Enhanced toxicity of triphenyl phosphate to zebrafish in the presence of micro- and nano-plastics

Co-occurrence of microplastics and chemicals was a complex environmental issue, whereas little concerned on the effect of microplastics on the toxicity of chemicals. In this study, we studied the changes of toxicity of triphenyl phosphate (TPhP) to zebrafish, in the presence of micro-polystyrene (MPS, 5.8 μm) and nano-polystyrene (NPS, 46 nm). Results indicated that separate MPS and NPS had no acute toxicity and little reproductive toxicity on zebrafish. TPhP alone was a highly toxic substance with a median lethal concentration (LC50) of 976 μg/L, the presence of MPS and NPS did not have significant effect on the acute toxicity of TPhP. TPhP alone stimulated the enlargement of liver and gonad of fish (except the testis) by 1.25–2.12 fold, and the presence of NPS further aggravated this stimulation by 1.23–2.84 fold, while MPS did not. The gonadal histology indicated that comparing with TPhP alone, the addition of MPS and NPS further inhibited the process of spermatogenesis and oogenesis, even causing obvious lacunas in testis and atretic follicles oocytes in ovary. Meanwhile, TPhP did not significantly disturb the hormone homeostasis (E2/T) and vitellogenin (Vtg) content in fish, but the presence of NPS increased the E2/T ratio and Vtg content in male fish, while slightly decreased those in female fish, which implying that effects of PS was sex-dependent. As a result, the egg production, the fertilization rate and hatchability of eggs significantly reduced after combined TPhP+PS exposure, demonstrating that co-occurrence of TPhP and PS, especially NPS, could greatly impaired the reproductive performance of zebrafish.