Multi-walled carbon nanotubes enhance the toxicity effects of dibutyl phthalate on early life stages of zebrafish (Danio rerio): Research in physiological, biochemical and molecular aspects

Phthalate esters (PAEs) are widely used as plasticizers. PAEs are ubiquitous in natural water bodies, with dibutyl phthalate (DBP) being one of the most common PAEs. DBP is prone to leaching or migration into the environment, posing serious health and environmental risks. Carbon nanotubes (CNTs) have been widely used in various fields with the rapid development of nanotechnology. CNTs could alter the environmental behavior and toxicity of co-existing pollutants. CNTs have been shown to rapidly adsorb PEAs. However, current knowledge about the effects of CNTs on DBP toxicity is limited. Here we show that the toxic effects of single and combined exposure to DBP (0.1, 0.5, 1.0 mg/L) and different CNTs (MWCNTs/MWCNTs-COOH, 0.5 mg/L) on the early growth stage of zebrafish. The results suggested that a significant increase in heart rate and heart malformation rate was observed after co-exposure of DBP and MWCNTs/MWCNTs-COOH (p < 0.05). Furthermore, combined exposure increased antioxidant enzyme activity during early developmental stages in zebrafish (p < 0.05). The qRT-PCR results revealed that DBP and MWCNTs/MWCNTs-COOH co-exposure significantly interfered with the expression of genes related to oxidative stress, energy metabolism, development of cardiac function, and apoptosis (p < 0.05). In addition, for oxidative stress and cardiotoxicity, MWCNTs/MWCNTs-COOH aggravated the toxic effects of 0.5 mg/L DBP on embryos/larvae. The metabolomics results showed that co-exposure mitigated the disturbance of amino acid metabolism mediated by single DBP exposure. In general, MWCNTs/MWCNTs-COOH increased the impact of DBP in the early developmental stages of zebrafish. This study provides new insights into the toxicology of early developmental stages of aquatic organisms exposed to co-exist pollutants of DBP and CNTs.