Nanomaterials with at least one dimension of 100 nm or less, were classified into three types based on their dimensions, including zero-dimensional nanomaterials (e.g., nanoparticles), 1-dimensional nanomaterials (e.g., nanowires, nanorods, and nanotubes), and 2-dimensional nanomaterials (e.g., nanolayers) (Prasad et al. 2021). Nanomaterials have gained tremendous attention owing to their beneficial applications in electronics, life science, environmental protection, energy, national defense, and the chemical industry (Li et al. 2023). In recent years, with the improvement of production technology of nanomaterials and the increased demand of the downstream industry, the market for nanomaterials has shown an increasing trend in terms of global market value (Lee et al. 2014). However, the advancement of nanomaterial industry has been found to be correlated with the occurrence of environmental pollution, consequently leading to potential risks to public health. In the natural environment, organisms are likely exposed to mixtures of discharged pollutants, which may interact with each other and change the potential effects. The adverse effects of the mixtures have aroused great attention among researchers (Ye et al. 2018).
ZnO nanoparticles (ZnONPs), a type of zero-dimensional nanomaterials, are typical versatile metal oxide nanoparticles with unique features, such as low cost and chemical stability. They are widely utilized in the drug delivery, food packaging, pigments, fire retardants, and nutritional supplements (Chupani et al. 2019). The primary cause of ZnONPs toxicity is the presence of dissolved Zn (Bondarenko et al. 2013). These particles release Zn ions into animal cells, which are eliminated from the body via gills or kidneys once they surpass the required levels for fish maintenance. Whereas, the release of Zn ions from the gill and kidney is limited. Excessive accumulation of Zn ions or nano-form may cause damage to tissues (Sayadi et al. 2020).
One-dimensional carbon nanostructured materials, commonly known as carbon nanotubes (CNTs), are among the most celebrated entities in the field of nanotechnology. They have been applied in diverse fields, such as semiconductor chips, fuel cells, and lasers, due to their extraordinary mechanical and electrical properties arising from their nanoscopic dimensions (Samiei et al. 2020). Previous studies have shown that CNTs were associated with toxic effects, such as growth, development, reproduction, and immune response in several experimental animals (Omori et al. 2021; Salehcheh et al. 2020). The destiny of other contaminants could be impacted by CNTs possessing extensive surface areas (Qu et al. 2014). In recent years, several studies have reported the effects of CNTs on the uptake, accumulation, tissue distribution, or toxicity of contaminants, such as phenanthrene, copper, benzo[a]pyrene, triphenyltin, and terbium (Kim et al. 2010; Yi et al. 2019; Azari et al. 2020).
Common carp (Cyprinus carpio), one of the most crucial fish in central Asia, is a well laboratory model for toxicological researches (Ali et al. 2021). In the present study, we intend to explore the adverse effects of ZnONPs in combination with CNTs on the pathological changes and apoptosis in the liver of common carp after four weeks-exposure.