The large-scale mining and utilization of rare earth elements have significantly increased their concentration in the environment, especially in regions surrounding mining areas. These environmentally-enriched rare earth elements accumulate in agricultural products and organisms through soil and water, potentially impacting in human health through the food chain. Erbium (Er), a rare earth element of the lanthanide series (Group IIIB), plays a crucial role in various modern technological applications. It is primarily utilized in ceramics, glass coloring, optical fibers, laser technology, and the nuclear industry, among others. However, a paucity of information on the health effects and ecotoxicity of erbium is currently available. In this study, we used the zebrafish as experimental animal to investigate the potential impact of the rare earth element erbium on the immune system. We exposed fertilized zebrafish embryos to different concentrations of erbium (0, 4, 8 and 16 mg/L) from 6 hours post-fertilization (hpf) until 72 hpf. We found that with increasing concentrations of erbium exposure, there was an increasing and dispersing trend in the number of zebrafish neutrophils
a decreasing trend in the number of macrophages. Exposure to erbium was demonstrated to impair the phagocytic capability of macrophages, reduce the recruitment of neutrophils to the wound site, and lower the resistance of zebrafish to Escherichia coli infection. Erbium exposure led to macrophage apoptosis and upregulation of oxidative stress in the zebrafish. The individual application of the reactive oxygen species (ROS) scavenger N-acetyl-L-cysteine, the IKBKB inhibitor resveratrol and the NF-κB inhibitor andrographolide were demonstrated to alleviate erbium-induced immune toxicity, as confirmed by assays including acridine orange staining, neutrophils enumeration and recruitment, and real-time quantitative PCR. Therefore, the rare earth element erbium induced immune toxicity in zebrafish through the ROS/NF-κB pathway. The findings of this study provide information for assessing the impact of rare earth elements on human health and ecosystems.