# Toxicological Mechanism of the Size–Form Synergy of Nano-Copper Oxide in Danio rerio

## TL;DR

This study explores how the size and shape of copper oxide nanoparticles affect their toxicity in zebrafish, revealing that smaller and flake-shaped particles cause more damage.

## Contribution

The study identifies the size–form synergy in CuO-NP toxicity and links it to organ-specific damage and microbial diversity changes.

## Key findings

- Flake-shaped CuO-NPs caused greater toxicity than spherical particles in zebrafish.
- Smaller CuO-NPs showed increased toxicity, linked to reduced antioxidant capacity and microbial diversity.
- Changes in microbial taxonomic abundance at phylum and genus levels contributed to multi-organ toxicity.

## Abstract

The widespread industrial use of copper oxide nanoparticles (CuO-NPs) has inevitably led to their release into aquatic ecosystems. However, the toxicological effects of CuO-NPs, that is, its biological toxicity, particularly its correlation with particle size and morphology, remains inadequately studied. This study employed zebrafish to evaluate the toxicity of CuO-NPs with varying particle sizes and morphologies. Organ-specific damage was observed in gills, livers, and intestines. Flake-shaped CuO-NPs (SC) exhibited greater toxicity than spherical particles, with smaller particle sizes showing increased toxicity. The primary mechanisms involved reduced tissue antioxidant capacity and diminished microbial α-diversity. Changes in the relative abundance of dominant taxonomic groups at phylum and genus levels contributed to multi-organ toxicity. These findings lay a foundation for the study of the toxicity mechanism of nanomaterials.

CuO-NPs demonstrate significant potential across biomedical, environmental protection, and electronic technology domains. This widespread utilization inevitably leads to their discharge into aquatic ecosystems. Research on the biotoxicity of CuO-NPs constitutes a current scientific priority; however, toxicological impacts related to particle size and morphology remain inadequately documented. The zebrafish (Danio rerio Roloff, 1956) is employed as a model animal organism to assess acute and subchronic toxicity of differentially sized/shaped CuO-NPs. Organ-specific damage manifested in the gills, liver, and muscles. It was found that sheet-shaped CuO-NPs (SC) could induce the most severe histomorphological alterations. Among spherical CuO-NPs (SP), smaller particles exhibited higher toxicity (SC > 40 nm SP-S > 150–250 nm SP-L). Tissue antioxidant capacity followed the same decreasing trend. The three CuO-NPs in the present study reduced microbial alpha-diversity. Altered relative abundance of dominant taxa is observed at the phylum and genus levels. These results expand toxicological datasets for nanomaterial–vertebrate interactions and support environmental risk assessment for nano-pollutants in natural conditions.