Lead accumulation, growth responses and biochemical changes of three plant species exposed to soil amended with different concentrations of lead nitrate

Unravelling the halophyte Suaeda maritima as an efficient candidate for phytostabilization of cadmium and lead: Implications from physiological, ionomic, and metabolomic responses

Cadmium (Cd) and lead (Pb) are among the most toxic heavy metals affecting human health and crop yield. Suaeda maritima (L.) Dumort is an obligate halophyte that is well adapted to saline soil. The inbuilt salinity tolerance mechanisms of halophytes help them to survive in heavy metal-contaminated rhizospheric soil. In the present study, growth and ionomic responses, reactive oxygen species (ROS) accumulation, modulations of phytochelatins, antioxidative defense, and metabolomic responses were studied in S. maritima imposed to Cd and Pb stresses with an aim to elucidate Cd and Pb tolerance mechanisms and phytoremediation potential of this halophyte. Our results showed a reduction of biomass in S. maritima, which may serve as an energy conservation strategy for survival under heavy metal stress. The increased accumulation of ROS with concomitant higher expression of various antioxidative enzymes suggests the efficient scavenging of ROS. The metabolite profiling revealed significant up-regulation of sugars, sugar alcohols, amino acids, polyphenols, and organic acids under Cd and Pb stresses suggesting their possible role in osmotic balance, ionic homeostasis, ROS scavenging, and signal transduction for stress tolerance. In S. maritima, the translocation factors (Tf) are <1 in both Cd and Pb treatments, which indicates that this halophyte has high phytostabilization potential for Cd and Pb in roots and through restricted translocation of heavy metal ions to the aboveground part. The findings of this study offer comprehensive information on Cd and Pb tolerance mechanisms in S. maritima and suggest that this halophyte can detoxify the HMs through physiological, ionic, antioxidative, and metabolic regulations.

Phosphate-solubilizing bacteria improve the antioxidant enzyme activity of Potamogeton crispus L. and enhance the remediation effect on Cd-contaminated sediment

Phosphorus-solubilizing bacteria (PSB) assisted phytoremediation of cadmium (Cd) pollution is an effective method, but the mechanism of PSB-enhanced in-situ remediation of Cd contaminated sediment by submerged plants is still rare. In this study, PSB (Leclercia adecarboxylata L1-5) was inoculated in the rhizosphere of Potamogeton crispus L. (P. crispus) to explore the effect of PSB on phytoremediation. The results showed that the inoculation of PSB effectively improved the Cd extraction by P. crispus under different Cd pollution and the Cd content in the aboveground and underground parts of P. crispus all increased. The μ-XRF images showed that most of the Cd was enriched in the roots of P. crispus. PSB especially showed positive effects on root development and chlorophyll synthesis. The root length of P. crispus increased by 51.7 %, 80.5 % and 74.2 % under different Cd pollution, and the Ca/Cb increased by 38.9 %, 15.2 % and 8.6 %, respectively. Furthermore, PSB enhanced the tolerance of P. crispus to Cd. The contents of soluble protein, MDA and H2O2 in 5 mg·kg-1 and 7 mg·kg-1 Cd content groups were decreased and the activities of antioxidant enzymes were increased after adding PSB. The results showed that the application of PSB was beneficial to the in-situ remediation of submerged plants.

Mitigation of Salinity Stress and Lead Toxicity in Maize by Exogenous Application of the Sorghum Water Extract

The increased concentration of lead (Pb) in soils is a serious threat to human beings and plants all over the world. Salinity stress is also a major issue across the globe, which limits crop productivity. The use of allelochemicals has become an effective strategy to mitigate the toxic effects of abiotic stresses. Sorghum is an important crop grown across the globe, and it also possesses an appreciably allelopathic potential. Therefore, this study was planned to determine the impacts of the sorghum water extract (SWE) on improving maize growth under Pb and salinity stress. The experiment included different treatments; control, SWE (3%), and different levels of Pb and salinity stress; T1: control, T2: 50 mM NaCl, T3: 100 mM NaCl, T4: 250 μM Pb, and T5: 500 μM Pb. Lead and salinity stress reduced the maize growth by the genesis of reactive oxygen species (ROS), as evidenced by higher production of malondialdehyde (MDA: 39.1 and 32.28%) and hydrogen peroxide (H2O2: 20.62 and 17.81%). Spraying plants with SWE improved the maize growth by increasing antioxidant activities (ascorbate peroxidase: APX, catalase: CAT, peroxidase: POD and superoxide dismutase: SOD), photosynthetic pigments, relative water contents (RWC), osmolyte accumulation (proline, total soluble proteins: TSP, free amino acids: FAA), potassium accumulation, and decreasing MDA, H2O2, sodium, chloride, and Pb accumulation. In conclusion, the application of SWE mitigates adverse impacts of Pb and salinity stresses by improving chlorophyll synthesis and osmolyte accumulation, activating the antioxidant defense system, and preventing the entry of toxic ions.

Distribution characteristics, risk assessment, and relevance with surrounding soil of heavy metals in coking solid wastes from coking plants in Shanxi, China

Heavy metal concentrations represent important pollution evaluation indices, and it is necessary to assess the potential environmental and health risks from heavy metals associated with coking wastes from coking plants. In this study, coking sludge (CS), tar residue (TR), coke powder (CP), and sulfur paste (SP) from three coking plants (Plant A, Plant B, and Plant C) in central, western, and southern Shanxi Province and from soils surrounding Plant A were selected as the research objects, and the distributions of Cu, Ni, Pb, Zn, Mn, Cd, and Cr were determined. The results showed that Cd in the four solid wastes far exceeded the soil background value by a factor of 16~195, and the contents of Pb in TR (three plants) and CS (Plant C) exceeded the soil background values 19.70-, 23.57-, 14.46-, and 12.56-fold, respectively. Similarly, the concentrations of Cu, Ni, Pb, Zn, and Cd in soils were higher than the background values by factors of 31.18, 8.35, 34.79, 29.48, and 3.43, respectively. In addition, the Cu, Ni, Pb, and Cr in the four solid wastes and soils mainly existed in the residual state. As depth increased, the overall Ni, Pb, Mn, and Cd concentrations in soils increased. The high ecological risks associated with the four solid wastes were mainly due to the enrichment of Cd. Workers in coking plants face certain Cr health risks. This study provides theoretical support for the coking industry with respect to the treatment, disposal, and management of solid wastes.

Widely targeted metabolomic analysis revealed the effects of alkaline stress on nonvolatile and volatile metabolites in broomcorn millet grains

Broomcorn millet (BM) is a future smart food. However, no information is available on the metabolism of BM grains under alkaline stress. In this study, the effects of alkaline stress on nonvolatile and volatile metabolites in the BM grains of two varieties (S223 and T289) were investigated through metabolomics approaches. All 933 nonvolatile metabolites and 313 volatile metabolites were identified, with 114 and 89 nonvolatile metabolites and 16 and 20 volatile metabolites accumulating differentially under normal vs. alkaline stresses of S223 and T289, respectively. The results indicated that alkaline stress altered phenylpropanoids, flavonoids, flavone and flavonol, valine, leucine, and isoleucine biosynthesis, as well as arginine, proline, tryptophan, and ascorbate metabolism. The effects of alkaline stress were not identical between the two varieties, which could lead to variations in active substance content. These results provide valuable information for further studies on food chemistry and the functional food development of BM grains.

Effect of sodium alginate-gelatin-polyvinyl pyrrolidone microspheres on cucumber plants, soil, and microbial communities under lead stress

Lead is highly persistent and toxic in soil, hindering plant growth. Microspheres are a novel, functional, and slow-release preparation commonly used for controlled release of agricultural chemicals. However, their application in the remediation of Pb-contaminated soil has not been studied; furthermore, the remediation mechanism involved has not been systematically assessed. Herein, we evaluated the Pb stress mitigation ability of sodium alginate-gelatin-polyvinyl pyrrolidone composite microspheres. Microspheres effectively attenuated the Pb toxic effect on cucumber seedlings. Furthermore, they boosted cucumber growth, increased peroxidase activity, and chlorophyll content, while reducing malondialdehyde content in leaves. Microspheres promoted Pb enrichment in cucumber, especially in roots (about 4.5 times). They also improved soil physicochemical properties, promoted enzyme activity, and increased soil available Pb concentration in the short term. In addition, microspheres selectively enriched functional (heavy metal-tolerating and plant growth promoting) bacteria to adapt to and resist Pb stress by improving soil properties and nutrients. These results indicated that even a small amount (0.025-0.3 %) of microspheres can significantly reduce the adverse effects of Pb on plants, soil, and bacterial communities. Composite microspheres have shown great value in Pb remediation, and their application potential in phytoremediation is also worth evaluating to expand the application.

A meta-analysis on the heavy metal uptake in Amaranthus species

Metals can accumulate in different parts of plant species in high concentrations, which gives the basis for the plant-based technology called phytoremediation. Among annual species, Amaranthus is a well-studied, potential metal accumulator genus; however, some conflicts are found among published results. Thus, we studied the metal (Cd, Cu, Fe, Ni, Pb, and Zn) accumulation potential of Amaranthus plant parts (root, stem, and leaf) by meta-analysis, furthermore, by calculation of bioaccumulation factor (BAF) values. After the extensive literature search and the calculation of relative interaction intensity (RII) values, we found significant accumulation for each metal by Amaranthus individuals growing on contaminated soils compared to plants collected from uncontaminated ones. Differences among plant parts were significant for Cu and Fe, minor for Ni, Pb, and Zn, and negligible for Cd. The BAF values indicated high accumulation in the leaf, moderate in root and stem for Cd, moderate in each plant part for Pb, and very low in each plant part for Fe, Ni, and Zn. We highlight that Amaranthus species are good prospects for metal phytoremediation projects, although, due to specific plant part-metal patterns, special attention should be paid to the harvesting practice.

Interaction of Lead and Cadmium Reduced Cadmium Toxicity in Ficus parvifolia Seedlings

Potentially toxic elements (PTEs) pollution occurs widely in soils due to various anthropogenic activities. Lead (Pb) and cadmium (Cd) coexist in soil frequently, threatening plant growth. To explore the interaction effect between Pb and Cd in Ficus parvifolia and the response of plant physiological characteristics to Pb and Cd stress, we designed a soil culture experiment. The experiment demonstrated that Pb stress improved leaf photosynthesis ability, while Cd stress inhibited it. Furthermore, Pb or Cd stress increased malonaldehyde (MDA) content, but plants were able to reduce it by increasing antioxidant enzyme activities. The presence of Pb could alleviate Cd phytotoxicity in plants by inhibiting Cd uptake and accumulation as well as increasing leaf photosynthesis and antioxidant ability. Pearson correlation analysis illustrated that the variability of Cd uptake and accumulation between Pb and Cd stress was related to plant biomass and antioxidant enzyme activities. This research will offer a new perspective on alleviating Cd phytotoxicity in plants.

Lead Responses and Tolerance Mechanisms of Koelreuteria paniculata: A Newly Potential Plant for Sustainable Phytoremediation of Pb-Contaminated Soil

Phytoremediation could be an alternative strategy for lead (Pb) contamination. K. paniculata has been reported as a newly potential plant for sustainable phytoremediation of Pb-contaminated soil. Physiological indexes, enrichment accumulation characteristics, Pb subcellular distribution and microstructure of K. paniculata were carefully studied at different levels of Pb stress (0-1200 mg/L). The results showed that plant growth increased up to 123.8% and 112.7%, relative to the control group when Pb stress was 200 mg/L and 400 mg/L, respectively. However, the average height and biomass of K. paniculata decrease when the Pb stress continues to increase. In all treatment groups, the accumulation of Pb in plant organs showed a trend of root > stem > leaf, and Pb accumulation reached 81.31%~86.69% in the root. Chlorophyll content and chlorophyll a/b showed a rising trend and then fell with increasing Pb stress. Catalase (CAT) and peroxidase (POD) activity showed a positive trend followed by a negative decline, while superoxide dismutase (SOD) activity significantly increased with increasing levels of Pb exposure stress. Transmission electron microscopy (TEM) showed that Pb accumulates in the inactive metabolic regions (cell walls and vesicles) in roots and stems, which may be the main mechanism for plants to reduce Pb biotoxicity. Fourier transform infrared spectroscopy (FTIR) showed that Pb stress increased the content of intracellular -OH and -COOH functional groups. Through organic acids, polysaccharides, proteins and other compounds bound to Pb, the adaptation and tolerance of K. paniculata to Pb were enhanced. K. paniculata showed good phytoremediation potential and has broad application prospects for heavy metal-contaminated soil.

Lead, zinc tolerance mechanism and phytoremediation potential of Alcea rosea (Linn.) Cavan. and Hydrangea macrophylla (Thunb.) Ser. and ethylenediaminetetraacetic acid effect

In this study, we aimed to elucidate the defense mechanism of Alcea rosea (Linn.) Cavan. and Hydrangea macrophylla (Thunb.) Ser. against the single and compound toxicity of lead (Pb) and zinc (Zn) along with the synergistic effect of ethylenediaminetetraacetic acid (EDTA) in accumulation of metals in these two species. The two plant species were subjected to single metal treatment (Pb 1000 mg kg^-1, Zn 600 mg kg^-1) and compound metal treatment (Pb 1000 mg kg^-1 + Zn 600 mg kg^-1) in a greenhouse. Besides, different levels of EDTA were applied (2.5, 5.0, and 10.0 mmol kg^-1) with compound metal treatment. Several physiological and biochemical parameters, including plant photosynthetic parameters, enzymatic antioxidant system, accumulation concentration of metals, and subcellular distribution were estimated. The results showed that the antioxidative enzymes, proline, root morphological changes, and metal localization all played important roles in resisting Pb and Zn toxicity. A notable difference was that Zn was concentrated in the roots (58.5%) of H. macrophylla to reduce the damage but in the leaves (38.5%) of A. rosea to promote photosynthesis and resist the toxicity of metals. In addition, Zn reduced the toxicity of Pb to plants by regulating photosynthesis, Pb absorption and Pb distribution in subcells. The biological concentration factors (BCF) and translocation factors (TF) for Pb in two plants were less than 1, indicating that they could be considered as phytostabilizators in Pb-contaminated soils. Moreover, EDTA could enhance the enrichment and transport capacity of Pb and Zn to promote the phytoremediation effect. In summary, both plants have a certain application potential for repairing Pb-Zn-contaminated soil.

Application of multivariate analysis to assess stress by Cd, Pb and Al in basil (Ocimum basilicum L.) using caffeic acid, rosmarinic acid, total phenolics, total flavonoids and total dry mass in response

Basil is an edible, aromatic plant, which makes the study of the ecotoxicity of metals in plant metabolism relevant. Given the above, the objective of this study was to evaluate the effects of metals, aluminum, lead, and cadmium, in the synthesis of phenolic compounds and in the dry mass of basil plants (O. basilicum L.) grown in a hydroponic system. The plants were subjected to four different concentrations of cadmium (0.2, 0.6, 1.2, and 1.8 mmol L-1), lead and aluminum (0.04, 0.08, 0.12, and 0.16 mmol L-1), and compared with the control. After desiccation of the plant material, the total dry mass was obtained and then, hydroethanolic extracts (43% distilled water and 57% ethanol) were made for biochemical analyzes, which consisted of the determination of caffeic acid (CA) and rosmarinic acid (RA) by high performance liquid chromatography analysis with a diode detector (HPLC-DAD); total phenolics (TP) and total flavonoids (TF) by spectrophotometry. The data were submitted to analysis of variance and multivariate analysis (principal component analysis-PCA and hierarchical cluster analysis-HCA) was applied for data association. The phenolic compounds showed a high positive correlation with each other, and the total dry mass showed low and negative correlations with the analyzed variables. The results showed that the metals aluminum, lead, and cadmium promoted a stress condition in basil plants, which resulted in the reduction of the dry matter mass and an increase in the synthesis of phenolic compounds, according to the type and concentration of the metal.

Metal tolerance in plants: Molecular and physicochemical interface determines the "not so heavy effect" of heavy metals

An increase in technological interventions and ruthless urbanization in the name of development has deteriorated our environment over time and caused the buildup of heavy metals (HMs) in the soil and water resources. These heavy metals are gaining increased access into our food chain through the plant and/or animal-based products, to adversely impact human health. The issue of how to restrict the entry of HMs or modulate their response in event of their ingress into the plant system is worrisome. The current knowledge on the interactive-regulatory role and contribution of different physical, biophysical, biochemical, physiological, and molecular factors that determine the heavy metal availability-uptake-partitioning dynamics in the soil-plant-environment needs to be updated. The present review critically analyses the interactive overlaps between different adaptation and tolerance strategies that may be causally related to their cellular localization, conjugation and homeostasis, a relative affinity for the transporters, rhizosphere modifications, activation of efflux pumps and vacuolar sequestration that singly or collectively determine a plant's response to HM stress. Recently postulated role of gaseous pollutants such as SO₂ and other secondary metabolites in heavy metal tolerance, which may be regulated at the whole plant and/or tissue/cell is discussed to delineate and work towards a "not so heavy" response of plants to heavy metals present in the contaminated soils.

Inga uruguensis response to lead: effects on growth and nitrogenous compounds

Abstract Lead (Pb) is a heavy metal considered one of the major soil pollutants. Phytoremediation is a sustainable and economically viable biological method for reducing Pb content in the environment. Inga uruguensis is a tree legume species that has characteristics favorable to phytoremediation, such as rapid growth and high biomass production. The objective of this work was an initial evaluation of tolerance and phytoremediation potential of I. uruguensis to Pb. The experiment was carried out in a greenhouse. In addition to the control, soil contamination was carried out with the following Pb doses: 100, 200, 300, 400, and 500 mg.dm³, with 5 repetitions in each treatment, totaling 30 vases. We assessed growth, number and mass of nodules, chlorophyll content, ureids, amino acid, protein and soluble carbohydrates in leaves, roots and nodules, tolerance index, dry matter, and tissues Pb content of I. uruguensis. The data were analyzed by the Tukey test using R and SISVAR software. There was no negative effect of Pb in soil on I. uruguensis growth, the symbiotic relationship with rhizobia was kept, even at high Pb content and the tolerance index was not lower than 0.69. Inga uruguensis has initial tolerance and potential to be used as phytoremediation in soils contaminated by Pb.

Heavy metal phytoremediation potential of the roadside forage Chloris barbata Sw. (swollen windmill grass) and the risk assessment of the forage-cattle-human food system

This study presents the assessment of the risks incidental to the growth of the common tropical grass species Chloris barbata Sw. (swollen windmill grass) on road margins contaminated with Pb and Cd. Pot experiments were first carried out to quantify the Pb and Cd accumulation potential of the plant species in various plant parts as a function of the metal concentration in soil. C. barbata was found to be a hyperaccumulator for Cd (BCF>1, for aerial parts) and an excluder of Pb (BCF<1, for aerial parts). As the plant was found to accumulate Pb in its roots with TF<1, it can be considered a phytostabilizer of Pb. The mathematical relationship developed between soil concentrations of Pb and Cd and their corresponding concentrations in aerial parts were used in combination with the concentrations of these heavy metals reported in roadside soils to obtain estimates of their accumulation in the forage and consequently in the animal organs. Risk to the consumers of offal was estimated. It was found that the consumption of kidney meat was riskier than the consumption of liver meat. Furthermore, it was seen that despite the nearly two order less concentrations of Cd in roadside soils compared to Pb, it was posing a higher risk. For the median concentrations of Pb reported in roadside soils and cattle feeding exclusively on C. barbata growing on roadside soils, the HQ exceeded 1 for weekly consumption of kidney meat above 650 g. For median Cd concentrations, consumption of kidney meat above 230 g/week resulted in HQ>1. The scenario considered for risk assessment is significant for India, where stray grazing of cattle on road margins is common and offal offers a cheap source of animal protein for the economically poor.

Impacts of heavy metals and medicinal crops on ecological systems, environmental pollution, cultivation, and production processes in China

Heavy metals are widely distributed in the environment due to the natural processes and anthropogenic human activities. Their migration into no contaminated areas contributing towards pollution of the ecosystems e.g. soils, plants, water and air. It is recognized that heavy metals due to their toxicity, long persistence in nature can accumulate in the trophic chain and cause organism dysfunction. Although the popularity of herbal medicine is rapidly increasing all over the world heavy metal toxicity has a great impact and importance on herbal plants and consequently affects the quality of herbal raw materials, herbal extracts, the safety and marketability of drugs. Effective control of heavy metal content in herbal plants using in pharmaceutical and food industries has become indispensable. Therefore, this review describes various important factors such as ecological and environmental pollution, cultivation and harvest of herbal plants and manufacturing processes which effects on the quality of herbal plants and then on Chinese herbal medicines which influence human health. This review also proposes possible management strategies to recover environmental sustainability and medication safety. About 276 published studies (1988-2021) are reviewed in this paper.

Lead acetate ecotoxicity in tropical soils

Lead acetate (AcPb) is an important raw material used in chemical industries worldwide. The potential toxicity of AcPb is generally attributed to the presence of Pb. However, the effect of AcPb on the environment as a whole is still poorly known. This study aimed to evaluate AcPb toxicity on three standard species of soil invertebrates and two plant species using ecotoxicology tests. Three tropical soils (Oxisol, Inceptisol, and Tropical Artificial Soil (TAS)) were contaminated with different concentrations of AcPb and one dose of K-acetate (positive control). These soils were used in tests with Eisenia andrei (earthworm), Folsomia candida (springtail), Enchytraeus crypticus (enchytraeid), Zea mays (maize), and Phaseolus vulgaris (common bean). Dose-response curves obtained in the laboratory tests were used to estimate the EC₅₀ values for each species. Among invertebrates, the highest sensitivity to AcPb was observed for E. crypticus in the TAS (EC₅₀ = 29.8 mg AcPb kg^-1), whereas for E. andrei and F. candida the highest sensitivity was observed in the Oxisol (EC₅₀ = 141.9 and 1835 mg AcPb kg^-1, respectively). Folsomia candida was the least sensitive invertebrate species to AcPb in all soils. Among plant species, Z. mays was less sensitive (EC₅₀ = 1527.5 mg AcPb kg^-1) than P. vulgaris (EC₅₀ = 560.5 mg AcPb kg^-1) in the Oxisol. The present study evidenced that the toxicity of AcPb should not be attributed uniquely to the presence of Pb, as the treatment containing uniquely Ac provoked the same toxicity as the highest dose of AcPb.

Histological and proteome analyses of Microbacterium foliorum-mediated decrease in arsenic toxicity in Melastoma malabathricum

Arsenic (As) is an increasing threat across the globe, widely known as a non-threshold carcinogen, and it is reaching harmful values in several areas of the world. In this study, the effect of plant growth promoting bacteria (Microbacterium foliorum) on inorganic arsenic (Arsenate) phytoremediation by Melastoma malabathricum plants was investigated through histological analysis and proteome profiling of the M. malabathricum plants. Two-dimensional gel electrophoresis and transmission electron microscopy were used to conduct the proteome and histological analysis. When arsenic-treated cells were compared to untreated cells, substantial changes were found (1) severely altered the morphology of the cells, intensely disturbed; (2) the cell wall was thicker; (3) drastically changed the cytoplasm, the cells were polygonal in shape, different in size (scattered), and relatively dense. Compared to the control group, the ultra-structure of the root cells of the control group revealed intact cytoplasm, vacuole, and cell wall under exposure to As + bacteria that had a minor effect on the cell form. To further understand As + bacteria interaction, proteome profiling of the root cell was analyzed. The As-induced oxidative stress enrichment was confirmed by the up-regulation of tubulin, nucleoside diphosphate kinase, and major allergen during As + bacteria exposure It was observed that the profusion of proteins involved in defence, protein biogenesis, signaling, photosynthesis, nucleoside and energy metabolism was greater in As + bacteria as compared to the rooting out of As only. Overall, it can be obviously seen that the current study demonstrates the effectiveness of phytoremediation by M. foliorum on proteins involved and responsive pathways in dealing with As toxicity in M. malabathricum plant.

Understanding Potential Heavy Metal Contamination, Absorption, Translocation and Accumulation in Rice and Human Health Risks

Rice is a worldwide staple food and heavy metal contamination is often reported in rice production. Heavy metal can originate from natural sources or be present through anthropogenic contamination. Therefore, this review summarizes the current status of heavy metal contamination in paddy soil and plants, highlighting the mechanism of uptake, bioaccumulation, and health risk assessment. A scoping search employing Google Scholar, Science Direct, Research Gate, Scopus, and Wiley Online was carried out to build up the review using the following keywords: heavy metals, absorption, translocation, accumulation, uptake, biotransformation, rice, and human risk with no restrictions being placed on the year of study. Cadmium (Cd), arsenic (As), and lead (Pb) have been identified as the most prevalent metals in rice cultivation. Mining and irrigation activities are primary sources, but chemical fertilizer and pesticide usage also contribute to heavy metal contamination of paddy soil worldwide. Further to their adverse effect on the paddy ecosystem by reducing the soil fertility and grain yield, heavy metal contamination represents a risk to human health. An in-depth discussion is further offered on health risk assessments by quantitative measurement to identify potential risk towards heavy metal exposure via rice consumption, which consisted of in vitro digestion models through a vital ingestion portion of rice.

Anatomical and ultrastructural alterations in Ceratopteris pteridoides under cadmium stress: A mechanism of cadmium tolerance

The present research is an appraisal of anatomical and ultrastructural alterations in aquatic fern, Ceratopteris pteridoides under cadmium (Cd) exposure. Plants were cultured hydroponically for 12 consecutive days in different Cd treatments: 10 µM L-1 (CDT1), 20 µM L-1 (CDT2), 40 µM L-1 (CDT3) and 60 µM L-1 (CDT4). Anatomical and ultrastructural changes of different vegetative tissues of C. pteridoides were investigated using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Cd stress significantly (P < 0.05) decreased water content percentage (WC%), relative growth rate (RGR) and root activity in C. pteridoides, especially at highest Cd concentration (treatment CDT4). Significant (P < 0.05) drop of stress tolerance indices (STI) was noticed in C. pteridoides under treatment CDT4. Anatomical study of the Cd-treated C. pteridoides showed stomatal closure of leaves, reduction of diameter in xylem tracheids of stem and root, and decrease of intercellular spaces. Furthermore, ultrastructural alterations of leaf, stem, and root cells were evident with a damaged membrane system of chloroplast and mitochondria, disorganization of chloroplastic components, accumulation of large starch grains and plastoglobules, and formation of multivesicular bodies. The deposition of electron-dense material in the cell wall of root cells can be regarded as an important tolerance mechanism of C. pteridoides under Cd stress. Fourier transform infrared (FTIR) spectroscopy analysis of Cd-treated C. pteridoides biomass illustrated Cd-binding interaction with O-H, N-H, C-H, C≡C, C˭O, P˭O, -C-OH and CS functional groups of different metabolites.

Assisted phytostabilization of Pb-spiked soils amended with charcoal and banana compost and vegetated with Ricinus communis L. (Castor bean)

A greenhouse experiment was performed to elucidate the potency of Prosopis juliflora charcoal (PJC) and banana waste compost (BWC) to improve soil fertility and enhance plant growth rate. Plantlets of Ricinus communis were grown in 0, 400, and 800 mg kg^-1 Pb-spiked soil ameliorated with P. juliflora charcoal and banana waste compost at 0, 5%, and 10% (w/w) for 60 days. PJC and BWC significantly (p < 0.05) increased plant growth parameters, that is, number of leaves, node number, plant height, and leaf diameter and reduced oxidative stress manifested by the lesser production of proline, hydrogen peroxide (H₂O₂), and malondialdehyde (MDA) with respect to control plants. Soil usage of PJC at 10% decreased the Pb accumulation by 61%, whereas BWC decreased Pb concentration in roots by 56% concerning control. Field emission scanning electron microscope (FE-SEM) coupled with energy-dispersive X-ray spectroscopy (EDS) showed high macro and microspores on the surface of charcoal while banana compost showed significant raise in the nutrient content (N, P, K, Zn, Ca, Fe, and Mg). Thermogravimetric (TG) and Fourier-transform infrared spectroscopy (FTIR) analysis of banana compost showed enhanced molar convolution of carbohydrate composites and nitrogen content. These findings pave a clear understanding that PJC and BWC are recalcitrant for Pb phytotoxicity and can also be used as nutrient-rich composites for increased crop production.

Biomass allocation strategies and Pb-enrichment characteristics of six dwarf bamboos under soil Pb stress

Dwarf bamboos are clonal plants with potential applications in the remediation of heavy metal-polluted soils, although their pollution adaptation strategies are unknown. This study examined the biomass allocation strategies and lead (Pb) enrichment characteristics of various dwarf bamboo tissues by the end of the growing season and explored their potential for phytoremediation of Pb stress in the soils. Six dwarf bamboo genotypes were treated with three levels (0, 300, and 1500 mg kg^-1) of soil Pb stress. The majority of the bamboos adopted two biomass allocation strategies to adapt to Pb stress, namely, "reducing biomass allocation into new bamboo growth" and "increasing/stabilizing biomass allocation into rhizomes". Pb accumulation was highest in the roots, rhizomes, and old stems and showed the following trend: rhizomes/old stems> new roots/old roots> old leaves> new leaves> new stems among various tissues. Moreover, the six bamboos used three different Pb-enrichment strategies, as follows: (i) "rhizome domination and old stem synergy" (Sasaella glabra (Nakai) f. albo-striata Muroi, Sasa auricoma (Mitford) E.G. Camus, Sasa fortunei (Van Houtte) Fiori, and Shibataea lanceifolia C.H. Hu); (ii) "old stem domination and rhizome synergy" (Indocalamus decorus Q.H. Dai); and (iii) "old stem domination and new root synergy" (Sasa argenteostriata (Regel) E.G. Camus). In Pb-contaminated soils, genotypes with TFs greater than 1 were Sasa fortunei (Van Houtte) Fiori, Sasa argenteostriata (Regel) E.G. Camus, and Indocalamus decorus Q.H. Dai; in addition, only S. argenteostriata had BCF values greater than 1. Furthermore, this study provides the first evidence that S. argenteostriata can extract 0.22 and 0.58 mgplant^-1 of Pb ions in soil polluted with 300 and 1500 mg kg^-1 Pb, respectively. S. argenteostriata showed the greatest potential for phytoremediation among the bamboo genotypes in both Pb-contaminated urban and mining sites.

Deciphering lead tolerance mechanisms in a population of the plant species Biscutella auriculata L. from a mining area: Accumulation strategies and antioxidant defenses

The uptake and distribution of Pb and the mechanisms involved in the metal tolerance have been investigated in a mine population of Biscutella auriculata. Seedlings were exposed to 125 μM Pb(NO₃)₂ for 15 days under semihydroponic conditions. The results showed an increase in the size of Pb-treated seedlings and symptoms of toxicity were not observed. ICP-OES analyses showed that Pb accumulation was restricted to root tissue. Imaging of Pb accumulation by dithizone histochemistry revealed the presence of the metal in vacuoles and cell wall in root cells. The accumulation of Pb in vacuoles could be stimulated by an increase in phytochelatin PC2 content. Pb did not promote oxidative damage and this is probably due the increase of antioxidative defenses. In the leaves, Pb produced a significant increase in superoxide dismutase activity, while in roots an increase in catalase and components of the Foyer- Halliwell-Asada cycle were observed. The results indicated that Biscutella auriculata has a high capacity to tolerate Pb and this is mainly due to a very efficient mechanism to sequester the metal in roots and a capacity to avoid oxidative stress. This species could therefore be very useful for phytostabilization and repopulation of areas contaminated with Pb.

Characterisation of early responses in lead accumulation and localization of Salix babylonica L. roots

BACKGROUND

Lead (Pb) is a harmful pollutant that disrupts normal functions from the cell to organ levels. Salix babylonica is characterized by high biomass productivity, high transpiration rates, and species specific Pb. Better understanding the accumulating and transporting Pb capability in shoots and roots of S. babylonica, the toxic effects of Pb and the subcellular distribution of Pb is very important.

RESULTS

Pb exerted inhibitory effects on the roots and shoots growth at all Pb concentrations. According to the results utilizing inductively coupled plasma atomic emission spectrometry (ICP-AES), S. babylonica can be considered as a plant with great phytoextraction potentials as translocation factor (TF) value > 1 is observed in all treatment groups throughout the experiment. The Leadmium™ Green AM dye test results indicated that Pb ions initially entered elongation zone cells and accumulated in this area. Then, ions were gradually accumulated in the meristem zone. After 24 h of Pb exposure, Pb accumulated in the meristem zone. The scanning electron microscopy (SEM) and energy-dispersive X-ray analyses (EDXA) results confirmed the fluorescent probe observations and indicated that Pb was localized to the cell wall and cytoplasm. In transverse sections of the mature zone, Pb levels in the cell wall and cytoplasm of epidermal cells was the lowest compared to cortical and vessel cells, and an increasing trend in Pb content was detected in cortical cells from the epidermis to vascular cylinder. Similar results were shown in the Pb content in the cell wall and cytoplasm of the transverse sections of the meristem. Cell damage in the roots exposed to Pb was detected by propidium iodide (PI) staining, which was in agreement with the findings of Pb absorption in different zones of S. babylonica roots under Pb stress.

CONCLUSION

S. babylonica L. is observed as a plant with great potential of Pb-accumulation and Pb-tolerance. The information obtained here of Pb accumulation and localization in S. babylonica roots can furthers our understanding of Pb-induced toxicity and its tolerance mechanisms, which will provide valuable and scientific information to phytoremediation investigations of other woody plants under Pb stress.

Growth responses and physiological and biochemical changes in five ornamental plants grown in urban lead-contaminated soils

An increasing concentration of lead (Pb) in urban contaminated soil due to anthropogenic activities has been a global issue threatening human health. The use of urban ornamental plants as phytoremediation of Pb-contaminated soil is a new choice. In the present experiment, the physiological and biochemical response of five ornamental plants to increase in concentrations of C₄H₆O₄Pb·H₂O in the soil were measured to investigate these plans' Pb tolerance strategies and abilities. Our results showed that Pb stress significantly inhibited the growth and the biomass of all the plants. The root activity (RA), net photosynthetic rate (P _n), and chlorophyll (Chl) content in Pb-stressed leaves were significantly decreased, whereas the leaf proline (Pro), soluble sugar (SS), and membrane stability index (MSI) were remarkable increased compared with those in the control group. By application of all-subsets regression and linear regression, the reduction in photosynthetic capacity in the five plants is mainly due to the decrease in the leaf Chl content caused by Pb stress. The bioconcentration factor (BCF) in Canna generalis was greater than 1, while in the other plants were lower than 1, suggesting that Canna generalis had the highest Pb accumulation ability. The translocation factor (TF) in all the plants were lower than 1, suggesting that Pb preferentially accumulated in the external part of roots. By calculating the comprehensive evaluation value (CEV), Iris germanica L. was found to be the most sensitive species, and Canna generalis was the most tolerant species, to Pb stress among the five ornamental plants.

Different strategies for lead detoxification in dwarf bamboo tissues

Dwarf bamboo Sasa argenteostriata (Regel) E.G. Camus is considered as potential plants for metal phytoremediation in previous filed observations. However, the mechanisms of lead (Pb) detoxification has not been described. The objective of this study was to explore the difference strategies or mechanisms of Pb detoxification in plant tissues. In this regard, four Pb treatments with hydroponics including 0 (control), 300, 600, and 900 mg L^-1 were conducted to examine subcellular compartmentalization, Pb accumulation/species and antioxidant-assisted chelation. Our findings showed the retention of Pb by the whip-root system is one of its detoxification mechanisms to avoid damage the shoots. In addition, the cell wall retention is the dominant detoxification strategy of whips, new roots, old roots and new/old stems, while vacuolar compartmentalization is for new/old leaves. Interestingly, four low-mobility/-toxicity Pb species (i.e., FNaCl, FHAc, FHCl and FR) are distributed in roots, whips and stems, while two high-mobility/-toxicity Pb species (FE and FW) in leaves. The conversion of Pb to low-toxicity/-migration is a Pb-detoxification strategy in roots, whips and stems but not in leaves. Besides, the new/old roots and leaves can alleviate Pb damage through the synthesis of non-protein thiol, glutathione and phytochelatins. Among these, phytochelatins play a leading role in the detoxification in new/old roots, while glutathione is in new/old leaves. This study provides the first comprehensive evidence regarding the different strategies for Pb detoxification in dwarf bamboo tissues from physiological to cellular level, supporting that this plant could be rehabilitated for phytoremediation in Pb-contaminated media.

Comparative efficacy of organic and inorganic silicon fertilizers on antioxidant response, Cd/Pb accumulation and health risk assessment in wheat (Triticum aestivum L.)

In wheat production areas of China, soil lead (Pb) pollution is generally accompanied by cadmium (Cd) pollution and it is of considerable significance in repairing the Cd and Pb co-contaminated soils for safe agronomic production. Organosilicon fertilizer (OSiF) is a new type of silicon (Si) fertilizer that can effectively alleviate heavy metal toxicity in plants, but the mechanisms on its heavy metal detoxification are poorly understood. A soil pot experiment was conducted to evaluate and compare the effects of two OSiFs (OSiFA and OSiFB) and an inorganic silicon fertilizer (InOSiF) on wheat heavy metal uptake and biochemical parameters in a Cd and Pb co-contaminated soil. The results demonstrated that OSiFA, OSiFB and InOSiF could alleviate the Cd and Pb toxicity of wheat, as indicated by increasing wheat grain yield by 65%, 45% and 22%, respectively. The Si fertilizers enhanced leaf gas exchange attributes and chlorophyll content, whereas diminished the oxidative damage, as indicated by a lower level of hydrogen peroxide (H₂O₂) and malondialdehyde (MDA) content, and lower activity of superoxide dismutase (SOD) and catalase (CAT) activity, as compared with control. Adding OSiFA, OSiFB and InOSiF increased Si uptake in roots and shoots, thus reducing Cd and Pb accumulation in the wheat shoot, bran and flour, especially, flour Cd contents by 17%, 10% and 31% respectively, flour Pb contents by 74%, 53% and 48% respectively. Also, Si fertilizers application decreased the health risk index (HRI) of both Cd and Pb. The grey correlation degrees of OSiFA, OSiFB and InOSiF are 0.72, 0.77 and 0.61, respectively, indicating that the effects of OSiFs on detoxifying Cd and Pb could be better than that of InOSiF in wheat. Thus, the use of OSiFs might be a feasible approach to reduce Cd and Pb entry into the human body through crops.

Biochar and rice husk ash assisted phytoremediation potentials of Ricinus communis L. for lead-spiked soils

Soil contamination with lead (Pb) is a serious global concern, adversely affecting crop production. Pot experiments were conducted to assess the efficacy of Prosopis biochar and rice husk ash for plant growth and mitigating Pb translocation in Ricinus communis. Physico-chemical characterization of both the amendments was carried out on a dry weight basis. Seedlings of R.communis were grown in 0, 400 and 800 mg kg^-1 Pb spiked soil amended with Prosopis juliflora biochar (PJB) and rice husk ash (RHA) at 0, 2.5% and 5% (w/w) of soil for 60 days. Addition of biochar and rice husk ash to soils increased the Pb tolerance in R.communis, improved soil pH, nutrient intake, and antioxidant enzymatic activities. The biochar amendment significantly (p < 0.05) increased plant growth parameters (height, leaf diameter, nodes, and leaf number), protein (72%) and chlorophyll contents (38-52%), as did RHA to a lesser extent (increase of 10-31% in chlorophyll and 77% protein content) compared to unamended plants. Soil usage of RHA resulted in a more consistent decrease in Pb accumulation in the root, shoot, and leaf relative to PJB. Treatment with PJB at 5% decreased the accumulation of Pb in roots by 59% whereas RHA decreased Pb concentration in roots by 87%. The two distinct amendments significantly reduced the availability of soil Pb and decreased oxidative damage, as evidenced by the lower production of proline, malondialdehyde (MDA), and hydrogen peroxide (H₂O₂) in plants. Changes in infrared spectra confirmed that oxygenated phosphate, amide, ester and ether functional groups played a key role in binding accumulated Pb in roots as well as alleviation of Pb-induced phytotoxicity. Our findings conclude the amendments can be used as a stress regulator in mitigating Pb toxicity, which is important for all economic crop plants, including R.communis.

Comparison of heavy metal accumulation ability in rainwater by 10 sponge city plant species

Rainwater heavy metal contamination is a growing problem worldwide, which damages the environment and human health. A primary challenge of sponge city designers is selecting suitable plants capable of surviving the toxic metals present in city rainwater. The concept of a sponge city to tackle urban surface-rainwater flooding and related urban rainwater management issues was established by People's Republic of China in 2014. Therefore, we studied the ability of sponge city plants to accumulate heavy metals from rainwater. Ophiopogon japonicus (Linn. f.) Ker-Gawl., Carex heterostachya Bge., Cornus officinalis Sieb. et Zucc., Sedum spectabile Boreau., Typha orientalis Presl., Lythrum salicaria L., Fatsia japonica (Thunb.) Decne. et Planch., Ilex chinensis Sims., Rosa chinensis Jacq., and Buxus bodinieri Levl. were selected as test plants, and their ability to accumulate four heavy metals (lead [Pb], cadmium [Cd], copper [Cu], and zinc [Zn]) was compared. Growth response and heavy metal accumulation across different species were compared over a 28-day enrichment cycle. The results showed that (1) Plant growth responses to heavy metals were significantly different. The most tolerant to heavy metals was Lythrum salicaria and the least tolerant was Rosa chinensis. (2) Concentrations of the heavy metals differed among sponge city plant species. In general, the concentration of Zn was highest, followed by Cu, Cd, and Pb. (3) The accumulation content of the same metal in different test species was related to the bioconcentration factor of the metal and the plant biomass. At the end of the enrichment cycle, Ophiopogon japonicus had the largest accumulation content for Pb, Cu, and Zn, and Lythrum salicaria had the highest accumulation content for Cd. (4) Considering the growth responses of plants and their final accumulation of heavy metals after the enrichment cycle, we concluded that Lythrum salicaria, Typha orientalis, and Ophiopogon japonicus are suitable for use in sponge cities to restore heavy metal-contaminated rainwater.

Milli-channel array for direct and quick reading of root elongation bioassays

A novel platform to perform systematic analysis and direct reading of root elongation bioassays is presented. The device was designed to include multiplexed microenvironments for the germination and growth of individual seeds, which allows observation by the naked eye or by optical systems, notably cellphone cameras. Prototypes were fabricated by laser micromachining on a highly transparent material that is fully compatible with biological systems. The effectiveness of the milli-channel array was verified against the conventional system (Petri dish). Lactuca sativa was chosen as a model species and glyphosate as a typical toxic agent. All tests were run according to standardized procedures and data analysis was carried out through different statistical indicators such as the root elongation and germination indexes. Results attained in the milli-channel array were identical to those in Petri dish, with the remarkable benefit that several steps required in the conventional system were avoided, which enormously decreases the operation time and the possibility of experimental errors. Further advantages of the milli-channel array are also reported, such as the capability to achieve live imaging of plant organs growth through a simple experiment. The developed device has been proven to be effective, versatile, easy-to-use, and integrable to cellphones, which naturally provide facilities for data recording, analysis, and networking. These improvements open the route to novel applications of bioassays in the wide field of ecotoxicology and environmental studies.

Phytoremediation: Environmentally sustainable way for reclamation of heavy metal polluted soils

Soil contamination with toxic metals is a widespread environmental issue resulting from global industrialization within the past few years. Therefore, decontamination of heavy metal contaminated soils is very important to reduce the associated risks and for maintenance of environmental health and ecological restoration. Conventional techniques for reclamation of such soils are expensive and environmental non-friendly. Phytoremediation is an emerging technology implementing green plants to clean up the environment from contaminants and has been considered as a cost-effective and non-invasive alternative to the conventional remediation approaches. There are different types of phytoremediation including, phytostabilization, phytostimulation, phytotransformation, phytofiltration and phytoextraction, the latter being most extensively acknowledged for remediation of soils contaminated with toxic heavy metals. Recent literature is gathered to critically review the sources, hazardous effects of toxic heavy metals and environmentally sustainable phytoremediation technique for heavy metal polluted soils to offer widespread applicability of this green technology. Different strategies to enhance the bioavailability of heavy metals in the soil are also discussed shortly. It can be concluded that phytoremediation of heavy metal contaminated soils is a reliable tool and necessary for making the land resource accessible for crop production.