 Metal oxide nanoparticles, N-piece, have been widely used in many different applications, but their potential toxicity has raised concerns among researchers and the general public. This review focuses on two specific types of N-piece, CuO and ZNL, to explore the mechanisms behind their toxicity. The authors discuss how factors such as particle size, surface characteristics, dissolution, and exposure route can influence the toxicity of these particles. They also examine the role of oxidative stress, coordination effects, and non-homostatic effects in the toxicity of these particles. This article was authored by Yanen Zhang, Jun Zhang, Gingmei Xing, and others.