Pb Accumulation Research Articles

Sulfur availability and nodulation modify the response of Robinia pseudoacacia L. to lead (Pb) exposure

Both sulfur (S) supply and legume-rhizobium symbiosis can significantly contribute to enhancing the efficiency of phytoremediation of heavy metals (HMs). However, the regulatory mechanism determining the performance of legumes at lead (Pb) exposure have not been elucidated. Here, we cultivated black locust (Robinia pseudoacacia L.), a leguminous woody pioneer species at three S supply levels (i.e., deficient, moderate, and high S) with rhizobia inoculation and investigated the interaction of these treatments upon Pb exposure. Our results revealed that the root system of Robinia has a strong Pb accumulation and anti-oxidative capacity that protect the leaves from Pb toxicity. Compared with moderate S supply, high S supply significantly increased Pb accumulation in roots by promoting the synthesis of reduced S compounds (i.e., thiols, phytochelatin), and also strengthened the antioxidant system in leaves. Weakened defense at deficient S supply was indicated by enhanced oxidative damage. Rhizobia inoculation alleviated the oxidative damage of its Robinia host by immobilizing Pb to reduce its absorption by root cells. Together with enhanced Pb chelation in leaves, these mechanisms strengthen Pb detoxification in the Robinia-rhizobia symbiosis. Our results indicate that appropriate S supply can improve the defense of legume-rhizobia symbiosis against HM toxicity.

Nutrient strengthening and lead alleviation in Brassica Napus L. by foliar ZnO and TiO2-NPs modulating antioxidant system, improving photosynthetic efficiency and reducing lead uptake

With the anticipated foliar application of nanoparticles (NPs) as a potential strategy to improve crop production and ameliorate heavy metal toxicity, it is crucial to evaluate the role of NPs in improving the nutrient content of plants under Lead (Pb) stress for achieving higher agriculture productivity to ensure food security. Herein, Brassica napus L. grown under Pb contaminated soil (300 mg/kg) was sprayed with different rates (0, 25, 50, and 100 mg/L) of TiO2 and ZnO-NPs. The plants were evaluated for growth attributes, photosynthetic pigments, leaf exchange attributes, oxidant and antioxidant enzyme activities. The results revealed that 100 mg/L NPs foliar application significantly augmented plant growth, photosynthetic pigments, and leaf gas exchange attributes. Furthermore, 100 mg/L TiO2 and ZnO-NPs application showed a maximum increase in SPAD values (79.1%, 68.9%). NPs foliar application (100 mg/L TiO2 and ZnO-NPs) also substantially reduced malondialdehyde (44.3%, 38.3%), hydrogen peroxide (59.9%, 53.1%), electrolyte leakage (74.8%, 68.3%), and increased peroxidase (93.8%, 89.1%), catalase (91.3%, 84.1%), superoxide dismutase (81.8%, 73.5%) and ascorbate peroxidase (78.5%, 73.7%) thereby reducing Pb accumulation. NPs foliar application (100 mg/L) significantly reduced root Pb (45.7%, 42.3%) and shoot Pb (84.1%, 76.7%) concentration in TiO2 and ZnO-NPs respectively, as compared to control. Importantly, macro and micronutrient analysis showed that foliar application 100 mg/L TiO2 and ZnO-NPs increased shoot zinc (58.4%, 78.7%) iron (79.3%, 89.9%), manganese (62.8%, 68.6%), magnesium (72.1%, 93.7%), calcium (58.2%, 69.9%) and potassium (81.5%, 68.6%) when compared to control without NPs. The same trend was observed for root nutrient concentration. In conclusion, we found that the TiO2 and ZnO-NPs have the greatest efficiency at 100 mg/L concentration to alleviate Pb induced toxicity on growth, photosynthesis, and nutrient content of Brassica napus L. NPs foliar application is a promising strategy to ensure sustainable agriculture and food safety under metal contamination.

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.

Oxidative response to cadmium and lead accumulations in the tissues of blue swimming crabs Portunus pelagicus from the Trang Province coastline, Southern Thailand.

Metals have been reported to alter the oxidative status of both redox-active and redox-inactive metals accompanying oxidative stress induction. In aquatic ecosystems, metal contamination is regarded as serious pollutants and bioaccumulation, especially when aquatic seafood products are involved, which results in human risk. The blue swimming crab Portunus pelagicus is a highly popular crab species for consumption as seafood in Thailand. The meat parts and the hepatopancreas (HP) together with gonad are consumed and in high demand. Therefore, the present study aimed to investigate bioaccumulation of cadmium (Cd) and lead (Pb) along with tissue oxidative responses in P. pelagicus. Sixty-seven samples of P. pelagicus were obtained from small-scale fishers along the coastline of Trang Province. Bioaccumulation of Cd and Pb and oxidative response in gill, muscle, and HP + gonad were evaluated. Cadmium and Pb accumulation levels were highest in the HP and gonad, followed by the gill and then muscle, indicating that Cd and Pb have a high affinity to be concentrated in the HP and gonad. An organ-specific oxidative response to Cd and Pb accumulation was demonstrated in which Cd significantly activated superoxide dismutase (SOD) activity in the gills and muscle tissue, while Pb significantly activated the SOD activity only in the HP and gonad. Only Cd accumulation in gill tissue represented a significant activation of lipid peroxidation, as indicated by the malondialdehyde level. This study implied that P. pelagicus exhibits an "adaptive stage" in the oxidative response of tissue due to metal accumulation. Additionally, the data presented here further indicate that the consumption of only the meat parts and removal of the HP and gonad would reduce human exposure to metal toxicity.

Contribution assessment and accumulation prediction of heavy metals in wheat grain in a smelting-affected area using machine learning methods

Due to the diverse controlling factors and their uneven spatial distribution, especially atmospheric deposition from smelters, assessing and predicting the accumulation of heavy metals (HM) in crops across smelting-affected areas becomes challenging. In this study, integrating HM influx from atmospheric deposition, a boosted regression tree model with an average R2 > 0.8 was obtained to predict accumulation of Pb, As, and Cd in wheat grain across a smelting region. The atmospheric deposition serves as the dominant factor influencing the accumulation of Pb (28.2 %) and As (31.2 %) in wheat grain, but shows a weak influence on Cd accumulation (12.1 %). The contents of available HM in soil affect HM accumulation in wheat grain more significantly than their total contents in soil with relative importance rates of Pb (14.4 % > 8.2 %), As (30.9 % > 4.0 %), and Cd (55.0 % > 16.9 %), respectively. Marginal effect analysis illustrates that HM accumulation in wheat grain begins to intensify when Pb content in atmospheric dust reaches 5140 mg/kg and available Cd content in soil exceeds 1.15 mg/kg. The path analysis rationalizes the cascading effects of distances from study sites to smelting factories on HM accumulation in wheat grain via negatively influencing atmospheric HM deposition. The study provides data support and a theoretical basis for the sustainable development of non-ferrous metal smelting industry, as well as for the restoration and risk management of HM-contaminated soils.

Deterministic and probabilistic assessment of heavy metals in herbal teas sold in Lanzhou City, China

To evaluate the health risks of consuming herbal teas to residents in Lanzhou City, this study used ICP-MS to determine the Hg, Cd, and Pb content in 131 herbal tea samples (leaf, flower, and fruit) and conducted risk assessment by two methods. The Hg contents were all within safe limit of China, but the Cd and Pb levels in some samples were higher than the same limit. At the P95 exposure level, the ranking of heavy metals based on hazard quotient (HQ) was Pb > Cd > Hg in both methods. The deterministic assessment showed that HQs of Hg, Cd, and Pb were below 1, hazard index (HI) was also below 1, but cancer risk (CR) of Cd was above 10−4. In probability assessment, the HQs of Hg and Pb were less than 1, but the HQ of Cd had a certain probability of being greater than 1, and the CR of Cd is greater than 10−4. Therefore, we conclude that Hg and Pb in herbal teas may not pose a health risk, but Cd pose a health risk to consumers. Thus, measures should be taken to minimize the excessive accumulation of Pb and Cd in the cultivation and production process of floral tea.

Investigation of Trace Element Levels and Toxic Metals in Obese Children: A Single-Center Experienc.

The complete role of factors contributing to the pathogenesis of childhood obesity remains to be fully elucidated. Limited research has addressed trace elements in the context of child obesity. Our objective was to assess trace element and lead (Pb), copper (Cu) (are toxic metal) levels in both healthy and obese children, and to investigate the potential correlations between these elements and obesity-related anthropometric measurements, lipid profiles, as well as insulin and glucose levels. Furnace atomic absorption spectrophotometry was employed to measure the concentrations of trace elements in the serum. Additionally, fasting glucose, insulin, and lipid levels were determined in obese children (body mass index ≥ 95th percentile for age and sex), along with 50 healthy children. Only the obesity group underwent an oral glucose tolerance test (OGTT). Significantly reduced levels of Fe, Mg, Zn, and Co were observed in obese children, whereas Cu, Pb, and Mn levels were elevated (P < .001, P <.001, P = .002, P = .008, P <.001, P = .001, P = .007, respectively). Significant positive correlations were found between the 2-hour glucose level in OGTT and Mn (P = .013), as well as between peak insulin and insulin levels at the 30th and 60th minutes, and Fe (P = .001, P = .025, P = .001). This study indicates that an imbalance in trace element levels and the accumulation of Pb may be associated with obesity, while levels of Mn and Fe may be linked to glucose intolerance.

A phased small interfering RNA-derived pathway mediates lead stress tolerance in maize.

Phased small interfering RNAs (phasiRNAs) are a distinct class of endogenous small interfering RNAs, which regulate plant growth, development and environmental stress response. To determine the effect of phasiRNAs on maize (Zea mays L.) tolerance to lead (Pb) stress, the roots of 305 maize lines under Pb treatment were subjected to generation of individual databases of small RNAs. We identified 55 high-confidence phasiRNAs derived from 13 PHAS genes (genes producing phasiRNAs) in this maize panel, of which 41 derived from nine PHAS loci were negatively correlated with Pb content in the roots. The potential targets of the 41 phasiRNAs were enriched in ion transport and import. Only the expression of PHAS_1 (ZmTAS3j, Trans-Acting Short Interference RNA3) was regulated by its cis-expression quantitative trait locus and thus affected the Pb content in the roots. Using the Nicotiana benthamiana (N. benthamiana) transient expression system, 5'-rapid amplification of cDNA ends, and Arabidopsis heterologously expressed, we verified that ZmTAS3j was cleaved by zma-miR390 and thus generated tasiRNA targeting ARF genes (tasiARFs), and that the 5' and 3' zma-miR390 target sites of ZmTAS3j were both necessary for efficient biosynthesis and functional integrity of tasiARFs. We validated the involvement of the zma-miR390-ZmTAS3j-tasiARF-ZmARF3-ZmHMA3 pathway in Pb accumulation in maize seedlings using genetic, molecular, and cytological methods. Moreover, the increased Pb tolerance in ZmTAS3j-overexpressed lines was likely attributed to the zma-miR390-ZmTAS3j-tasiARF-ZmARF3-SAURs pathway, which elevated indole acetic acid levels and thus reactive oxygen species scavenging capacity in maize roots. Our study reveals the importance of the TAS3-derived tasiRNA pathway in plant adaptation to Pb stress.

Comparative assessment of pantothenic, aspartic, ascorbic and tartaric acids assisted Pb-phytoextraction by sunflower (Helianthus annuus L.).

Phytoextraction of lead (Pb) is a challenging task due to its extremely low mobility within soil and plant systems. In this study, we tested the influence of some novel chelating agents for Pb-phytoextraction using sunflower. The Pb was applied at control (0.0278mM) and 4.826mM Pb as Pb(NO3)2 through soil-spiking. After 10days of Pb addition, four different organic ligands (aspartic, ascorbic, tartaric, and pantothenic acids) were added to the soil at 1mM concentration each. respectively. In the absence of any chelate, sunflower plants grown at 4.826mM Pb level accumulated Pb concentrations up to 104µgg-1 DW in roots, whereas 64µgg-1 DW in shoot. By contrast, tartaric acid promoted significantly Pb accumulation in roots (191µgg-1 DW; + 45.5%) and shoot (131.6µgg-1 DW; + 51.3%). Pantothenic acid also resulted in a significant Pb-uptake in the sunflower shoots (123µgg-1 DW; + 47.9%) and in roots (177.3µgg-1 DW; + 41.3%). The least effective amongst the chelates tested was aspartic acid, but it still contributed to + 40.1% more Pb accumulation in the sunflower root and shoots. In addition, plant growth, biochemical, and ionomic parameters were positively regulated by the organic chelates used. Especially, an increase in leaf Ca, P, and S was evident in Pb-stressed plants in response to chelates. These results highlight that the use of biocompatible organic chelates positively alters plant physio-biochemical traits contributing to higher Pb-sequestration in sunflower plant parts.

PIP family-based association studies uncover ZmPIP1;6 involved in Pb accumulation and water absorption in maize roots

Excessive lead (Pb) in the soil affects crop growth and development, thus threatening human beings via food chains. Plasma membrane intrinsic proteins (PIPs) facilitate the transport of substrates across cell membranes. Herein, we characterized maize PIPs and identified eight Pb accumulation-associated PIP genes using association studies. Among these, ZmPIP1;6 was simultaneously correlated with root Pb concentrations under various Pb treatment stages. Significant correlations were observed between the ZmPIP1;6 expression abundance and Pb accumulation in maize roots. Ectopic expression in yeast showed that ZmPIP1;6 conferred Pb accumulation in the cells and affected Pb tolerance in yeast. Overexpression in maize demonstrated that ZmPIP1;6 altered the Pb concentration performance and root moisture content under Pb stress. Meanwhile, protein interaction analyses suggested that ZmPIP1; 6 and three PIP2 members formed isoforms and facilitate water uptake in maize roots. However, ZmPIP1; 6 improved Pb absorption in maize roots probably by interacting with CASP-like protein 2C3 and/or another metal transporter. Moreover, the significant variants in the ZmPIP1;6 promoter caused the variations in ZmPIP1;6 expression level and Pb accumulation among various maize germplasms. Our study will contribute to understanding of PIP family-mediated Pb accumulation in crops and bioremediation of Pb-polluted soils.

Molecular and eco-physiological responses of soil-borne lead (Pb2+)-resistant bacteria for bioremediation and plant growth promotion under lead stress

Lead (Pb) is the 2nd known portentous hazardous substance after arsenic (As). Being highly noxious, widespread, non-biodegradable, prolonged environmental presence, and increasing accumulation, particularly in arable land, Pb pollution has become a serious global health concern requiring urgent remediation. Soil-borne, indigenous microbes from Pb-polluted sites have evolved diverse resistance strategies, involving biosorption, bioprecipitation, biomineralization, biotransformation, and efflux mechanisms, under continuous exposure to Pb in human-impacted surroundings. These strategies employ a wide range of functional bioligands to capture Pb and render it inaccessible for leaching. Recent breakthroughs in molecular technology and understanding of lead resistance mechanisms offer the potential for utilizing microbes as biological tools in environmental risk assessment. Leveraging the specific affinity and sensitivity of bacterial regulators to Pb2+ ions, numerous lead biosensors have been designed and deployed worldwide to monitor Pb bioavailability in contaminated sites, even at trace levels. Besides, the ongoing degradation of croplands due to Pb pollution poses a significant challenge to meet the escalating global food demands. The accumulation of Pb in plant tissues jeopardizes both food safety and security while severely impacting plant growth. Exploring Pb-resistant plant growth-promoting rhizobacteria (PGPR) presents a promising sustainable approach to agricultural practices. The active associations of PGPR with host plants have shown enhancements in plant biomass and stress alleviation under Pb influence. They thus serve a dual purpose for plants grown in Pb-contaminated areas. This review aims to offer a comprehensive understanding of the role played by Pb-resistant soil-borne indigenous bacteria in expediting bioremediation and improving the growth of Pb-challenged plants essential for potential field application, thus broadening prospects for future research and development.

Profiling and health risk assessment of trace metal contents in bovine tissues: A case study in Gondar City, Ethiopia

This study aimed to determine six trace metal (Cu, Mn, Zn, Cd, Cr, and Pb) concentrations in three bovine tissues (kidney, liver and muscle) from Gondar City abattoir, Ethiopia, and assess associated health risks. Samples were digested with HNO3/HClO4, and metal concentrations were analyzed by Inductively Coupled Plasma Optical Emission Spectroscopy. Zn exhibited the highest concentration in muscle (52.1 mg/kg), whereas Cd was below the LOD (0.6 µg/kg) in all muscle samples. The levels of Cd, Cr, and Mn in liver and kidney tissues, as well as Zn in muscle, exceeded FAO/WHO safety thresholds. Principal component analysis revealed distinct metal accumulation patterns among the tissues where liver is the target organ for accumulation of Pb, Mn and Cu, while kidney appears to be the organ of preference for Cd and Cr accumulation. Zn had the highest chronic daily intake for both children and adults, followed by Cu. Hazard index values for both age groups were below one, indicating no non-carcinogenic risks. However, the incremental lifetime cancer risks and cumulative carcinogenic risks of Cr exceeded the tolerable limit for adults and children, indicating a high cancer likelihood from this trace metal. In contrast, the incremental lifetime cancer risks of Pb for both adults and children were within acceptable limits. In conclusion, cumulative carcinogenic risk values indicate that consuming muscle tissue poses health risks for both adults and children, highlighting the need for stricter cattle feed regulations in the study area to safeguard public health.

ZnO nanoparticles in composted sewage sludge enhance soil fertility and rice nutrition but elevate As and Pb accumulation

The widespread use of metal-based nanoparticles (NPs) in a variety of industries results in their release into sewage systems. This presents a risk when composted sewage sludge (CSS) is used as fertilizer. This study examined the effects of ZnO NPs in CSS on rice-soil systems and assessed the health risks associated with consuming rice grown under these circumstances. ZnO NPs were added to CSS at concentrations lower than the regulatory safety limit of 2800 mg Zn kg⁻¹. The results show that higher levels of ZnO NPs in CSS improved the mineral composition of rice grains and increased soil fertility, as evidenced by significant increases in N (1.6–2.3-fold) and K levels. The levels of tyrosine-like fraction, C4, and the biological index (BIX) in soil dissolved organic matter increased upon the introduction of ZnO NPs into CSS, indicating that microbial activity and nutrient cycling have been enhanced. However, the concentrations of As and Pb in rice grains were significantly increased by the elevated levels of ZnO NPs in CSS, reaching up to 1.5 and 2.3 times the control levels, respectively. This increased hazard quotients and pushed hazard indexes beyond acceptable levels, suggesting that rice consumers are at significant health risk. This study underscores the critical need for more stringent and comprehensive regulatory frameworks to ensure the safety of CSS application in crop production and to manage the intricacies of NP use in agriculture.

Biochar Blended with Alkaline Mineral Can Better Inhibit Lead and Cadmium Uptake and Promote the Growth of Vegetables.

Three successive vegetable pot experiments were conducted to assess the effects on the long-term immobilization of heavy metals in soil and crop yield improvement after the addition of peanut shell biochar and an alkaline mineral to an acidic soil contaminated with lead and cadmium. Compared with the CK treatment, the change rates of biomass in the edible parts of the three types of vegetables treated with B0.3, B1, B3, B9, R0.2 and B1R0.2 were -15.43%~123.30%, 35.10%~269.09%, 40.77%~929.31%, -26.08%~711.99%, 44.14%~1067.12% and 53.09%~1139.06%, respectively. The cadmium contents in the edible parts of the three vegetables treated with these six additives reduced by 2.08%~13.21%, 9.56%~24.78%, 9.96%~35.61%, 41.96%~78.42%, -4.19%~57.07% and 12.43%~65.92%, respectively, while the lead contents in the edible parts reduced by -15.70%~59.47%, 6.55%~70.75%, 3.40%~80.10%, 55.26%~89.79%, 11.05%~70.15% and 50.35%~79.25%, respectively. Due to the increases in soil pH, soil cation-exchange capacity and soil organic carbon content, the accumulation of Cd and Pb in the vegetables was most notably reduced with a high dosage of 9% peanut shell biochar alone, followed by the addition of a low dosage of 1% peanut shell biochar blended with 0.2% alkaline mineral. Therefore, the addition of a low dosage of 1% peanut shell biochar blended with 0.2% alkaline mineral was the best additive in increasing the vegetable biomass, whereas the addition of 9% peanut shell biochar alone was the worst. Evidently, the addition of 0.2% alkaline mineral can significantly reduce the amount of peanut shell needed for passivating heavy metals in soil, while it also achieves the effect of increasing the vegetable yield.

Immobilization of Heavy Metals by Phosphorus-solubilizing Bacteria and Inhibition of Cd and Pb Uptake by Wheat

Phosphorus-solubilizing microorganisms convert insoluble phosphorus in the soil into phosphorus that can be absorbed by plants. Soluble phosphate combines with heavy metals to form precipitation, reducing the content of available heavy metals, thereby reducing the absorption of heavy metals by crops, which plays an important role in the remediation of heavy metal-contaminated soil. The effects of the immobilization of Cd and Pb and the release of PO43- by the phosphorus-solubilizing bacterium Klebsiella sp. M2 were studied through solution culture experiments. In addition, the effects of strain M2 on wheat uptake of Cd and Pb and its microbiological mechanism were also explored through pot experiments. The results showed that strain M2 reduced the concentrations of Cd and Pb and increased the concentration of PO43- in the solution through cell wall adsorption and induced phosphate precipitation. Pot experiments showed that compared to those in the CK group and inactivated strain M2 group, inoculation with live strain M2 significantly increased （123%-293%） the contents of Ca2-P and Ca8-P in rhizosphere soil, decreased the content of DTPA-Cd （34.48%） and DTPA-Pb （36.72%） in wheat rhizosphere soil, and thus hindered the accumulation of Cd and Pb in wheat grains. Moreover, high-throughput sequencing results showed that strain M2 significantly increased the diversity of wheat rhizosphere bacterial communities； increased the relative abundance of Proteobacteria, Gemmatimonadetes, and Bacteroidota in wheat rhizosphere soil； and increased the proportion of heavy metal-immobilizing and phosphorus-promoting bacteria in wheat rhizosphere soil （mainly Sphingomonas, Nocardioides, Bacillus, Gemmatimonas, and Enterobacter）. These bacterial genera played an important role in immobilizing heavy metals and preventing wheat from absorbing heavy metals. These results provide bacterial resources and theoretical basis for the bioremediation of heavy metal-contaminated farmland.

Interactive effects of ammonium sulfate and lead on alfalfa in rare earth tailings: Physiological responses and toxicity thresholds

Ion-adsorption rare earth ore contains significant levels of leaching agents and heavy metals, leading to substantial co-contamination. This presents significant challenges for ecological rehabilitation, yet there is limited understanding of the toxicity thresholds associated with the co-contamination of ammonium sulfate (AS) and lead (Pb) on pioneer plants. Here, we investigated the toxicity thresholds of various aspects of alfalfa, including growth, ultrastructural changes, metabolism, antioxidant system response, and Pb accumulation. The results indicated that the co-contamination of AS-Pb decreased the dry weight of shoot and root by 26 %–77 % and 18 %–92 %, respectively, leading to irregular root cell morphology and nucleus disintegration. The high concentration and combined exposures to AS and Pb induced oxidative stress on alfalfa, which stimulated the defense of the antioxidative system and resulted in an increase in proline levels and a decrease in soluble sugars. Structural equation modeling analysis and integrated biomarker response elucidated that the soluble sugars, proline, and POD were the key physiological indicators of alfalfa under stresses and indicated that co-exposure induced more severe oxidative stress in alfalfa. The toxicity thresholds under single exposure were 496 (EC5), 566 (EC10), 719 (EC25), 940 (EC50) mg kg−1 for AS and 505 (EC5), 539 (EC10), 605 (EC25), 678 (EC50) mg kg−1 for Pb. This study showed that AS-Pb pollution notably influenced plant growth performance and had negative impacts on the growth processes, metabolite levels, and the antioxidant system in plants. Our findings contribute to a theoretical foundation and research necessity for evaluating ecological risks in mining areas and assessing the suitability of ecological restoration strategies.

Evaluation of heavy metal accumulation and tolerance in oxalic acid-treated Phragmites australis wetlands for textile effluent remediation

Water contamination with metals poses significant environmental challenges. The occurrence of heavy metals (HMs) prompts modifications in plant structures, emphasizing the necessity of employing focused safeguarding measures. Cadmium (Cd), lead (Pb), and chromium (Cr) emerge as particularly menacing toxins due to their high accumulation potential. Increasing the availability of organic acids is crucial for optimizing toxic metal removal via phytoremediation. This constructed wetland system (CWs) was used to determine how oxalic acid (OA) treatments of textile wastewater (WW) effluents affected morpho-physiological characteristics, antioxidant enzyme activity, oxidative stress, and HM concentrations in Phragmites australis. Multiple treatments, comprising the application of OA at a concentration of 10 mM and WW at different dilutions (25%, 50%, 75%, and 100%), were employed, with three replications of each treatment. WW stress decreased chlorophyll and carotenoid content, and concurrently enhanced HMs adsorption and antioxidant enzyme activities. Furthermore, the application of WW was found to elevate oxidative stress levels, whereas the presence of OA concurrently mitigated this oxidative stress. Similarly, WW negatively affected soil-plant analysis development (SPAD) and the total soluble proteins (SP) in both roots and shoots. Conversely, these parameters showed improvement with OA treatments. P. australis showed the potential to enhance HM accumulation under 100% WW stress. Specifically, there is an increase in root SP ranging from 9% to 39%, an increase in shoot SP from 6% to 91%, and an elevation in SPAD values from 4% to 64% compared to their respective treatments lacking OA inclusion. The OA addition resulted in decreased EL contents in the root and shoot by 10%–19% and 13%–15%, MDA by 9%–14% and 9%–20%, and H2O2 by 14%–21% and 9%–17%, in comparison to the respective treatments without OA. Interestingly, the findings further revealed that the augmentation of OA also contributed to an increased accumulation of Cr, Cd, and Pb. Specifically, at 100% WW with OA (10 mM), the concentrations of Cr, Pb, and Cd in leaves rose by 164%, 447%, and 350%, in stems by 213%, 247%, and 219%, and in roots by 155%, 238%, and 195%, respectively. The chelating agent oxalic acid effectively alleviated plant toxicity induced by toxins. Overall, our findings demonstrate the remarkable tolerance of P. australis to elevated concentrations of WW stress, positioning it as an eco-friendly candidate for industrial effluent remediation. This plant exhibits efficacy in restoring contaminants present in textile effluents, and notably, oxalic acid emerges as a promising agent for the phytoextraction of HMs.

Enhancing heavy metal phytoremediation in landfill soil by Chrysopogon zizanioides (L.) roberty through the application of bacterial-biochar pellets

This work investigated the performance of bacterial-biochar pellets (BBP) on promoting heavy metal phytoremediation by Chrysopogon zizanioides (L.) Roberty planted in landfill soil. Micrococcus sp. MU1, an indole-3-acetic acid (IAA)-producing bacterium, was incorporated into biochar pellets (MU1-BBP). MU1-BBP contained a high number of viable bacterial cells with 90 % viability after storage at 4°C for two months. In addition, it had a greater survival capability in heavy metals-contaminated landfill soil than MU1-free cells. The application of MU1-BBP significantly promoted the growth performance and chlorophyll synthesis of C. zizanioides planted in landfill soil. Cd, Cu, Pb and Zn were mostly retained in the roots relative to the shoots of C. zizanioides. The accumulation of Cd, Cu, Pb, and Zn in the roots of C. zizanioides were significantly boosted by MU1-BBP inoculation. Plants with MU1-BBP inoculation enhanced the accumulation coefficient (AC) of all four heavy metals. The values of AC values of Cd, Cu, and Zn in C. zizanioides with MU1-BBP inoculation were greater than 1.0. However, translocation factors of all four metals were low. The findings suggest C. zizanioides may be a good heavy metal phytostabilizer. The findings support the potential of bacterial-biochar pellets to enhance the efficiency of heavy metal phytostabilization of C. zizanioides in landfill sites.

Phytoremediation Potentiality of Bottle Gourd Plant (Lagenaria siceraria)

A pot experiment of bottle gourd plant with Pb, Zn, NPK and Vermicompost (VC) was carried out at the Department of Soil, Water and Environment, University of Dhaka. The aim of the study was to introduce a phytoremedial technique. The bottle gourd (Lagenaria siceraria) plant was used in the trial for evaluating its potentiality to accumulate Pb and Zn from soil and translocate these elements to different parts of the plant. Twelve treatments (T) were utilized in the experiment including control (T1). The remaining treatment groups were composed of different ratios of VC and recommended dose of NPK- with and without lead and Zinc. Tolerance to metal stress by the bottle gourd plant was evident in terms of higher biomass and yield production with the Pb and Zn. The maximum total biomass (leaf + stem + root) of fresh (67.49 g) and dry yield (8.41g) was achieved with Pb addition to T11. Bioconcentration factor (BCF) and Translocation Factor (TF) greater than one (BCF&gt;1 and TF&gt;1) were considered indicators of heavy metal accumulators and translocators, respectively. Among the Pb treatments, highest BCF achieved in leaf (1.67) with T12, in stem (1.82) with T8, in root (4.67) with T11 and maximum TF (2.87) found with T11. The Zn treatments exerted the highest BCF value in leaf (1.80), and in stem (1.64) with T10, in root (2.70) with T12, lowest value of BCF and TF were displayed in control (T1). Research exposed that bottle gourd plants had transferred both the heavy metals from soil significantly. The highest Pb accumulation in leaf was found to be 0.0023% (dry weight) in T10 and the lowest (0%) in T1. The highest translocation factor was found in T5 for Pb and in T11 for Zn. Moreover, bioconcentration factor (Pb) in shoots exhibited a significant, strong, and negative correlation (r = -0.804, p = 0.002) with the soil organic carbon content. There was also a strong, significantly negative correlation between total Pb content in soil and BCF (leaf) (r = -0.717, p = 0.009), as well as BCF (stem) (r = -0.692, p = 0.013). Similar relationship was found in case of Zn. The study revealed that bottle gourd plants possess phytoremedial potentiality which will be beneficial for the pollution context of Bangladesh. Further investigation is needed for greater research interest. Biodivers. Conserv. Bioresour. Manag. 2024, 10(1): 59-74

Role of arbuscular mycorrhizal fungi in lead translocation from Bidens pilosa L. plants to soil

Bidens pilosa frequently forms a symbiotic association with arbuscular mycorrhizal fungi (AMF). This plant species can grow in Pb-polluted soils, accumulating Pb in its tissues. The aims of the study were to determine whether Pb accumulated in the tissues of B. pilosa can be transferred to the soil through AMF and to compare the role of AMF communities that have a history of exposure to the contaminant with those that have never been exposed. The experiment combined plants with and without Pb accumulated in their tissues, and inoculated with AMF collected from the rhizosphere of B. pilosa in soils contaminated and not contaminated with Pb. The results showed that AMF participate in the removal of Pb that had entered the plant and release it into the soil, as evidenced by the presence of Pb in the AMF spores and in the glomalin produced by AMF. We propose that Pb accumulation in AMF spores would be a protection mechanism that interrupts Pb uptake by the plant; however, that mechanism would not be fully exploited in detoxification, whereas the production of Pb-enriched glomalin could be an important detoxification mechanism to eliminate Pb already taken up by plants. AMF with a history of Pb exposure achieved only higher rates of root colonization, while AMF without previous exposure showed higher Pb concentration in the spores and higher glomalin production, and successfully removed Pb from both the roots and aboveground parts of the plant. The use of AMF communities not adapted to Pb may be a more effective option for microbe-mediated phytoremediation methods in which detoxification mechanisms are desirable.