Daphnia magna and freshwater snails are used as delicate bioindicators of contaminated aquatic habitats. Due to their distinctive characteristics, selenium oxide nanoparticles (SeONPs) have received interest regarding their possible implications on aquatic environments. The current study attempted to investigate the probable mechanisms of fungal-mediated selenium nanoparticles’ ecotoxicological effects on freshwater Biomphalaria alexandrina snails and Daphnia magna. SeONPs revealed a toxicological impact on D. magna, with a half-lethal concentration (LC₅₀) of 1.62 mg/L after 24 h and 1.08 mg/L after 48 h. Survival, fecundity, and reproductive rate were decreased in B. alexandrina snails exposed to SeONPs. Furthermore, the aspartate aminotransferase (AST) and alanine aminotransferase (ALT) levels were markedly elevated, while albumin and total protein levels decreased. Histopathological damage in the hermaphrodite and digestive glands was detected by light, electron microscopy, and immunohistochemistry studies. The molecular docking study revealed interactions of selenium oxide with the ALT and AST. In conclusion, B. alexandrina snails and D. magna could be employed as bioindicators of selenium nanomaterial pollution in aquatic ecosystems. This study emphasizes the possible ecological effects of releasing SeONPs into aquatic habitats, which could serve as motivation for regulatory organizations to monitor and control the use and disposal of SeONPs in industry.

In 2023, breast cancer is expected to have nearly 2 million new cases, making it the second most common cancer overall and the most prevalent among women. Multidrug resistance limits the effectiveness of chemotherapy; however, quercetin, a natural flavonoid, helps combat this issue. The goal of the current investigation is to determine the impact of a novel composite of quercetin and selenium nanoparticles (SeNPs) on the breast cancer cell lines MDA-MB-231 and MCF-7 in order to enhance quercetin’s tumor-suppressive action and decrease selenium (Se) toxicity. Particle size, zeta potential, FTIR, SEM, UV–VIS spectroscopy, and EDX were used to characterize quercetin-selenium nanoparticles (Que-SeNPs), in addition to evaluation of the antioxidant, apoptotic, and anticancer properties. Moreover, autophagy (Atg-13) protein receptors and PD-1/PD-L1 checkpoint were targeted using molecular docking modeling and molecular dynamics (MD) simulations to assess the interaction stability between Que-SeNPs and three targets: PDL-1, PD-1, and Atg-13^HORMA domain. Que-SeNPs, synthesized with quercetin, were stable, semi-spherical (80–117 nm), and had a zeta potential of − 37.8 mV. They enhanced cytotoxicity, antioxidant activity, and apoptosis compared to quercetin alone in MCF-7 and MDA-MB-231 cells. Docking simulations showed strong binding to the PD-1/PD-L1 checkpoint and Atg-13^HORMA protein receptors. Moreover, the molecular dynamics simulation revealed that the behavior of the PD-L1 intriguing insights into its structural dynamics, therefore, suggesting a stable phase where the complex is adjusting to the simulation environment. The present data confirmed that the stable formula of Que-SeNPs is cytotoxic, antioxidant, and has a potential activity to increase apoptosis in breast cancer cells, with the potential to inhibit PD-1/PD-L1 and Atg-13 proteins. Graphical Abstract Role of Que-SeNPs on breast cancer cells in vitro against two breast cancer cell lines MDA-MB-231 and MCF-7.