Impact of Erbium and Gadolinium on Xenopus laevis Embryo Development: A Study of Rare Earth Element Toxicity

Rare earth elements (REE), such as gadolinium (Gd) and erbium (Er), are increasingly recog- nised as emerging environmental contaminants due to their widespread use in industrial processes, electronics, and medical imaging applications. Despite their extensive presence in aquatic ecosystems, little is known about their developmental toxicity. In this study, Xenopus laevis embryos were exposed to environmentally relevant concentrations of Gd and Er during critical early developmental stages. The assessed endpoints included survival, malformations, growth (body length), and heart rate. Both Gd and Er caused significant sublethal effects, including increased axial malformations, reduced growth, and altered cardiac activity. To explore potential mechanisms of toxicity, the expression patterns of key developmental genes (fgf8, bmp4, sox9, egr2, rax1, pax6) and pro-inflammatory cytokines (tnfα, il1β, p65) were analysed using Real-Time PCR. The results showed dysregulation of gene expression, indicating disruption to pathways involved in morphogenesis and neurodevelopment. Elevated reactive oxygen species levels suggested that oxidative stress was a contributing factor. Raman spectroscopy confirmed biochemical changes affecting proteins, lipids, and nucleic acids, providing evidence of cellular stress and metabolic imbalance. Overall, our findings demonstrate that even low-level exposure to Gd and Er can impair amphibian embryonic development and disturb molecular homeostasis. These results emphasise the ecological risks of REE pollution and highlight the importance of ongoing environmental monitoring and long-term toxicological research.