Cerium chloride heptahydrate (CeCl3 · 7H2O) induces muscle paralysis in the generalist herbivore, Melanoplus sanguinipes (Fabricius) (Orthoptera: Acrididae), fed contaminated plant tissues

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.

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.

Ingestion and effects of cerium oxide nanoparticles on Spodoptera frugiperda (Lepidoptera: Noctuidae)

The objective of this study was to evaluate the biological and nutritional characteristics of Spodoptera frugiperda (Lepidoptera: Noctuidae), an arthropod pest widely distributed in agricultural regions, after exposure to nano-CeO₂ via an artificial diet and to investigate the presence of cerium in the body of this insect through X-ray fluorescence mapping. Nano-CeO₂, micro-CeO₂, and Ce(NO₃)₃ were incorporated into the diet (0.1, 1, 10, and 100 mg of Ce L^-1). Cerium was detected in caterpillars fed with diets containing nano-CeO₂ (1, 10 and 100 mg of Ce L^-1), micro-CeO₂ and Ce(NO₃)₃, and in feces of caterpillars from the first generation fed diets with nano-CeO₂ at 100 mg of Ce L^-1 as well. The results indicate that nano-CeO₂ caused negative effects on S. frugiperda. After it was consumed by the caterpillars, the nano-CeO₂ reduced up to 4.8% of the pupal weight and 60% of egg viability. Unlike what occurred with micro-CeO₂ and Ce(NO₃)₃, nano-CeO₂ negatively affected nutritional parameters of this insect, as consumption rate two times higher, increase of up to 80.8% of relative metabolic rate, reduction of up to 42.3% efficiency of conversion of ingested and 47.2% of digested food, and increase of up to 1.7% of metabolic cost and 8.7% of apparent digestibility. Cerium caused 6.8-16.9% pupal weight reduction in second generation specimens, even without the caterpillars having contact with the cerium via artificial diet. The results show the importance of new ecotoxicological studies with nano-CeO₂ for S. frugiperda in semi-field and field conditions to confirm the toxicity.

Recovering rare earth elements from contaminated soils: Critical overview of current remediation technologies

Rare earth elements (REE) are essential for sustainable energies such as solar and wind power, with rising demand due to the ambitious goal for a circular society. REE are currently mined from virgin ores while REE-rich contaminated soil is left untreated in the environment. Soil remediation strategies are needed that concomitantly cleanup soil and harvest metals that contribute to process circular economy. In this review we aim to (i) define REE concentrations in contaminated soils as well as (ii) identify soil remediation techniques used in remediating REE from soils, emphasizing the ones that extract REE. Current literature lists REE polluted soils in the vicinities of REE mines, coal mines, high traffic roads and agricultural soils (due to REE association with phosphate fertilizers). We first list the conventional separation methods used in the mining industry and their main strategies in extracting/precipitating REE. Solvent extraction is the most commonly conventional method used followed by electrodeposition of REE at high temperatures. We then highlight soil remediation techniques that are used to treat REE. These techniques can be separated into two types: the ones that (a) stabilize REE in soils, and the ones that (b) extract REE from soils. Bioremediation, soil amendments and others offer stabilization of REE, eventually creating a legacy problem since REE keep accumulating in the soil. Soil remediation techniques that achieve REE extraction are a step closer to resource recovery, contributing to the circularity of REE. Techniques such as phytoremediation, soil washing and electrokinetic treatment show promising extraction results.

Rare earth elements regulate the endocytosis and DNA methylation in root cells of Arabidopsis thaliana

With increasing application of rare earth elements (REEs), the resulting environmental safety has attracted extensive attention. When REEs act on plant leaves, REEs can initiate endocytosis in leaf cells, causing more REEs enter plant cells and then severe damage to plants. But when REEs directly act on plant roots, whether and how REEs affect the endocytosis in root cells remain unknown. Here, we characterized effects of lanthanum [La(III)], a REE with high accumulation in environment, on the endocytosis in root cells of Arabidopsis thaliana, and revealed effect mechanism from the perspective of DNA methylation. We found that La(III) enhanced the endocytosis in root cells and the extent of enhancement depended on the dose and time of La(III) exposure: 160 μM > 80 μM >30 μM (12 h); 80 μM > 30 μM >160 μM (24 h); 24 h  > 12 h. La(III)-enhanced endocytosis in root cells resulted from DNA methylation, which was closely related to the expression level of genes encoding DNA methylases/demethylases: CMT3, DRM2 and DNMT2 for 12 h, MET1, CMT1, CMT2, CMT3, DRM2, DNMT2, ROS1, DME, DML2, DML5a, and DML5b for 24 h. Conversely, enhanced endocytosis also promoted the expression level of genes encoding DNA methylases/demethylases. Our findings provide references for understanding the mechanisms by which REEs impact plants.

Cerium ion promotes the osteoclastogenesis through the induction of reactive oxygen species

Cerium and cerium containing materials have been drawing increasing attentions in industrial and biomedical applications in recent decades. The increased applications of cerium have also increased the risk of human body exposed to cerium ions. Due to its similar ionic radius to calcium(II), cerium(III) have found mainly deposited in the skeletal system. However, the effects of cerium(III) on the bone metabolism homeostasis remain poorly understood. In the present study, the effect of cerium(III) on the osteoclastogenesis which plays a pivotal role in bone metabolism homeostasis was investigated. Cerium(III) could enhance the expression and activity of NADPH oxidase1 (Nox1) leading to the elevation of intracellular reactive oxygen species (ROS) level. The augmentation of ROS level activated the RANKL dependent osteoclasts differentiation pathways resulted in the promotion of osteoclastogenesis, while anions associated with cerium(III) cation have no effects on the differentiation of osteoclasts. The cerium(III) activated osteoclasts exhibited enhanced bone resorption capability. These results provided fundamental information for understanding the potential effects of cerium(III) on the metabolism homeostasis of skeletal system which is of great reference value for future biomedical applications of cerium salts.

Direct imaging of how lanthanides break the normal evolution of plants

After rare earth elements [REE(III)] are anchored outside of the plasma membrane, REE(III) break plant evolution to initiate leaf cell endocytosis, which finally affects plant growth. However, the molecule for anchoring REE(III) in the acidic environment outside of the plasma membrane is not clear, which is crucial for exploring the mechanism of REE(III) breaking plant evolution. Here, lanthanum(III) [La(III)] and terbium(III) [Tb(III)] were respectively served as a representative of REE(III) without and with f electrons, and Arabidopsis was served as a representative of plants, cellular and molecular basis for arabinogalactan proteins (AGP) anchoring REE(III) outside of the plasma membrane was investigated. By using interdisciplinary methods, when REE(III) initiated leaf cell phagocytosis, we observed the increase in the expression of AGP and their migration to the outside of the plasma membrane. In the acidic environment outside of the plasma membrane, Tb(III) formed more stable Lewis acid-base [REE(III)-AGP] complexes with a higher apparent binding constant (1.51 × 10^-6) than La(III) (1.24 × 10^-6). In REE(III)-AGP complexes, the bond lengths of REE(III)-O were in normal range and H-bonds were strong H-bonds. The formation of REE(III)-AGP complexes sequentially disturbed the secondary and tertiary structure of AGP, which were enhanced with increasing the concentration of REE(III), and Tb(III) caused stronger structural changes than La(III). Hence, AGP could be molecules for anchoring REE(III) outside of the plasma membrane. The results of this study are direct imaging of how lanthanides break the normal evolution of plants, and can serve as an important guidance for investigating mechanism of lanthanides in organisms.

Lanthanum exerts acute toxicity and histopathological changes in gill and liver tissue of rare minnow (Gobiocypris rarus)

We evaluated the acute toxicity effects of lanthanum (La(III)) on gill and liver of rare minnow (Gobiocypris rarus). The median lethal concentration of La (III) at 96 h was 1.92 mg L^-1. Rare minnow were reared in freshwater and exposed to 0.04, 0.08, 0.16, 0.32 and 0.80 mg L^-1 La (III) for 21 d. Gill and liver samples were analyzed by light microscopy. The main histopathological changes induced by La (III) in gills were epithelial lifting, filamentary epithelial proliferation,edema, lamellar fusion, desquamation, and necrosis. Histopathological changes induced by La (III) in the liver included dilation of sinusoids, focal congestion, pyknotic nuclei, karyohexis and karyolysis, vacuolar degeneration, and numerous necrosis areas. Hypsometric analysis indicated significant changes in the measures of gill dimensions (average length, width, area), suggesting metabolic disturbance (gas exchange) upon La (III) exposure. The result showed that La (III) severely affects fish gill and liver.

Cerium chloride heptahydrate (CeCl3 · 7H2O) induces muscle paralysis in the generalist herbivore, Melanoplus sanguinipes (Fabricius) (Orthoptera: Acrididae), fed contaminated plant tissues

Of increasing economic importance are the rare earth elements (REEs). Pollution from mining and processing activity is expected to rise with industrial demand. Plants are known to accumulate REEs, although levels vary with species and soil content. However, the effect on wildlife of ingesting REE contaminated vegetation is not well understood. Here we examined the effect of consuming vegetation with elevated levels of cerium on the generalist grasshopper, Melanoplus sanguinipes (Fabricius). Adults excreted a substantial portion of ingested contamination. However, after only four-days of feeding, accumulation in the body occurred at all doses and paralysis of appendages resulted at the highest doses. Short-term toxicity studies may underestimate the impact of ingesting REE contamination. Metals tend to be low in toxicity; however, their persistence in the environment may be better represented by exposure over longer portions of the life cycle.