Bioaugmentation-assisted phytoremediation of lead and salinity co-contaminated soil by Suaeda salsa and Trichoderma asperellum

The monokaryotic filamentous fungus Ustilago sp. HFJ311 promotes plant growth and reduces Cd accumulation by enhancing Fe transportation and auxin biosynthesis

Infection with smut fungus like Ustilago maydis decreases crop yield via inducing gall formation. However, the in vitro impact of Ustilago spp. on plant growth and stress tolerance remains elusive. This study investigated the plant growth promotion and cadmium stress mitigation mechanisms of a filamentous fungus discovered on a cultural medium containing 25 μM CdCl2. ITS sequence alignment revealed 98.7 % similarity with Ustilago bromivora, naming the strain Ustilago sp. HFJ311 (HFJ311). Co-cultivation with HFJ311 significantly enhanced the growth of various plants, including Arabidopsis, tobacco, cabbage, carrot, rice, and maize, and improved Arabidopsis tolerance to abiotic stresses like salt and metal ions. HFJ311 increased chlorophyll and Fe contents in Arabidopsis shoots and enhanced root-to-shoot Fe translocation while decreasing root Fe concentration by approximately 70 %. Concurrently, HFJ311 reduced Cd accumulation in Arabidopsis by about 60 %, indicating its potential for bioremediation in Cd-contaminated soils. Additionally, HFJ311 stimulated IAA concentration by upregulating auxin biosynthesis genes. Overexpression of the Fe transporter IRT1 negated HFJ311's growth-promotion effects under Cd stress. These results suggest that HFJ311 stimulates plant growth and inhibits Cd uptake by enhancing Fe translocation and auxin biosynthesis while disrupting Fe absorption. Our findings offer a promising bioremediation strategy for sustainable agriculture and food security.

Indigenous fungi with the ability to biodegrade hydrocarbons in diesel-contaminated soil are isolated and selected using a simple methodology

Soil contamination by hydrocarbons is a problem that causes severe damage to the environment and public health. Technologies such as bioremediation using native microbial species represent a promising and environmentally friendly alternative for decontamination. This study aimed to isolate indigenous fungi species from the State of Rio de Janeiro, Brazil and evaluate their diesel degrading capacity in soils contaminated with crude oil. Seven filamentous fungi were isolated after enrichment cultivation from soils collected from contaminated sites and subjected to growth analysis on diesel nutrient media. Two fungal species were pre-selected and identified by morphological genus analysis and molecular techniques as Trichoderma asperellum and Penicillium pedernalense. The microdilution test showed that T. asperellum presented better fungal growth in high diesel concentrations than P. pedernalense. In addition, T. asperellum was able to degrade 41 and 54% of the total petroleum hydrocarbon (TPH) content present in soil artificially contaminated with diesel (10 g/kg of soil) in 7 and 14 days of incubation, respectively. In higher diesel concentration (1000 g of diesel/kg of soil) the TPH degradation reached 26%, 45%, and 48%, in 9, 16, and 30 d, respectively. The results demonstrated that the selected species was suitable for diesel degradation. We can also conclude that the isolation and selection process proposed in this work was successful and represents a simple alternative for obtaining native species with hydrocarbon degradation capacity, for use in the bioremediation process in the recovery of contaminated areas in an ecologically acceptable way.

Effects of blast furnace slag on the immobilization, plant uptake and translocation of Cd in a contaminated paddy soil

The potential toxicity of Cd to soil and rice plant severely threaten human health. This study was conducted to investigate the remediation effects of blast furnace slag (BFS) on the bioavailability of Cd in a contaminated paddy soil from a perspective of soil solution chemistry. Batch experiments, pot culture experiments, and principal analysis (PCA) were used to study the effects and mechanisms of BFS addition changing Cd chemical behavior and Cd toxicity. Results indicated that BFS facilitated Cd adsorption in soils, increased pH, Eh, and EC values in soil solution, whereas reduced dissolved Cd content. BFS amendment was efficient in decreasing root Cd intake and Cd upward transport in rice plant, with the Cd translocation factor in brown rice decreased by ∼ 75% (BFS treatment, 6‰ wt) relative to Cd treatment, which in turn increased rice biomass and grain yield. PCA indicated that the dissolved Cd concentration had a close relationship with soil pH and metal concentration in soil solution. Results from this study indicated that BFS had potential ability for either immobilization or remobilization of Cd in soils, and the findings have important implications for Cd-polluted soil remediation or other resource utilization with slag-based materials.

Dynamic mechanisms of cadmium accumulation and detoxification by Lolium perenne grown in soil inoculated with the cadmium-tolerant bacterium strain Cdq4-2

Cadmium (Cd) contamination is a serious threat to food security and human health. The cost-effective in situ method of remediating Cd-contaminated soil uses Cd-tolerant microorganisms and Cd-enriching plants. The present study investigated the dynamic effects of inoculating soil with a Cd-tolerant bacteria strain Cdq4-2 (Enterococcus sp.) on the physiological and biochemical properties of perennial ryegrass Lolium perenne. The combined effects of remediating Cd-contaminated soil with this plant and these bacteria were also studied. An experiment was used to compare three treatments of L. perenne crops: 1) CK (control soil without Cd), 2) C (20 mg/kg Cd-contaminated soil), and 3) CB (20 mg/kg Cd-contaminated soil inoculated with bacteria Cdq4-2). The results show that compared with treatment C, the aboveground biomass, underground biomass, and total biomass of CB were 46.83-69.31%, 131.76-462.79%, and 62.65-101.53% greater, respectively. The superoxide dismutase activity of CB was 17.62-54.63% lower, while its peroxidase activity was 67.49-146.51% higher. The malondialdehyde concentration in CB was 30.40-40.24% more significant, the ascorbic acid concentration was 6.20-188.22% higher, and its glutathione concentration was 16.25-63.63% lower. The Cd concentrations of aboveground parts of a plant in treatment CB were 18.55% and 30.53% higher than those of C at days 20 and 40, respectively, while that of underground parts was 24.25% higher on day 40. The bioconcentration factors of aboveground and underground parts were higher in treatment CB on day 40. The inoculation of Cd-contaminated soils with bacteria Cdq4-2 promoted growth in L. perenne, improved its antioxidant ability, and promoted the absorption, translocation, and accumulation of Cd. Hence, it improved the effectiveness of L. perenne in remediating Cd-contaminated soils.

Effect of NaCl and EDDS on Heavy Metal Accumulation in Kosteletzkya pentacarpos in Polymetallic Polluted Soil

The ability of plants to accumulate heavy metals is a crucial factor in phytoremediation. This study investigated the effect of NaCl and S,S-ethylenediaminesuccinic acid (EDDS) on heavy metal accumulation in Kosteletzkya pentacarpos in soil polluted with arsenic, cadmium, lead, and zinc. The addition of NaCl reduced the bioavailability of arsenic and cadmium, while EDDS increased the bioavailability of arsenic and zinc. The toxicity of the polymetallic pollutants inhibited plant growth and reproduction, but NaCl and EDDS had no significant positive effects. NaCl reduced the accumulation of all heavy metals in the roots, except for arsenic. In contrast, EDDS increased the accumulation of all heavy metals. NaCl reduced the accumulation of arsenic in both the main stem (MS) and lateral branch (LB), along with a decrease in cadmium in the leaves of the main stem (LMS) and zinc in the leaves of the lateral branch (LLB). Conversely, EDDS increased the accumulation of all four heavy metals in the LB, along with an increase in arsenic and cadmium in the LMS and LLB. Salinity significantly decreased the bioaccumulation factor (BF) of all four heavy metals, while EDDS significantly increased it. NaCl had different effects on heavy metals in terms of the translocation factor (TFc), increasing it for cadmium and decreasing it for arsenic and lead, with or without EDDS. EDDS reduced the accumulation of all heavy metals, except for zinc, in the presence of NaCl in polluted soil. The polymetallic pollutants also modified the cell wall constituents. NaCl increased the cellulose content in the MS and LB, whereas EDDS had little impact. In conclusion, salinity and EDDS have different effects on heavy metal bioaccumulation in K. pentacarpos, and this species has the potential to be a candidate for phytoremediation in saline environments.

Current status and future prospect of managing lead (Pb) stress through microbes for sustainable agriculture

Soil is an important residence under various biotic and abiotic conditions. Contamination of soil by various means has hazardous effects on both plants and humans. Soil contamination by heavy metals occurs due to various man-made activities, including improper industrial and agricultural practices. Among the heavy metals, after arsenic, lead (Pb) was found to be the second most toxic metal and potent pollutants that accumulate in sediments and soils. Pb is not considered an essential element for promoting plant growth but is readily absorbed and accumulated in different plant parts. Many parameters such as pH, root exudation, soil particle size, cation exchange capacity, and other physicochemical parameters are involved in Pb uptake in plants. Excess amounts of Pb pose a threat to plant growth and cause toxicity such as chlorosis, blackening of the root system, and stunted growth. Pb toxicity may inhibit photosynthesis, disturb water balance and mineral nutrition, and alter the hormonal status, structure, and membrane permeability of plants. Therefore, this review addresses the effects of Pb toxicity and its impact on plant growth, including the morphological, physiological, and biological effects of Pb toxicity, the mechanisms behind different strategies promoting plant growth, and in combating Pb-induced stress. The bioremediation strategy for Pb removal from Pb-contaminated soil also plays an important role in combating Pb toxicity using bacterial community. Pb-contaminated soil may be remediated using different technologies such as rhizofiltration and phytoremediation, which tend to have a great capacity to curb Pb-contamination within the soil.

Phytoremediation of Potentially Toxic Elements: Role, Status and Concerns

Environmental contamination with a myriad of potentially toxic elements (PTEs) is triggered by various natural and anthropogenic activities. However, the industrial revolution has increased the intensity of these hazardous elements and their concentration in the environment, which, in turn, could provoke potential ecological risks. Additionally, most PTEs pose a considerable nuisance to human beings and affect soil, aquatic organisms, and even nematodes and microbes. This comprehensive review aims to: (i) introduce potentially toxic elements; (ii) overview the major sources of PTEs in the major environmental compartments; (iii) briefly highlight the major impacts of PTEs on humans, plants, aquatic life, and the health of soil; (iv) appraise the major methods for tackling PTE-caused pollution; (v) discuss the concept and applications of the major eco-technological/green approaches (comprising phytoextraction, rhizofiltration, phytostabilization, phytovolatilization, and phytorestoration); (vi) highlight the role of microbes in phytoremediation under PTE stress; and (vii) enlighten the major role of genetic engineering in advancing the phytoremediation of varied PTEs. Overall, appropriate strategies must be developed in order to stop gene flow into wild species, and biosafety issues must be properly addressed. Additionally, consistent efforts should be undertaken to tackle the major issues (e.g., risk estimation, understanding, acceptance and feasibility) in order to guarantee the successful implementation of phytoremediation programs, raise awareness of this green technology among laymen, and to strengthen networking among scientists, stakeholders, industrialists, governments and non-government organizations.

A comprehensive review on bio-stimulation and bio-enhancement towards remediation of heavy metals degeneration

Pollution of heavy metals is one of the risky contaminations that should be managed for all intents and purposes of general well-being concerns. The bioaccumulation of these heavy metals inside our bodies and pecking orders will influence our people in the future. Bioremediation is a bio-mechanism where residing organic entities use and reuse the squanders that are reused to one more form. This could be accomplished by taking advantage of the property of explicit biomolecules or biomass that is equipped for restricting by concentrating the necessary heavy metal particles. The microorganisms can't obliterate the metal yet can change it into a less harmful substance. In this unique circumstance, this review talks about the sources, poisonousness, impacts, and bioremediation strategies of five heavy metals: lead, mercury, arsenic, chromium, and manganese. The concentrations here are the ordinary strategies for bioremediation such as biosorption methods, the use of microbes, green growth, and organisms, etc. This review demonstrates the toxicity of heavy metal contamination degradation by biotransformation through bacterioremediation and biodegradation through mycoremediation.

Phytoremediation, Bioaugmentation, and the Plant Microbiome

Understanding plant biology and related microbial ecology as a means to phytoremediate soil and groundwater contamination has broadened and advanced the field of environmental engineering and science over the past 30 years. Using plants to transform and degrade xenobiotic organic pollutants delivers new methods for environmental restoration. Manipulations of the plant microbiome through bioaugmentation, endophytes, adding various growth factors, genetic modification, and/or selecting the microbial community via insertion of probiotics or phages for gene transfer are future areas of research to further expand this green, cost-effective, aesthetically pleasing technology─phytoremediation.

Diversity, function and assembly of the Trifolium repens L. root-associated microbiome under lead stress

Root-associated microbial layers provide unique niches that drive specific microbe assemblies. While the rhizosphere microbiome has long received much attention, endophytic microbes remain largely elusive. Characterizing metal-tolerant plants' strategies for assembling different root-associated microbial layers is important for optimizing phytoremediation. Here, a pre-stratified rhizo-box assay was conducted with Trifolium repens L. under greenhouse conditions with artificial Pb-contaminated soil. Cultivation compensated for the pollution-driven loss of soil microbial biomass carbon, enzyme activities and abundance. The acid-soluble Pb proportion increased in the rhizosphere (from 6.5-13.7% to 7.1-18.0%) compared with bulk soil. Under stress, root-layer variants were a considerable source of variation in the microbiome, with the endosphere representing a unique and independent niche. A core set of root microbes were selected by T. repens, with Proteobacteria and Actinobacteria composed of diverse plant-growth-promoting bacteria (PGPBs) and metal-tolerant members. Cluster analysis revealed endosphere-enriched genera, with Rhizobium, Nocardioides, Novosphingobium, Phyllobacterium, and Sphingomonas being the most dominant. Finally, inferred microbial metabolic pathways suggested that these potential metal-tolerant PGPB species provide critical services to hosts, enabling them to tolerate and even flourish in contaminated soil. Our results provide novel insights for understanding how root-associated microbes help metal-tolerant plants cope with abiotic stress.

Plants-Microorganisms-Based Bioremediation for Heavy Metal Cleanup: Recent Developments, Phytoremediation Techniques, Regulation Mechanisms, and Molecular Responses

Rapid industrialization, mine tailings runoff, and agricultural activities are often detrimental to soil health and can distribute hazardous metal(loid)s into the soil environment, with harmful effects on human and ecosystem health. Plants and their associated microbes can be deployed to clean up and prevent environmental pollution. This green technology has emerged as one of the most attractive and acceptable practices for using natural processes to break down organic contaminants or accumulate and stabilize metal pollutants by acting as filters or traps. This review explores the interactions between plants, their associated microbiomes, and the environment, and discusses how they shape the assembly of plant-associated microbial communities and modulate metal(loid)s remediation. Here, we also overview microbe-heavy-metal(loid)s interactions and discuss microbial bioremediation and plants with advanced phytoremediation properties approaches that have been successfully used, as well as their associated biological processes. We conclude by providing insights into the underlying remediation strategies' mechanisms, key challenges, and future directions for the remediation of metal(loid)s-polluted agricultural soils with environmentally friendly techniques.

Nickel tolerance and phytoremediation potential of quinoa are modulated under salinity: multivariate comparison of physiological and biochemical attributes

Soils salinization along with heavy metals contamination is among the serious environmental menaces. The present experiment was conducted to study the combined influence of salinity and nickel (Ni) on growth and physiological attributes of quinoa (Chenopodium quinoa Willd.). Thirty-day-old healthy and uniform seedlings of quinoa genotype A7 were exposed to different concentrations of Ni (0, 100, 200, 400 µM), NaCl (0, 150, 300 mM) and their combinations for three weeks. Results indicated that plant growth, pigments and stomatal conductance decreased with increasing Ni concentrations in nutrient solution. Combining lower level of salt (150 mM NaCl) with Ni resulted in improvement in growth and physiological attributes of quinoa. However, the combined application of higher level of salt (300 mM NaCl) with Ni was more detrimental for plant growth and caused more oxidative stress (H₂O₂ and TBARS) than the alone treatments. The oxidative stress was mitigated by 5.5-fold, 5-fold and 15-fold increase in the activities of SOD, CAT and APX, respectively. The concentration of Na was increased, while K and Ni decreased under the combined treatment of Ni and salinity. Multivariate analysis revealed that a moderate level of salinity had positive effects on growth and Ni phytoremediation potential of quinoa. The higher tolerance index, bioconcentration factor and lower translocation factor depicted that quinoa genotype A7 can be cultivated for phytostabilization of Ni under salinity stress. It was concluded that NaCl salinity level of 150 mM is promising for increasing growth of quinoa on Ni contaminated soils.

Potassium and Silicon Synergistically Increase Cadmium and Lead Tolerance and Phytostabilization by Quinoa through Modulation of Physiological and Biochemical Attributes

Cadmium (Cd) and lead (Pb) contaminated soils have increased recently, resulting in limited crop productivity. The ameliorative role of potassium (K) and silicon (Si) is well established in plants under heavy metals stress; however, their combined role under the co-contamination of Cd and Pb is not well understood. We hypothesized that the synergistic application of K and Si would be more effective than their sole treatment for increasing the Pb and Cd tolerance and phytostabilization potential of quinoa (Chenopodium quinoa Willd.). In the current study, quinoa genotype ‘Puno’ was exposed to different concentrations of Cd (0, 200 µM), Pb (0, 500 µM) and their combination with or without 10 mM K and 1.0 mM Si supplementation. The results revealed that the combined stress of Cd and Pb was more detrimental than their separate application to plant biomass (66% less than the control), chlorophyll content and stomatal conductance. Higher accumulation of Pb and Cd led to a limited uptake of K and Si in quinoa plants. The supplementation of metal-stressed plants with 10 mM K and 1.0 mM Si, particularly in combination, caused a significant increase in the growth, stomatal conductance and pigment content of plants. The combined stress of Cd and Pb resulted in an overproduction of H₂O₂ (11-fold) and TBARS (13-fold) and a decrease in membrane stability (59%). Oxidative stress induced by metals was lessened by 8-fold, 9-fold, 7-fold and 11-fold increases in SOD, CAT, APX and POD activities, respectively, under the combined application of K and Si. It is concluded that the exogenous supply of K and Si in combination is very promising for increasing Cd and Pb tolerance and the phytostabilization potential of quinoa.

A critical review on the phytoremediation of heavy metals from environment: Performance and challenges

Phytoremediation is an effective, green and economical technique. Different types of phytoremediation methods can be used for the reduction of heavy metal contaminations, such as phytoextraction, phytovolatilization, phytostabilization and phytofiltration. The biomass of plants and the bioavailability of heavy metals in soil are the key factors affecting the efficiency of phytoremediation. It's worth noting that the low remediation efficiency and the lack of effective disposal methods for contaminated biomass have limited its development and application. At present, biological, physical, chemical, agronomic and genetic approaches have been used to enhance phytoremediation. Disposal methods of contaminated biomass usually include pyrolysis, incineration, composting and compaction. They are effective, but are costly and have security problems. Improper disposal of contaminated biomass can lead to leaching of heavy metals. The leaching possibility of different forms of heavy metal in plants is different. Hence, it has great significance to explore the different forms of heavy metals in plants which can help to explore appropriate disposal methods. According to the challenges of phytoremediation, we put forward some views and recommendations for the sustainable and rapid development of phytoremediation technology.

Differential Uptake and Translocation of Cadmium and Lead by Quinoa: A Multivariate Comparison of Physiological and Oxidative Stress Responses

Contamination of soils with cadmium (Cd) and lead (Pb) has emerged as a serious environmental issue that reduces crop productivity. However, the metals tolerance and accumulation potential of quinoa (Chenopodium Quinoa Willd) under the combined stress of Cd and Pb has not yet been explored. In the present hydroponic study, the physiological and biochemical characteristics of quinoa exposed to Cd and Pb were explored. Four-week-old plants of quinoa genotype ‘Puno’ were grown under different concentrations of Cd (0, 50 and 100 µM), Pb (0, 250 and 500 µM) alone as well as in combinations. The results showed that with increasing Cd and Pb levels in the nutrient solution, the plant biomass, stomatal conductance and chlorophyll contents were decreased. However, the concurrent application of higher concentrations of Cd (100 µM) and Pb (500 µM) caused even more reduction in the plant biomass (more than 50% than the control) and physiological attributes. The combined application of Pb and Cd caused oxidative stress through an overproduction of H2O2 (10-fold) and TBARS (12.5-fold), leading to decrease in membrane stability (52%). The oxidative stress was alleviated by a 7-fold, 10-fold and 9-fold overactivation of superoxide dismutase (SOD), peroxidase (POD) and catalase (CAT), respectively. An excessive uptake of Cd resulted in a limited uptake of Pb and K in the roots and shoots of quinoa plants. The Cd and Pb tolerance and uptake potential of Puno showed its ability to stabilize Cd and Pb in co-contaminated soils.

Salinity modulates lead (Pb) tolerance and phytoremediation potential of quinoa: a multivariate comparison of physiological and biochemical attributes

Salinity and lead (Pb) contamination of soil are important environmental issues. A hydroponics experiment was performed to unravel the effects of salinity on modulation of Pb tolerance and phytoremediation potential of quinoa. Four-week-old plants of quinoa genotype "Puno" were treated with different concentrations of NaCl (0, 150 and 300 mM), Pb (0, 250 and 500 μM) and their combinations. It was noticed that plant biomass, chlorophyll contents and stomatal conductance of quinoa were slightly affected at 150 mM NaCl or 250 μM Pb. However, the higher concentrations of NaCl (300 mM) and Pb (500 μM) caused significant decline in these attributes. The accumulation of Na in quinoa increased under the combined application of salt with highest level of Pb. The uptake of K was not affected at the lower levels of either salinity or Pb, but decreased significantly at their highest levels. The combination of salinity and Pb increased H₂O₂ contents and caused lipid peroxidation that was mitigated by the activation of antioxidant enzymes (superoxide dismutase, catalase, peroxidase, ascorbate peroxidase). The activities of these enzymes increased by 4-, 3.75-, 5.4- and 2-fold, respectively, in the combined application of 500 μM Pb and 300 mM NaCl with respect to control. A multivariate analysis indicated that Pb tolerance potential of quinoa under combined application of NaCl and Pb was higher at 150 than 300 mM NaCl. The bioconcentration factor and translocation factor for Pb remained less than one either in the absence or presence of salinity. Lead accumulation and tolerance potential indicated that quinoa genotype "Puno" is suitable for phytostabilization of Pb under saline conditions.

Phytoremediation of secondary saline soil by halophytes with the enhancement of γ-polyglutamic acid

Soil salinization has severely affected the quality of tillage land in China, and most greenhouse soils in Shanghai suburb suffer from secondary salinization with high salinity levels dominated by Ca²⁺, Mg²⁺ and NO₃^-. In this work, a sandy loam soil (Calcaric Fluvisols) contaminated by the above ions was selected as research object, and the binding conditions and abilities of γ-polyglutamic acid (γ-PGA) to water-soluble Ca²⁺ and Mg²⁺ in the soil were examined, and then pot experiments were conducted to remove Ca²⁺, Mg²⁺ and NO₃^- by two halophytes (Sedum aizoon L., Sesbania cannabina Pers.) integrated with γ-PGA application. The results showed that under the conditions of adding 1000 mg L^-1γ-PGA (pH 7) and 25 °C, the binding efficiencies of Ca²⁺ and Mg²⁺ were 51.59% and 68.03%, respectively. Compared with Sesbania cannabina Pers., Sedum aizoon L. displayed better remediation performance for the soil with γ-PGA application in pot experiments, and the removal efficiencies of Ca²⁺, Mg²⁺ and NO₃^- reached 93.25%, 94.78% and 84.26% after applying 1000 mg L^-1γ-PGA for 56 d, respectively. Moreover, γ-PGA application could mitigate salt stress and promote plant growth, and activate antioxidant defense systems. Compared with the control, 1000 mg L^-1γ-PGA application significantly increased plant height and fresh weight of Sedum aizoon L., and the removal efficiencies of Ca²⁺, Mg²⁺ and NO₃^- increased by 45.48%, 82.62% and 69.91%, respectively. In the future, more in-depth mechanism of joint effect and field-scale investigation need to be further studied.

Kosteletzkya pentacarpos: A Potential Halophyte Candidate for Phytoremediation in the Meta(loid)s Polluted Saline Soils

Kosteletzkya pentacarpos (L.) Ledebour is a perennial facultative halophyte species from the Malvacea family that grows in coastal areas with high amounts of salt. The tolerance of K. pentacarpos to the high concentration of salt (0.5–1.5% salinity range of coastal saline land) has been widely studied for decades. Nowadays, with the dramatic development of the economy and urbanization, in addition to the salt, the accumulation of mate(loid)s in coastal soil is increasing, which is threatening the survival of halophyte species as well as the balance of wetland ecosystems. Recently, the capacity of K. pentacarpos to cope with either single heavy metal stress or a combination of multiple meta(loid) toxicities was studied. Hence, this review focused on summarizing the physiological and biochemical behaviors of K. pentacarpos that has been simultaneously exposed to the combination of several meta(loid) toxicities. How the salt accumulated by K. pentacarpos impacts the response to meta(loid) stress was discussed. We conclude that as a potential candidate for phytoremediation, K. pentacarpos was able to cope with various environmental constrains such as multiple meta(loid) stresses due to its relative tolerance to meta(loid) toxicity.

Effects of excessive nitrogen on nitrogen uptake and transformation in the wetland soils of Liaohe estuary, northeast China

It remains unclear whether excessive nitrogen additions lead to the degradation of Suaeda salsa (S. salsa) by affecting the nitrogen pool, enzyme activities, and bacterial community structure of wetland soils. This study investigated the effect of five added nitrogen concentrations (0, 1, 2, 4, and 6 mmol L^-1 N with NH₄NO₃ = group C, group L, group M, group H, and group G, respectively) on nitrogen uptake by S. salsa and nitrogen transformation in the wetland soils of the Liaohe estuary. The height, weight, and total nitrogen (TN) of S. salsa in group G was significantly lower than in the other groups (p <0.05). The NH₄⁺-N concentration in the soil tended to increase with increasing nitrogen addition, but the TN concentration in the soil tended to decrease. The nitrogenase, protease, urease, ammonia monooxygenase (AMO), nitrous oxide reductase (NOR), and dehydrogenase (DHA) activities increased with increasing nitrogen addition within the range of 0 to 4 mmol L^-1. We identified 30 phyla and 48 known genera across all five groups. The predominant phyla were Proteobacteria (52.68%), Bacteroidetes (22.58%), and Planctomycetes (3.94%). The most abundant genus was Acinetobacter (13.38%), followed by Proteiniphilum (11.88%) and Brevundimonas (6.03%). The total number of soil bacterial species increased with increasing nitrogen addition. Group G had lower soil bacterial activity and diversity than the other groups. It was concluded that appropriate levels of nitrogen addition could promote nitrogen uptake by S. salsa and nitrogen transformation in the wetland soils of the Liaohe estuary by affecting soil enzyme activities and soil bacterial activity, diversity, abundance, and composition, while excessive nitrogen additions may be one of the reasons for the degradation of S. salsa.

Bottom Ash Modification via Sintering Process for Its Use as a Potential Heavy Metal Adsorbent: Sorption Kinetics and Mechanism

Heavy metal pollution in the environment is a critical issue, engendering ecosystem deterioration and adverse effects on human health. The main objective of this study was to evaluate heavy metal adsorbents by modifying industrial byproducts. The bottom ash was sintered and evaluated for Cd and Pb sorption. Three adsorbents (bottom ash, sintered bottom ash (SBA), and SBA mixed with microorganisms (SBMA)) were tested to evaluate the sorption kinetics and mechanism using a lab-scale batch experiment. The results showed that the highest sorption efficiency was observed for Cd (98.16%) and Pb (98.41%) with 10% SBA. The pseudo-second-order kinetic model (R² > 0.99) represented the sorption kinetics better than the pseudo-first-order kinetic model for the SBA and SBMA, indicating that chemical precipitation could be the dominant sorption mechanism. This result is supported by X-ray photoelectron spectroscopy analysis, demonstrating that -OH, -CO₃, -O, and -S complexation was formed at the surface of the sintered materials as Cd(OH)₂ and CdCO₃ for Cd and PbO, and PbS for Pb. Overall, SBA could be utilized for heavy metal sorption. Further research is necessary to enhance the sorption capacity and longevity of modified industrial byproducts.

Root fungal endophytes: identity, phylogeny and roles in plant tolerance to metal stress

Metal trace elements accumulate in soils mainly because of anthropic activities, leading living organisms to develop strategies to handle metal toxicity. Plants often associate with root endophytic fungi, including nonmycorrhizal fungi, and some of these organisms are associated with metal tolerance. The lack of synthetic analyses of plant-endophyte-metal tripartite systems and the scant consideration for taxonomy led to this review aiming (1) to inventory non-mycorrhizal root fungal endophytes described with respect to their taxonomic diversity and (2) to determine the mutualistic roles of these plant-fungus associations under metal stress. More than 1500 species in 100 orders (mainly Hypocreales and Pleosporales) were reported from a wide variety of environments and hosts. Most reported endophytes had a positive effect on their host under metal stress, but with various effects on metal uptake or translocation and no clear taxonomic consistency. Future research considering the functional patterns and dynamics of these associations is thus encouraged.

Salinity relief aniline induced oxidative stress in Suaeda salsa: Activities of antioxidative enzyme and EPR measurements

Wastewater from printing and dyeing processes often contains aniline and high salinity, which are hazardous to aquatic species. Glycophytic plants cannot survive under high-salinity conditions, whereas halophytes grow well in such an environment. In this study, we investigated the influence of NaCl on the antioxidant level in Suaeda salsa affected by aniline stress. The seedlings showed various growth toxicity effects under different concentrations of aniline. The results showed that the effect of the aniline was more severe for the root growth compared to that for the shoot growth. Aniline exposure significantly increased the total free radicals and ·OH radicals in the plants. Suaeda salsa exposure to aniline caused oxidative stress by altering the superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD) activity, which resulted in the overproduction of H₂O₂ and the inducement of lipid peroxidation. Analysis revealed that the malondialdehyde (MDA) content was enhanced after aniline exposure and that the chlorophyll content was significantly decreased. The results showed that aniline induced the production of free radicals and reactive oxygen species (ROS), and changed the antioxidant defense system. This ultimately resulted in oxidative damage in S. salsa; however, it was found that moderate salinity could mitigate the effects. In conclusion, salinity may alleviate the growth inhibition caused by aniline by regulating the antioxidant capacity of S. salsa.

Heavy metal tolerance and potential for remediation of heavy metal-contaminated saline soils for the euhalophyte Suaeda salsa

Due to irrigation practices and industrial pollution, large areas of the lands in the world are simultaneously affected by salinity and heavy metal contamination. It has been considered that halophytes have adapted to salinity, and can be used to remediate heavy metal-contaminated saline soils. Suaeda salsa L. (S. salsa) is a high salt-resistance plant, which can efficiently absorb and accumulate salt and toxic metals from saline soils, suggesting that this may be potential plant species that can be used for the restoration of saline soils contaminated with heavy metals. The present brief review sheds light on the characteristics of S. salsa in the uptake and accumulation of high levels of heavy metals. Furthermore, the physiological and molecular mechanisms for heavy metal tolerance were highlighted. The potential values of S. salsa in the remediation of saline soils were also summarized.

High-Performance Estimation of Lead Ion Concentration Using Smartphone-Based Colorimetric Analysis and a Machine Learning Approach

Traditional methods for detection of lead ions in water samples are costly and time-consuming. In this work, an accurate smartphone-based colorimetric sensor was developed utilizing a novel machine learning algorithm. In the presence of Pb²⁺ ions in the solution of specifically functionalized gold nanoparticles, the color of solution turns from red to purple. Indeed, the color variation of the solution is proportional to Pb²⁺ concentration. The smartphone camera captures the corresponding color change, and the image is processed by an efficient artificial intelligence protocol. The nonlinear regression approach was used for concentration estimation, in which the parameters of the proposed model are obtained using a new feature extraction algorithm. In prediction of Pb²⁺ concentration, the average absolute error and root-mean-square error were 0.094 and 0.124, respectively. The influence of pH of the medium, temperature, oligonucleotide concentration, and reaction time on the performance of the proposed sensor was carefully investigated and understood to achieve the best sensor response. This novel sensor exhibited good linearity for the detection of Pb²⁺ in the concentration range of 0.5-2000 ppb with a detection limit of 0.5 ppb.

Securing of an Industrial Soil Using Turfgrass Assisted by Biostimulants and Compost Amendment

This work aimed to study the effects of compost (applied at two rates) and two commercial microbial biostimulants on the mobility and bioavailability of potentially toxic elements (PTEs) in an industrial soil phytostabilized by Dactylis glomerata L. or a mixed stand of grasses (Lolium perenne L., Poa pratensis L. and Festuca arundinacea Shreb.). The soil showed very high pseudototal and bioavailable concentrations of cadmium (Cd) and lead (Pb), due to improper lead-acid batteries storage. Compost amendment in combination with the two biostimulants produced the best outcomes in terms of plant growth and nutrient uptake. The same mix of beneficial microbes improved soil biological fertility enhancing soil nitrogen fixing and ammonia oxidizing bacteria, while reduced the pore water and NH4NO3 extractable concentrations of Cd and at lower extent of Pb in soil. Accordingly, the lower mobility and bioavailability of Cd in soil determined a lower uptake and accumulation of Cd in shoots of different grass species. Our results suggest that a green cap with turfgrass assisted by biostimulants and compost amendment in PTE-contaminated industrial sites could be a reliable and effective practice to protect and restore soil biological fertility and to reduce the risk of PTE dispersion in the surrounding environment.

Monitoring Suaeda salsa Spectral Response to Salt Conditions in Coastal Wetlands: A Case Study in Dafeng Elk National Nature Reserve, China

This paper reports on monitored Suaeda salsa spectral response to salt conditions in coastal wetlands, using spectral measurements and remotely sensed algorithms. Suaeda salsa seedlings were collected from the Dafeng Elk National Nature Reserve (DENNR) in Jiangsu Province, China. We treated 21 Suaeda salsa seedlings planted in pots with 7 different salt concentrations (n = 3 for each concentration) to assess their response to varying salt conditions. Various plant growth indicators, including chlorophyll content, fresh weight, dry weight, and canopy hyperspectral reflectance, were measured. One-way analysis of variance (ANOVA) and post hoc multiple comparisons of least-significant difference (LSD) were used to explore the physiological indicators of sensitivity to salt treatment. Red edge parameters and spectral reflectance indices were used to analyze spectral response to salt conditions and to investigate the potential for remotely sensing physiological parameters which are sensitive to salt conditions. The results indicated that among these physiological indicators, the total chlorophyll content differed significantly with salt conditions, being highest at 50 mmol/L, whereas the differences observed for the morphological parameters were highest at 200 mmol/L. In addition, new vegetation indices were significantly more responsive to salt concentrations than were traditional red edge parameters. The two vegetation indices, D854/D792 and (D792 − D854)/(D792 + D854), were the most sensitive to the total chlorophyll content, and these also strongly correlated with salt concentrations. An analysis of the responses of plant growth indicators to salt treatment showed that soil having a salt concentration of 50~200 mmol/L is most suitable for the growth of Suaeda salsa. These results suggest the potential for using remote sensing to effectively interpret the causes of salt-induced spectral changes in Suaeda salsa. This methodology also provides a new reference for the inversion model of estimating the total chlorophyll content of Suaeda salsa under different salt concentrations in similar coastal wetlands, whether in China or elsewhere.

Toxicity, migration and transformation characteristics of lead in soil-plant system: Effect of lead species

Lead (Pb) is a typical hazardous element of high concern in species characteristics involving toxicity, migration and transformation. A greenhouse experiment was conducted using Solanum nigrum L. grown in soils treated by divalent (Pb²⁺), tetravalent (Pb⁴⁺), trimethyl (TML) and triethyl (TEL) lead for 60 days. Results of physio-biochemical parameters indicated Pb toxicity was ranked as TEL > TML > Pb²⁺ > Pb⁴⁺ in a dose-dependent manner, and the correlation levels of organic species were higher than inorganic species. S. nigrum L. adopted phytostabilization strategy through fixing Pb in roots and restricting its transfer to shoots. More phytotoxic Pb was absorbed from soils treated by Pb²⁺ than Pb⁴⁺ as well as TEL than TML. In soils, inorganic Pb species were mainly present in residues while organic Pb species in Fe/Mn oxide and exchangeable fractions. Although most of Pb species in plant existed in the low-bioavailable extractions of 1 M NaCl and 2% HAC, the water-soluble Pb extracted by d-H₂O and 80 % ethanol were increased to a large extent under high-level exposure. The occurrence of reduction and (de)alkylation were considered as the major pathways in the biotransformation of Pb species. This study will conduce to the ecological risk management for Pb-contaminated soils.

Health risk assessment of heavy metal and its mitigation by glomalin-related soil protein in sediments along the South China coast

Knowledge regarding the exposure risk of heavy metals in estuarine wetland is important for people (especially fishermen and consumers of local fish) living in the coastal area and the coastal reclamation. Here, we assessed the ecological and human health risks of sediment-associated metals in the large-scale estuary area based on different sediment textures (Mud, Mud-Sand, and Sand). To investigate the potential impact of terrestrial material on the contamination risks, glomalin-related soil protein (GRSP), a recalcitrant soil protein fraction, was used. Results showed that the estuarine sediment texture played a rather important role in the heavy metal distribution, risk assessment, and the metal sequestration capacity of the land-derived GRSP fraction. We found arsenic, Pb, Cd, and Cr had the highest enrichment in the estuarine wetlands by calculating multiple contamination indices, and that confirmed similar findings of heavy metal contents, except Cd. The average pollution load index (PLI) was 1.67 in all the estuarine sediments, indicating multi-element contamination, with the Muddy sediments (PLI = 2.07) significantly higher than the Mud-Sand mixed sediments (PLI = 1.85), and the lowest (0.78 < 1) in the Sandy sediments. The health risk assessment suggested that the potential cancer risk occurred (>1.00E-6) but no obvious non-carcinogenic effects occurred (<1). Arsenic was found to be the primary contributor to non-carcinogenic risk, accounting for 44.2% of hazard index, while Ni is the primary control metal for carcinogenic risk (except arsenic in the Sandy sediments). As a proxy of terrestrial organic matter, GRSP fraction possessed a high sequestration capacity for heavy metal, especially in the Sandy sediments, and it was significantly associated with the mitigation of ecological and health risks, which may provide new insights into the in situ remediation of anoxic estuarine wetlands.

Phytoremediation of Cadmium: Physiological, Biochemical, and Molecular Mechanisms

Cadmium (Cd) is one of the most toxic metals in the environment, and has noxious effects on plant growth and production. Cd-accumulating plants showed reduced growth and productivity. Therefore, remediation of this non-essential and toxic pollutant is a prerequisite. Plant-based phytoremediation methodology is considered as one a secure, environmentally friendly, and cost-effective approach for toxic metal remediation. Phytoremediating plants transport and accumulate Cd inside their roots, shoots, leaves, and vacuoles. Phytoremediation of Cd-contaminated sites through hyperaccumulator plants proves a ground-breaking and profitable choice to combat the contaminants. Moreover, the efficiency of Cd phytoremediation and Cd bioavailability can be improved by using plant growth-promoting bacteria (PGPB). Emerging modern molecular technologies have augmented our insight into the metabolic processes involved in Cd tolerance in regular cultivated crops and hyperaccumulator plants. Plants’ development via genetic engineering tools, like enhanced metal uptake, metal transport, Cd accumulation, and the overall Cd tolerance, unlocks new directions for phytoremediation. In this review, we outline the physiological, biochemical, and molecular mechanisms involved in Cd phytoremediation. Further, a focus on the potential of omics and genetic engineering strategies has been documented for the efficient remediation of a Cd-contaminated environment.

Bioremediation Methods for the Recovery of Lead-Contaminated Soils: A Review

Currently, the pollution of soils by heavy metals is a problem of paramount relevance and requires the development of proper remediation techniques. In particular, lead is a frequently detected soil contaminant that poses adverse effects to the environment and human health. In this review, we provide an overview of the bioremediation treatments promoted by plants (phytoremediation), fungi, or bacteria that could be applied to areas polluted by lead. These restoration processes have the advantage of being environmentally friendly and cost-effective solutions that exploit plants to immobilize and extract contaminants from soil and water, and fungi and bacteria to degrade them. Phytoremediation is an extensively studied and mature practice, with many in-the-field applications where numerous plant species have been employed. In contrast, bioremediation processes promoted by fungi and bacteria are very promising but, up to now, studies have been mostly performed at a laboratory scale with only a few implementations in real-world situations; therefore, further research is needed.

Naturally selected dominant weeds as heavy metal accumulators and excluders assisted by rhizosphere bacteria in a mining area

Managers need more practical and promising plants for use in heavy metal phytoremediation. Although previous studies have identified the potential of some weeds and microbial strains in phytoremediation, the potential of dominant weeds and the relationship between weeds and their rhizosphere bacterial strains are still unknown. In our study, we examined dominant weeds in the Dabaoshan mine located in Guangdong province, China to test their abilities as heavy metal accumulators and excluders. Results suggest that Ludwigia prostrata exhibited the highest potential for accumulating Cu, Pb and Zn compared with the other plants. Specifically, L. prostrata accumulated 71.58, 130.76 and 454.72 mg kg^-1 of Cu, Pb and Zn, respectively; the species' translocation factor of Zn was 2.04, indicating a high accumulation of Zn. In contrast, the Cd translocation factor (TF) of Digitaria sanguinalis was 0.18, significantly lower than that of other plant species examined. Our results suggest that Ludwigia prostrata hyperaccumulates Zn and may also serve as a potential candidate remediation plant for Cu and Pb due to its high absolute accumulation amount of Cu and Pb, while Digitaria sanguinalis may be a potential candidate as a Cd excluder. We also found that rhizosphere bacterial communities were shaped by individual dominant plant species. Chloroflexi was the most dominant phylum in accumulator plant such as Fimbristylis miliacea, while Cyanobacteria was the most dominant phylum in excluder plant such as Digitaria sanguinalis. Our study provides insights for selecting new weedy forbs and grasses, rhizosphere bacterial species and developing approaches for phytoremediation and phytostabilization.

Lead toxicity induced phytotoxic effects on mung bean can be relegated by lead tolerant Bacillus subtilis (PbRB3)

Being a primary toxic heavy metal, lead (Pb) contamination presents an imposing environmental and public health concern worldwide. A Bacillus subtilis PbRB3, displaying higher Pb tolerance, was isolated from the textile effluent. The bacterial culture was able to remove >80% of Pb from culture solution. Upon screening in the presence of Pb, PbRB3 strain exhibited significant plant growth promoting potential. A 3 weeks long pot experiment was established to examine the capability of PbRB3 strain for physiological and biochemical traits, and Pb accumulation tendency of mung bean at 250 and 500 mg kg^-1 of Pb toxicity, respectively. With respect to control treatments, photosynthetic pigments, protein synthesis, net assimilation rate, transpiration rate and stomatal conductance were significantly constrained by Pb toxicity levels. Intrinsic and instantaneous water use efficiencies were considerably improved in inoculated plants under Pb toxicity. Compared to inoculated control, significantly higher superoxide dismutase activity in both Pb toxicity treatments, while higher malondialdehyde contents only at Pb500 treatment was recorded with PbRB3 inoculation. Catalase activity between Pb250 and Pb500 treatments was comparable at both inoculation level. Moreover, PbRB3 inoculation led to significantly higher peroxidase activity under Pb toxicity treatments compared to inoculated control. The PbRB3 inoculation led to comparable differences in root Pb content between Pb250 and Pb500 treatments. These results suggest that inoculation of Pb tolerant, Bacillus subtilis PbRB3, could be employed to improve mung bean growth potential and adaptation against Pb toxicity, and thereby accelerated Pb rhizoaccumulation from metal contaminated environment.

Salinity modifies heavy metals and arsenic absorption by the halophyte plant species Kosteletzkya pentacarpos and pollutant leaching from a polycontaminated substrate

Phytomanagement of polycontaminated soils is challenging, especially in areas simultaneously affected by salinity. The wetland halophyte plant species Kosteletzkya pentacarpos was cultivated in a column device allowing leachate harvest, on a polycontaminated spiked soil containing Cd (6.5 mg kg^-1 DW), As (75 mg kg^-1 DW), Zn (200 mg kg^-1 DW) and Pb (300 mg kg^-1 DW) and irrigated with salt water (final soil electrical conductivity 5.0 ms cm^-1). Salinity increased Cd bioavailability in the soil and Cd accumulation in the shoots while it had an opposite effect on As. Salinity did not modify Pb and Zn bioavailability and accumulation. Cultivating plants on the polluted soil drastically reduced the volume of leachate. In all cases, salinity reduced the total amounts of heavy metals removed by the leachate and significantly increased the proportion of Cd and Zn removed by the plants. Heavy metal contamination induced a decrease in shoot dry weight and an increase in malondialdehyde (an indicator of oxidative stress); both symptoms were alleviated by the additional presence of NaCl but this positive impact was not related to increase in protecting phytochelatins synthesis. It is concluded i) that bioavailability estimated by the 0.01M CaCl₂ extraction procedure is not fully relevant from the heavy metal mobility, ii) that salinity decreased heavy metal percolation, especially in soils cultivated with K. pentacarpos and iii) that salinity improves plant tolerance to heavy metals in K. pentacarpos and that this species is a promising plant material for phytoremediation of polycontaminated soils.

Salinity-induced alterations in plant growth, antioxidant enzyme activities, and lead transportation and accumulation in Suaeda salsa: implications for phytoremediation

Halophytes have been considered promising candidates for accumulating heavy metals from saline soils; however, little information has been given on plant physiological responses and heavy metal transportation and accumulation in halophytes that grow in heavy metal-polluted saline soils. This study hypothesized that salinity or heavy metals could induce alterations in plant growth, antioxidant enzyme activities and accumulation and transportation of heavy metals or sodium (Na) in Suaeda salsa. Pot experiments were conducted to test the above hypothesis. Lead (Pb) was selected as the representative heavy metal, and NaCl was added to simulate the Pb-polluted saline soil. The results showed that 0.5% NaCl addition alleviated the inhibition of plant growth under moderate Pb stress (35 and 100 mg kg^-1 Pb levels), while the phytotoxicity on plants was magnified by 1.0% NaCl addition. NaCl weakened the oxidative stress in Pb-treated plants by increasing the activity levels of antioxidative enzymes (dismutase (SOD), peroxidase (POD) and catalase (CAT)). At all Pb levels, as the NaCl addition increased, significant increases were observed in the concentration of Na. The 100 mg kg^-1 Pb induced a greater increase in Na concentrations than the 35 mg kg^-1 Pb did, while the latter induced a greater increase than the 300 mg kg^-1 Pb did. NaCl improved Pb translocation factor and its accumulation in Suaeda salsa under Pb stress, indicating that NaCl improves Pb uptake and translocation from roots to shoots and enhances the phytoextraction of Pb. Compared with the 0.1% NaCl treatment, the 0.5 and 1.0% NaCl treatments increased the concentrations of bioavailable Pb in the rhizosphere by 15.0-19.2 and 28.6-35.1%, respectively, indicating the contribution of salinity in producing more available Pb for plant uptake. Moderate salinity may be profitable for Pb transportation and accumulation in plants when there are positive effects on plant growth, antioxidant enzyme activities and Pb availability. These facts suggest that the halophyte Suaeda salsa may be exploited to remediate heavy metal-contaminated saline soils.