of soil nutrients, microbial biomass carbon and nitrogen, and the activities of soil urease, sucrase, and alkaline phosphatase. Soil CO2 emissions increased by 7.9% with PE-MPs alone, decreased by 46.3% with single Pb, and reduced by 69.4% with PE-MPs and Pb co-exposure, compared to uncontaminated soils. Specifically, the presence of PE-MPs and Pb, individually and in combination, facilitated the soil metabolic quotient, leading to reduced microbial metabolic efficiency. Moreover, the addition of Pb and PE-MPs modified the composition of the microbial community, leading to the enrichment of specific taxa. Tax4Fun analysis showed the effects of Pb, PE-MPs and their combination on the biogeochemical processes and ecological functions of microbes were mainly by altering amino acid metabolism, carbohydrate metabolism, membrane transport, and signal transduction. These findings offer valuable insights into the ecotoxicological effects of combined PE-MPs and Pb on soil microbial dynamics, reveals key assembly mechanisms and environmental drivers, and highlights the potential threat of MPs and heavy metals to the multifunctionality of soil ecosystems.

Bioremediation potential of consortium Pseudomonas Stutzeri LBR and Cupriavidus Metallidurans LBJ in soil polluted by lead.

Pollution by lead (Pb) is an environmental and health threat due to the severity of its toxicity. Microbial bioremediation is an eco-friendly technique used to remediate contaminated soils. This present study was used to evaluate the effect of two bacterial strains isolated and identified from Bizerte lagoon: Cupriavidus metallidurans LBJ (C. metallidurans LBJ) and Pseudomonas stutzeri LBR (P. stutzeri LBR) on the rate of depollution of soil contaminated with Pb from Tunisia. To determine this effect, sterile and non-sterile soil was bioaugmented by P. stutzeri LBR and C. metallidurans LBJ strains individually and in a mixture for 25 days at 30°C. Results showed that the bioaugmentation of the non-sterile soil by the mixture of P. stutzeri LBR and C. metallidurans LBJ strains gave the best rate of reduction of Pb of 71.02%, compared to a rate of 58.07% and 46.47% respectively for bioaugmentation by the bacterial strains individually. In the case of the sterile soil, results showed that the reduction rate of lead was in the order of 66.96% in the case of the mixture of the two bacterial strains compared with 55.66% and 41.86% respectively for the addition of the two strains individually. These results are confirmed by analysis of the leachate from the sterile and non-sterile soil which showed an increase in the mobility and bioavailability of Pb in soil. These promising results offer another perspective for a soil bioremediation bioprocess applying bacterial bioremediation.

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Immobilization is an efficient method in the remediation of heavy metal-polluted soils. A greenhouse experiment was conducted to investigate the influence of fish scale powder, chitin, and chitosan on the growth and chemical composition of rice grown on a soil contaminated with Zn, Pb, Cd, and Ni. Results showed that the application of fish scale powder, chitin, and chitosan significantly increased root and shoot dry matter yield of rice, but decreased Pb phytoextraction efficiency. Further, the translocation factor of Ni decreased following the application of fish scale powder and chitosan. Application of fish scale powder decreased Ni, Cd, Zn, and Pb bioavailability in soil. The addition of chitosan caused 56% decrease in shoots Ni concentration as compared to control. Among different amendments, only the application of chitosan had a significant effect on the reduction of Zn content in rice root by 70% as compared to control. Considering that the translocation factors were less than one in all treatments, it can be concluded that biostabilization of the studied metals has occurred. Based on the obtained results, fish scale derivatives including fish scale powder and chitosan play an important role in the removal of heavy metals due to having suitable functional groups. Therefore, it can be deduced that due to the economic feasibility, environmentally friendly, and high metal removal capability of chitosan and fish scale powder, these two amendments are highly recommendable to be applied in multi-metal polluted soils for increasing metals removal and hence decreasing their phytotoxicity.

Climatic CO2 level-driven changes in the bioavailability, accumulation, and health risks of Cd and Pb in paddy soil–rice systems

Rising atmospheric carbon dioxide (CO2) and soil heavy metal pollution, which affects safe rice production and soil ecosystem stability, have caused widespread concern. In this study, we evaluated the effects of elevated CO2 on Cd and Pb accumulation in rice plants (Oryza sativa L.), Cd and Pb bioavailability, and soil bacterial communities in Cd–Pb co-contaminated paddy soils via rice pot experiments. We showed that elevated CO2 accelerates the accumulation of Cd and Pb in rice grains by 48.4–75.4% and 20.5–39.1%, respectively. Elevated CO2 levels decreased soil pH value by 0.2 units, which increased Cd and Pb bioavailability in soil but inhibited iron plaque formation on rice roots, ultimately promoting Cd and Pb uptake. 16S rRNA sequencing analysis revealed that elevated CO2 increased the relative abundance of certain soil bacteria (e.g., Acidobacteria, Alphaproteobacteria, Holophagae, and Burkholderiaceae). A health risk assessment showed that elevated CO2 markedly increased the total carcinogenic risk values for children, adult males, and adult females by 75.3% (P < 0.05), 65.6% (P < 0.05), and 71.1% (P < 0.05), respectively. These results demonstrate the serious performance of elevated CO2 levels in accelerating the bioavailability and accumulation of Cd and Pb in paddy soil–rice ecosystems, with particular risks for future safe rice production.

Does freeze-thaw action affect the extractability and bioavailability of Pb and As in contaminated soils?

As global warming intensifies, there will be increased uncertainty as to the environmental behavior and risks from heavy metals in industrial/legacy contaminated sites in permafrost regions. Bioavailability has been increasingly used for human health risk assessment of heavy metals in contaminated soils. Soil heavy metal bioavailability depends on soil physicochemical properties, and freeze-thaw affects soil physical, chemical and biological processes. However it is not clear whether freeze-thaw has an effect on the bioavailability of soil heavy metals. In this study, soils contaminated with Pb and As were collected from 10 industrial sites in northeast China. Extractability and bioavailability of soil Pb and As were determined by the Tessier sequential extraction method and four in vitro gastron-intestinal simulation methods under control and freeze-thaw treatments. The aims were: to compare the results of extraction and bioavailability from laboratory experiments which artificially simulate freeze-thaw conditions against control soils; to explore the correlation between bioavailability of Pb/As and soil properties. Freeze-thaw significantly decreased soil pH, and increased the soil weight surface area. Freeze-thaw decreased the percentage in the residual fraction, and increased the percentage of Pb and As in the exchangeable fraction, carbonate-bound fraction, Fe-Mn oxides-bound fraction and organic-bound fraction, relative to control soils. Freeze-thaw significantly increased Pb and As bioavailability compared to the controls. Pb and As released in the gastric phase of the four methods was significantly higher than that in the intestinal phase. Further analysis of correlations between Pb and As bioavailability and soil properties indicated that total concentrations of Al, Fe and Mn, particle size, and weight surface area significantly correlated to Pb and As bioavailability. Overall, this study demonstrated that freeze-thaw did influence the bioavailability of soil heavy metals. It suggests the freeze-thaw action should be comprehensively considered in the human risk assessment of soil pollutants in permafrost regions.

Lead-Immobilization, transformation, and induced toxicity alleviation in sunflower using nanoscale Fe°/BC: Experimental insights with Mechanistic validations

ABSTRACT Lead (Pb) is a biologically non-essential element in the soil that brutally affects plants and other living organisms in soil; hence, its removal has become a worldwide concern. In this work, a multifunctional nanoscale zerovalent-iron assisted biochar (nFe°/BC) was used to minimize the Pb bioavailability in soil with aim of alleviating the Pb-induced toxicity in sunflower. Results revealed that nFe°/BC treatment had significantly improved plant growth (58%), chlorophyll contents (66%), intracellular permeability (60%), and ratio factor (93%), while decreasing the Pb uptake (78%) in plants. The Pb-immobilization and transformation mechanisms were proposed, suggesting that the presence of organic functional groups over the nFe°/BC surface might induce the complex formation with Pb by the ions exchange process in soil solution. The XPS analysis confirmed that surface-active components (Fe+, O2−, O*, C═O) were the key factor for high Pb-immobilization within soil matrix. In addition, 87% of stable Pb species, including PbCO3, PbO, Pb (OH)2, and Pb-O-Fe were found in the soil surface. Current findings have exposed the diverse functions of nFe°/BC on plant health and established a phenomenon that nFe°/BC application could improve the plant agronomic attributes by regulating the homeostasis of antioxidants and Pb uptake.

Remediation of Pb-contaminated soil using modified bauxite refinery residue

This study examines amendment of Pb-contaminated soil with modified bauxite refinery residue (MBRR) to decrease soil Pb mobility and bioaccessibility. Amendment experiments were conducted using four soils contaminated with Pb from various sources, including smelting, shooting-range activities and Pb-based paint waste. Lead L3-edge X-ray absorption spectroscopy (XAS) indicated that Pb speciation in these soils was a mixture of Pb sorbed to Fe (hydr)oxide and clay minerals, along with Pb bound to organic matter. Amendment with MBRR decreased water-soluble Pb and/or Toxicity Characteristic Leachate Procedure (TCLP) Pb concentrations. Lead L3-edge XAS and X-ray diffraction (XRD) indicated that Pb retention by MBRR occurred via sorption to Fe- and Al-(hydr)oxides at low Pb loadings, in addition to formation of hydrocerussite (Pb3(CO3)2(OH)2) at high loadings. Soil amendment with MBRR had relatively little effect on gastric-phase Pb bioaccessibility; as quantified via the Solubility/Bioavailability Research Consortium, SBRC, in vitro assay. In contrast, amendment with MBRR caused substantial decreases in relative intestinal-phase Pb bioaccessibility (Rel-SBRC-I) due to increased Pb sorption by MBRR’s Fe- and Al-hydr(oxide) minerals as simulated GI tract conditions shifted from the gastric- to the intestinal-phase. These decreases in Rel-SBRC-I point to the potential efficacy of using amendment with MBRR to decrease soil Pb bioavailability.

Growth and Pb Uptake of Brassica campestris Enhanced by Two Ecological Earthworm Species in Relation to Soil Physicochemical Properties

A comprehensive understanding of the influence of earthworms on the growth and Pb accumulation of leafy vegetables is significant for soil management and human health. This study was aimed to evaluate the different influences of two ecological earthworm species on the growth and Pb accumulation of Brassica campestris in a Pb-contaminated soil and their relationship with soil physico-chemical properties. In a 30-day microcosm experiment, the anecic and native earthworm species Amynthas aspergillum and the epigeic species Eisenia fetida were inoculated in soil artificially contaminated with Pb at different levels (i.e., 0, 100, 500, and 1,000 mg kg−1), and B. campestris was grown. With a survival rate of 81%–100%, A. aspergillum was more tolerant to Pb contamination than E. fetida with 46%–84%. At the same time, earthworm inoculation significantly increased soil Pb bioavailability (p &amp;lt; 0.05). At the 500 and 1,000 mg kg−1 Pb levels, the treatments with earthworm inoculation showed higher plant biomass, leaf area, and chlorophyll concentration than the treatments without earthworm. The principal component analysis (PCA) showed that earthworm inoculation exerted a stronger effect on soil properties than Pb contamination, but the latter had a stronger effect on plant growth and Pb accumulation. Compared with A. aspergillum, E. fetida had a greater effect on soil cation exchange capacity, available Pb, and plant growth and Pb accumulation. In contrast, A. aspergillum had a greater effect on soil C and N contents than E. fetida. The co-inertia analysis revealed that plant Pb accumulation was positively correlated with soil available Pb and CEC. The leaf chlorophyll concentration was closely related to soil Eh, pH, and Dissolved organic carbon. The findings of this study showed that in the Pb-contaminated soils, earthworm inoculation exerted a strong effect on soil physicochemical properties and the growth and Pb accumulation of the leafy vegetable B. campestris. Both the epigeic earthworm species E. fetida and the anecic species A. aspergillum were associated with higher Pb accumulation or concentration in B. campestris, which may bring a possible risk to food security.

Fruit lead concentrations of tomato (Solanum lycopersicum L.) grown in lead-contaminated soils are unaffected by phosphate amendments and can vary by season, but are below risk thresholds

Urban agriculture in post-industrial cities faces concerns on human health risks posed by elevated lead (Pb) concentrations of edible plant tissues grown in Pb-enriched soils. A recommended mitigation strategy to decrease soil Pb bioavailability to humans is the addition of soluble phosphate (PO43−-P), but it is unclear if this strategy can also reduce crop Pb uptake and accumulation in edible tissues. Across urban agriculture sites in Chicago, Illinois (6 site-years) with elevated total soil Pb, we tested the hypothesized decrease in tomato fruit Pb following soil-based application of three phosphate-based mitigation amendments: triple superphosphate, composted biosolids, and air dried biosolids. Fruit Pb concentrations (mg Pb kg−1 dry mass) and loads (mg Pb m−2) were unaffected by mitigation amendments. However, fruit Pb concentrations were higher by an order of magnitude in 2020 (≥0.13 mg kg−1) compared to 2019 (0.01 mg kg−1) for two of the three sites. Though highly variable across site-years, the bioconcentration factor (BCF) of Pb from soil to fruit varied was unaffected by mitigation amendments. Relatively low BCF values were consistent with fruit Pb concentrations being below FAO/WHO risk limits. Collectively, our findings support previous propositions that fruits of plants grown in soils with elevated Pb generally pose lower risk to consumers. To mitigate health risks of consuming tomatoes grown in soils with Pb contamination, the seasonality of Pb uptake should be investigated, and greater focus should be placed on where tomatoes are grown rather than phosphate-based immobilization strategies originally designed to mitigate human bioavailability.

The effects of biochar and redox conditions on soil Pb bioaccessibility to people and waterfowl

Biochar can reduce lead (Pb) bioavailability to plants in metal-contaminated soil, but the ability of biochar to reduce the bioavailability of soil Pb to people and wildlife remains unknown. In this study, 17 biochars were evaluated as in situ amendments for three soils with distinct sources of Pb contamination (smelter emissions, ceramics waste, mining waste), hydrology (upland, well-drained soil vs submerged wetland soil), and biological receptors (human vs waterfowl). Biochars were made from blends of 30% manure (poultry litter or dairy manure) and 70% lignocellulosic material (wheat straw or grand fir shavings) and pyrolyzed at 300, 500, 700, and 900 °C. Soils were amended with 2% biochar (w/w) and incubated for 6 months. A suite of standard (e.g., EPA Method 1340) and experimental soil Pb bioaccessibility assays were used to assess the impact of the treatments. The results showed that biochar amendments to upland soils resulted in modest reductions in gastrointestinal Pb bioaccessibility (maximum reduction from 78 to 68% bioaccessibility as a percent of total, EPA Method 1340 at pH 2.5). In the wetland soil, sample redox status had a greater impact on Pb bioaccessibility than any amendment. Low-solubility Pb sulfides in this soil oxidized over the course of the study and no treatment was able to offset the increase in Pb bioaccessibility caused by this oxidation. The impact of redox status on Pb bioaccessibility was only evident when soil bioaccessibility assays were adapted to preserve sample redox status. This result highlights the importance of maintaining in situ redox conditions when processing/analyzing samples from low-oxygen environments and that soil remediation efforts should consider the role of redox conditions on Pb bioaccessibility.

Using cow dung and mineral vermireactors to produce vermicompost for use as a soil amendment to slow Pb2+ migration

The widespread existence of lead (Pb) contamination in soil has received extensive attention. To effectively slow lead-ion (Pb2+) migration and promote plant growth in heavy metal-contaminated soil as well as to realize the resource utilization of solid waste, vermireactors were used to obtain vermicompost using cow dung mixed with modified mineral (MM) as feedstock material for Eisenia fetida. Vermicompost was characterized first, and then its slowing effect on Pb2+ migration in soil was further evaluated through pot experiments. The results demonstrated that earthworms could grow well in cow dung and mineral vermireactors, and earthworm activity increased the cation exchange capacity (CEC), total nutrient content and surface area but decreased the pH, carbon to nitrogen ratio (C/N) and organic matter content in the vermicompost. The addition of MM resulted in an increase in the pH, CEC, and surface area but a decrease in the C/N of the vermicompost. X-ray diffraction analysis showed that the addition of MM increased the contents of quartz, CaCO3, CaO and MgO in the vermicompost. Fourier transform infrared spectroscopy analysis indicated that comparatively less carbohydrates, lipids and polysaccharides and more aromatic compounds existed in the vermicompost, and the addition of MM increased the number of Me-O groups. Pot experiments showed that the application of vermicompost from cow dung and mineral vermireactors significantly promoted the growth of celery cabbage and reduced the Pb content in its edible parts and the Pb bioavailability in soil. Thus, it is possible to use cow dung and mineral vermireactors to optimize the properties of vermicompost for its use as a soil amendment to remediate Pb contamination.

Legacy of anthropogenic lead in urban soils: Co-occurrence with metal(loids) and fallout radionuclides, isotopic fingerprinting, and in vitro bioaccessibility

Anthropogenic lead (Pb) in soils poses risks to human health, particularly to the neuropsychological development of exposed children. Delineating the sources and potential bioavailability of soil Pb, as well as its relationship with other contaminants is critical in mitigating potential human exposure. Here, we present an integrative geochemical analysis of total elemental concentrations, radionuclides of 137Cs and 210Pb, Pb isotopic compositions, and in vitro bioaccessibility of Pb in surface soils sampled from different locations near Durham, North Carolina. Elevated Pb (>400 mg/kg) was commonly observed in soils from urban areas (i.e., near residential house foundation and along urban streets), which co-occurred with other potentially toxic metal(loids) such as Zn, Cd, and Sb. In contrast, soils from city parks and suburban areas had systematically lower concentrations of metal(loids) that were comparable to geological background. The activities of 137Cs and excess 210Pb, coupled with their correlations with Pb and co-occurring metal(loids) were used to indicate the persistence and remobilization of historical atmospherically deposited contaminants. Coupled with total Pb concentrations, the soil Pb isotopic compositions further indicated that house foundation soils had significant input of legacy lead-based paint (mean = 1.1895 and 2.0618 for 206Pb/207Pb and 208Pb/206Pb, respectively), whereas urban streetside soils exhibited a clear mixed origin, dominantly of legacy leaded gasoline (1.2034 and 2.0416) and atmospheric deposition (1.2004–1.2055 and 2.0484–2.0525). The in vitro bioaccessibility of Pb in contaminated urban soils furthermore revealed that more than half of Pb in the contaminated soils was potentially bioavailable, whose Pb isotope ratios were identical to that of bulk soils, demonstrating the utility of using Pb isotopes for tracking human exposure to anthropogenic Pb in soils and house dust. Overall, this study demonstrated a holistic assessment for comprehensively understanding anthropogenic Pb in urban soils, including its co-occurrence with other toxic contaminants, dominant sources, and potential bioavailability upon human exposure.

Relationship of soil pH value and soil Pb bio-availability and Pb enrichment in tea leaves.

Lead (Pb) is not an essential element for the growth of tea trees, but it is an important index for evaluating the quality and safety of tea. Lead is a sensitive metal to pH. Exploring the changing trend of soil Pb and enrichment coefficient of Pb in tea leaves affected by soil acidification is significant for tea planting and tea quality safety control. A percent of 37.57% of the 364 tea plantations in Anxi county of China showed soil acidification that is a soil pH value < 4.5. However, the total Pb content in the soil and Pb content of tea leaves met the requirements stipulated in China. The soil available Pb content and Pb content in tea leaves were both significantly negatively correlated with soil pH value, and increased with the decrease of soil pH value. The soil available Pb content had a significant positive correlation with soil total Pb content. However, the soil total Pb content had no significant correlation with soil pH value. Moreover, the soil Pb bio-availability coefficient and the Pb enrichment coefficient of tea leaves decreased with the increase of soil pH value. More than a third of tea plantations in Anxi county had been acidified. The decrease of pH value leads to an increase in the bio-availability coefficient of soil Pb content and the enrichment coefficient of Pb content in tea leaves. The lower soil pH value resulted in the increase of the absorption and accumulation of Pb by tea trees, thus an increase of Pb content in tea leaves. © 2021 Society of Chemical Industry.

Inoculation With Indigenous Rhizosphere Microbes Enhances Aboveground Accumulation of Lead in Salix integra Thunb. by Improving Transport Coefficients.

The application of plant–microbial remediation of heavy metals is restricted by the difficulty of exogenous microbes to form large populations and maintain their long-term remediation efficiency. We therefore investigated the effects of inoculation with indigenous heavy-metal-tolerant rhizosphere microbes on phytoremediation of lead (Pb) by Salix integra. We measured plant physiological indexes and soil Pb bioavailability and conducted widespread targeted metabolome analysis of strains to better understand the mechanisms of enhance Pb accumulation. Growth of Salix integra was improved by both single and co-inoculation treatments with Bacillus sp. and Aspergillus niger, increasing by 14% in co-inoculated plants. Transfer coefficients for Pb, indicating mobility from soil via roots into branches or leaves, were higher following microbial inoculation, showing a more than 100% increase in the co-inoculation treatment over untreated plants. However, Pb accumulation was only enhanced by single inoculation treatments with either Bacillus sp. or Aspergillus niger, being 10% greater in plants inoculated with Bacillus sp. compared with uninoculated controls. Inoculation mainly promoted accumulation of Pb in aboveground plant parts. Superoxide dismutase and catalase enzyme activities as well as the proline content of inoculated plants were enhanced by most treatments. However, soil urease and catalase activities were lower in inoculated plants than controls. Proportions of acid-soluble Pb were 0.34 and 0.41% higher in rhizosphere and bulk soil, respectively, of plants inoculated with Bacillus sp. than in that of uninoculated plants. We identified 410 metabolites from the microbial inoculations, of which more than 50% contributed to heavy metal bioavailability; organic acids, amino acids, and carbohydrates formed the three major metabolite categories. These results suggest that both indigenous Bacillus sp. and Aspergillus niger could be used to assist phytoremediation by enhancing antioxidant defenses of Salix integra and altering Pb bioavailability. We speculate that microbial strains colonized the soil and plants at the same time, with variations in their metabolite profiles reflecting different living conditions. We also need to consider interactions between inocula and the whole microbial community when applying microbial inoculation to promote phytoremediation.

Combined effects of biochar and chicken manure on maize (Zea mays L.) growth, lead uptake and soil enzyme activities under lead stress.

The goal of the present work was to evaluate the additive effects of biochar and chicken manure on maize growth in Pb-contaminated soils. In this study, we conducted a pot experiment to investigate how biochar in soil (20, 40 g·kg−1), chicken manure in soil (20, 40 g·kg−1), or a combination of biochar and chicken manure in soil (each at 20 g·kg−1) effect maize growth, Pb uptake, leaves’ antioxidant enzymatic activities, and soil enzyme activities under artificial conditions to simulate moderate soil pollution (800 Pb mg·kg−1). The results showed that all biochar and/or chicken manure treatments significantly (P < 0.05) increased maize plant height, biomass, and superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activity but decreased the malondialdehyde (MDA) content. These results indicated that amending the soil with biochar and/or chicken manure could alleviate Pb’s phytotoxicity. The biochar and/or chicken manure treatments remarkably decreased the Pb concentration in maize roots, stems, leaves, bioconcentration factor (BCF), translocation factor (TF), and available Pb concentration in the soil. Amending the soil with chicken manure alone was more effective at increasing maize growth and antioxidant enzymatic activity; the biochar treatment alone was more effective at inducing soil alkalinization and contributing to Pb immobilization. The combined use of biochar and chicken manure had an additive effect and produced the largest increases in maize growth, leaves’ antioxidant enzymatic activity, and soil enzyme activity. Their combined use also led to the most significant decreases in maize tissues Pb and soil available Pb. These results suggest that a combination of biochar and chicken manure was more effective at reducing soil Pb bioavailability and uptake by maize tissues, and increasing maize growth. This combination increased plant height by 43.23% and dry weight by 69.63% compared to the control.

Effects of Soil Amendments on Soil Pb Bioavailability and Pb Absorption by a low-Pb Accumulator Kumquat Grown in Two Types of Pb-Contaminated Soils.

A pot experiment was conducted to investigate the effects of 0.5% and 1% alkaline, clay mineral and phosphorus amendments, as well as 2% and 5% organic amendments, on lead (Pb) soil bioavailability and Pb absorption by the low-Pb accumulator kumquat (Citrus japonica Thunb.) 'Cuipi' in two typical Pb-contaminated soils, Jiyuan and Yangshuo, from northern and southern China, respectively. The diethylenetriaminepentaacetic acid-extractable Pb soil concentration and Pb accumulation in kumquat significantly decreased with amendment additions. High amendment doses had greater inhibitory effects than low doses but no significant effects on the kumquat's biomass in the two typical soils. Alkaline, but not clay mineral, amendments greatly increased the soil pH level. Organic amendments effectively reduced Pb accumulation owing to their strong adsorptive capacities. Thus, using organic amendments combined with a low-Pb accumulator kumquat forms a suitable farming practice for producing safe fruit in the two common types of Pb-contaminated soils in China.

Bioavailability and Ecotoxicity of Lead in Soil: Implications for Setting Ecological Soil Quality Standards.

Ecological soil quality standards for lead (Pb) that account for soil Pb bioavailability have not yet been derived. We derived such standards based on specific studies of the long‐term bioavailability and toxicity of Pb to soil organisms and a compilation of field data on the bioaccumulation of Pb in earthworms. Toxicity thresholds of Pb to plants, invertebrates, or microorganisms vary over more than 2 orders of magnitude, and the lowest values overlap with the range in natural Pb background concentrations in soil. Soils freshly spiked with Pb2+ salts exhibit higher Pb bioavailability and lower toxic thresholds than long‐term aged and leached equivalents. Comparative toxicity tests on leaching and aging effects suggest using a soil Pb threshold that is 4.0 higher, to correct thresholds of freshly spiked soils. Toxicity to plants and earthworms, and microbial N‐transformation and bioaccumulation of Pb in earthworms increase with decreasing effective cation exchange capacity (eCEC) of the soil, and models were derived to normalize data for variation of the eCEC among soils. Suggested ecological quality standards for soil expressed as total soil Pb concentration are lower for Pb toxicity to wildlife via secondary poisoning compared with direct Pb toxicity to soil organisms. Standards for both types of receptors vary by factors of approximately 4 depending on soil eCEC. The data and models we have collated can be used for setting ecological soil quality criteria for Pb in different regulatory frameworks. Environ Toxicol Chem 2021;40:1948–1961. © 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Aqueous solubility of Pb at equilibrium with hydroxypyromorphite over a range of phosphate concentrations.

Hydroxypyromorphite (HPM) is a low-solubility Pb phosphate mineral that has the potential to limit solubility and bioavailability of Pb in soils and water. Because of reported uncertainty regarding the solubility product of this important mineral, we re-evaluated the solubility of Pb and activity of the free Pb2+ ion in aqueous suspensions of microcrystalline HPM equilibrated up to 30 days over a wide range of added soluble phosphate. A small addition of phosphate (0.1 mM) reduced Pb solubility as measured by ICP-OES, but greater phosphate additions (up to 50 mM) had no further effect in lowering HPM solubility. However, free Pb2+ ion activity measured by ion-selective electrode progressively decreased from about 10-6.5 with no added phosphate to 10-9 as soluble phosphate was increased. The effect of soluble phosphate in lowering Pb2+ activity is attributed to inhibited dissolution of HPM as well as increased Pb2+-phosphate ion pair formation in solution at higher solution concentrations of phosphate. Measurement of the ion activity products (IAP) of the solutions at equilibrium with HPM gave highly variable IAP values that were sensitive to pH and were generally not consistent with the reported solubility product of this mineral. The high variability of the IAPs for solutions with variable pH and phosphate concentrations indicates that dissolution-precipitation reactions of HPM are not described by a constant solubility product at equilibrium, possibly because of the incongruent dissolution behavior of this mineral at near-neutral pH.

Prospective usage of magnesium potassium phosphate cement combined with Bougainvillea alba derived biochar to reduce Pb bioavailability in soil and its uptake by Spinacia oleracea L

Combining biochar (BR) with other immobilizing amendments has additive effects on Pb immobilization and been recognized to be effective for the restoration of Pb polluted soils. However, the impacts of different proportions between BR and a highly efficient Pb immobilizing agent called “magnesium potassium phosphate cement (MC)” have never been earlier investigated. This work aimed to investigate the consequences of BR and MC alone and their mixtures of 25:75, 50:50, and 75:25 ratios on Pb bioavailability, Pb immobilization index (Pb−IMMi), and enzymatic activities in Pb polluted soil. Furthermore, amendments effects on Pb distribution in spinach, growth, antioxidant capacity, biochemical, and nutritional spectrum were also investigated. We found that MC alone performed well to immobilize Pb in soil and reducing its distribution in shoots, but was less efficient to improve soil enzymatic activities and plant attributes. Conversely, the application of BR alone stimulated soil enzymatic activities, plant growth, and quality but was less effective to immobilize Pb in soil and reducing shoot Pb concentrations. The combinations of BR and MC of various ratios showed variable results. Interestingly, the most promising outcomes were obtained with BR50%+MC50% treatment which resulted in enhanced Pb−IMMi (73%), activities of soil enzymes, plant growth and quality, and antioxidant capacity, compared to control. Likewise, significant reductions in Pb concentrations in shoots (85%), roots (78%), extractable Pb (73%) were also obtained with BR50%+MC50% treatment, compared to control. Such outcomes point towards a cost-effective approach for reducing Pb uptake by the plants via using MC and BR at a 50:50 ratio.

Lead Toxicity: Health Hazards, Influence on Food Chain, and Sustainable Remediation Approaches.

Lead (Pb) toxicity has been a subject of interest for environmental scientists due to its toxic effect on plants, animals, and humans. An increase in several Pb related industrial activities and use of Pb containing products such as agrochemicals, oil and paint, mining, etc. can lead to Pb contamination in the environment and thereby, can enter the food chain. Being one of the most toxic heavy metals, Pb ingestion via the food chain has proven to be a potential health hazard for plants and humans. The current review aims to summarize the research updates on Pb toxicity and its effects on plants, soil, and human health. Relevant literature from the past 20 years encompassing comprehensive details on Pb toxicity has been considered with key issues such as i) Pb bioavailability in soil, ii) Pb biomagnification, and iii) Pb- remediation, which has been addressed in detail through physical, chemical, and biological lenses. In the review, among different Pb-remediation approaches, we have highlighted certain advanced approaches such as microbial assisted phytoremediation which could possibly minimize the Pb load from the resources in a sustainable manner and would be a viable option to ensure a safe food production system.