The demand for lanthanides (LN) has seen a steady increase and is anticipated to continue to grow. Due to their unique properties, they have become essential in key components of new technologies, such as batteries, wind turbines, electronic components and other devices needed to facilitate energy transition away from fossil fuels. These elements are also increasingly used in a range of new technologies, including medical applications and telecommunication. In this context, the concentrations of lanthanides are expected to increase in freshwater environments (Gwenzi et al., 2018). Our limited knowledge about the risk that they pose to organisms limits our ability to develop guidelines for environmental protection. Research on this issue has so far been hindered by the peculiar properties of lanthanides, that tend to form insoluble precipitates when added in standard ecotoxicological test media (Blinova et al., 2018). This and other challenges of studying lanthanide toxicity were addressed in this in-depth study that leaves few stones unturned. 

The study by Vignati and colleagues (2024) is the first to investigate the acute toxicity of all LN, with the exception of promethium, a radioactive element, on Daphnia magna, a model test species, following the ISO 6341 (2012) norm. The authors designed their study to generate data useable for the development of risk assessment guidelines for the LN series and to generate data-based recommendations for future studies on LN ecotoxicity. They exposed daphnids to nine to ten dilutions of all tested LN in a medium and carried out 48-hour acute immobilization assays. Initial and final pH was measured along with concentrations of LN in the test solutions sampled at various intervals by ICP-MS. This data allowed calculation of LN speciation, performed using VisualMinteq software. Effect concentrations were also calculated using different metrics based on initial (nominal), time-averaged or modelled LN3+ exposure concentrations.

In their multi-faceted investigation, the authors reported several observations that clearly contribute to a better understanding of the ecotoxicity of LN to aquatic organisms and provide useful advice for future studies, briefly summarized here. Proper characterization of exposure concentrations is a key in any ecotoxicological study. Their project shows that even for a short, 48 h exposure, LN concentrations decrease due to a combination of precipitation and, possibly, adsorption. The concentration decrease was inversely proportional to the LN atomic mass, which may reduce the analytical requirements for future studies using the same test medium. The addition of LN to the test medium also modified pH and a detailed hypothesis is formulated to explain this phenomenon that has implications for ecotoxicological endpoints. Conclusions on LN ecotoxicity drawn in this study are based on experimental data and on extensive thermodynamic speciation modeling. The values of EC50 presented in the study varied by several order of magnitude depending on the chosen exposure metric, underscoring the urgent need for consensus-building on this issue across the research community. The authors also provide a comparison of their conclusions on EC50 values for daphnids with the limited data available in the literature, further validating their data with cautions carefully laid out about experimental design. The paper concludes with a list of seven caveats that should be considered both for regulators who will want to use the data presented in the paper for environmental LN concentrations regulations and for future studies. These caveats highlight the importance of considering LN speciation and chemical behavior during ecotoxicity assays, their influence on exposure concentrations, and their importance for risk assessment. They also reiterate that since LN concentrations in filtered water collected in the field are not directly comparable to EC50 values derived from laboratory studies using total or free LN3+ concentrations, an effort must be made to harmonize the methods of LN concentration measurements in field and laboratory studies. Overall, this paper may be one of the most rigorous studies in the current literature about LN ecotoxicity in freshwater systems. In its approach, it sets a precedent for future studies aiming at generating EC50 values or other toxicological endpoints of inorganic contaminants. The paper, carefully reviewed by Carrie Rickwood and by an anonymous reviewer, is a major contribution towards our understanding of LN ecotoxicity.
 
References
Blinova, I., Lukjanova, A., Muna, M., Vija, H., & Kahru, A. (2018). Evaluation of the potential hazard of lanthanides to freshwater microcrustaceans. Sci. Tot. Environ. 642 :1100-1107. https://doi.org/10.1016/j.scitotenv.2018.06.155

Gwenzi, W., Mangori, L.,  Danha, C., Chaukura, N, Dunjana, N., Sanganyado, E. (2018). Sources, behaviour, and environmental and human health risks of high technology rare earth elements as emerging contaminants. Sci. Total Environ., 636:299-313. https://doi.org/10.1016/j.scitotenv.2018.04.235

ISO. (2012). Water quality — Determination of the inhibition of the mobility of Daphnia magna Straus (Cladocera, Crustacea) — Acute toxicity test (norm 6341). https://www.iso.org/standard/54614.html

Vignati, D.A.L., Martin, L.A., Poirier, L., Zalouk-Vergnoux, A., Fouque, C., Clément, B., Hissler, C., Cossu-Leguille, C. (2024). Ecotoxicity of lanthanides to Daphnia magna: insights from elemental behavior and speciation in a standardized test medium. Ver.3 peer-reviewed and recommended by Peer Community In Ecotoxicology and Environmental Chemistry. https://hal.science/LIEC-UL/hal-04302491v3

The overall pollution of air, water, and soil is currently recognized as one of the five main drivers of biodiversity loss (IPBES 2019). Among chemicals, pesticides play a significant role in this global crisis, as recently re-assessed at the scale of France (Pesce et al. 2023). In this context, although parent molecules are subject to national and international regulations, based on a priori ecological risk assessment (e.g., REACH) as well as monitoring in some environments (see e.g., pesticides classified in the priority list of substances by the Water Frame Directive), pesticide metabolites are rarely considered. In the case of the widely used herbicide glyphosate, a particular concern is rising about its primary metabolite, aminomethylphosphonic acid (AMPA), due to its persistence and overlooked toxicity. 

Amphibians are the most threatened class of vertebrates on earth, with two in every five species considered threatened with extinction (IUCN Red List). While this overall decline has multiple causes, the contribution of pesticides is suspected to be significant in some regions.

In this context, Tartu et al. (2024) studied the effects of AMPA on the gut microbiota of the spined toad, Bufo spinosus. This work complements a previous study which showed embryo mortality, oxidative stress, deformities at hatching, and delayed development (Tartu et al. 2022). Using a common garden experiment based on populations from contrasted habitats (agricultural vs woodland, same as in the previous study), the authors captured breeding pairs and collected the eggs laid in the laboratory. These were exposed to 0.4 µg/L AMPA during embryonic and larval development. Individual microbiota was analysed non-invasively, i.e., using the faeces collected in treatment vessels. Bacterial biodiversity was genetically assessed (16S rRNA). The community biomass and taxonomic structure were analysed as a function of chemical treatment, mother and father body condition (fat vs thin), as well as population of origin. 

As a primary effect, AMPA reduced the microbial biomass. Furthermore, a significant interaction was detected between AMPA and mother condition on the community structure and composition. This alteration, observed in « fat » females only, was reflected through a significant decrease in Bacteroidota and a significant increase in Actinobacteriota (the latter being consistent with the ability of some species in this phylum to use AMPA as a source of phosphorus). The higher sensitivity of tadpoles from females in better condition seems counterintuitive, since better body condition is expected to be associated with higher fitness (and possibly higher ability to face chemical stress), the authors discuss this in the light of the literature (which shows that microbiome-fitness relationships are not often evidenced in natural populations), and hypothesize that these females in better conditions host a microbiota that may be more efficient, yet also more sensitive to AMPA. Not ruling out other possible factors ignored in their study, in particular genotypic effects, the authors further discuss the importance of maternally transmitted effects via the microbiota. 

Altogether, the results published by Tartu et al. (2024) provide important new findings on AMPA toxicity to amphibian microbiota, and also confirm the occurrence of vertical transmission of the microbiota from mother to progeny in this vertebrate class.

References 

IPBES (2019). Global assessment report on biodiversity and ecosystem services of the Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services. E. S. Brondizio, J. Settele, S. Díaz, and H. T. Ngo (editors). IPBES secretariat, Bonn, Germany. 1148 pages. https://doi.org/10.5281/zenodo.3831673

Pesce, S., Mamy, L., Sanchez, W., et al. (2023). Main conclusions and perspectives from the collective scientific assessment of the effects of plant protection products on biodiversity and ecosystem services along the land–sea continuum in France and French overseas territories. Environ Sci Pollut Res . https://doi.org/10.1007/s11356-023-26952-z

Tartu, S., Renoirt, M., Cheron, M., Gisselmann, L.-L., Catoire, S., Brischoux, F. (2022). Did decades of glyphosate use have selected for resistant amphibians in agricultural habitats? Environ. Pollut. 310, 119823. https://doi.org/10.1016/j.envpol.2022.119823

Tartu, S., Pollet, N., Clavereau, I., Gauthier Bouchard, G., Brischoux, F. (2024). Maternal body condition affects the response of larval spined toads’ faecal microbiome to a widespread contaminant. bioRxiv,  ver. 2 peer-reviewed and recommended by Peer Community in Ecotoxicology and Environmental Chemistry. https://doi.org/10.1101/2023.12.18.572122

Our ability to anticipate and estimate how pollution affects biota is intrumental in the field of ecotoxicology. Impact of chemical pollution by metals, drugs or pesticides was widely studied in different species using acute and chronic scenarios. Since the ban on tributyltin in antifouling paints, other copper (Cu)-based paints are on the market, including a new generation of booster biocides:metal pyrithiones such as Cu pyrithione (CuPT). Pyrithione acts as a Cu ionophore facilitating Cu transport across the membranes. Although some data show their occurrence in aquatic ecosystems and few studies on the toxicity of CuPT in fish are published, major gaps in knowledge remain about their toxicity and toxic pathway. Few studies were previously conducted in animals exposed to CuPT pointing to reprotoxicity, developmental malformation and mortality (Li et al. 2021, Mochida et al., 2011; Mohamat-Yusuff et al., 2018, Shin et al., 2022). However, its toxicokinetic and toxicodynamic remain to be characterized in details. 

In this context, Bourdon et al. (2023) compared in juveniles of rainbow trout (Oncorhynchus mykiss), the effects of exposure to CuPT and ionic Cu2+ at equivalent Cu2+ molar concentrations. Presented data allow to compare the toxicity threshold, the accumulation of Cu and mechanisms of toxicity of both compounds. Acute and chronic exposures showed a higher bioaccumulation of Cu in the gills, and a higher toxicity of CuPT than that of ionic Cu2+, e.g. mortality , transcription levels of genes related to oxidative stress, detoxification and Cu transport. Intriguingly, the activities of enzymatic biomarkers used as proxy of antioxidant capacity were not significantly altered, although Cu is generally expected to trigger oxidative stress. In conlusion, this study brings new knowledge pointing that the presence of CuPT in the environment could induce toxic effects in non-target species. Moreover, it support the need to study in detail the toxicity of Cu-based paints to adapt regulations concerning their use and release in aquatic environments. Because of its low solubility in water, CuPT is expected to adsorb to suspended matter and food pellets. Future research should study this route of exposure.

References

Bourdon, C., Cachot, J., Gonzalez, P., Couture, P., 2023. Characterization of the bioaccumulation and toxicity of copper pyrithione, an antifouling compound, on juveniles of rainbow trout,  bioRxiv  ver. 3 peer-reviewed and recommended by Peer Community in Ecotoxicology and Environmental Chemistry. https://doi.org/10.1101/2023.01.31.526498

Li, X., S. Ru, H. Tian, S. Zhang, Z. Lin, M. Gao and J. Wang, 2021. Combined exposure to environmentally relevant copper and 2,2′-dithiobis-pyridine induces significant reproductive toxicity in male guppy (Poecilia reticulata). Science of the Total Environment 797, https://doi.org/10.1016/j.scitotenv.2021.149131

Mochida, K., Amano, H., Onduka, T., Kakuno, A., Fujii, K., 2011. Toxicity and metabolism of copper pyrithione and its degradation product, 2,2’-dipyridyldisulfide in a marine polychaete. Chemosphere 82, 390–397, https://doi.org/10.1016/j.chemosphere.2010.09.074

Mohamat-Yusuff, F., Sarah-Nabila, Ab.G., Zulkifli, S.Z., Azmai, M.N.A., Ibrahim, W.N.W., Yusof, S., Ismail, A., 2018. Acute toxicity test of copper pyrithione on Javanese medaka and the behavioural stress symptoms. Marine Pollution Bulletin 127, 150–153, https://doi.org/10.1016/j.marpolbul.2017.11.046

Shin, D., Y. Choi, Z. Y. Soon, M. Kim, D. J. Kim and J. H. Jung, 2022. Comparative toxicity study of waterborne two booster biocides (CuPT and ZnPT) on embryonic flounder (Paralichthys olivaceus). Ecotoxicology and Environmental Safety 233, https://doi.org/10.1016/j.ecoenv.2022.113337

Our ability to anticipate and estimate how pollution affects components of ecosystems is of paramount importance in the field of ecotoxicology. Dose-response modeling is instrumental, as it allows deriving sensitivity thresholds used at the basis of regulatory risk assessment. In recent years, omics have highly influenced how the impacts of stressors are understood by revealing molecular changes at all levels of biota biological organization (Ebner et al., 2021). To allow analysis of omics data obtained using a typical dose-response design, DRomics a freely available tool for dose-response was proposed composed of both an R package and a free web application (Larras et al. 2018). Advances in this field depend both on theoretical concepts, technology and data integration.

In this context, Delignette-Muller et al. (2023) address the question of how to better integrate omics information in dose-response questions. The paper lists previous possibilities of DRomics and presents new features. It is now able to handle all types of continuous omic and continuous non-omic data (e.g. growth data). This new version proposes new visualization tools, functional annotation and improved modeling workflow for a better robustness of analysis of data with few replicates. New features are meant to help for biological interpretation at the metabolic pathway level, to compare different measurements, biological materials or experimental settings.

References

Delignette-Muller, M. L., A. Siberchicot, F. Larras and E. Billoir (2023), DRomics, a workflow to exploit dose-response omics data in ecotoxicology. bioRxiv, 2023.2002.2009.527852, ver. 4 peer-reviewed and recommended by Peer Community in Ecotoxicology and Environmental Chemistry. https://doi.org/10.1101/2023.02.09.527852

Ebner JN. (2021) Trends in the Application of "Omics" to Ecotoxicology and Stress Ecology. Genes, 12(10):1481. https://doi.org/10.3390/genes12101481

Larras F, Billoir E, Baillard V, Siberchicot A, Scholz S, Wubet T, Tarkka M, Schmitt-Jansen M and Delignette-Muller ML (2018). DRomics: a turnkey tool to support the use of the dose-response framework for omics data in ecological risk assessment. Environmental science & technology, 52(24):14461.  https://doi.org/10.1021/acs.est.8b04752

In recent years, the use of environmental DNA (eDNA) to investigate biodiversity has gained considerable interest (Thomsen and Willerslev, 2015; Mauvisseau et al., 2022). It allows for the indirect detection of species but it requires a sound understanding of eDNA behaviour and persistence in the environment. This is, however, a complex task because eDNA may be found in several states (e.g., dissolved, adsorbed, intracellular or intraorganellar), which display specific decay rates controlled by environmental factors (Harrisson et al., 2019; Mauvisseau et al. 2022). In the environment, dissolved DNA may interact with the surfaces of various sorbents, including mineral and organic particles/colloids. Current knowledge on eDNA sorption suggests that eDNA–sorbent interactions are controlled by electrostatics as well as inner-sphere complex formation (Mauvisseau et al., 2022). 

In this context, the work undertaken by Jelavic et al. (2022), focused on the adsorption of eDNA by lesser-investigated carbonaceous materials (CMs), namely soot and charcoal, as common non-mineral environmental surfaces. 

The authors aimed to study the adsorption capacity of soot and charcoal surfaces with respect to eDNA, in relation to solution parameters (i.e., pH, ionic strength, concentration/type of cations), time and eDNA length, under both non‐equilibrium and equilibrium conditions. Using such an approach, Jelavic et al. demonstrated the large adsorption capacities of CMs and the strong binding of DNA to these sorbents. The authors did not provide definitive conclusions on the mechanisms of eDNA sorption onto CMs. However, they provided new elements suggesting that, along with electrostatic interactions, hydrophobic interactions might play an important role in the adsorption of eDNA to CMs such as soot and charcoal. 

Altogether, the results presented in this paper highlight the relevance of CMs as sources of biodiversity information. In addition, it is likely that those results will also prove useful for the community to improve protocols for eDNA extraction from environmental samples that contain high fractions of CMs, e.g. urban soils. 

References

Harrison JB, Sunday JM, Rogers SM (2019) Predicting the fate of eDNA in the environment and implications for studying biodiversity. Proceedings of the Royal Society B: Biological Sciences, 286, 20191409. https://doi.org/10.1098/rspb.2019.1409

Jelavic S, Thygesen LG, Magnin V, Findling N, Müller S, Meklesh V, Sand KK (2022) Soot and charcoal as reservoirs of extracellular DNA. ChemRxiv, ver. 5 peer-reviewed and recommended by Peer Community in Ecotoxicology and Environmental Chemistry. https://doi.org/10.26434/chemrxiv-2021-9pz8c-v5

Mauvisseau Q, Harper LR, Sander M, Hanner RH, Kleyer H, Deiner K (2022) The Multiple States of Environmental DNA and What Is Known about Their Persistence in Aquatic Environments. Environmental Science & Technology, 56, 5322–5333. https://doi.org/10.1021/acs.est.1c07638

Thomsen PF, Willerslev E (2015) Environmental DNA – An emerging tool in conservation for monitoring past and present biodiversity. Biological Conservation, 183, 4–18. https://doi.org/10.1016/j.biocon.2014.11.019