Integrated environmental risk assessment of rare earth elements mixture on aquatic ecosystems

Abstract

Rare Earth elements (REE) have become essential in strategical sectors such as high- and green-technologies. Their increasing use in human activities worldwide leads to anthropogenic REE releases detectable in all compartments of the environment, transforming REE into emerging contaminants. However, their potential impacts on ecosystems are still poorly understood. In order to have a comprehensive understanding of REE ecotoxicology and to properly assess their environmental risk, we analysed the toxicity of three representative REE (neodymium Nd, gadolinium Gd, and ytterbium Yb). Following recommendations of the European Chemicals Agency, we assessed REE hazard by performing standard ecotoxicological tests on three freshwater species belonging to different trophic levels (algae, crustacean and fish). EC50 were calculated using different modes of expression of REE exposure concentration (based on nominal, measured total and dissolved concentrations) in order to more properly and accurately determine REE toxicity. In order to get closer to environmental conditions, we also tested the toxicity of REE in mixture because all of them occur naturally as such in the environment. Moreover, we added dissolved organic matter (DOM) in the test medium because DOM is ubiquitous and drives REE speciation in freshwater systems. The Results showed that DOM significantly reduced REE bioaccumulation and toxicity, probably by formation of non-bioavailable REE-DOM complexes. The algal species was the most sensitive to REE. Despite slight differences between Nd, Gd and Yb in behaviour and bioaccumulation, the three REE exhibited comparable toxicity and additive effects in mixture to all tested organisms. Thus, we considered REE as a uniform group and, for the first time, we used mixture toxicity values and environmental mixture concentrations to assess the risk of REE in freshwater (instead of considering different REE separately). The results revealed that the risk is currently limited to wastewater treatment plants, and industrial and mining activities, where released quantities of REE can induce severe damage to exposed freshwater organisms. However, the risks are likely more widespread in the future because anthropogenic REE releases are expected to increase.

Photodissolution of Rare Earth Elements and Dissolved Organic Carbon from Subbituminous Coal: Effects of Environmental Variables and Implications for Biogeochemical Cycling

“…Little is known about the toxicity of REE–DOC complexes in aquatic ecosystems. Recent studies reported the complexing to organic ligands significantly reduce the bioavailability, bioaccumulation, and toxicity of REEs in aquatic ecosystems. ,− These reports highlight the significance of accounting for REE speciation in toxicity experiments, which is largely neglected in the literature, and further ecotoxicity studies on REEs are needed can help develop a environmental risk assessment criteria . REE–DOC interactions are another factor needing further research: DOM composition drives a wide range of global biogeochemical cycles. − Metal complexation can affect DOM-mediated processes, − and photochemistry is an environmental driver of DOM composition. ,,,, There is considerable uncertainty over how boreal soil–aquatic–marine system interactions will change over the coming years due to onset of rapid deglaciation and permafrost thaw. − As new stores of subbituminous coal are released from landslides and terrestrial throughfall into the marine environment, photochemistry, as a process, may affect increased REE bioavailability in the oceans.…”

“…Anthropogenic exposures of REEs in the environment are of growing concern due to increased refining, development, and use. , Bioavailability and environmental fate of REEs are dependent upon factors such as speciation, pH, ligand (organic and inorganic), salinity, redox potential, and cation exchange capacity. ,− REEs are reported to have toxicological effects on terrestrial and aquatic biota, as well as humans. ,,− Except for an enzymatic pathway of methanotrophic bacteria, there is currently no known biological role of REEs. − Although the exact biological action of REEs is not fully understood, previous studies suggested several mechanisms of toxicity, including intracellular membrane crossing, generation of reactive oxygen species, lipid peroxidation, and modulation of antioxidation pathways . The photodissolution of REEs from coal coupled with the toxicological impacts of REEs and the potential for increased prevalence due to climate change underscores the importance of understanding this environmental process.…”

Evaluation of acute toxicity of neodymium and yttrium in zebrafish (Danio rerio) embryos

“…Regarding the adverse effects that can be caused on the aquatic ecosystem, some current studies have been related to their absorption and accumulation in organic tissues, like, for example, in fish, shellfish or molluscs (Perrat et al, 2017;Trifuoggi et al, 2017;Bakhshalizadeh et al, 2023). However, few are concentrated on evaluating their toxicity (Pagano et al, 2016;Kang et al, 2022a;Kang et al, 2022b;Lachaux et al, 2022). One of the fish species commonly used to evaluate the toxicity of potentially harmful elements is the zebrafish (Danio rerio).…”

Bioaccumulation of rare earth elements and trace elements in different tissues of the golden grey mullet (Chelon auratus) in the southern Caspian Sea

“…Rare earth elements (REEs) are a group of seventeen elements, fifteen of which correspond to lathanides, from lanthanum (La) ( Z = 57) to lutetium (Lu) ( Z = 71), in addition to scandium (Sc) ( Z = 21) and yttrium (Y) ( Z = 39) (Wu et al, 2022 ). All of these elements share similar physicochemical properties and are found naturally in the earth’s crust (Lachaux et al, 2022 ; Zhuang et al, 2017 ), except for promethium (Pm), which does not have stable isotopes (Elkina and Kurushkin 2020 ). The REEs are never encountered in a pure form since they are majority or minority components of a wide variety of minerals, which are found in ashalides, carbonates, oxides, phosphates and silicates (Dostal, 2017 ).…”