Elucidating the Toxic Mechanism of NiWO₄ to a Neotropical Microcrustacean: Experimental and Theoretical Insights

In the present study, we describe the toxicity mechanism of nickel tungstate nanoparticles (NiWO₄ NPs) and present experimental and computational advancements achieved through a combined approach to evaluate the toxicity of this semiconductor in the freshwater aquatic organism Ceriodaphnia silvestrii (Cladocera). Results from the acute toxicity test indicated that NiWO₄ induced immobility in C. silvestrii at concentrations exceeding 40 mg L^-1 (Dunn's test, p < 0.05). The 48-h EC₅₀ was 33.76 mg L^-1 ± 5.67. The sublethal concentrations of NiWO₄, at 20 and 25 mg L^-1, significantly decreased the ingestion rates of C. silvestrii (Dunnett's test, p < 0.05), directly affecting cladoceran nutrition and potentially hindering population growth. Density functional theory (DFT) and ab initio atomistic thermodynamics analyses characterized the structural, electronic, and energetic properties of low-index NiWO₄ surfaces, revealing that oxygen-rich (111) facets may play a central role in oxidative stress and cellular damage in exposed organisms. Based on these findings, we propose a detailed toxicological mechanism that elucidates how nanoparticle properties influence biological responses in Neotropical microcrustaceans.