Lanthanum and Gadolinium availability in aquatic mediums: New insights to ecotoxicology and environmental studies

Gadolinium: a review on concentrations and impacts in marine and coastal systems

This review synthesizes current knowledge on gadolinium (Gd) contamination in marine and coastal environments from 209 scientific publications. Of these, 83 studies were selected for detailed analysis, focusing specifically on marine invertebrate taxa to ensure a targeted examination of Gd's effects on key sentinel species within this group, with 69 papers (83.1%) focusing on Gd concentrations in marine and coastal ecosystems, reporting concentrations ranging from 0.00002516 μg/L to 1176.77 μg/L. Out of the 83 papers, 14 (16.9%) were related to Gd ecotoxicological effects through laboratory exposure experiments, with test concentrations ranging from 10 μg/L to 5600 μg/L. The studies mainly investigated Gd bioaccumulation and toxicity in marine bivalves (e.g. Mytilus galloprovincialis, Crassostrea gigas, Ruditapes philippinarum), crustaceans (Callinectes sapidus, Crangon crangon) and echinoderms (Paracentrotus lividus, Arbacia lixula). Bivalves were the most studied taxonomic group due to their filter-feeding behavior and role as bioindicators of metal contamination. Laboratory results showed that Gd exposure led to oxidative stress, metabolic disorders and reproductive toxicity, especially in molluscs and echinoderms. M. galloprovincialis showed the highest bioaccumulation, with concentrations exceeding 2.5 μg/g under controlled exposure. Echinoderms, especially sea urchin larvae (P. lividus, Heliocidaris tuberculata), were among the most affected taxa, showing developmental abnormalities such as skeletal malformations and growth retardation. Crustaceans, although less studied, also showed bioaccumulation and enzymatic disorders. Given the persistence of anthropogenic Gd in marine and coastal environments and its increasing medical use, this review highlights the need for improved wastewater treatment technologies, stricter environmental regulations, and further research into the long-term effects on marine biodiversity.

Intracellular bioaccumulation of the rare earth element Gadolinium in ciliate cells resulting in biogenic particle formation and excretion

Ciliates are abundant unicellular organisms capable of resisting high concentrations of metal ions in the environment caused by various anthropogenic activities. Understanding the cellular pathways involved in resistance to and detoxification of elements is required to predict the impact of ciliates on environmental element cycles. Here, we investigated the so far unknown process of tolerance, cellular uptake and bioaccumulation of the emerging rare earth element gadolinium (Gd) in the common ciliate Tetrahymena pyriformis. Gd treatment results in the intracellular formation and excretion of biogenic Gd-containing particles. This cellular process effectively removes dissolved Gd from the organic growth medium by 53.37% within 72 h. Based on light and electron microscopic observations, we postulate a detoxification pathway: Cells take up toxic Gd³⁺ ions from the medium by endocytosis, process them into stable Gd-containing particles within food vacuoles, and exocytose them. Stable biogenic particles can be isolated, which are relatively homogeneous and have a diameter of about 3 µm. They consist of the elements Gd, C, O, P, Na, Mg, K, and Ca. These findings broaden the view of metal ion accumulation by protists and are of relevance to understand environmental elemental cycles and may inspire approaches for metal recovery or bioremediation.

Gadolinium ecotoxicity is enhanced in a warmer and acidified changing ocean as shown by the surf clam Spisula solida through a multibiomarker approach

Humans have exhaustively combusted fossil fuels, and released pollutants into the environment, at continuously faster rates resulting in global average temperature increase and seawater pH decrease. Climate change is forecasted to exacerbate the effects of pollutants such as the emergent rare earth elements. Therefore, the objective of this study was to assess the combined effects of rising temperature (Δ = + 4 °C) and decreasing pH (Δ = - 0.4 pH units) on the bioaccumulation and elimination of gadolinium (Gd) in the bioindicator bivalve species Spisula solida (Surf clam). We exposed surf clams to 10 µg L^-1 of GdCl₃ for seven days, under warming, acidification, and their combination, followed by a depuration phase lasting for another 7 days and investigated the Gd bioaccumulation and oxidative stress-related responses after 1, 3 and 7 days of exposure and the elimination phase. Gadolinium accumulated after just one day with values reaching the highest after 7 days. Gadolinium was not eliminated after 7 days, and elimination is further hampered under climate change scenarios. Warming and acidification, and their interaction did not significantly impact Gd concentration. However, there was a significant interaction on clam's biochemical response. The augmented total antioxidant capacity and lipid peroxidation values show that the significant impacts of Gd on the oxidative stress response are enhanced under warming while the increased superoxide dismutase and catalase values demonstrate the combined impact of Gd, warming & acidification. Ultimately, lipid damage was greater in clams exposed to warming & Gd, which emphasizes the enhanced toxic effects of Gd in a changing ocean.

Single and combined ecotoxicological effects of ocean warming, acidification and lanthanum exposure on the surf clam (Spisula solida)

Lanthanum (La) is one of the most abundant emergent rare earth elements. Its release into the environment is enhanced by its use in various industrial applications. In the aquatic environment, emerging contaminants are one of the stressors with the ability to compromise the fitness of its inhabitants. Warming and acidification can also affect their resilience and are another consequence of the growing human footprint on the planet. However, from information gathered in the literature, a study on the effects of ocean warming, acidification, and their interaction with La was never carried out. To diminish this gap of knowledge, we explored the effects, combined and as single stressors, of ocean warming, acidification, and La (15 μg L^-1) accumulation and elimination on the surf clam (Spisula solida). Specimens were exposed for 7 days and depurated for an additional 7-day period. Furthermore, a robust set of membrane-associated, protein, and antioxidant enzymes and non-enzymatic biomarkers (LPO, HSP, Ub, SOD, CAT, GPx, GST, TAC) were quantified. Lanthanum was bioaccumulated after just one day of exposure, in both control and climate change scenarios. A 7-day depuration phase was insufficient to achieve control values and in a warming scenario, La elimination was more efficient. Biochemical response was triggered, as highlighted by enhanced SOD, CAT, GST, and TAC levels, however as lipoperoxidation was observed it was insufficient to detoxify La and avoid damage. The HSP was largely inhibited in La treatments combined with warming and acidification. Concomitantly, lipoperoxidation was highest in clams exposed to La, warming, and acidification combined. The results highlight the toxic effects of La on this bivalve species and its enhanced potential in a changing world.