Assessing the dual toxicity of HfO₂ nanoparticles and quinalphos on Pila virens

Pila virens (P. virens) is an edible freshwater snail, widely distributed in Asia and Africa. P. virens is used as one of the most promising model organisms for monitoring environmental contamination in aquatic ecosystems. The physiological responses to the contaminants such as pesticides and nanomaterials are inadequate, especially in relation to the effects of co-exposure. In this work, we have investigated on the noxious effects of co-exposure between an organophosphorus pesticide, quinalphos and hafnium oxide nanoparticles (HfO₂NPs) on the antioxidant responses of P. virens. Phase pure forms of HfO₂NPs (monoclinic, P2₁/c) were obtained by sol-gel method. The crystallinity, structure and surface morphology were analysed with various spectroscopic methods like powder X-ray, Fourier-transform infrared spectroscopy (FT-IR), Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), High Resolution Scanning Electron Microscope (HR-SEM) and Transmission Electron Microscope (TEM). P. virens after exposure for 96 h to the different concentrations of quinalphos (0.25-2.25 mg/mL) and HfO₂NPs (10-50 mg/mL), the median lethal concentration (LC₅₀) was determined to be 1.159 mg/mL and 11.47 mg/mL, respectively and show a significant fatal effect against the snail. The P. virens were exposed to sub-lethal concentrations of LC₂₅ (0.57 mg/mL quinalphos and 5.73 mg/mL HfO₂NPs) individually and in combination as a binary toxicity (quinalphos + HfO₂NPs), (0.57 mg/mL + 5.73 mg/mL) for 24 and 48 h. Further, the antioxidant responses were assessed which included catalase (CAT), glutathione sulfo-transferase (GST), and malonaldehyde (MDA) activity in the group exposed to quinalphos and HfO₂NPs exhibited to show an enhancement in their activity in comparison to controls after 24 and 48 h and revealed that 48 h exposure has significant impact. These results provide a valuable insight towards increased awareness of the physiological defences of P. virens after co-exposure to quinalphos and HfO₂NPs in aquatic ecosystem.