Sex-specific reproductive toxicity of polystyrene nanoplastics and DEHP in adult zebrafish (Danio rerio)

Micro- and nanoplastics (MNPs) and di(2-ethylhexyl) phthalate (DEHP) are ubiquitous environmental contaminants; however, the risks of their combined exposure to aquatic reproductive health, particularly sex-specific differences, remain incompletely understood. This study investigated the effects of single and combined exposure to polystyrene nanoplastics (PS-NPs; 0.1 and 1 mg/L) and DEHP (10 μg/L) on the reproductive endocrine system of adult male and female zebrafish (Danio rerio) Results demonstrated that PS-NPs accumulated in the zebrafish intestine. High concentrations of PS-NP and DEHP and their combined exposures induced significant adverse effects in both sexes, including gonadal tissue damage and oxidative stress. A striking sexual dimorphism was observed in endocrine responses. Females exhibited a pronounced suppression of both 17β-estradiol (E2) and testosterone (T) levels, which correlated with inhibited ovarian cyp19a gene expression under co-exposure. Conversely, male E2 levels remained stable and T levels decreased only under co-exposure, increasing E2/T ratio. This distinct male endocrine profile was associated with differential regulation of testicular cyp19a and 17β-hsd expression. This study confirms that PS-NPs and DEHP exert profound sex-specific reproductive toxicity in zebrafish. These effects are mediated by disrupting the hypothalamic-pituitary-gonadal (HPG) axis, while inducing sex-specific alterations in brain and gonadal gene expression. Overall, this study highlights the critical importance of considering sex differences and pollutant mixture effects in environmental risk assessments.