Toxicity assay of lanthanum and cerium in solutions and soil

Addressing lanthanum toxicity in plants: Sources, uptake, accumulation, and mitigation strategies

Lanthanum (La), the second most abundant rare earth element (REE) is emerging as an environmental issue, with the potential to impact ecosystems and human health. Major sources of soil contamination by La include agricultural, and industrial activities. Lanthanum is non-essential for plant growth but accumulates in various plant parts. The uptake of La by plants is intricately influenced by various factors such as soil pH, redox potential, cation exchange capacity, presence of organic acids and rhizosphere composition. These factors significantly impact the availability and absorption of La ions. Lanthanum impact on plants depends on soil characteristics, cultivated species, developmental stage, La concentration, treatment period, and growth conditions. Excessive La concentrations affect cell division, DNA structure, nutrient uptake, and photosynthesis and induce toxicity symptoms. Plants employ detoxification mechanisms like vacuolar sequestration, osmolyte synthesis, and antioxidant defense system. However, higher concentrations of La can overwhelm these defense mechanisms, leading to adverse effects on plant growth and development. Further, accumulation of La in plants increases the risk for human exposure. Strategies to mitigate La toxicity are, therefore, vital for ecosystem protection. The application of phytoremediation, supplementation, chelation, amendments, and biosorption techniques contributes to the mitigation of La toxicity. This review provides insights into La sources, uptake, toxicity, and alleviation strategies in plants. Identifying research gaps and discussing advancements aims to foster a holistic understanding and develop effective strategies for protecting plant health and ecosystem resilience against La contamination.

Artisanal mining of monazite and cassiterite in the Amazon: Potential risks of rare earth elements for the environment and human health

Artisanal mining is intensely carried out in developing countries, including Brazil and especially in the Amazon. This method of mineral exploration generally does not employ mitigation techniques for potential damages and can lead to various environmental problems and risks to human health. The objectives of this study were to quantify the concentrations of rare earth elements (REEs) and estimate the environmental and human health risks in cassiterite and monazite artisanal mining areas in the southeastern Amazon, as well as to understand the dynamics of this risk over time after exploitation. A total of 35 samples of wastes classified as overburden and tailings in active areas, as well as in areas deactivated for one and ten years were collected. Samples were also collected in a forest area considered as a reference site. The concentrations of REEs were quantified using alkaline fusion and ICP-MS. The results were used to calculate pollution indices and environmental and human health risks. REEs showed higher concentrations in anthropized areas. Pollution and environmental risk levels were higher in areas deactivated for one year, with considerable contamination factors for Gd and Sm and significant to extreme enrichment factors for Sc. Human health risks were low (< 1) in all studied areas. The results indicate that artisanal mining of cassiterite and monazite has the potential to promote contamination and enrichment by REEs.

Unraveling the impact of lanthanum on methane consuming microbial communities in rice field soils

The discovery of the lanthanide requiring enzymes in microbes was a significant scientific discovery that opened a whole new avenue of biotechnological research of this important group of metals. However, the ecological impact of lanthanides on microbial communities utilizing methane (CH4) remains largely unexplored. In this study, a laboratory microcosm model experiment was performed using rice field soils with different pH origins (5.76, 7.2, and 8.36) and different concentrations of La3+ in the form of lanthanum chloride (LaCl3). Results clearly showed that CH4 consumption was inhibited by the addition of La3+ but that the response depended on the soil origin and pH. 16S rRNA gene sequencing revealed the genus Methylobacter, Methylosarcina, and Methylocystis as key players in CH4 consumption under La3+ addition. We suggest that the soil microbiome involved in CH4 consumption can generally tolerate addition of high concentrations of La3+, and adjustments in community composition ensured ecosystem functionality over time. As La3+ concentrations increase, the way that the soil microbiome reacts may not only differ within the same environment but also vary when comparing different environments, underscoring the need for further research into this subject.

Human and environmental exposure to rare earth elements in gold mining areas in the northeastern Amazon

Rudimentary methods are used to exploit gold (Au) in several artisanal mines in the Amazon, producing hazardous wastes that may pose risks of contamination by rare earth elements (REEs). The objectives of this study were to quantify the concentrations of REEs and assess their environmental and human health risks in artisanal Au mining areas in the northeastern Amazon. Thus, 25 samples of soils and mining wastes were collected in underground, colluvial, and cyanidation exploration sites, as well as in a natural forest that was considered as a reference area. The concentrations of REEs were quantified using alkaline fusion and inductively coupled plasma mass spectrometry, and the results were used to estimate pollution indices and risks associated with the contaminants. All REEs showed higher concentrations in waste deposition areas than in the reference area, especially Ce, Sc, Nd, La, Pr, Sm, and Eu. Pollution and enrichment levels were higher in the underground and cyanidation mining areas, with very high contamination factors (6.2-27) for Ce, Eu, La, Nd, Pr, Sm, and Sc, and significant to very high enrichment factors (5.5-20) for Ce, La, Nd, Pr, and Sc. The ecological risk indices varied from moderate (167.3) to high (365.7) in the most polluted sites, but risks to human health were low in all areas studied. The results of this study indicate that artisanal Au mining has the potential to cause contamination, enrichment, and ecological risks by REEs in the northeastern Amazon. Mitigation measures should be implemented to protect the environment from the negative impacts of these contaminants.

Magnetic biochar with Mg/La modification for highly effective phosphate adsorption and its potential application as an algaecide and fertilizer

In this study, a highly efficient phosphate adsorbent (MBC/Mg-La) based on magnetic biochar was successfully synthesized through Mg-La modification. The phosphate adsorption capacity of biochar was significantly enhanced after Mg-La modification. The adsorbent exhibited an excellent phosphate adsorption performance, particularly for treating low-concentration phosphate wastewater. Within a wide pH range, the adsorbent maintained a stable phosphate adsorption capacity. Furthermore, it showed a high adsorption selectivity for phosphate. Therefore, given the excellent phosphate adsorption performance, the adsorbent could effectively inhibit algae growth by removing phosphate from water. Furthermore, the adsorbent after phosphate adsorption can be easily recycled through magnetic separation, which can serve as a phosphorus fertilizer to promote the growth of Lolium perenne L.

Cerium and samarium blocked antioxidant enzymes in wheat plants

This work was conducted to study positive and negative impacts of cerium (Ce) and samarium (Sm) on two cultivars (Arta and Baharan) in wheat plant. Symbols of stress such as proline, malondialdehyde (MDA) and antioxidant enzymes, which may be complicated in the suppression responses of plants, were also studied. Wheat plants were exposed to 0, 2500, 5000, 7500, 10,000 and 15,000 μM of Ce and Sm for 7 days. The growth enhanced in plants treated with lesser Ce and Sm concentration (2500 μM) and declined in plants treated with upper concentrations as compared to untreated plants. The treatment with 2500 μM of Ce and Sm increased dry weigh in Arta by 68.42 and 20% and in Baharan by 32.14% and 27.3%. Thus, Ce and Sm had hormesis effect on growth in wheat plants. According to plant's growth parameter patterns, Arta cultivar had more sensitive to Sm than to Ce, whereas Baharan cultivar had sensitive to Ce than to Sm. Our results indicated impact of Ce and Sm on proline accumulation depended on the dosage of Ce and Sm. It was observed that Ce and Sm accumulated in wheat plants at higher exposure doses. Increment of MDA content by Ce and Sm treatments showed that these metals caused oxidative stress in wheat plants. Ce and Sm blocked enzymatic antioxidant system (superoxide dismutases, peroxidase and polyphenol peroxidase) in wheat. In wheat plants treated with lower Ce and Sm concentrations higher amounts of non-enzymatic antioxidant metabolites were detected. Thus, we showed the potential negative impact of unsuitable utilization of REEs in plants and suggested growth and interruption in physiological and biochemical mechanisms as a possible factor to recognize the underlying toxicological processes.

Evaluation of Rare Earth Element-Associated Hormetic Effects in Candidate Fertilizers and Livestock Feed Additives

Rare earth elements (REEs) are recognized as emerging contaminants with implications in human and environmental health. Apart from their adverse effects, REEs have been reported as having positive effects when amended to fertilizers and livestock feed additives, thus suggesting a hormetic trend, implying a concentration-related shift from stimulation to inhibition and toxicity, with analogous trends that have been assessed for a number of xenobiotics. In view of optimizing the success of REE mixtures in stimulating crop yield and/or livestock growth or egg production, one should foresee the comparative concentration-related effects of individual REEs (e.g., Ce and La) vs. their mixtures, which may display distinct trends. The results might prompt further explorations on the use of REE mixtures vs. single REEs aimed at optimizing the preparation of fertilizers and feed additives, in view of the potential recognition of their use in agronomy and zootechny.

Metagenomic study of carbon metabolism in black soil microbial communities under lead-lanthanum stress

Pollution of soil environments with heavy metals (HMs) and rare earth elements (REEs) cannot be ignored. We aimed to determine the effects of lead combined with lanthanum (Pb-La) on microbial community structure, carbon metabolism, and differences in carbon source utilization in black soils using EcoPlates™ and a macrogenomic approach. We found that Pb and La contents and the microbial community structure together influence and shape the response of soil carbon metabolism to Pb-La. Compared with controls, microorganisms under pollution stress preferentially use phenolic and carboxylic acids as growth carbon sources. Under Pb-La stress, the relative abundance of Proteobacteria significantly increased, thereby selectively displacing heavy metal-sensitive phyla, such as Chloroflexi, Acidobacteria, and Thaumarchaeota. Altered functional potential of the microbial carbon cycle manifested as differences in carbon metabolism, methane metabolism, and carbon fixation pathways. Furthermore, an appropriate concentration of La can reduce the environmental toxicity of Pb, whereas a high concentration of La has synergistic toxicity with Pb. These findings have important implications for understanding the impact of HM-REE contamination in microbial communities and the functions associated with carbon metabolism in black soils.

Mechanisms of cerium-induced stress in plants: A meta-analysis

A comprehensive evaluation of the effects of cerium on plants is lacking even though cerium is extensively applied to the environment. Here, the effects of cerium on plants were meta-analyzed using a newly developed database consisting of approximately 8500 entries of published data. Cerium affects plants by acting as oxidative stressor causing hormesis, with positive effects at low concentrations and adverse effects at high doses. Production of reactive oxygen species and its linked induction of antioxidant enzymes (e.g. catalase and superoxide dismutase) and non-enzymatic antioxidants (e.g. glutathione) are major mechanisms driving plant response mechanisms. Cerium also affects redox signaling, as indicated by altered GSH/GSSG redox pair, and electrolyte leakage, Ca²⁺, K⁺, and K⁺/Na⁺, indicating an important role of K⁺ and Na⁺ homeostasis in cerium-induced stress and altered mineral (ion) balance. The responses of the plants to cerium are further extended to photosynthesis rate (A), stomatal conductance (g_s), photosynthetic efficiency of PSII, electron transport rate, and quantum yield of PSII. However, photosynthesis response is regulated not only by physiological controls (e.g. g_s), but also by biochemical controls, such as via changed Hill reaction and RuBisCO carboxylation. Cerium concentrations <0.1-25 mg L^-1 commonly enhance chlorophyll a and b, g_s, A, and plant biomass, whereas concentrations >50 mg L^-1 suppress such fitness-critical traits at trait-specific concentrations. There was no evidence that cerium enhances yields. Observations were lacking for yield response to low concentrations of cerium, whereas concentrations >50 mg Kg^-1 suppress yields, in line with the response of chlorophyll a and b. Cerium affects the uptake and tissue concentrations of several micro- and macro-nutrients, including heavy metals. This study enlightens the understanding of some mechanisms underlying plant responses to cerium and provides critical information that can pave the way to reducing the cerium load in the environment and its associated ecological and human health risks.

Regulatory actions of rare earth elements (La and Gd) on the cell cycle of root tips in rice seedlings (Oryza sativa L.)

The continuous expansion of the application of rare earth elements (REEs) in various fields has attracted attention to their biosafety. At present, the molecular mechanisms underlying the biological effects of REEs are unclear. In this study, the effects of lanthanum (La) and gadolinium (Gd) on cell cycle progression in the root tips of rice seedlings were investigated. Low concentrations of REEs (0.1 mg L^-1) induced an increase in the number of cells in the prophase and metaphase, while high concentrations of REEs (10 mg L^-1) induced an increase in the number of cells in the late and terminal stages of the cell cycle, and apoptosis or necrosis. Additionally, low concentrations of REEs induced a significant increase in the expression of the cell cycle factors WEE1, CDKA;1, and CYCB1;1, and promoted the G2/M phase and accelerated root tip growth. However, at high REEs concentrations, the DNA damage response sensitized by BRCA1, MRE11, and TP53 could that prevent root tip growth by inhibiting the transcription factor E2F, resulting in obvious G1/S phase transition block and delayed G2/M phase conversion. Furthermore, by comparing the biological effect mechanisms of La and Gd, we found that these two REEs share regulatory actions on the cell cycle of root tips in rice seedlings.

Effects of rare earth elements (REE) on terrestrial organisms: current status and future directions

Rare Earth Elements (REE) are becoming increasingly important economically and highly exploited, thus contributing to REE increases in ecosystems. The ecotoxicological effects of REE on the terrestrial environment are, however, not fully understood and information on the biological effects of REE is urgently required for environmental risk assessments. In this review, studies and gaps in the existing scientific literature regarding the toxicological effects of REE on terrestrial organisms are presented. A total of 41 articles from the Web of Science database are discussed. La and Ce are the most studied elements, while little information is found concerning heavy REE. Most studies have been performed on plant species and few investigations are available for animals. Plant effects such as reduced mitotic index, germination and photosynthesis and antioxidant system enzyme alterations have been reported. Invertebrate effects include mortality, reproduction alterations and reduced locomotion. Based on the limited number of articles on terrestrial environment REE effects, this review highlights the need for more detailed studies in order to elucidate the effects associated with the REE hormesis and perform complete risk assessments with the establishment of safe REE usage limits.

Risk of Collapse in Water Quality in the Guandu River (Rio de Janeiro, Brazil)

The Guandu River, one of the main rivers in the state of Rio de Janeiro, provides water for more than nine million people in the metropolitan region. However, the Guandu has suffered from massive domestic and industrial pollution for more than two decades, leading to high levels of dissolved total phosphorus, cyanobacteria, and enteric bacteria observed during the summers of 2020 and 2021. The use of Phoslock, a palliative compound, was not effective in mitigating the levels of phosphorus in the Guandu River. Furthermore, potable water driven from the river had levels of 2-MIB/geosmin and a mud smell/taste. With all these problems, several solutions are proposed for improving the Guandu River water quality, including establishment of (i) sewage treatment plants (STPs), (ii) strict water quality monitoring, (iii) environmental recovery (e.g., reforestation), and (iv) permanent protected areas. The objective of this paper is to verify the poor water quality in the Guandu and the ineffectiveness and undesired effects of Phoslock.

Assessment of Tolerance to Lanthanum and Cerium in Helianthus Annuus Plant: Effect on Growth, Mineral Nutrition, and Secondary Metabolism

Rare earth elements (REEs) present a group of nonessential metals for the growth and development of plants. At high concentrations, they can induce internal stress and disturb the physiological and biochemical mechanisms in plants. The potential uptake of lanthanum (La) and cerium (Ce) by the horticultural plant Helianthus annuus and the effect of these elements on its growth, its absorption of macroelements, and the contents of phenolic compounds and flavonoids were assessed. The plants were exposed to 0, 1, 2.5, 5, and 10 µM of La and Ce for 14 days. The results showed a remarkable accumulation of the two REEs, especially in the roots, which was found to be positively correlated with the total phenolic compound and flavonoid content in the plant shoots and roots. The plant's growth parameter patterns (such as dry weight and water content); the levels of potassium, calcium, and magnesium; and the tolerance index varied with the concentrations of the two studied elements. According to the tolerance index values, H. annuus had more affinity to La than to Ce. Although these metals were accumulated in H. annuus tissues, this Asteraceae plant cannot be considered as a hyperaccumulator species of these two REEs, since the obtained REE content in the plant's upper parts was less than 1000 mg·Kg^-1 DW.

Physiological and Biochemical Behaviours and Antioxidant Response of Helianthus annuus under Lanthanum and Cerium Stress

The continuous progress of global manufacturing and anthropogenic activities has resulted in excessive environmental metallic pollution, particularly with rare earth elements (REEs) which have become a prevalent issue of global concern due to their high toxicity and widespread existence. REEs-contaminated soils could ruin agriculture by inducing plant physiology disturbances in various crops that are considered the principal link of the human food chain. The main purpose of the present work is to assess the phytotoxicity of two light REEs, lanthanum (La) and cerium (Ce), in Helianthus annuus after 14 days of exposure to different concentrations of La and Ce (0, 1, 2.5, 5, and 10 µM). Plants showed different variations in shoot and root lengths at the end of the trial period. The accumulation of photosynthetic pigments, such as chlorophylls and carotenoids, as well as the photosynthetic efficiency, the non-photochemical quenching, the photosynthetically active radiation, and the electron transport rate, increased in the two REE treatments. Hydrogen peroxide significantly increased in all applied concentrations of La and Ce. A significant increase in malondialdehyde content was noticed only when plants were exposed to 2.5 µM La and 10 µM Ce. Results also demonstrated that La and Ce induced an increase in the activity of superoxide dismutase, peroxidase, and catalase (only the highest concentration of La decreased catalase activity). The exposure to different REE concentrations induced the accumulation of La and Ce in the plants, mainly in roots. Helianthus annuus showed an effective resistance behaviour facing La- and Ce-induced stresses.

Stabilization of fluorine-contaminated soil in aluminum smelting site with biochar loaded iron-lanthanide and aluminum-lanthanide bimetallic materials

Trivalent metals-modified-biochar (BC) has been widely used for the removal of fluorine (F) in water, but little is known about its effects on the stability and mobility of F-contaminated soil. Two types of modified-BC materials (BC-loaded iron-lanthanide (BC/Fe-La) and BC-loaded aluminum-lanthanide (BC/Al-La)) were synthesized and used for the remediation of F-contaminated soil. The forms of BC/La_xFe_3x(OH)_y in BC/Fe-La and BC/La_xAl_3x(OH)_y in BC/Al-La were identified by spectroscopy, X-ray dispersion, thermogravimetric, and pore diameter/volume analyses. Following application (4-12%, w/w) to F-contaminated soil for 30 d, water soluble fluoride (WSF) decreased significantly. The modified-BC with a 1:1:1 molar ratio (BC: Al³⁺ or Fe³⁺: La³⁺) were more effective than those at 1:0.5:0.5. The BC/Al-La were the most effective to stabilize F. In particular, the highest decrease in WSF (by 91.75%) was obtained with the application of 12% BC/Al-La-2, while 8% BC/Al-La-2% and 12% BC/Al-La-1 reduced the WSF by 87.58% and 90.17%, respectively; all values obtained were lower than the national standard of China (< 1.5 mg/L). In addition, the sequential extraction results showed that modified-BC promoted the transformation of the other chemical speciation to the Fe/Mn-F.

Review of Rare Earth Elements as Fertilizers and Feed Additives: A Knowledge Gap Analysis

Rare earth elements (REEs) are key constituents of modern technology and play important roles in various chemical and industrial applications. They also are increasingly used in agricultural and zootechnical applications, such as fertilizers and feed additives. Early applications of REEs in agriculture have originated in China over the past several decades with the objective of increasing crop productivity and improving livestock yield (e.g., egg production or piglet growth). Outside China, REE agricultural or zootechnical uses are not currently practiced. A number of peer-reviewed manuscripts have evaluated the adverse and the positive effects of some light REEs (lanthanum and cerium salts) or REE mixtures both in plant growth and in livestock yield. This information was never systematically evaluated from the growing body of scientific literature. The present review was designed to evaluate the available evidence for adverse and/or positive effects of REE exposures in plant and animal biota and the cellular/molecular evidence for the REE-associated effects. The overall information points to shifts from toxic to favorable effects in plant systems at lower REE concentrations (possibly suggesting hormesis). The available evidence for REE use as feed additives may suggest positive outcomes at certain doses but requires further investigations before extending this use for zootechnical purposes.

Development of Fe3O4/CAC nanocomposite for the effective removal of contaminants of emerging concerns (Ce3+) from water: An ecotoxicological assessment

Contaminants of emerging concerns present in the ecosystems causes various adverse effects on all living organisms. In current study, removal of Ce³⁺ from water was performed using Fe₃O₄/CAC nanocomposite (MCAC) synthesized by co-precipitation technique. The synthesized MCAC was characterized using various analytical techniques. The magnetic behavior of the nanocomposite which is a crucial advantage in separation of MCAC after adsorption of Ce³⁺ from water was determined using vibrating sample magnetometer. MCAC was polycrystalline comprising both amorphous and crystalline regions with elements like C, O, Fe and N. The influence of process parameters was optimized through batch mode with the adsorption capacity of 86.206 mg/g. Ecotoxicological studies were performed using Danio rerio (Zebra fish) and seeds of Vigna mungo and Vigna radiata to assess the harmful effects of Ce³⁺ before and after adsorption process. The phytotoxicity studies on seeds revealed that inhibition of growth ranges from 50.39% to 12.55% (before adsorption) and 28.57%-3.89% (after adsorption). After 96 h the LC₅₀ value of Ce³⁺ on the Danio rerio before and after adsorption was 2.44 and 77.85 mg/L. Thus, the current study investigated the effective removal of Ce³⁺ by MCAC and evaluates its ecotoxicological effects.

Low-dose lanthanum activates endocytosis, aggravating accumulation of lanthanum or/and lead and disrupting homeostasis of essential elements in the leaf cells of four edible plants

Rare earth elements (REEs) are emerging as a serious threat to ecological safety due to their increasing accumulation in environments. The accumulation of REEs in environments has significantly increased its accumulation in the leaves of edible plants. However, the accumulation pathway of REEs in the leaves of edible plants are still unknown. In this study, lanthanum [La(III), a widely used and accumulated REE] and four edible plants (soybean, lettuce, pakchoi, and celery) with short growth cycles were selected as research objects. By using interdisciplinary research techniques, we found that low-dose La(III) activated endocytosis (mainly the clathrin-mediated endocytosis) in the leaf cells of four edible plants, which provided an accumulation pathway for low-dose La in the leaf cells of these edible plants. The accumulation of La in the leaf cells was positively correlated with the intensity of endocytosis, while the intensity of endocytosis was negatively correlated with the density of leaf trichomes. In addition to the accumulation of La, low-dose La(III) also brought other risks. For example, the harmful element (Pb) can also be accumulated in the leaf cells via La(III)-activated endocytosis; the homeostasis of the essential elements (K, Ca, Fe, Mg) was disrupted, although the chlorophyll synthesis and the growth of these leaf cells were accelerated; and the expression of stress response genes (GmNAC20, GmNAC11) in soybean leaves was increased. These results provided an insight to further analyze the toxicity and mechanism of REEs in plants, and sounded the alarm for the application of REEs in agriculture.

Cytogenetic and molecular studies on two faba bean cultivars revealed their difference in their aluminum tolerance

Two cultivars of faba bean (Vicia faba ‘Giza 843’ and ‘Nobaria 3’) that differ in aluminum (Al) tolerance were used to study cytogenetic and genomic alterations under the influence of Al Cl3 (5, 15, and 25 mmol AlCl3) for different periods (6, 12 and 24 h). Under Al treatments, mitotic index in both cultivars decreased and total chromosomal abnormalities increased. The frequencies of micronuclei and chromosomal abnormalities (C-anaphase, metaphase-star chromosomes, breaks, sticky and disturbed chromosomes during metaphase or anaphase) in ‘Giza 843’ were lower than in ‘Nabaria 3’. Increase of the registered cytogenetic events under the influence of Al stress led to increase the detected polymorphism using RAPD and ISSR markers. Application of RAPD primers gave the same value of polymorphism in both faba bean cultivars under Al stress. Polymorphism average of nine ISSR primers of ’Giza 843’ (65.36 %) was lower than that of ‘Nobaria 3’ (71.59 %). Molecular markers, cytogenetic characteristics and seedling growth data indicate that Al tolerance of ‘Giza 843’ was higher than of ‘Nobaria 3’. This work shows that cytogenetic and ISSR techniques could be used efficiently to distinguish between the ability of two faba bean cultivars to tolerate toxic effects of Al.

La, Ce and Nd in the soil-plant system in a vegetation experiment with barley (Hordeum vulgare L.)

Rare earth elements (REEs) have received enormous attention in recent years. However, there are many gaps in the understanding of their behavior in the soil-plant system. The aim of this study is to investigate the behavior of three most common REEs (La, Ce, Nd) in the soil-plant system directly on soil samples using barley (Hordeum vulgare L.) in a vegetation experiment. We attribute the absence of significant changes in plant biomass and photosynthetic pigment content to the reduced availability of REEs in soil samples. The concentration of water-soluble forms of La, Ce and Nd didn't exceed 1 mg/kg, while the concentration of exchangeable forms varied and decreased in a row La > Ce > Nd. The transfer factor (TF) from soil to above-ground biomass was low for all three elements (<1). The stem-to-leaf TF increased with the increase in REEs concentration in soil. The concentration in plant material increased in the row Ce < Nd < La. REEs concentrations in barley leaves didn't exceed 1-3% of the corresponding element concentration in soil samples. REEs concentration in plant tissues is in close direct correlation with the REEs total concentration in soil, water-soluble and exchange forms. REEs concentration in barley leaves is 3-4 times higher than in the stems and for the group with extraneous concentration of 200 mg/kg for La, Ce and Nd was 6.20 ± 1.48, 2.10 ± 0.51, 6.90 ± 3.00 mg/kg, respectively. We show that there were no major changes in barley plants, but further study is needed of the relationship between the absorption of lanthanides by plants and the content of various forms of lanthanides in the soil.

A mini-review of X-ray photodynamic therapy (XPDT) nonoagent constituents' safety and relevant design considerations

Conventional photodynamic therapy (PDT) has proved effective in the management of primary tumors and individual metastases. However, most cancer mortality arises from wide-spread multiple metastases. The latter has thus become the principal target in oncology, and X-ray induced photodynamic therapy (XPDT or PDTX) offers a great solution for adapting the PDT principle to deep tumors and scattered metastases. Developing agents capable of being excited by X-rays and emitting visible light to excite photosensitizers is based on challenging physical and chemical technologies, but there are fundamental biological limitations that are to be accounted for as well. In the present review, we have established eight major groups of safety determinants of NPs encompassing 22 parameters of clinical applicability of XPDT nanoparticulate formulations. Most, if not all, of these parameters can be accounted for and optimized during the design and development of novel XPDT nanoparticles.

Sustainable carboxylated cellulose filters for efficient removal and recovery of lanthanum

Carboxylated cellulose filters were fabricated by oxidation of a cellulose fibrous mat via TEMPO-mediated oxidation. These carboxylated cellulose filters were employed as sustainable filters for removal and recovery of lanthanum ions (La (III)) with high adsorption capability. The surface chemistry of the carboxylated cellulose fibers before and after adsorption of La (III) was investigated systematically. The distribution of La (III) on carboxylated cellulose fibers were explored by EDX mapping approach, which revealed that the adsorption occurred on both the surface and the internal structure of the cellulose fibers. The kinetics and isotherms of the adsorption were conducted to understand the adsorption mechanism of the carboxylated cellulose filter and to learn the maximum adsorption capacity for La (III) which was as high as 33.7 mg/g. The adsorption selectivity of the carboxylated cellulose filter for La (III) was determined when interfering ions including mono- and di-covalent ions were involved. The carboxylated cellulose filter exhibited high adsorption capability and high permeation flux evidenced by the breakthrough curves of the dynamic adsorption of La (III) under an extremely low pressure of 0.07 kPa. A variety of desorption reagents were selected to recover lanthanum from the carboxylated cellulose filter, where the optimized conditions for recovery were explored. Finally, a spiral wound cartridge of the carboxylated cellulose fibrous mat was fabricated and the removal and the recovery of La (III, 2.5 ppm) from massive lanthanum-containing water were demonstrated. It was very impressive that the high rejection ratio of 94.3% was achieved under the low pressure drop of 3.0 kPa remaining throughout the separation process, and the treated solution volume was high up to 21.4 L, which was about six-times higher than that of commercially available nanofibrous adsorption membranes, indicating that the carboxylated cellulose filter could be used as a highly efficient adsorption medium for industrial recovery of rare earth metals.

Modification of NaY zeolite by lanthanum and hexadecyl trimethyl ammonium bromide and its removal performance for nitrate

Nitrate in the effluent of wastewater treatment plants (WWTPs) is the main nitrogen resource in natural water. The excessive nitrogen in natural water causes ecological issues such as aqueous eutrophication. A novel modified NaY zeolite (SMZ-La) with hexadecyl trimethyl ammonium bromide (HDTMA) and lanthanum (La) as modifying agents for NO 3 - -N adsorption was investigated in this study. Results showed that SMZ-La had a higher adsorption capacity (3.82 mg NO 3 - -N/g) than zeolite only modified with HDTMA or La (2.75 and 2.23 mg NO 3 - -N/g, respectively). Moreover, the adsorption process was endothermic with a maximum theoretic adsorption of 14.49 mg NO 3 - -N/g. X-ray photoelectron spectroscopy (XPS) analysis indicated that adsorption rate principally depended on chemisorption between SMZ and NO 3 - -N. Thermogravimetric analysis showed that HDTMA was loaded on the surface of NaY zeolite with double layer. Scanning electron microscope and X-ray spectroscopy analysis illustrated that La was primarily loaded in the pore of NaY zeolite, and the loading of HDTMA and La did not affect the original crystal structure of NaY zeolite. The novel adsorbent provided a promising perspective for nitrogen control in WWTPs and natural water. PRACTITIONER POINTS: A novel modified zeolite (SMZ-La) was prepared successfully with HDTMA and La. SMZ-La had an excellent adsorption capacity compared to SMZ and NaY-La. There were both physical and chemical adsorptions in the adsorption process of SMZ-La on NO 3 - -N.

Lanthanum chloride impairs spatial learning and memory by inducing [Ca2+]m overload, mitochondrial fission–fusion disorder and excessive mitophagy in hippocampal nerve cells of rats

Lanthanum chloride damages hippocampal nerve cells of rats through inducing [Ca²⁺]_m overload, mitochondrial fission–fusion disorder, and excessive mitophagy.

Potential roles of melatonin and sulfur in alleviation of lanthanum toxicity in tomato seedlings

Owing to the active use of rare-earth elements in many areas, it is necessary to study their behavior in the environment and their biological impact on plants. Despite the role of melatonin and sulfur in plant growth, development and abiotic stress tolerance; it is still not clear how they have a strong regulatory influence and synergistic effect on growth, physiological and biochemical characteristics of plants under different environmental stresses. Therefore, this study highlights how melatonin and sulfur together potentially involved in a reversal of lanthanum-inhibited photosynthetic and growth responses in tomato seedlings. Here, we reported that seedlings grown in a medium containing 150 μM lanthanum exhibited increased overproduction of reactive oxygen species (ROS) and lipid peroxidation together with increased Chlorophyll degradation, and activity of chlorophyllase, proline dehydrogenase and glycolate oxidase (GOx), and decreased photosynthesis and growth. However, the application of melatonin and sulfur showed significant responses on tomato seedlings, although the response of their combined treatment was more effective by further increasing photosynthesis and growth under lanthanum toxicity. Melatonin supplied with sulfur suppressed ROS formation, lipid peroxidation and activity of GOx, and increased photosynthesis by upregulating activities of carbonic anhydrase and ribulose-1,5-bisphosphate carboxylase/oxygenase. Also, sulfur supplementation with melatonin to seedlings resulted in an elevation in the accumulation of Chl and proline by increasing δ-aminolevulinic acid and activity of δ-aminolevulinic acid dehydratase and Δ¹-pyrroline-5-carboxylate synthetase activity. The administration of melatonin with sulfur substantially induced upregulation of enzymes (superoxide dismutase, ascorbate peroxidase, monodehydroascorbate reductase, dehydroascorbate reductase and glutathione reductase) activities involved in the antioxidant system, thereby mitigating ROS-induced oxidative damage. Thus, this study provides strong evidence that melatonin and sulfur have strong regulatory influence and synergistic role in alleviating the adverse effect of lanthanum-toxicity by increasing photosynthesis and growth.

The cation competition and electrostatic theory are equally valid in quantifying the toxicity of trivalent rare earth ions (Y3+ and Ce3+) to Triticum aestivum

There is a lack of appropriate models to delineate the toxicity of rare earth elements (REEs) while taking into account the factors that affect bioavailability. Here, standardized wheat (Triticum aestivum L.) root elongation tests were conducted to examine the impact of exposure conditions (i.e., varying Ca, Mg, Na, K and pH levels) on Y and Ce toxicity. Cation competition and electrostatic theory were examined for their applicability in explaining the observed variations in toxicity. Only Ca²⁺ and Mg²⁺ significantly alleviated the toxicity of Y³⁺ and Ce³⁺, while Na⁺, K⁺ and H⁺ showed no significant effects. Based on the cation competition, the derived binding constants for the hypothetical biotic ligands of wheat logK_CaBL, logK_MgBL, logK_YBL, and logK_CeBL were 3.87, 3.59, 6.70, and 6.48, respectively. The biotic ligand model (BLM) succeeded in predicting toxicities of Y and Ce, with more than 93% of the variance in toxicity explained. Given the BLM requires large data sets for deriving model parameters, attempts were further made to explore a simpler electrostatic based model to quantify REEs toxicity. The results demonstrated that the predictive capacity of the electrostatic approach, which considers ion activities at the plasma membrane surface, was comparable to that of BLM with at least 87% of the variations in toxicity explained. This suggested that the electrostatic theory can serve as a surrogate to BLM in modeling Y and Ce toxicities. Therefore, we recommend the BLM and electrostatic-based model as effective approaches to incorporate bioavailability in quantifying REEs toxicity in the presence of various levels of other major cations.

Cytotoxic evaluation of sodium hypochlorite, using Pisum sativum L as effective bioindicator

The objective of this study was to evaluate the cytotoxic effect of different sodium hypochlorite concentrations, using apical root cells of P. sativum as a bioindicator. Initially, the seeds of P. sativum were exposed to different concentrations of sodium hypochlorite (0.1, 0.2, 0.4, 0.8, 1.6, 2 mg L-1) and to a control solution based on distilled water. Next, root growth was measured during 24, 48 and 72 h. Subsequently, the mitotic index (MI) and cellular anomalies (5000 cells per treatment) were determined at 72 h. According to the results obtained, a decrease in root growth was observed at concentrations of 0.4, 1.6 and 2 mg L-1. Likewise, it was evident that, among all the evaluated concentrations, an inhibition of mitosis higher than 50% was presented. Additionally, chromosomal anomalies were also generated, such as Nuclear notch, lagging chromosomes and Chromosomal break, which were present in all the concentrations evaluated. In addition, the presence of micronuclei at concentrations of 2.0 and 1.6 mg L-1 indicate that sodium hypochlorite is a highly cytotoxic substance. Therefore, P. sativum is a specie that offers a feasible experimental model to be implemented in the laboratory with the aim to evaluate the cytotoxic effect of any cytotoxic substance.