Selectivity sequences and sorption capacities of phosphatic clay and humus rich soil towards the heavy metals present in zinc mine tailing

Machine learning-based analysis of heavy metal contamination in Chinese lake basin sediments: Assessing influencing factors and policy implications

Sediments are important heavy metal sinks in lakes, crucial for ensuring water environment safety. Existing studies mainly focused on well-studied lakes, leaving gaps in understanding pollution patterns in specific basins and influencing factors.We compiled comprehensive sediment contamination data from literature and public datasets, including hydro-geomorphological, climatic, soil, landscape, and anthropogenic factors. Using advanced machine learning, we analyzed typical pollution factors to infer potential sources and migration pathways of pollutants and predicted pollution levels in basins with limited data availability. Our analysis of pollutant distribution data revealed that Cd had the most extensive pollution range, with the most severe pollution occurring in the Huaihe and Yangtze River basins. Furthermore, we identified distinct groups of driving factors influencing various heavy metals. Cd, Cr, and Pb were primarily influenced by human activities, while Cu and Ni were affected by both anthropogenic and natural factors, and Zn tended more towards natural sources. Our predictions indicated that, in addition to the typical highly polluted areas, the potential risk of Cd, Cu and Ni is higher in Xinjiang, and in Tibet and Qinghai, the potential risk of Cd, Cr, Cu and Ni is higher. Pb and Zn presented lower risks, except in the Huaihe and Yangtze River Basins. Temperature, wind, precipitation, precipitation rate, and the cation exchange capacity of soil significantly impacted the predictions of heavy metal pollution in sediments, suggesting that particulate migration, rainfall runoff, and soil erosion are likely the main pathways for pollutant migration into sediments. Considering the migration, pathways, and sources of pollutants, we propose strategies such as low-impact development and promoting sustainable transportation to mitigate pollution. This study provides the latest insights into heavy metal pollution in Chinese lake sediments, offering references for policy-making and water resource management.

Physicochemical properties and performance of non-woody derived biochars for the sustainable removal of aquatic pollutants: A systematic review

Biochar is a carbon-rich material produced from the partial combustion of different biomass residues. It can be used as a promising material for adsorbing pollutants from soil and water and promoting environmental sustainability. Extensive research has been conducted on biochars prepared from different feedstocks used for pollutant removal. However, a comprehensive review of biochar derived from non-woody feedstocks (NWF) and its physiochemical attributes, adsorption capacities, and performance in removing heavy metals, antibiotics, and organic pollutants from water systems needs to be included. This review revealed that the biochars derived from NWF and their adsorption efficiency varied greatly according to pyrolysis temperatures. However, biochars (NWF) pyrolyzed at higher temperatures (400-800 °C) manifested excellent physiochemical and structural attributes as well as significant removal effectiveness against antibiotics, heavy metals, and organic compounds from contaminated water. This review further highlighted why biochars prepared from NWF are most valuable/beneficial for water treatment. What preparatory conditions (pyrolysis temperature, residence time, heating rate, and gas flow rate) are necessary to design a desirable biochar containing superior physiochemical and structural properties, and adsorption efficiency for aquatic pollutants? The findings of this review will provide new research directions in the field of water decontamination through the application of NWF-derived adsorbents.

Effective removal of malachite green oxalate from aqueous solution using Newbouldia laevis husk/MWCNTs nanocomposite: equilibrium, kinetics, and thermodynamics

The discharge of colored effluent into water bodies is a big concern; hence, the current work was designed to fabricate a superior nanocomposite (NBM) using the Newbouldia laevis husk (NB) and functionalized multiwalled carbon nanotubes (f-MWCNTs) for the adsorption of malachite green oxalate (MGO). Brunauer-Emmett-Teller (BET) surface analysis was used to assess the specific surface area of NB (0.7699 m2 g-1) and NBM (94.006 m2 g-1). Fourier transform infrared spectroscopy (FTIR) was employed to determine the chemical moieties on the surface of the adsorbent. Field emission scanning electron microscopy (FESEM) and thermogravimetric analysis (TGA) were used to analyze the surface morphology and the thermal behavior of the adsorbents. Essential factors of the adsorption process were investigated, and it was revealed that pH 6.0, adsorbent dose of 0.05 g, contact time 80 min, concentration of 100 mg dm-3 and maximum adsorption capacity of 35.78 mg g-1 (NB) and 69.97 mg g-1 (NBM) were the optimal parameters. The NB and NBM adsorption processes followed a pseudo-first-order kinetic model. The exothermic and endothermic adsorptive processes were noticed to be the best descriptions of MGO elimination by NB and NBM, respectively. The uptake of MGO by NB and NBM was best described by models of Freundlich and Langmuir isotherms. Besides, NBM demonstrated uptake efficiency that is >80% after the fourth adsorption/desorption cycle. As a result, NBM has a wide range of possible uses in environmental remediation.

Bioaccumulation, transfer characteristics of metals in six vascular plants, and soil pollution assessment from Wachangping karst bauxite residue areas

Bauxite residue (BR) is a large volume by-product generated during bauxite smelting process and metal pollution problem is becoming increasingly prominent in residue areas. Accumulation and transfer of metals in six vascular plants were analyzed and soil environment was evaluated. Results found levels of Al (2,110-26,280 mg kg-1), Fe (990 to 9,880 mg kg-1), Ca (8,020 to 49,250 mg kg-1), Mg (2,060 to 17,190 mg kg-1), K (16,840 to 39,670 mg kg-1), and Ti (80 to 1,240 mg kg-1) in plants. Metal concentrations in soils exceeded background levels. Bioconcentration factor (BCF) found that Al, Fe, and Ti in plants (roots, stems, and leaves) were relatively depleted (BCF <1). Transfer factor (TF) of Al, Fe, Ca, K, and Ti in plants was distinctly higher than 1 and mainly concentrated in stems and leaves. Pollution indices revealed that soil environment was at moderated to serious contaminated risk. Principal components analysis (PCA) showed that Artemisia caruifolia Buch. and Siegesbeckia orientalis L. plants had a good ability to absorb Al and Fe, which can be used as biological indicators and restoration materials.

Review on interactions between nanomaterials and phytohormones: Novel perspectives and opportunities for mitigating environmental challenges

Nanotechnology offers the potential to provide innovative solutions for sustainable crop production as plants are exposed to a combination of climate change factors (CO2, temperature, UV radiation, ozone), abiotic (heavy metals, salinity, drought), and biotic (virus, bacteria, fungi, nematode, and insects) stresses. The application of particular sizes, shapes, and concentration of nanomaterials (NMs) potentially mitigate the negative impacts in plants by modulation of photosynthetic rate, redox homeostasis, hormonal balance, and nutrient assimilation through upregulation of anti-stress metabolites, antioxidant defense pathways, and genes and genes network. The present review inculcates recent advances in uptake, translocation, and accumulation mechanisms of NMs in plants. The critical theme of this review provides detailed insights into different physiological, biochemical, molecular, and stress tolerance mechanism(s) of NMs action and their cross-talk with different phytohormones. The role of NMs as a double-edged sword for climate change factors, abiotic, and biotic stresses for nutrients uptake, hormones synthesis, cytotoxic, and genotoxic effects including chromosomal aberration, and micronuclei synthesis have been extensively studied. Importantly, this review aims to provide an in-depth understanding of the hormesis effect at low and toxicity at higher doses of NMs under different stressors to develop innovative approaches and design smart NMs for sustainable crop production.

Assessment of environmental pollution and human health risks of mine tailings in soil: after dam failure of the Córrego do Feijão Mine (in Brumadinho, Brazil)

The dam failure of the Córrego do Feijão Mine (CFM) located in Minas Gerais State, Brazil, killed at least 278 people. In addition, large extensions of aquatic and terrestrial ecosystems were destroyed, directly compromising the environmental and socioeconomic quality of the region. This study assessed the pollution and human health risks of soils impacted by the tailing spill of the CFM dam, along a sample perimeter of approximately 200 km. Based on potential ecological risk and pollution load indices, the enrichments of Cd, As, Hg, Cu, Pb and Ni in soils indicated that the Brumadinho, Mário Campos, Betim and São Joaquim de Bicas municipalities were the most affected areas by the broken dam. Restorative and reparative actions must be urgently carried out in these areas. For all contaminated areas, the children's group indicated an exacerbated propensity to the development of carcinogenic and non-carcinogenic diseases, mainly through the ingestion pathway. Toxicological risk assessments, including acute, chronic and genotoxic effects, on people living and working in mining areas should be a priority for public management and mining companies to ensure effective environmental measures that do not harm human health and well-being over time.

Synergistic effects of adsorption and chemical reduction towards the effective Cr(VI) removal in the presence of the sulfur-doped biochar material

In this study, the anaerobic sludge withdrawn from thickener in a sewage treatment plant served as the precursor for sludge-based biochar fabrication, which was further modified via sulfur (S) heteroatom doping (i.e., S-BC). The S atom doping resulted in the adjustment of the physicochemical properties towards the carbon material, endowment of abundant functional groups on biochar surface, and increasing the binding sites between biochar and Cr(VI). Compared to the primary biochar (i.e., biochar without heteroatomic doping, named BC), S-BC exhibited a rough surface and possessed remarkable advantages in ash content, specific surface area, and pore volume. The existence of graphene carbon crystal structure for S-BC was confirmed through S-BC by XRD and FTIR analysis. The studies of adsorption kinetics and isotherms showed that pseudo-second-order kinetics and the Langmuir model more fitted the Cr(VI) removal behavior in the presence of S-BC. Therefore, the chemisorption and monolayer adsorption were the primary mechanisms involved in the Cr(VI) removal process. Additionally, XPS analysis results illustrated the aqueous Cr(VI) was efficiently eliminated through the synergistic effect of chemisorption and reduction to Cr(III) in the presence of S-BC. Moreover, S-BC could still achieve the Cr(VI) eliminating efficiency of 85.31% undergoing five cycles with unchanged functional group and crystal structure via FTIR and XRD analysis. Thus, the results of this study may shed light on a new approach for simultaneous economical sludge disposal and the sustainable remediation of the Cr(VI)-contaminated wastewater.

Overlooked role of aqueous chromate (VI) as a photosensitizer in enhancing the photochemical reactivity of ferrihydrite and production of hydroxyl radical

The reactive oxygen species (ROS) photochemically generated from natural iron minerals have gained significant attention. Amidst the previous studies on the impact of heavy metal ions on ROS generation, our study addresses the role of the anion Cr(VI), with its intrinsic photoactivity, in influencing ROS photochemical generation with the co-presence of minerals. We investigated the transformation of inorganic/organic pollutants (Cr(VI) and benzoic acid) at the ferrihydrite interface, considering sunlight-mediated conversion processes (300-1000 nm). Increased photochemical reactivity of ferrihydrite was observed in the presence of aqueous Cr(VI), acting as a photosensitizer. Meanwhile, a positive correlation between hydroxyl radical (•OH) production and concentrations of aqueous Cr(VI) was observed, with a 650% increase of •OH generation at 50 mg L-1 Cr(VI) compared to systems without Cr(VI). Our photochemical batch experiments elucidated three potential pathways for •OH photochemical production under varying wet chemistry conditions: (1) ferrihydrite hole-mediated pathway, (2) chromium intermediate O-I-mediated pathway, and (3) chromium intermediates CrIV/V-mediated pathway. Notably, even in the visible region (> 425 nm), the promotion of aqueous Cr(VI) on •OH accumulation was observed in the presence of ferrihydrite and TiO2 suspensions, attributed to Cr(VI) photosensitization at the mineral interface. This study sheds light on the overlooked role of aqueous Cr(VI) in the photochemical reactivity of minerals, thereby enhancing our understanding of pollutant fate in acid mining-impacted environments.

Resourcization of Argillaceous Limestone with Mn3O4 Modification for Efficient Adsorption of Lead, Copper, and Nickel

Argillaceous limestone (AL) is comprised of carbonate minerals and clay minerals and is widely distributed throughout the Earth's crust. However, owing to its low surface area and poorly active sites, AL has been largely neglected. Herein, manganic manganous oxide (Mn3O4) was used to modify AL by an in-situ deposition strategy through manganese chloride and alkali stepwise treatment to improve the surface area of AL and enable its utilization as an efficient adsorbent for heavy metals removal. The surface area and cation exchange capacity (CEC) were enhanced from 3.49 to 24.5 m2/g and 5.87 to 31.5 cmoL(+)/kg with modification, respectively. The maximum adsorption capacities of lead (Pb2+), copper (Cu2+), and nickel (Ni2+) ions on Mn3O4-modified argillaceous limestone (Mn3O4-AL) in mono-metal systems were 148.73, 41.30, and 60.87 mg/g, respectively. In addition, the adsorption selectivity in multi-metal systems was Pb2+ > Cu2+ > Ni2+ in order. The adsorption process conforms to the pseudo-second-order model. In the multi-metal system, the adsorption reaches equilibrium at about 360 min. The adsorption mechanisms may involve ion exchange, precipitation, electrostatic interaction, and complexation by hydroxyl groups. These results demonstrate that Mn3O4 modification realized argillaceous limestone resourcization as an ideal adsorbent. Mn3O4-modified argillaceous limestone was promising for heavy metal-polluted water and soil treatment.

Poultices as biofilms of titanium dioxide nanoparticles/carboxymethyl cellulose/Phytagel for cleaning of infected cotton paper by Aspergillus sydowii and Nevskia terrae

In this study, TiO2 nanoparticle (TiO2NP)-coated film was produced to protect manuscripts against microorganisms using ecofriendly benign materials. As a result, a simple method was created that uses poultice biofilm made of carboxymethyl cellulose (CMC) and Phytagel plant cell (PGP) loaded with TiO2NPs to preserve manuscripts against microbes in an environmentally responsible way. Three volumes (1, 2, 4 mL) of TiO2NPs were put into a biofilm combination to produce the poultices known as CMC/PGP/TiO2-1, CMC/PGP/TiO2-2, and CMC/PGP/TiO2-3. The synthesized TiO2NPs were nearly spherical in shape, small in size (98 nm), and stable (zeta potential value - 33 mV). The results showed that the unique deposition of TiO2NPs on the biofilm surface gave the produced films loaded with TiO2NPs a rough structure. The highest values of mechanical characteristics were determined to be in CMC/PGP/TiO2-1 with values of 25.4 g, 6.6 MPa, and 11.4%, for tensile strength, elongation at break, and tear strength, respectively. Based on molecular identification, the fungus Aspergillus sydowii and the bacterium Nevskia terrae, with accession numbers MG991624 and AB806800, respectively, were isolated and identified from an antiquated manuscript formed from cellulosic fibers. Before the experiments, the produced cotton paper samples were aged, and then, one group was infected for 6 months by A. sydowii and the second group with N. terrae. Following the preparation of a CMC/PGP biofilm loaded with various volumes of TiO2NPs, poultices were applied to infected cotton paper in order to clean it. The infected cotton paper was placed inside the sandwich-like poultices that were created. The poultice CMC/PGP/TiO2-2 demonstrated potential for preventing the growth of A. sydowii and N. terrae-infected cotton paper, when the fibers were saved, cleaned, and coated with CMC/PGP/TiO2-2 after absorbing the fungus and the bacterium and exhibiting exceptional antimicrobial activities. Finally, the novel biofilms have demonstrated their capacity to lessen microbial contamination of cotton paper. In order to generalize the usage of these poultices, it is also advised that they be produced on a large scale and tested on a variety of organic materials in the future.

Optimization and mechanistic approach for removal of crystal violet and methylene blue dyes via activated carbon from pyrolyzed-ZnCl2 bamboo waste

In this study, bamboo waste (BW) was subjected to pyrolysis-assisted ZnCl2 activation to produce mesoporous activated carbon (BW-AC), which was then evaluated for its ability to remove cationic dyes, specifically methylene blue (MB) and crystal violet (CV), from aqueous environments. The properties of BW-AC were characterized using various techniques, including potentiometric-based point of zero charge (pHpzc), scanning electron microscopy with energy dispersive X-rays (SEM-EDX), X-ray diffraction (XRD), gas adsorption with Brunauer-Emmett-Teller (BET) analysis, infrared (IR) spectroscopy. To optimize the adsorption characteristics (BW-AC dosage, pH, and contact time) of PBW, a Box-Behnken design (BBD) was employed. The BW-AC dose of 0.05 g, solution pH of 10, and time of 8 min are identified as optimal operational conditions for achieving maximum CV (89.8%) and MB (96.3%) adsorption according to the BBD model. The dye removal kinetics for CV and MB are described by the pseudo-second-order model. The dye adsorption isotherms revealed that adsorption of CV and MB onto BW-AC follow the Freundlich model. The maximum dye adsorption capacities (qmax) of BW-AC for CV (530 mg/g) and MB (520 mg/g) are favorable, along with the thermodynamics of the adsorption process, which is characterized as endothermic and spontaneous. The adsorption mechanism of CV and MB dyes by BW-AC was attributed to multiple contributions: hydrogen bonding, electrostatic forces, π-π attraction, and pore filling. The findings of this study highlight the potential of BW-AC as an effective adsorbent in wastewater treatment applications, contributing to the overall goal of mitigating the environmental impact of cationic dyes and ensuring the quality of water resources.

Titanium dioxide nanoparticles potentially regulate the mechanism(s) for photosynthetic attributes, genotoxicity, antioxidants defense machinery, and phytochelatins synthesis in relation to hexavalent chromium toxicity in Helianthus annuus L

Chromium (VI) is one of the hazardous heavy metal, heavily discharged into the soil and severely hampers the plants yield. The TiO₂ NPs was selected due to its potential to alleviate the heavy metals toxicity. This manuscript unravels the mechanisms for Cr(VI) induced toxicity and how foliar application of TiO₂ NP_S potentially ameliorate the toxicity by regulating the photosynthetic attributes, DNA damage, antioxidants defense machinery, and phytochelatins synthesis in Helianthus annuus L. Plants were exposed to Cr(VI) concentrations [0, 15, 30, and 60 mg Cr(VI) kg^-1 of soil], and TiO₂ NP_S (15 mg L^-1, 25 nm size₎ were foliar sprayed thrice to the plants at three days interval. The maximum accumulation of total chromium was recorded in root (12.53 µg g^-1 DW) followed by shoot (5.67 µg g^-1 DW) at 60 mg Cr(VI) treatment. The presence and localization of TiO₂ NPs inside the plant leaf cells were confirmed by TEM-EDS analysis. The results revealed that Cr(VI) exposure had a dose-dependent inhibitory effects on photosynthetic attributes, structure of guard and epidermal cells, photosynthetic pigments; inducing impacts on H₂O₂ and MDA productions, DNA damage, AsA-GSH cycle, and most importantly on PC₂, and PC₃ synthesis which is rarely reported. However, TiO₂ NPs exposure minimized Cr(VI) induced toxicity through reduction of total chromium accumulation, H₂O₂ and MDA productions, thereby reducing DNA damage reported first time under combined treatment of Cr(VI)+ TiO₂ NPs as evidenced through comet assay. It also positively regulate the photosynthetic pigments, AsA-GSH cycle, and modulates PC₂ and PC₃ synthesis which have crucial impacts on ROS quenching and Cr(VI) detoxification, respectively, and in turn, minimizes Cr(VI) toxicity in H. annuus L. Besides, this study strengthens the less acknowledged report that Cr(VI) is an inducer of PCs synthesis and also confirms that TiO₂ NPs potentially counteract Cr(VI) toxicity.

Selenium in soil-plant system: Transport, detoxification and bioremediation

Selenium (Se) is an essential micronutrient for humans and a beneficial element for plants. However, high Se doses always exhibit hazardous effects. Recently, Se toxicity in plant-soil system has received increasing attention. This review will summarize (1) Se concentration in soils and its sources, (2) Se bioavailability in soils and influencing factors, (3) mechanisms on Se uptake and translocation in plants, (4) toxicity and detoxification of Se in plants and (5) strategies to remediate Se pollution. High Se concentration mainly results from wastewater discharge and industrial waste dumping. Selenate (Se [VI]) and selenite (Se [IV]) are the two primary forms absorbed by plants. Soil conditions such as pH, redox potential, organic matter and microorganisms will influence Se bioavailability. In plants, excessive Se will interfere with element uptake, depress photosynthetic pigment biosynthesis, generate oxidative damages and cause genotoxicity. Plants employ a series of strategies to detoxify Se, such as activating antioxidant defense systems and sequestrating excessive Se in the vacuole. In order to alleviate Se toxicity to plants, some strategies can be applied, including phytoremediation, OM remediation, microbial remediation, adsorption technique, chemical reduction technology and exogenous substances (such as Methyl jasmonate, Nitric oxide and Melatonin). This review is expected to expand the knowledge of Se toxicity/detoxicity in soil-plant system and offer valuable insights into soils Se pollution remediation strategies.

Factors affecting the toxicity and oxidative stress of layered double hydroxide-based nanomaterials in freshwater algae

Layered double hydroxide (LDH) nanomaterials are utilized extensively in numerous fields because of their distinctive structural properties. It is critical to understand the environmental behavior and toxicological effects of LDHs to address potential concerns caused by their release into the environment. In this work, the toxicological effects of two typical LDHs (Mg-Al-LDH and Zn-Al-LDH) on freshwater green algae (Scenedesmus obliquus) and the main affecting factors were examined. The Zn-Al-LDH exhibited a stronger growth inhibition toxicity than the Mg-Al-LDH in terms of median effect concentration. This toxicity difference was connected to the stability of particle dispersion in water and the metallic composition of LDHs. The contribution of the dissolved metal ions to the overall toxicity of the LDHs was lower than that of their particulate forms. Moreover, the joint toxic action of different dissolved metal ions in each LDH belonged to additive effects. The Mg-Al-LDH induced a stronger oxidative stress effect in algal cells than the Zn-Al-LDH, and mitochondrion was the main site of LDH-induced production of reactive oxygen species. Scanning electron microscope observation indicated that both LDHs caused severe damage to the algal cell surface. At environmentally relevant concentrations, the LDHs exhibited joint toxic actions with two co-occurring contaminants (oxytetracycline and nano-titanium dioxide) on S. obliquus in an additive manner mainly. These findings emphasize the impacts of the intrinsic nature of LDHs, the aqueous stability of LDHs, and other environmental contaminants on their ecotoxicological effects.

Assessment of the intrinsic bioremediation capacity of a complexly contaminated Yamuna River of India: a algae-specific approach

Nearly 57 million people depend on Yamuna's water for their daily needs and agriculture. This is the first study of assessment of the Yamuna River for five major pollutants - Nitrate, Sulfate, Phosphate, Silicon, and Chloride, and the role of inhabitant algal species for phycoremediation. Water samples were collected from 11 different locations across three different seasons and it was found that the concentration of these pollutants varies in different locations and seasons. The concentration of Nitrate 392.93 mg/L at ITO Monsoon 2021, Phosphate 86.25 mg/L at Baghpat, Silicon 257.34 mg/L at Faridabad, Sulfate 2165.949 mg/L at ITO during winter 2020, and Chloride 4400.741 mg/L at Old bridge during Monsoon 2021 are found maximum. A significant variation (p < 0.05) in the concentrations of Nitrate, Sulfate, Phosphate, Silicon, and Chloride before and after treatment with microalgae was observed in water samples. All six algae significantly remove all the pollutants, and the maximum pollutants removed are Phosphate and Nitrite. Scenedesmus sp., removes the highest 99.21% Phosphate and 86.31% Nitrate, whereas 78.50% of Sulfate was removed by Klebsormidium sp. The highest 92.77% Silicon and 86.20% Chloride were removed by Oocystis sp. This finding suggests that out of six algae, Scenedesmus sp., in the Yamuna water has grown primarily at all the sites and reduces maximum pollutants. The outcomes from this study confirms that Yamuna River is highly contaminated at all the sites from these five major pollutants and algae are still survive in highly contaminated Yamuna water where no other plants are grown and phycoremediate the water bodies even in the presence of very high-stress condition. These algae can further be utilized for biotreatment of any contaminated water body.

Lead remediation is promoted by phosphate-solubilizing fungi and apatite via the enhanced production of organic acid

Lead (Pb) is one of the most common heavy metal pollutants in the environment, which can indirectly or directly threaten human health. Lead immobilization by apatite can reduce the effectiveness of Pb cations via the formation of pyromorphite (Pyro). However, the formation of Pyro is always depending on the release of phosphorus (P) from apatite. Phosphate-solubilizing fungi (PSF) can secrete large amounts of organic acid to promote the release of P from apatite. Although the combination of PSF and apatite has shown a huge potential in Pb remediation, this pathway needs to be more attention, especially for organic acid secretion by PSF. This research mainly reviews the possible pathway to strengthen Pb immobilization by PSF and apatite. Meanwhile, the limitation of this approach is also reviewed, with the aim of a better stabilizing effect of Pb in the environment and promoting the development of these remediation technologies.

High-efficiency stabilization of lead in contaminated soil by thermal-organic acid-activated phosphate rock

Phosphate rock powder (PR) has been shown to possess the potential to stabilize lead (Pb) in soil. Most of the phosphorus (P) minerals in the world are low-grade ores, making it difficult to achieve the expected stabilization effect on heavy metals. This study compared the changes in the phase composition and structure of PR and three kinds of activated phosphate rock powder (APR) (organic acid-activated PR, thermal-activated PR, and thermal-organic acid-activated PR). The stabilization effectiveness of APR on Pb-contaminated soil was evaluated by toxicity leaching procedure; the Pb products adsorbed on APR and stabilization mechanism of APR on Pb were analyzed. The results demonstrated that APR showed decreased crystallinity and 3.4-fold increase in specific surface area, and a 53.07% and 49.32% increase in soluble P content in oxalic acid-activated PR and citric acid-activated PR, respectively, when compared with those of PR. These changes improved the stabilization effect of APR on Pb-contaminated soil, in which oxalic acid-600 °C-activated PR showed the best effect, presenting 94.0-99.8% reduction in Pb leaching concentration following addition of 2-10% modifier. Product characterization after Pb adsorption on APR showed that Pb was adsorbed onto APR by forming fluoropyromophite precipitation with APR.

Polymer-coated manganese fertilizer and its combination with lime reduces cadmium accumulation in brown rice (Oryza sativa L.)

Manganese (Mn) has the potential to reduce cadmium (Cd) uptake by rice; however, the efficiency depends on its soil availability. Therefore, this study designed a slow-release Mn fertilizer by employing a polyacrylate coating. Pot trials were conducted to study the effects of coated-Mn and uncoated-Mn alone or in combination with lime on the dynamics of soil dissolved-Mn and available Cd, and the transportation of Mn and Cd within rice. The results showed that coated-Mn declined the release of Mn until the 7th day of application; however, it consistently supplied more dissolved-Mn than uncoated-Mn. As a result, coated-Mn induced a greater Cd reduction (45.8%) in brown rice than uncoated-Mn (9.7%). The total Cd of rice and its proportion in brown rice were greatly reduced by coated-Mn, indicating the inhibition of root uptake and interior transport of Cd. Additionally, lime addition prominently increased the soil pH and decreased the CaCl₂-extractable Cd (90.1-93.9%). However, since lime reduced the soil dissolved-Mn, downregulated the OsHMA3 expression and upregulated the OsNramp5 expression, brown rice Cd was reduced by only 43.0%. The combined addition of lime and coated-Mn alleviated the liming effect on soil Mn and gene expression in roots, thereby reducing brown rice Cd by 71.5%.

Leaching characteristic of potentially toxic metals of artificial soil made from municipal sludge compost

Landscaping of municipal sludge is a good choice to solve the sludge disposal problem, and EDTA treatment can effectively promote the uptake of heavy metals (HMs) by plants, but the heavy metal leaching process and its main control factors are still poorly understood during the sludge landscaping disposal. In this study, the migration behavior of HMs in artificial soil made from municipal sludge compost (MSC) were investigated using soil column experiments. After six leaching events for a total of one year's rainfall, the average reduction percentage of total phosphorus, total nitrogen, organic matter in the MSC artificial soil were 13.4%, 10.1%, and 7.8%, respectively, while those of copper, lead, zinc, cadmium, nickel were 12.9%, 8.37%, 11.5%, 5.94%, and 10.7%, respectively. Treating ethylenediaminetetraacetic acid (EDTA) to the MSC artificial soil further enhanced the leach index of HMs to different degrees. HM concentration in leachate were increased with peak times postponed. Though EDTA treatment increased HM concentrations in subsoil, it did not change their water washing efficiency. The retention of HMs in subsoil was related to properties of local soil and its interaction with leachate. The potential ecological risk was of quite strong risk category in the MSC artificial soil and rapidly decreased from moderate to slight risk in subsoil. Cadmium was the main contribution accounting for 46%-93% of ecological risk. For landscaping applications, the composition of MSC artificial soil and local soil, as well as the capacity of the surrounding water, needs to be considered.

Analysis of the Importance of Oxides and Clays in Cd, Cr, Cu, Ni, Pb and Zn Adsorption and Retention with Regression Trees

This study determines the influence of the different soil components and of the cation-exchange capacity on the adsorption and retention of different heavy metals: cadmium, chromium, copper, nickel, lead and zinc. In order to do so, regression models were created through decision trees and the importance of soil components was assessed. Used variables were: humified organic matter, specific cation-exchange capacity, percentages of sand and silt, proportions of Mn, Fe and Al oxides and hematite, and the proportion of quartz, plagioclase and mica, and the proportions of the different clays: kaolinite, vermiculite, gibbsite and chlorite. The most important components in the obtained models were vermiculite and gibbsite, especially for the adsorption of cadmium and zinc, while clays were less relevant. Oxides are less important than clays, especially for the adsorption of chromium and lead and the retention of chromium, copper and lead.

Phytoextraction of toxic metals: a central role for glutathione

Phytoextraction has a promising potential as an environmentally friendly clean-up method for soils contaminated with toxic metals. To improve the development of efficient phytoextraction strategies, better knowledge regarding metal uptake, translocation and detoxification in planta is a prerequisite. This review highlights our current understanding on these mechanisms, and their impact on plant growth and health. Special attention is paid to the central role of glutathione (GSH) in this process. Because of the high affinity of metals to thiols and as a precursor for phytochelatins (PCs), GSH is an essential metal chelator. Being an important antioxidant, a direct link between metal detoxification and the oxidative challenge in plants growing on contaminated soils is observed, where GSH could be a key player. In addition, as redox couple, oxidized and reduced GSH transmits specific information, in this way tuning cellular signalling pathways under environmental stress conditions. Possible improvements of phytoextraction could be achieved by using transgenic plants or plant-associated microorganisms. Joined efforts should be made to cope with the challenges faced with phytoextraction in order to successfully implement this technique in the field.