Toxicity of three rare earth elements, and their combinations to algae, microcrustaceans, and fungi

Into the deep: Exploring the molecular mechanisms of hyperactive behaviour induced by three rare earth elements in early life-stages of the deep-sea scavenging amphipod Tmetonyx cicada (Lysianassidae)

With increasing socio-economic importance of the rare earth elements and yttrium (REY), Norway has laid out plans for REY mining, from land-based to deep-sea mining, thereby enhancing REY mobility in the marine ecosystem. Little is known about associated environmental consequences, especially in the deep ocean. We explored the toxicity and modes of action of a light (Nd), medium (Gd) and heavy (Yb) REY-Cl3 at four concentrations (3, 30, 300, and 3000 μg L-1) in the Arcto-boreal deep-sea amphipod Tmetonyx cicada. At the highest concentration, REY solubility was limited and increased with atomic weight (Nd < Gd < Yb). Lethal effects were practically restricted to this treatment, with the lighter elements being more acutely toxic than Yb (from ∼50 % mortality in the Gd-group at dissolved 689-504 μg L-1 to <20 % in the Yb-group at ca. 2000 μg L-1), which could be a function of bioavailability. All three REY induced hyperactivity at the low-medium concentrations. Delving into the transcriptome of T. cicada allowed us to determine a whole array of potential (neurotoxic) mechanisms underlying this behaviour. Gd induced the vastest response, affecting serotonin-synthesis; sphingolipid-synthesis; the renin-angiotensin system; mitochondrial and endoplasmic reticulum functioning (Gd, Nd); and lysosome integrity (Gd, Yb); as well as the expression of hemocyanin, potentially governing REY-uptake (Gd, Yb). While Nd and Yb shared only few pathways, suggesting a link between mode of action and atomic weight/radius, almost all discussed mechanisms imply the disruption of organismal Ca-homeostasis. Despite only fragmental genomic information available for crustaceans to date, our results provide novel insight into the toxicophysiology of REY in marine biota. The neurotoxic/behavioural effects in T. cicada at concentrations with potential environmental relevance warn about the possibility of bottom-up ecological consequences in mining exposed fjords and deep-sea ecosystems, calling for follow-up studies and regulatory measures prior to the onset of REY mining in Norway.

Occurrence and health risk assessment of toxic metals and rare earth elements in microalgae: Insight into potential risk factors in new sustainable food resources

Microalgae are a promising sustainable food source with high nutritional value and environmental benefits. This study investigated the presence of toxic metals and rare earth elements (REEs) in 68 microalgal-based food products and conducted a probabilistic risk assessment to evaluate potential health risks. The findings revealed high detection rates of REEs (80.96% to 100%) and heavy metals (83.82% to 100%), with REE concentrations ranging from 0.0055 to 0.5207 mg/kg. Heavy metals were detected at the following average concentrations: As (2.80 mg/kg) > Cr (1.27 mg/kg) > Pb (0.30 mg/kg) > Cd (0.20 mg/kg) > Hg (0.01 mg/kg). Carcinogenic risk analysis for Cd (3.004 × 10-3), Cr (1.484 × 10-3), and As (1.1283 × 10-2) indicated that 95th percentile values exceeded established safety thresholds (10-4). These findings highlight the critical need for stringent monitoring and the establishment of comprehensive regulatory frameworks for the safety of novel microalgae foods.

Acute and chronic toxicity of rare earth elements-enriched sediments from a prospective mining area: Effects on life history traits, behavioural and physiological responses of Gammarus fossarum (Crustacea Amphipoda)

Rare earth elements (REE) have an essential role and growing importance in the world's economy. They are attracting interest from society, policymakers, and scientists. The rapidly growing global demand for REE in several strategic industrial and agricultural sectors led many countries to consider the (re)-opening of mining activities for REE extraction. Hence, their increasing use led to the disruption of their biogeochemical cycles with anthropic abnormalities already observed in aquatic ecosystems. Nonetheless, REE remain less studied, and their mechanisms of toxicity actions are not fully understood. As amphipods, Gammarus fossarum represent an important part of the aquatic macroinvertebrate assemblage and are generally used in ecotoxicological studies for their high ecological relevance. However, their use for the study of REE effects has been rather limited so far. The current study aims to assess the potential effects of two naturally REE-enriched sediments (N2 and B4) on G. fossarum. Effects on life history traits, behavioural and physiological responses have been evaluated. Exposing G. fossarum males for 72h to sediments N2 and B4 led to a decrease in haemolymph osmolality and locomotion while an increase in ventilatory activity was observed. Exposing G. fossarum pre-copula pairs with females at the same reproductive stage to the naturally REE-enriched sediments, for one moult cycle duration (∼30 days) showed that sediment B4 led to i) a significant uptake of REE, ii) a significant decrease in the proportion of females with oocytes and iii) a significant reduction in the total number of juveniles. The physicochemical analyses of sediments showed that B4 contains the highest amount of REE with a higher proportion of light REE. The present study gives the first insights into the potential toxicity of REE on G. fossarum as they may have deleterious effects on G. fossarum population's dynamics, which may alter the functioning of aquatic ecosystems.

Settling selection of Chlamydomonas reinhardtii for samarium uptake

Samarium (Sm) is a rare-earth element recently included in the list of critical elements due to its vital role in emerging new technologies. With an increasing demand for Sm, microbial bioremediation may provide a cost-effective and a more ecologically responsible alternative to remove and recover Sm. We capitalized on a previously selected Chlamydomonas reinhardtii strain tolerant to Sm (1.33 × 10-4 M) and acidic pH and carried out settling selection to increase the Sm uptake performance. We observed a rapid response to selection in terms of cellular phenotype. Cellular size decreased and circularity increased in a stepwise manner with every cycle of selection. After four cycles of selection, the derived CSm4 strain was significantly smaller and was capable of sequestrating 41% more Sm per cell (1.7 × 10-05 ± 1.7 × 10-06 ng) and twice as much Sm in terms of wet biomass (4.0 ± 0.4 mg Sm · g-1) compared to the ancestral candidate strain. The majority (~70%) of the Sm was bioaccumulated intracellularly, near acidocalcisomes or autophagic vacuoles as per TEM-EDX microanalyses. However, Sm analyses suggest a stronger response toward bioabsorption resulting from settling selection. Despite working with Sm and pH-tolerant strains, we observed an effect on fitness and photosynthesis inhibition when the strains were grown with Sm. Our results clearly show that phenotypic selection, such as settling selection, can significantly enhance Sm uptake. Laboratory selection of microalgae for rare-earth metal bioaccumulation and sorption can be a promising biotechnological approach.

The impact of global climate changes on trace and rare earth elements mobilization in emerging periglacial terrains: Insights from western shore of Admiralty Bay (King George Island, Antarctic)

In the rapidly changing climate, the biogeochemical behaviours of trace elements and Rare Earth Elements (REEs) in emerging periglacial environments assumes profound importance. This study provides pivotal insights into this dynamic by investigating the Antarctic's response to global climate change. The bedrock of King George Island is rich in REEs, with the presence of trace metals (TEs), with the highest concentrations of metals found in ornithogenic soil (∑REE 84.01-85.53 mg∙kg-1 dry weight). REEs in the studied soil, found mainly in igneous rocks, as is indicated by the positive correlation of these elements with sodium and calcium. The TEs released as a result of weathering are leached by water flowing down local watercourses to Admiralty Bay, as indicated by the decreasing results of ∑REE = 11.59 μg∙dm-3 in watercourse water, ∑REE = 1.62 μg∙dm-3 in watercourse pools and ∑REE = 0.66 μg∙dm-3 in the water of Admiralty Bay at the outlet of the watercourse. Water originating from the melting of snow on the glacier also carried REEs (∑REE = 0.14 μg∙dm-3), a fact which suggest the further influx of these elements from atmospheric deposition. The Prasiola crispa turned out to be the most susceptible to the accumulation of REEs (∑ 80.73 ± 5.05 μg g-1) and TEs, with the exception of chromium and zinc, whose concentrations were found to be at their highest in Deschampsia antarctica. In Usnea antarctica, Xanthoria candelaria, and Ceratodon purpureus and Politrichastrum alpinum, a dominant role in the accumulation of REEs was played by HREEs. The determined enrichment factor (EF) indicates that the soil cover is a source of REEs (EFAlgae for ∑REE = 5.07; EFLichen for ∑REE = 6.65; EFBryophyta for ∑REE = 5.04; EFVascular for ∑REE = 4.38), while Ni, As and Pb accumulated in plants may originate from other sources than the soil.

Mechanistic analysis of the sub chronic toxicity of La and Gd in Daphnia magna based on TKTD modelling and synchrotron X-ray fluorescence imaging

The release of lanthanides (Ln) into the environment has increased in recent decades due to their expanding applications in society. Studying their toxicity in aquatic ecosystems is urgent and challenging, with contradictory evidence presented in the literature. This study compared the biodistribution of La and Gd in Daphnia magna exposed to sub-chronic conditions and developed the first Toxicokinetic-Toxicodynamic (TKTD) model for these lanthanides with this model crustacean. D. magna were initially exposed for 7 days to concentrations close to the LC50 of La (2.10 mg L-1) and Gd (1.70 mg L-1). After exposure, half of the live daphnids were introduced in a clean media to allow depuration over 24 h, while the other organisms were directly prepared for synchrotron imaging measurements. Synchrotron X-ray fluorescence analysis revealed that metal distribution in the organisms was similar for both La and Gd, predominantly localized in the intestinal tract, even after the depuration process. These results indicate that ingested metal can adversely affect organisms under sub-chronic exposure conditions, highlighting the importance of using nominal concentrations as a more suitable indicator of metal bioavailability for risk assessment. The General Unified Threshold Model of Survival (GUTS) TKTD framework, in its reduced form (GUTS-RED), was developed for La and Gd using dissolved and nominal concentrations. D. magna were exposed for 7 days to concentrations from 0.5 to 5 mg L-1 of La or Gd and mortality monitored daily. The mechanistic model revealed a faster toxicokinetics for La than Gd and a higher toxicity for Gd than La in the organism. This study confirmed, despite similar chemical properties, the variation in both toxicity and toxicokinetics between these two metals.

Modulation of proteins by rare earth elements as a biotechnological tool

Although rare earth element (REE) complexes are often utilized in bioimaging due to their photo- and redox stability, magnetic and optical characteristics, they are also applied for pharmaceutical applications due to their interaction with macromolecules namely proteins. The possible implications induced by REEs through modification in the function or regulatory activity of the proteins trigger a variety of applications for these elements in biomedicine and biotechnology. Lanthanide complexes have particularly been applied as anti-biofilm agents, cancer inhibitors, potential inflammation inhibitors, metabolic elicitors, and helper agents in the cultivation of unculturable strains, drug delivery, tissue engineering, photodynamic, and radiation therapy. This paper overviews emerging applications of REEs in biotechnology, especially in biomedical imaging, tumor diagnosis, and treatment along with their potential toxic effects. Although significant advances in applying REEs have been made, there is a lack of comprehensive studies to identify the potential of all REEs in biotechnology since only four elements, Eu, Ce, Gd, and La, among 17 REEs have been mostly investigated. However, in depth research on ecotoxicology, environmental behavior, and biological functions of REEs in the health and disease status of living organisms is required to fill the vital gaps in our understanding of REEs applications.

Short-term influence of polytetrafluoroethylene micro/nano-plastics on the inhibition of copper and/or ciprofloxacin on the nitrifying sludge activities based on concentration addition and independent action models

Short-term influence of polytetrafluoroethylene micro/nano-plastics (PTFE-MPs/NPs) on the inhibition of copper (Cu2+) and/or ciprofloxacin (CIP) on the nitrifying sludge activities was explored based on concentration addition (CA) and independent action (IA) models. The half maximal inhibitory concentration (IC50) of Cu2+, CIP, PTFE-MPs (3 μm), and PTFE-NPs (800 nm) on the specific ammonium oxidation rate (SAOR) of nitrifying sludge was 64.57, 51.29, 102.33 and 93.33 mg L-1, respectively, while those on the specific nitrite oxidation rate (SNOR) of nitrifying sludge were 77.62, 32.36, 104.70 and 97.72 mg L-1, respectively. Among the five binary mixtures and two ternary mixtures composed by Cu2+, CIP, and/or PTFE-MPs/NPs, it was found that the two joint inhibitory actions from ternary mixtures on the SAOR and SNOR of the sludge showed time-dependent characteristics by analyzing of CA and IA models, while the five combined inhibitory effects from different binary mixtures did not all have time-dependent features. The two joint inhibition actions from diverse ternary mixtures on the SAOR at the exposure time of 60 min and on the SNOR at 90 min showed always concentration-dependent features, while the combined inhibitions with concentration-dependent characteristics had never been observed in the binary Cu2+ and PTFE-NPs mixtures at different exposure time. The Cu2+, CIP, and PTFE-MPs mixtures (or Cu2+, CIP, and PTFE-NPs mixtures) had synergistic actions on the SAOR at 90 min and antagonistic effects on the SNOR at 60 min based on CA and IA models, and these combined inhibitions did not exhibit concentration-dependent characteristics. In contrast, the joint inhibitory effects (on the SAOR and SNOR) with concentration-dependent features were found in the binary mixtures of CIP and PTFE-MPs at different exposure time, and the join inhibition changed from synergism to antagonism as the increasing concentration of mixed CIP and PTFE-MPs. This study provides novel perspectives for understanding the combined influence of plastic particles with different sizes, antibiotics, and heavy metals on the biological wastewater treatment process.

Evaluation of Holmium(III), Erbium(III), and Gadolinium(III) Accumulation by Cyanobacteria Arthrospira platensis Using Neutron Activation Analysis and Elements' Effects on Biomass Quantity and Biochemical Composition

Rare-earth elements are released into the aquatic environment as a result of their extensive use in industry and agriculture, and they can be harmful for living organisms. The effects of holmium(III), erbium(III), and gadolinium(III) when added to a growth medium in concentrations ranging from 10 to 30 mg/L on the accumulation ability and biochemical composition of Arthrospira platensis were studied. According to the results of a neutron activation analysis, the uptake of elements by cyanobacteria occurred in a dose-dependent manner. The addition of gadolinium(III) to the growth medium did not significantly affect the amount of biomass, whereas erbium(III) and holmium(III) reduced it up to 22% compared to the control. The effects of rare-earth elements on the content of proteins, carbohydrates, phycobiliproteins, lipids, β carotene, and chlorophyll a were evaluated. The studied elements had different effects on the primary biomolecule content, suggesting that holmium(III) and erbium(III) were more toxic than Gd(III) for Arthrospira platensis.

Hormesis and Low Toxic Effects of Three Lanthanides in Microfungi Isolated from Rare Earth Mining Waste in Northwestern Russia

The low-dose toxicity of chloride and nitrate salts of three lanthanides (La, Ce and Nd) was tested on six microfungal species. Five of them (Geomyces vinaceus, Aspergillus niveoglaucus, Pseudogymnoascus pannorum, Penicillium simplicissimum and Umbelopsis isabellina) were isolated from the loparite ore tailings on the Kola Peninsula, northwestern Russia. Sydowia polyspora was a control strain. In the case of nitrate salts, the toxicity of REEs to four of six microorganisms was significantly (p < 0.5) lower compared to chloride salts. In this case, nitrates can play the role of exogenous nutrients, compensating for the toxic effect of REEs. Interestingly, U. isabellina only showed an opposite response, indicating the highest toxicity of nitrate (IC5 = 9-20 mg/L) REEs' salts compared to chlorides (IC5 = 80-195 mg/L) at low concentration levels. In addition, treatment with lanthanides showed a "hormesis effect" on fungal growth with stimulation at low doses and inhibition at high doses. However, U. isabellina and S. polyspora demonstrated the absence of hormetic response under the treatment of REEs' nitrate salt. Taking into account the specific hormetic responses and high tolerance of P. simplicissimum and U. isabellina to lanthanides, our findings may be useful in the assessment of the potential application of the selected fungi to bioremediation and REE bioleaching.

Long-term effect of light rare earth element neodymium on Anammox process

During the mining of rare earth minerals, the application of neodymium-containing manures, and the treatment of spent neodymium iron boron magnet, the generation of ammonia wastewater containing neodymium is increasing. Thus, the effects of neodymium (Nd(III)) on anaerobic ammonium oxidation (Anammox) were investigated from the aspects of performance, kinetics, statistics, microbial community and sludge morphology, and the recovery strategy of EDTA-2Na wash was discussed. The nitrogen removal efficiency of the Anammox reactor decreased significantly and eventually collapsed at the Nd(III) dosing levels of 20 and 40 mg L-1, respectively. And the toxicity of Nd(III) to AnAOB was determined by the amount internalized into the cells. The EDTA-2Na wash successfully increased the total nitrogen removal rate (TNRR) of Nd(III)-inhibited Anammox to 41.60% of its initial value within 30 days, and the modified Boltzmann model accurately simulated this recovery process. The transient and extended effects of Nd(III), self-recovery, and EDTA-2Na wash on Anammox were effectively assessed using a one-sample t-test. 16S rRNA gene sequencing indicated that Nd(III) remarkably decreased the relative abundance of Planctomycetes and Candidatus Brocadia. The scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS) revealed crystal-like neodymium particles on the surface of Anammox sludge. The above-mentioned results demonstrate that the concentration of Nd(III) should be below the toxicity threshold (20 mg L-1) when treating ammonia wastewater containing neodymium by Anammox, and also emphasize the importance of an appropriate recovery strategy.

Determination of the distribution of rare earth elements La and Gd in Daphnia magna via micro and nano-SXRF imaging

While our awareness of the toxicity of rare earth elements to aquatic organisms increases, our understanding of their direct interaction and accumulation remains limited. This study describes the acute toxicity of lanthanum (La) and gadolinium (Gd) in Daphnia magna neonates and discusses potential modes of action on the basis of the respective patterns of biodistribution. Ecotoxicological bioassays for acute toxicity were conducted and dissolved metal concentrations at the end of the tests were determined. The results showed a significant difference in nominal EC50 (immobility) between La (>30 mg L-1) and Gd (13.93 (10.92 to 17.38) mg L-1). Daphnids that were then exposed to a concentration close to the determined EC50 of Gd (15 mg L-1, nominal concentration) for 48 h and 72 h were studied by synchrotron micro and nano-X-ray fluorescence to evaluate the biodistribution of potentially accumulated metals. X-ray fluorescence analyses showed that La was mainly found in the intestinal track and appeared to accumulate in the hindgut. This accumulation might be explained by the ingestion of solid La precipitates formed in the media. In contrast, Gd could only be detected in a small amount, if at all, in the intestinal tract, but was present at a much higher concentration in the tissues and became more pronounced with longer exposure time. The solubility of Gd is higher in the media used, leading to higher dissolved concentrations and uptake into tissue in ionic form via common metal transporting proteins. By studying La and Gd biodistribution in D. magna after an acute exposure, the present study has demonstrated that different uptake pathways of solid and dissolved metal species may lead to different accumulation patterns and toxicity.

Cytotoxicity and hemolysis of rare earth ions and nanoscale/bulk oxides (La, Gd, and Yb): Interaction with lipid membranes and protein corona formation

The widespread application of rare earth elements (REEs) has raised concerns about their potential release into the environment and subsequent ingestion by humans. Therefore, it is essential to evaluate the cytotoxicity of REEs. Here, we investigated the interactions between three typical REEs (La, Gd, and Yb) ions as well as their nanometer/μm-sized oxides and red blood cells (RBCs), a plausible contact target for nanoparticles when they enter the bloodstream. Hemolysis of REEs at 50-2000 μmol L^-1 was examined to simulate their cytotoxicity under medical or occupational exposure. We found that the hemolysis due to the exposure of REEs was highly dependent on their concentration, and the cytotoxicity followed the order of La³⁺ > Gd³⁺ > Yb³⁺. The cytotoxicity of REE ions (REIs) is higher than REE oxides (REOs), while nanometer-sized REO caused more hemolysis than that μm-sized REO. The production of reactive oxygen species (ROS), ROS quenching experiment, as well as the detection of lipid peroxidation, confirmed that REEs causes cell membrane rupture by ROS-related chemical oxidation. In addition, we found that the formation of a protein corona on REEs increased the steric repulsion between REEs and cell membranes, hence mitigating the cytotoxicity of REEs. The theoretical simulation indicated the favorable interaction of REEs with phospholipids and proteins. Therefore, our findings provide a mechanistic explanation for the cytotoxicity of REEs to RBCs once they have entered the blood circulation system of organisms.

Molecular changes in phenolic compounds in Euglena gracilis cells grown under metal stress

Metal presence in the aquatic ecosystem has increased and diversified over the last decades due to anthropogenic sources. These contaminants cause abiotic stress on living organisms that lead to the production of oxidizing molecules. Phenolic compounds are part of the defense mechanisms countering metal toxicity. In this study, the production of phenolic compounds by Euglena gracilis under three different metal stressors (i.e. cadmium, copper, or cobalt) at sub-lethal concentration was assessed using an untargeted metabolomic approach by mass spectrometry combined with neuronal network analysis (i.e. Cytoscape). The metal stress had a greater impact on molecular diversity than on the number of phenolic compounds. The prevalence of sulfur- and nitrogen-rich phenolic compounds were found in Cd- and Cu-amended cultures. Together these results confirm the impact of metallic stress on phenolic compounds production, which could be utilized to assess the metal contamination in natural waters.

Tolerance of Rare-Earth Elements in Extremophile Fungus Umbelopsis isabellina from Polar Loparite Ore Tailings in Northwestern Russia

In this study, extremophile fungal species isolated from pure loparite-containing sands and their tolerance/resistance to the lanthanides Ce and Nd were investigated. The loparite-containing sands were collected at the tailing dumps of an enterprise developing a unique polar deposit of niobium, tantalum and rare-earth elements (REEs) of the cerium group: the Lovozersky Mining and Processing Plant (MPP), located in the center of the Kola Peninsula (northwestern Russia). From the 15 fungal species found at the site, one of the most dominant isolates was identified by molecular analysis as the zygomycete fungus Umbelopsis isabellina (GenBank accession no. OQ165236). Fungal tolerance/resistance was evaluated using different concentrations of CeCl₃ and NdCl₃. Umbelopsis isabellina exhibited a higher degree of tolerance/resistance to cerium and neodymium than did the other dominant isolates (Aspergillus niveoglaucus, Geomyces vinaceus and Penicillium simplicissimum). The fungus began to be inhibited only after being exposed to 100 mg L^-1 of NdCl₃. The toxic effects of Ce were not observed in fungus growth until it was subjected to 500 mg∙L^-1 of CeCl₃. Moreover, only U. isabellina started to grow after extreme treatment with 1000 mg∙L^-1 of CeCl₃ one month after inoculation. This work indicates, for the first time, the potential of Umbelopsis isabellina to remove REEs from the loparite ore tailings, making it a suitable candidate for the development of bioleaching methods.

Acute toxicity of single and combined rare earth element exposures towards Daphnia similis

The increasing use of Rare Earth Elements (REE) in emerging technologies, medicine and agriculture has led to chronic aquatic compartment contamination. In this context, this aimed to evaluate the acute toxic effects of lanthanum (La), neodymium (Nd) and samarium (Sm), as both single and binary and ternary mixtures on the survival of the microcrustacean Daphnia similis. A metal solution medium with (MS) and without EDTA and cyanocobalamin (MSq) as chelators was employed as the assay dilution water to assess REE bioavailability effects. In the single exposure experiments, toxicity in the MS medium decreased following the order La > Sm > Nd, while the opposite was noted for the MSq medium, which was also more toxic than the MS medium. The highest MS toxicity was observed for the binary Nd + La (1:1) mixture (EC₅₀ 48 h of 11.57 ± 1.22 mg.L^-1) and the lowest, in the ternary Sm + La + Nd (2:2:1) mixture (EC₅₀ 48 h 41.48 ± 1.40 mg.L^-1). The highest toxicity in the MSq medium was observed in the single assays and in the binary Sm + Nd (1:1) mixture (EC₅₀ 48 h 10.60 ± 1.57 mg.L^-1), and the lowest, in the ternary Sm + La + Nd (1:2:2) mixture (EC₅₀ 48 h 36.76 ± 1.54 mg.L^-1). Concerning the MS medium, 75 % of interactions were additive, 19 % antagonistic, and 6 % synergistic. In the MSq medium, 56 % of interactions were synergistic and 44 % additive. The higher toxicity observed in the MSq medium indicates that the absence of chelators can increase the concentrations of more toxic free ions, suggesting that the MS medium should be avoided in REE assays. Additive interactions were observed in greater or equivalent amounts in both media and were independent of elemental mixture ratios. These findings improve the understanding of environmental REE effects, contributing to the establishment of future guidelines and ecological risk calculations.

Molecular Characterization of Distinct Fungal Communities in the Soil of a Rare Earth Mining Area

The exploitation of ion-absorbed rare earth elements (REEs) has caused serious ecological destruction and environmental pollution. Effects on soil fungal structure and diversity exerted by mining activities are usually ignored, although fungus is one of the most important components in soil ecosystems. In the present research, quantitative polymerase chain reaction (qPCR) and high-throughput Illumina MiSeq sequencing were conducted to characterize fungal community composition and structure in soil of a rare earth mining area after in situ leaching. Statistical analyses, network, and FUNGuild were used to conduct in-depth analyses. Ascomycota, Basidiomycota, and Glomeromycota were the most abundant phyla in the mining soils. Fungal community structures were stable after leaching practice, but nutrition contents (organic matter, TC, and TN) significantly and positively contributed to fungal abundances and diversities. Saprotrophs in phyla Ascomycota and Basidiomycota were the dominant fungal trophic mode, and they played critical roles in nutrient cycling, transformation processes, and reducing REE toxicity. Symbiotrophs of phyla Glomeromycota contributed to soil aggregation and slowing down nutrient losses after in situ leaching practice. In addition, fungi could regulate the interactions between species to resist the harsh environment of REE toxicity or ammonium caused by in situ leaching practice.

Genotoxicity in Artemia spp.: An old model with new sensitive endpoints

Artemia spp. represent models species widely used in ecotoxicological studies due to its simple and fast manipulation in laboratory conditions that makes this crustacean well adaptable to several methodological approaches. Although cysts hatching, swimming behavior, reproductive success and mortality are the main endpoints used for the determination of toxicity, the detection of slight alterations induced by certain substances found at low concentrations in the environment may require more sensitive biomarkers. For this reason, the identification of DNA or chromosomal damages has been proposed as an additional and appreciable endpoint for the ecotoxicological assessment of environmental chemicals. Concerning Artemia models, only few studies indicated that the exposure to organic and inorganic compounds (i.e. pesticides, nanoparticles, bacterial products or heavy metals) can reduce the survival and fitness through the onset of DNA breaks or the dysregulation of key genes. In contrast, literature research revealed a lot of works primarily focusing on the mortality and hatching rates of Artemia nauplii and cysts despite the well-known low sensitivity of these species. The present review reports the current state of knowledge concerning the effects induced by various chemicals, including organic and inorganic compounds, on the common parameters and genotoxicity in both Artemia franciscana and Artemia salina. Advantages and limitations of Artemia spp. models in eco-toxicological investigations together with the most used classes of compounds are briefly discussed. Moreover, a mention is also addressed to scarce availability of literature data focusing on genotoxic effects and the great reliability of molecular approaches observed in this poorly sensitive model organism. Thus, the opportunity to take advantage of genotoxic analyses has also been highlighted, by suggesting this approach as a novel endpoint to be used for the eco-toxicological assessment of several stressors.

Untangling microbial diversity and assembly patterns in rare earth element mine drainage in South China

Ion-adsorption rare earth element (REE) deposits are the main reservoirs of REEs worldwide, and are widely exploited in South China. Microbial diversity is essential for maintaining the performance and function of mining ecosystems. Investigating the ecological patterns underlying the REE mine microbiome is essential to understand ecosystem responses to environmental changes and to improve the bioremediation of mining areas. We applied 16S rRNA and ITS gene sequence analyses to investigate the composition characteristics of prokaryotic (bacteria, archaea) and fungal communities in a river impacted by REE acid mine drainage (REE-AMD). The river formed a unique micro-ecosystem, including the main prokaryotic taxa of Proteobacteria, Acidobacteria, Crenarchaeota, and Euryarchaeota, as well as the main fungal taxa of Ascomycota, Basidiomycota, and Chytridiomycota. Analysis of microbial diversity showed that, unlike prokaryotic communities that responded drastically to pollution disturbances, fungal communities were less affected by REE-AMD, but fluctuated significantly in different seasons. Ecological network analysis revealed that fungal communities have lower connectivity and centrality, and higher modularity than prokaryotic networks, indicating that fungal communities have more stable network structures. The introduction of REE-AMD mainly reduced the complexity of the community network and the number of keystone species, while the proportion of negative prokaryotic-fungal associations in the network increased. Ecological process analysis revealed that, compared to the importance of environmental selection for prokaryotes, stochastic processes might have contributed primarily to fungal communities in REE mining areas. These findings confirm that the different assembly mechanisms of prokaryotic and fungal communities are key to the differences in their responses to environmental perturbations. The findings also provide the first insights into microbiota assembly patterns in REE-AMD and important ecological knowledge for the formation and development of microbial communities in REE mining areas.

Gadolinium Accumulation and Toxicity on In Vitro Grown Stevia rebaudiana: A Case-Study on Gadobutrol

Gadolinium-based contrast agents are molecular complexes which are extensively used for diagnostic purposes. Apart from their tremendous contribution to disease diagnostics, there are several issues related to their use. They are extremely stable complexes and potential contaminants of surface and ground waters, an issue which is documented worldwide. The irrigation of fields with contaminated surface waters or their fertilization with sludge from wastewater treatment plants can lead to the introduction of Gd into the human food supply chain. Thus, this study focused on the potential toxicity of Gd on plants. For this purpose, we have studied the molecular effects of gadobutrol (a well-known MRI contrast agent) exposure on in vitro-grown Stevia rebaudiana. The effects of gadobutrol on plant morphology, on relevant plant metabolites such as chlorophylls, carotenoids, ascorbic acids (HPLC), minerals (ICP-OES), and on the generation of free radical species (MDA assay and EPR) were assessed. Exposures of 0.01, 0.05, 0.1, 1, and 3 mM gadobutrol were used. We found a correlation between the gadobutrol dose and the plant growth and concentration of metabolites. Above the 0.1. mM dose of gadobutrol, the toxic effects of Gd+3 ions became significant.

Assessment of the toxicity of a mixture of five rare earth elements found in aquatic ecosystems in Hydra vulgaris

Rare earth elements (REEs) are considered critical elements for technology and their extraction through mining activities is expected to increase in the future. Due to their chemical similarities, they often co-occur in minerals and thus their ecotoxicity should be assessed as a group/family. However, the available ecotoxicological studies focused mainly on the evaluation of the potential toxicological impacts of individual REEs rather than their mixtures. The aim of this study was therefore to evaluate the toxicity of a representative mixture of five REEs (La, Ce, Pr, Nd and Sm) spanning environmentally relevant concentrations ranging from 0.05X (29 µg REEs L^-1) to 5X (2926 µg REEs L^-1) to the test organism, Hydra vulgaris, at the morphological, reproductive and regenerative levels. The data showed that lethality occurred at concentrations near (2.5 fold) to those inducing sublethal effects after chronic exposure of 7 days. The mixture affected reproduction and head regeneration and even lethality at concentrations even below those reported at environmental concentration (0.5X = 293 µg REEs L^-1) in lakes. This suggests that REEs concentrations found in lakes near mining activities could disrupt regeneration and impair embryonic development. Our data also revealed that combining the 5 REEs results in an antagonistic effect, suggesting that those elements share the same receptor and that low molecular weight and high radius elements (approaching iron) were less toxic. Taken together, hydra could be used as a sensitive model organism for the assessment of aquatic ecotoxicological risks of REE mixtures but further analyses of biochemical and gene expressions should improve our understanding of the long-term effects of REEs mixtures.

Water quality criteria for lanthanum for freshwater aquatic organisms derived via species sensitivity distributions and interspecies correlation estimation models

The increasing exploitation and application of rare earth elements (REEs) may induce hazardous risks to freshwater aquatic organisms. Due to the lack of water quality criteria (WQC) and sufficient reliable toxicity data, little information is available on the ecological risk of REEs in surface water. In this study, lanthanum (La) toxicity data were collected from published toxicological studies, and the data quality was assessed using a toxicological data reliability assessment tool. To obtain more toxicity data, Daphnia magna, Cyprinus carpio, and Dania rerio embryos were selected as surrogate species, and an interspecies correlation estimation (ICE) model was used to predict the toxicity of La for untested species. The species sensitivity distributions (SSDs) of La toxicity and WQC were investigated. Differences were observed in the hazardous concentrations for 5% of species (HC₅), but no statistically significant differences were noted in the SSD curves between the measured acute toxicity data and the predicted data. For the SSDs constructed from the measured toxicity data, the ICE-predicted toxicity data and all acute data supplemented with the ICE-predicted data, the acute WQC values of La were 88, 1022 and 256 μg/L, respectively. According to the SSD and corresponding HC₅ of chronic toxicity data, the chronic WQC was 14 μg/L. The results provide a scientific reference for establishing WQC for freshwater aquatic organisms and ecological risk assessments of REEs.

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.

The toxicity of neodymium and genome-scale genetic screen of neodymium-sensitive gene deletion mutations in the yeast Saccharomyces cerevisiae

The wide usage of neodymium (Nd) in industry, agriculture, and medicine has made it become an emerging pollutant in the environment. Increasing Nd pollution has potential hazards to plants, animals, and microorganisms. Thus, it is necessary to study the toxicity of Nd and the mechanism of Nd transportation and detoxification in microorganisms. Through genome-scale screening, we identified 70 yeast monogene deletion mutations sensitive to Nd ions. These genes are mainly involved in metabolism, transcription, protein synthesis, cell cycle, DNA processing, protein folding, modification, and cell transport processes. Furthermore, the regulatory networks of Nd toxicity were identified by using the protein interaction group analysis. These networks are associated with various signal pathways, including calcium ion transport, phosphate pathways, vesicular transport, and cell autophagy. In addition, the content of Nd ions in yeast was detected by an inductively coupled plasma mass spectrometry, and most of these Nd-sensitive mutants showed an increased intracellular Nd content. In all, our results provide the basis for understanding the molecular mechanisms of detoxifying Nd ions in yeast cells, which will be useful for future studies on Nd-related issues in the environment, agriculture, and human health.

Mixture toxicity of TiO2 NPs and tetracycline at two trophic levels in the marine ecosystem: Chlorella sp. and Artemia salina

Increasing usage of both nanomaterials and pharmaceuticals and their unabated release to the marine ecosystem pose a serious concern nowadays. The toxicity of the mixture of TiO₂ NPs and tetracycline (TC) in the marine species are not very well covered in prior literature. The current study explores the joint toxic effects of TiO₂ NPs and TC in a simulated marine food chain: Chlorella sp. and Artemia salina. Chlorella sp. was interacted with pristine TiO₂ NPs (0.05, 05, and 5 mg/L), TC (0.5 mg/L), and their combinations for 48 h. The toxicity induced in Chlorella sp. by pristine TiO₂ NPs through oxidative stress and chloroplast damage was not significantly changed in the presence of TC. Principal component analysis for the toxicity parameters revealed a strong association between growth inhibition and adsorption/internalization. In the second trophic level (A. salina), the waterborne exposure of TC additively increased the toxicity of TiO₂ NPs. Both adsorption and degradation played a major role in the removal of TC from the suspension, resulting in additive toxic effects in both Chlorella sp. and A. salina. Compared to the waterborne exposure, the foodborne exposure of TiO₂ NPs and TC induced lesser toxic effects owing to reduced uptake and accumulation in A. salina. Biomagnification results indicate that the dietary transfer of TiO₂ NPs and TC does not pose a serious environmental threat in this two-level marine food chain.

Transfer of La, Ce, Sm and Yb to alfalfa and ryegrass from spiked soil and the role of Funneliformis mosseae

Rare earth elements (REEs) are widely used in high-tech industries, and REE waste emissions have become a concern for ecosystems, food quality and human beings. Arbuscular mycorrhizal fungi (AMF) have repeatedly been reported to alleviate plant stress in metal-contaminated soils. To date, little information is available concerning the role of AMF in REE-contaminated soils. We recently showed that there was no transfer of Sm to alfalfa by Funneliformis mosseae, but only a single REE was examined, while light and heavy REEs are present in contaminated soils. To understand the role of AMF on the transfer of REEs to plants, we carried out an experiment using alfalfa (Medicago sativa) and ryegrass (Lolium perenne) in compartmented pots with separate bottom compartments that only were accessible by F. mosseae fungal hyphae. The bottom compartments contained a mixture of four REEs at equal concentrations (La, Ce, Sm and Yb). The concentration of REEs in plants was higher in roots than in shoots with higher REE soil-root than root-shoot transfer factors. Moreover, significantly higher light-REEs La and Ce were transferred to ryegrass shoots than Sm and the heavy-REE Yb, but this was not observed for alfalfa. Alfalfa dry weight was significantly increased by F. mosseae inoculation, but not ryegrass dry weight. For both plant species, there was significantly higher P uptake by the mycorrhizal plants than the nonmycorrhizal plants, but there was no significant transfer of La, Ce, Sm or Yb to alfalfa and ryegrass roots or shoots due to F. mosseae inoculation.

Rare earth elements biomonitoring using the mussel Mytilus galloprovincialis in the Portuguese coast: Seasonal variations

Increased Rare earth elements (REE) usage culminates in discharges into the environment. Mussels have been chosen as models in biomonitoring, hence, REE concentrations in Mytilus galloprovincialis from six locations on the Portuguese coast were accessed to determine natural concentrations and possible linkage to local ecosystem characteristics and temporal variations, by determining them in distinct seasons (autumn and spring). Samples from Porto Brandão (located on the south bank of the Tagus estuary) exhibited the highest REE concentrations, while mussels from Aljezur (the southernmost point on the Portuguese coast) exhibited the lowest, in both seasons. Overall, ∑REE concentration was greater in the spring. LREE enrichment relative to HREE occurs and a negative Ce and Eu anomaly was observed. This study constitutes the first assessment of REE composition on this model species in the Portuguese coast, in two distinct seasons and contributes to a better understanding of REE uptake for future biomonitoring studies.

Sources, distribution and effects of rare earth elements in the marine environment: Current knowledge and research gaps

Rare earth elements and yttrium (REY) are critical elements for a wide range of applications and consumer products. Their growing extraction and use can potentially lead to REY and anthropogenic-REY chemical complexes (ACC-REY) being released in the marine environment, causing concern regarding their potential effects on organisms and ecosystems. Here, we critically review the scientific knowledge on REY sources (geogenic and anthropogenic), factors affecting REY distribution and transfer in the marine environment, as well as accumulation in- and effects on marine biota. Further, we aim to draw the attention to research gaps that warrant further scientific attention to assess the potential risk posed by anthropogenic REY release. Geochemical processes affecting REY mobilisation from natural sources and factors affecting their distribution and transfer across marine compartments are well established, featuring a high variability dependent on local conditions. There is, however, a research gap with respect to evaluating the environmental distribution and fate of REY from anthropogenic sources, particularly regarding ACC-REY, which can have a high persistence in seawater. In addition, data on organismal uptake, accumulation, organ distribution and effects are scarce and at best fragmentary. Particularly, the effects of ACC-REY at organismal and community levels are, so far, not sufficiently studied. To assess the potential risks caused by anthropogenic REY release there is an urgent need to i) harmonise data reporting to promote comparability across studies and environmental matrices, ii) conduct research on transport, fate and behaviour of ACC-REY vs geogenic REY iii) deepen the knowledge on bioavailability, accumulation and effects of ACC-REY and REY mixtures at organismal and community level, which is essential for risk assessment of anthropogenic REY in marine ecosystems.

Kinetics and equilibrium study for the biosorption of lanthanum by Penicillium simplicissimum INCQS 40,211

Lanthanum (La) is a light rare-earth element that plays an essential role in manufacturing technological products, clean technologies, medical products, electron cathodes, scintillators, fluorescent lamps, and fertilizers. This study is the first investigation of La³⁺ biosorption using inactive lyophilized biomass from Penicillium simplicissimum INCQS 40,211. The maximum sorption capacity (q_max) for P. simplicissimum was 7.81 mg g^-1. La ³⁺ biosorption followed the Freundlich model, where the biosorption system possibly multilayer coverage of P. simplicissimum by lanthanum ions. The kinetic data for the adsorption process obeyed a pseudo-second-order (R ² > 0.92), indicating chemical sorption. The results indicated that inactive lyophilized biomass from Penicillium simplicissimum INCQS 40211are an excellent candidate for removing light rare-earth elements from aquatic environments.

Dynamic interaction processes of rare earth metal mixtures in terrestrial organisms interpreted by toxicokinetic and toxicodynamic model

Despite the progress in explanation of mixture toxicity of rare earth elements (REEs), a large knowledge gap still exists in interpreting their mixed effects from a dynamic perspective. Here, we investigated the effects of La-Ce mixtures in Enchytraeus crypticus at different exposure times. The single and mixture toxicity of La and Ce increased with time, as reflected by the reduced LC50/MT50 values. With concentration addition as the reference model, the interactions between La and Ce were quantified by MIXTOX modelling tool, showing a time-dependent pattern with antagonistic effect after 1 and 2 d but additive effects afterwards. The dynamic accumulation and toxicity of La/Ce in organisms exposed to REE mixtures was fitted using a process-based toxicokinetic and toxicodynamic (TK-TD) model to unravel how the elements interacted. Generally, the estimated uptake, elimination, and damage rate constants of La/Ce declined with increasing level of each other, suggesting inhibited uptake and subsequently reduced toxicity of La/Ce due to competition effect. The interplay of La and Ce in TK and TD processes seemed responsible for the observed antagonism. Our study showed that mixture toxicity and interaction of REEs are time-dependent processes and application of TK-TD model may provide more insight into this dynamic effect.

Toxicity evaluation of nano-TiO2 in the presence of functionalized microplastics at two trophic levels: Algae and crustaceans

The rising use of contaminants such as nanoparticles and microplastics has taken a heavy toll on the marine environment. However, their combined toxic effects on the species across various trophic levels remain quite unexplored. The aim of this study was to explore the effects of three surface-functionalized (carboxylated, plain, and aminated) polystyrene microplastics on nano-TiO₂ toxicity across two trophic levels containing Chlorella sp. as the prey and Artemia salina as the predator. The experiments carried out on Chlorella sp. include the toxicity assessment, oxidative stress determination, and uptake of nano-TiO₂ (both in the presence and absence of microplastics). Results revealed that the aminated and plain polystyrene microplastics enhanced nano-TiO₂ toxicity, while carboxylated microplastics decreased the toxic effects in Chlorella sp. On the other hand, toxicity assessment in Artemia salina was carried out using two different modes of exposure: aqueous and dietary routes. The aqueous route involving the direct exposure of nano-TiO₂ and microplastics indicated greater toxicity, uptake, and accumulation in Artemia salina than the dietary route of exposure. Since dietary exposure decreased the toxicity, uptake, and accumulation of nano-TiO₂, no change (p > 0.05) in the biomagnification factors of nano-TiO₂ was noted for all the test concentrations of nano-TiO₂ combined with and without microplastics. The computed values were less than 1, indicating negligible transfer of nano-TiO₂ from Chlorella sp. to Artemia salina. Overall, the study highlights the two-level trophic toxicity and the transfer potential of nano-TiO₂ under the influence of different microplastics.

Do essential elements (P and Fe) have mitigation roles in the toxicity of individual and binary mixture of yttrium and cerium to Triticum aestivum?

Essential elements can affect the bioavailability, uptake, and toxicity of metals. However, hardly any research has focused on the roles of essential elements on the toxicity of rare earth metals. Here we examined how P and Fe modified the individual and binary toxicity of Y and Ce to Triticum aestivum, respectively. Standard root elongation tests were used to quantify the toxicity of both single and binary mixtures at three levels of P addition (1, 5, and 10 μM) and Fe addition (0.1, 1, and 5 mM). Our results showed that both P and Fe can alleviate individual toxicity of Y or Ce irrespective of the dose indicators as suggested by the enhanced EC50 values. Both P and Fe might mitigate Y/Ce toxicity by limiting Y/Ce uptake into roots and improving nutritional status of wheats, whereas P can also decrease free Y/Ce ion activities in the exposure media. As for the mixture toxicity of Y and Ce, only improved P, but not Fe can exhibit approximately additive mixture toxicity, which can be adequately predicted by the simple Concentration Addition model. Our results suggested the important roles of P and Fe in assessing Y and Ce toxicity accurately.

Ecotoxicity Responses of the Macrophyte Algae Nitellopsis obtusa and Freshwater Crustacean Thamnocephalus platyurus to 12 Rare Earth Elements

Due to unique chemical properties, rare earth elements (REEs) are increasingly used in versatile technological applications. They are considered emerging environmental contaminants, since they become mobile instead of being bound in rocks. At present, the information on REE effects to aquatic biota is scarce and contradictory. This study aims to explore the ecotoxicity of 11 lanthanides (La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Er, and Lu) and yttrium (Y) to charophyte algae Nitellopsis obtusa and microcrustaceans Thamnocephalus platyurus. Median lethal concentrations (LC50) were assessed in characean cells at 8, 12, 16, 20, and 24 days of exposure, and 24-h LC50s were determined in shrimps. According to the EU−Directive 93/67/EEC hazard classification scheme and 24-day LC50 values generated for N. obtusa, REE effects were assigned from “harmful” to “very toxic” (Gd), while 24-h LC50s for T. platyurus were classified as “harmful” or “toxic” (based on nominal concentrations) and as “toxic” or “very toxic” (based on REE free ion concentrations calculated with CHEAQS Next software). The data obtained for algae showed correlations with the REE atomic numbers (r = −0.68, p < 0.05) and ionic radii (r = 0.65, p < 0.05) at the most extended 24-day exposure only. The analysis of the trends of concentration−response (c–r) curves obtained at increasing exposure durations (8–24 days), alongside the 24-day LC50s ranging within almost two orders of magnitude, allowed a more-toxic heavy REE group to be distinguished, and somewhat different modes REE actions to be envisioned for N. obtusa.