A Comparative Analysis of Zinc Oxide as Nanoparticles and Its Bulk Form through In Vitro Toxicogenetics and In Vivo Zebrafish Embryotoxicity Models.

Zinc oxide nanoparticles (ZnO-NP) are widely used due to their enhanced biological activity compared to the bulk counterpart (ZnO-BK), raising concerns about potential toxic effects on living organisms and the environment. This study investigated the toxicity of ZnO-NP and ZnO-BK using alternative in vitro and in vivo models. The Salmonella/Microsome assay (±metabolic activation) was conducted according to the Organisation for Economic Co-operation and Development (OECD) guidelines. HepG2 cell viability and genotoxicity were assessed using the WST-1 and cytokinesis-block micronucleus (CBMN) assays. Acute toxicity was evaluated using the fish embryotoxicity (FET) test in zebrafish (Danio rerio) embryos. Both forms induced mutagenic responses in TA98 and TA102 strains, while ZnO-BK showed mutagenicity in TA100 only in the absence of metabolic activation. In HepG2 cells, both forms induced dose-dependent cytotoxicity in the WST-1 model, with ZnO-BK exhibiting greater cytotoxic potency. The CBMN assay revealed higher cytogenetic damage for ZnO-BK, including micronuclei, nuclear buds, and nucleoplasmic bridges, while both forms exhibited dose-dependent cytotoxic and cytostatic effects. In vivo, ZnO-NP exerted a more pronounced impact on embryonic development, altering eye diameter and body size compared to ZnO-BK. Overall, both forms demonstrated significant toxicological effects, highlighting their relevance for regulatory toxicogenetics and environmental safety.