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.