Environmentally relevant concentrations of nanoplastic increase the accumulation and endocrine effects of BDE47 and its metabolite 6-OH-BDE-47 in male frogs’ testes

Emerging pollutants such as polystyrene-nanoplastics (PS-NPs) and polybrominated diphenyl ethers (PBDEs) are a threat to human health and ecological safety. However, NP-mediated PBDE exposure and toxicity remain poorly understood. Herein, male frogs ( Pelophylax nigromaculatus ) were exposed to 2,2′,4,4′-tetrabromodiphenyl ether (BDE-47) and 6-hydroxy-2,2′,4,4′-tetrabromodiphenyl ether (6-OH-BDE-47) alone or in combination with PS-NPs for 30 days to explore the carrier toxicity effect and mechanism of co-exposure. Transcriptome data verified that both BDE-47 and 6-OH-BDE-47 could mediate the steroid hormone synthesis signaling pathway to induce reproductive toxicity. The presence of PS-NPs increased the bioconcentration of BDE-47 and 6-OH-BDE-47 by 54.36 % and 51.49 %, respectively, and aggravate the damage of the testes. To investigate the mechanism underlying the disrupted steroidogenesis, changes in hormones of the hypothalamic-pituitary-gonadal (HPG) axis and gene expression involved in synthesis and transformation of sex hormones were assessed. AR, StAR, CYP11A1 and HSD3B1 were all downregulated, while mRNA expression levels of CYP19A1 and ESR1 were upregulated, accompanied by a decrease in testosterone and an increase in oestradiol. The results demonstrated that PS-NPs can exacerbate the estrogen-like effects of BDE-47 and 6-OH-BDE-47 in male frogs, highlighting the potential risks posed by these pollutants in aquatic ecosystems.