Pb uptake and toxicity to Iris halophila tested on Pb mine tailing materials

Mechanistic insight into lead immobilization on bone-derived carbon/hydroxyapatite composite at low and high initial lead concentration

The contamination of heavy metal lead has a serious impact on the natural environment and organisms. Among various materials for lead removal, animal bone derived hydroxyapatite has received extensive attention. However, there are different opinions among researchers regarding the mechanism of lead removal by hydroxyapatite, possibly due to varying initial lead concentrations used in different studies and lack of accuracy in the study of lead removal mechanisms. In present work, we synthesized a carbon-containing hydroxyapatite (CHAP) through pyrolysis of bovine bone with excellent lead removal efficiency, and further investigated the lead removal mechanism of CHAP under high and low initial lead concentrations by combining XRD Rietveld refinement, FTIR, XPS, HRTEM etc. methods. The results showed that under low initial Pb2+ concentration condition, the main mechanism of lead removal by CHAP was chemical precipitation (94.1 %), with small contributions of lead complexation with carbon functional groups and cation-π interactions on the amorphous carbon in CHAP, and surface adsorption on the precipitates. Under high initial Pb2+ concentration condition, chemical precipitation remained the main mechanism (74.68 %), but the contributions of the other three mechanisms increased, and ion exchange appeared in the later stage of the removal process. This study provides new insights on the lead immobilization mechanism by CHAP at different initial Pb2+ concentrations in water.

Removal of heavy metals using Iris species: A potential approach for reclamation of heavy metal-polluted sites and environmental beautification

Globally, the number of heavy metal (HM)-polluted sites has increased rapidly in recent years, posing a serious threat to agricultural productivity, human health, and environmental safety. Hence, it is necessary to remediate HM-polluted sites to increase cultivatable lands for agricultural productivity, prevent hazardous effects to human health, and promote environmental safety. Removal of HMs using plants (phytoremediation) is a promising method as it is eco-friendly. Recently, ornamental plants have been widely used in phytoremediation programs as they can simultaneously eliminate HMs and are aesthetically pleasing. Among the ornamental plants, Iris species are frequently used; however, their role in HM remediation has not been reviewed yet. Here, the importance of Iris species in the ornamental industry and their different commercial aspects are briefly described. Additionally, the mechanisms of how the plant species absorb and transport the HMs to the above-ground tissues and tolerate HM stress are highlighted. The variation in HM remediation efficiency depending on the plant species, HM type and concentration, use of certain supplements, and experimental conditions are also discussed. Iris species are able to remove other hazards as well, such as pesticides, pharmaceutical compounds, and industrial wastes, from polluted soils or waste-water. Owing to the valuable information presented in this review, we expect more applications of the species in reclaiming polluted sites and beautifying the environment.

Experimental Research on the Remediation Ability of Four Wetland Plants on Acid Mine Drainage

In order to study the economical, efficient, and environmentally friendly techniques for the treatment of acid mine drainage (AMD), this paper investigated the effects of watering with AMD on the growth condition, the resilience of four wetland plants, as well as the uptake and transport of pollutants by plants. The results showed that Typha orientalis was more resistant to AMD (irrigation with AMD increased its catalase activity and glutathione content and promoted its growth), so it was suitable for treating high concentrations of AMD (SO42− ≈ 9400 mg/L); Cyperus glomeratus was suitable for treating medium concentrations of AMD (SO42− ≈ 4600 mg/L); and Scirpus validus and Phragmites australis could be used to treat low concentrations of AMD (SO42− ≈ 2300 mg/L). All four plants could be used for phytoextraction for Mn-contaminated water (TF > 1). Phragmites australis could be used for phytoextraction for Zn-contaminated water, and the other three plants could be used for phytostabilisation for Zn-contaminated water (TF < 1); the microbial biomass in the soil was affected not only by the concentration of AMD but also by plant species. This study provides a scientific basis for the phytoremediation technology of AMD.

Fluorescence "off-on" probe for lead (II) detection based on Atractylodes III CQDs and bioimaging

In this work, a type of carbon quantum dots (CQDs) with bright blue emission were readily fabricated through one-step hydrothermal treatment from Atractylodes III. We explored the surface morphology and optical properties of CQDs by Transmission electron microscope (TEM), X-ray diffraction patterns (XRD), X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR) and UV-vis spectrophotometer. The obtained CQDs possessed good photoluminescence properties, water solubility and biocompatibility. The fluorescence quantum yield of them was 3.72%. It was found that the fluorescence intensity of CQDs will be quenched by picric acid (PA). After adding lead (II), the fluorescence can be effectively recovered. Hence, an "off-on" fluorescence probe was designed to detect lead (II) in the range of 0-580 μM and the limit of detection (LOD) was 0.068 μM. In the meanwhile, the experiments showed that the CQDs can be successfully used in bioimaging and as a hidden fluorescent ink.

Experimental Study on the Hydroponics of Wetland Plants for the Treatment of Acid Mine Drainage

Acid Mine Drainage (AMD) has become an important issue due to its significant ecological pollution. In this paper, phytoremediation technology and mechanism for AMD were investigated by hydroponic experiments, using six wetland plants (Phragmites australis, Typha orientalis, Cyperus glomeratus, Scirpus validus, Iris wilsonii, Juncus effusus) as research objects. The results showed that (1) the removal of sulfate from AMD was highest for Juncus effusus (66.78%) and Iris wilsonii (40.74%) and the removal of Mn from AMD was highest for Typha orientalis (>99%) and Phragmites australis (>99%). In addition, considering the growth condition of the plants, Juncus effusus, Iris wilsonii, and Phragmites australis were finally selected as the dominant plants for the treatment of AMD. (2) The removal pathway of pollutants in AMD included two aspects: one part was absorbed by plants, and the other part was removed through hydrolysis and precipitation processes. Our findings provide a theoretical reference for phytoremediation technology for AMD.

Two-dimensional BCN nanosheets self-assembled with hematite nanocrystals for sensitively detecting trace toxic Pb(II) ions in natural water

In the present work, hematite-boron-carbonitride (Fe₂O₃-BCN) nanosheets were synthesized by a simple hydrothermal reaction and the following high temperature treatment. The morphology, structure and chemical composition of the as-prepared material were carefully characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). The Fe₂O₃-BCN nanosheets were used to modified on the surface of the glassy carbon electrode to fabricate an electrochemical sensor for lead ions (Pb(II)) via differential pulse anodic stripping voltammetry (DPASV). At the same time, the influence of the modification concentration, solution acidity, deposition potential and deposition time on response peak current of Pb(II) at the Fe₂O₃-BCN-based electrochemical sensor was well investigated. Under the optimized conditions, the electrochemical signal and concentration of Pb(II) show two-stage linear relationship in the range of 0.5 - 40 μg/L and 40 -140 μg/L, with a limit of detection (LOD) of 0.129 μg/L. The Fe₂O₃-BCN-based electrochemical sensor shows excellent selectivity and anti-interference ability in the anti-interference experiments and actual sample analysis experiments, revealing its broad application in environmental monitoring of Pb(II).

Cyclocarya paliurus for Phytomanagement of Lead-Contaminated Soils

Cyclocarya paliurus seedlings were cultivated in three types of lead (Pb)-contaminated soils with Pb concentration of 305 ± 17 mg/kg (T1), 1964 ± 59 mg/kg (T2) and 3502 ± 107 mg/kg (T3), respectively. The results showed that after 180 days of cultivation, the contents of exchangeable and carbonate-bound Pb fractions significantly decreased in T1 and T2, but increased in T3. The growth indices of C. paliurus seedlings decreased with increasing Pb concentration; however, no difference was found between that in T1 and in Pb-free soil. The Pb concentration in the roots was an order of magnitude higher than that in the stems and in the leaves. The bioconcentration factor (BCF) of the leaves was the lowest among the three tissues investigated, and decreased with the higher concentration of Pb in the soils. These results suggest that C. paliurus can be used as a sustainable and profitable plant for the phytomanagement of Pb-contaminated soil.

Photosynthesis Performance and Antioxidative Enzymes Response of Melia azedarach and Ligustrum lucidum Plants Under Pb-Zn Mine Tailing Conditions

Lead-zinc (Pb-Zn) mine tailings pose a great risk to the natural environment and human health because of their high toxicity. In this study, the responses of photosynthesis, chlorophyll fluorescence, and antioxidative enzyme of Melia azedarach and Ligustrum lucidum in the soil contaminated by Pb-Zn mine tailings were investigated. Results showed that Pb-Zn mine tailings significantly reduced net photosynthetic rates and leaf photosynthetic pigment content of both trees, and the reduction of net photosynthetic rates was mainly caused by their biochemical limitation (BL). The chlorophyll fluorescence parameters from Pb-Zn tailing stressed leaves indicated that Pb-Zn tailings affected PSII activity which was evident from the change values of energy fluxes per reaction center (RC): probability that an electron moves further than QA - (ETO/TRO), maximum quantum yield for primary photochemistry (TRO/ABS), the density of PSII RC per excited cross-section (RC/CSO), the absorption of antenna chlorophylls per PSII RC (ABS/RC), and the turnover number of QA reduction events (N). Pb-Zn mine tailings also affected the oxidation and reduction of PSI, which resulted in a great increase of reactive oxygen species (ROS) contents and then stimulated the rate of lipid peroxidation. Both trees exhibited certain antioxidative defense mechanisms as elevated superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) activities, then declined under high level of Pb-Zn tailing treatment. Comparatively, L. lucidum showed less extent effect on photosynthesis and higher antioxidative enzyme activities than M. azedarach; thus L. lucidum was more tolerant than M. azedarach at least under the described Pb-Zn tailing treatment. These results indicate that the effect of Pb-Zn mine tailings on photosynthesis performance mainly related to imbalance of the PSII activity and PSI redox state in both trees. We propose that M. azedarach and L. lucidum could relieve the oxidative stress for phytoremediation under the appropriate Pb-Zn mine tailing content.

Does jasmonic acid regulate photosynthesis, clastogenecity, and phytochelatins in Brassica juncea L. in response to Pb-subcellular distribution?

The present experiment unravels how exogenous jasmonic acid regulates photosynthesis, clastogenecity, AsA-GSH cycle and phytochelatins in Brassica juncea L. in response to Pb-subcellular distribution. The plants were evaluated for leaf gas exchange parameters, Fv/Fm, lipid peroxidation, leaf epidermal structures and ABA content. Besides lead accumulation in root, shoot and its subcellular distribution pattern, its role as clastogen and/or aneuploidogen via DNA damage, genome size and ploidy variations, AsA-GSH cycle and quantification of PC₂ and PC₃ were performed as well. Results revealed that Pb inhibited plant growth, disturbed epidermal and guard cells and consequently worsen leaf gas exchange parameters (E, GH₂O, A), F_v/F_m and photosynthetic pigments. For clastogenecity, results revealed considerable DNA damage and analysis for genome size showed that differences between unstressed, Pb-stress and JA application were not significant (P ≤ 0.05), however, ploidy ratio analysis proved partial aneuploidogenic role of Pb. The highest Pb exposure affected AsA-GSH cycle negatively but increased PC₂ and PC₃ contents uniformly in roots and leaves. Surprisingly, exogenous JA inhibits plant growth under non-stress but positively regulates growth, photosynthesis, AsA-GSH cycle, PC₂ and PC₃ contents and DNA damage but has no significant effect on variations in total genome size and ploidy under Pb-stress.

Woody species Rhus chinensis Mill. seedlings tolerance to Pb: Physiological and biochemical response

Screening potential plant species is a crucial consideration in phytoremediation technology. Our previous study demonstrated that Rhus chinensis Mill. seedlings had potentials for phytoremediation of Pb contaminated soil. However, its bioaccumulation and tolerance characteristics remain unclear. Seedling growth, LMWOAs secreted by roots, Pb subcellular distribution and chemical forms, and mineral elements in R. chinensis tissues were evaluated under different Pb concentrations (0, 25, 50, 100, 200 and 400 mg/L) in culture solution at 14 days after planting. R. chinensis did not show visual symptoms of Pb toxicity under lower Pb treatments; however, Pb significantly declined the growth of seedlings under higher Pb treatments. Higher Pb stress also decreased the concentrations of nitrogen in leaves, but increased the concentrations of P and K in roots. Pb stress also decreased Mn concentrations in leaves. A great quantity of Pb was uptake and mostly retained in R. chinensis roots. Nonetheless, R. chinensis can still concentrate 459.3 and 1102.7 mg/kg Pb in leaves and stems, respectively. Most of Pb in R. chinensis tissues was stored in the cell wall with HAc-, HCl-, and NaCl-extractable form. LMWOAs secreted by R. chinensis roots showed a strong positive correlation with Pb concentrations in all plant tissues and with P in roots. Our results suggested that Pb deposited in the cell wall and integration with phosphate or oxalate might be responsible for the tolerance of R. chinensis under Pb stress in short period.

Counteractive mechanism (s) of salicylic acid in response to lead toxicity in Brassica juncea (L.) Czern. cv. Varuna

Salicylic acid alleviates lead toxicity in Brassica juncea (L.) by promoting growth under non-stress and activating stress-defense mechanism (s) under lead stress conditions. It also boosts the ascorbate-glutathione cycle and thus helps in minimizing oxidative and DNA damage. Brassica juncea plants were exposed to different concentrations (0, 500, 1000 and 2000 mg kg^-1) of lead (Pb) and subsequently sprayed with 0.5 mM of salicylic acid (SA) to check for morphological and leaf gas exchange parameters like transpiration rate (E), stomatal conductance (GH₂O), net photosynthetic rate (A) and maximum quantum yield of PS II (F_v/F_m). Leaf epidermis by scanning electron microscopy (SEM), enzymatic and non-enzymatic components of ascorbate-glutathione (AsA-GSH) cycle, DNA damage by comet assay, lipid peroxidation and endogenous SA quantification by HPLC were analyzed. Lead accumulation in root, shoot and its sub-cellular distribution ratio (SDR) and localization was also determined using atomic absorption spectroscopy (AAS) and rhodizonate-dye staining method, respectively. Results revealed that notable amount of Pb was accumulated in root and shoot in dose-dependent manner which significantly (P ≤ 0.05) posed the toxicity on the majority of morphological parameters, structural integrity of epidermal and guard cells, photosynthetic pigments, malondialdehyde (MDA) and H₂O₂ content. Notable decrease in leaf gas exchange parameters, F_v/F_m, poor performance of AsA-GSH cycle and striking amount of DNA damage, was found as well. However, SA revoked Pb toxicity to a great extent by promoting growth, chlorophyll content, improving the A, F_v/F_m, boosting the overall performance of AsA-GSH cycle and by lessening the DNA damage.

Toxicological responses on cytochrome P450 and metabolic transferases in liver of goldfish (Carassius auratus) exposed to lead and paraquat

As the producer of reactive oxygen species (ROS), both lead (Pb) and paraquat (PQ) can generate serious oxidative stress in target organs which result in irreversible toxic effects on organisms. They can disturb the normal catalytic activities of many enzymes by means of different toxicity mechanism. The changed responses of enzymes are frequently used as the biomarkers for indicating the relationship between toxicological effects and exposure levels. In this work, goldfish was exposed to a series of test groups containing lead and paraquat in the range of 0.05-10mg/L, respectively. Four hepatic enzyme activities, including 7-ethoxyresorufinO-deethylase (EROD), 7-benzyloxy-4-trifluoromethyl-coumarin-O-debenzyloxylase (BFCOD), glutathione S-transferase (GST) and UDP-glucuronosyltransferase (UGT) were determined after 1, 7, 14, 28 days exposure. The results showed that the activities of EROD and BFCOD in fish were significantly inhibited in response to paraquat at all exposure levels during the whole experiment. Similarly, the inhibitory effects of lead exposure on BFCOD activity were found in our study, while different responses of lead on EROD were observed. There were no significant differences on EROD activity under lower concentrations of lead (less than 0.1mg/L) before 14 days until an obvious increase was occurred for the 0.5mg/L lead treatment group at day 14. Furthermore, lead showed stronger inhibition on GST activity than paraquat when the concentrations of the two toxicants were more than 0.5mg/L. However, the similar dose and time-dependent manners of UGT activity were found under lead and paraquat exposure. Our results indicated that higher exposure levels and longer accumulations caused inhibitory effects on the four enzymes regardless of lead or paraquat stress. In addition, the responses of phase I enzymes were more sensitive than that of phase II enzymes and they may be served as the acceptable biomarkers for evaluating the toxicity effects of both lead and paraquat.

Effects of sulfur on toxicity and bioavailability of Cu for castor (Ricinus communis L.) in Cu-contaminated soil

The biogeochemical cycling of sulfur (S) in soil has an important impact on the bioavailability of heavy metals and affects the utilization of soil polluted by heavy metals. In addition, S-containing compounds are involved in heavy metal detoxification. This study investigated the effects of S on the toxicity and bioavailability of copper (Cu) in castor (Ricinus communis L.) grown in Cu-contaminated mine tailings. The results showed that the application of S reduced the accumulation of Cu in castor and promoted its growth. With the addition of S, the malondialdehyde (MDA) content of castor leaves decreased significantly compared with control plants, indicating the alleviation of oxidative stress. Superoxide dismutase (SOD) and catalase (CAT) activities and glutathione (GSH) content decreased significantly with the alleviation of oxidative stress. The sequential extraction of Cu fractions showed that the application of S significantly reduced the reducible Cu fraction, and increased the oxidizable Cu fraction. It also increased the residual Cu fraction in the soil. The transformation of chemical speciation reduced the bioavailability of Cu in soil, which then reduced the accumulation of Cu in castor. Our results demonstrated that S application was effective at promoting castor growth by reducing the bioavailability and uptake of Cu in Cu-contaminated mine tailings.

Transcriptomic and physiological analyses of Medicago sativa L. roots in response to lead stress

Lead (Pb) is one of the nonessential and toxic metals that threaten the environment and human health. Medicago sativa L. is a legume with high salt tolerance and high biomass production. It is not only a globally important forage crop but is also an ideal plant for phytoremediation. However, the biological and molecular mechanisms that respond to heavy metals are still not well defined in M. sativa. In this study, de novo and strand-specific RNA-sequencing was performed to identify genes involved in the Pb stress response in M. sativa roots. A total of 415,350 unigenes were obtained from the assembled cDNA libraries, among which 5,416 were identified as significantly differentially expressed genes (DEGs) (false discovery rate < 0.005) between cDNA libraries from control and Pb-treated plants. Gene ontology and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway enrichment analyses of the DEGs showed they mainly clustered with terms associated with binding, transport, membranes, and the pathways related to signal and energy metabolism. Moreover, a number of candidate genes included antioxidant enzymes, metal transporters, and transcription factors involved in heavy metal response were upregulated under Pb stress. Quantitative real-time PCR(qRT-PCR) validation of the expression patterns of 10 randomly selected candidate DEGs were consistent with the transcriptome analysis results. Thus, this study offers new information towards the investigation of biological changes and molecular mechanisms related to Pb stress response in plants.

Accumulation efficiency, genotoxicity and antioxidant defense mechanisms in medicinal plant Acalypha indica L. under lead stress

The present study was designed to assess the physiological and biochemical changes in roots and shoots of the herb Acalypha indica grown under hydroponic conditions during exposure to lead (Pb) (100-500 mg L^-1) for 1-12 d. The accumulation of Pb by A. indica plants was found to be 121.6 and 17.5 mg g^-1 dry weight (DW) in roots and shoots, respectively, when exposed to a Pb concentration of 500 mg L^-1. The presence of Pb ions in stem, root and leaf tissues was confirmed by scanning electron microscope (SEM) and Energy-dispersive X-ray spectroscopy (EDX) analyses. Concerning the activity of antioxidant enzymes, viz., peroxidase (POX) catalase (CAT) and ascorbate peroxidase (APX), they were induced at various regimes during 5, 8 and 12 d of Pb exposure in both the leaves and roots than untreated controls. Lead treatment increased superoxide dismutase (SOD) activity in both the leaf and root tissues over control, irrespective of the duration of exposure. Anew, it was observed that Pb treatments induced variations in the number and intensity of protein bands. Random amplified polymorphic DNA (RAPD) results show that the Pb treatment caused genotoxicity on DNA molecules as evidenced by the amplification of new bands and the absence of normal DNA amplicons in treated plants. Results confirm that A. indica is a Pb accumulator species, and the antioxidants might play a crucial role in the detoxification of Pb-induced toxic effects.

Potential of polyaniline modified clay nanocomposite as a selective decontamination adsorbent for Pb(II) ions from contaminated waters; kinetics and thermodynamic study

BACKGROUND

Nowadays significant attention is to nanocomposite compounds in water cleaning. In this article the synthesis and characterization of conductive polyaniline/clay (PANI/clay) as a hybrid nanocomposite with extended chain conformation and its application for water purification are presented.

METHODS

Clay samples were obtained from the central plain of Abhar region, Abhar, Zanjan Province, Iran. Clay was dried and sieved before used as adsorbent. The conductive polyaniline was inflicted into the layers of clay to fabricate a hybrid material. The structural properties of the fabricated nanocomposite are studied by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR) and scanning electron microscope (SEM). The elimination process of Pb(II) and Cd(II) ions from synthetics aqueous phase on the surface of PANI/clay as adsorbent were evaluated in batch experiments. Flame atomic absorption instrument spectrophotometer was used for determination of the studied ions concentration. Consequence change of the pH and initial metal amount in aqueous solution, the procedure time and the used adsorbent dose as the effective parameters on the removal efficiency was investigated.

RESULTS

Surface characterization was exhibited that the clay layers were flaked in the hybrid nanocomposite. The results show that what happen when a nanocomposite polyaniline chain is inserted between the clay layers. The adsorption of ions confirmed a pH dependency procedure and a maximum removal value was seen at pH 5.0. The adsorption isotherm and the kinetics of the adsorption processes were described by Temkin model and pseudo-second-order equation. Time of procedure, pH and initial ion amount have a severe effect on adsorption efficiency of PANI/clay.

CONCLUSIONS

By using suggested synthesise method, nano-composite as the adsorbent simply will be prepared. The prepared PANI/clay showed excellent adsorption capability for decontamination of Pb ions from contaminated water. Both of suggested synthesise and removal methods are affordable techniques.