Biodistribution of synthesized polyethylene terephthalate fibers in adult zebrafish, their sex hormone disruption effect, and mitigation using natural organic matter.

Although polyethylene terephthalate (PET) fibers are a representative form of plastic pollutants, studies on their toxicity are currently limited compared to other plastic types. Moreover, the effect of natural organic matter (NOM) on their toxicity has not been investigated. In this study, female and male adult zebrafish were exposed to synthesized PET fibers at concentrations of 0.1, 1, 10, and 100 mg/L in the presence and absence of 10 mg/L of NOM for 10 d. Bioaccumulation of PET fibers in zebrafish intestine, liver, and gills was identified and expression levels of reactive oxygen species (ROS) generation, sex hormones, and oxidative stress and sex hormone-related genes were measured. In addition, the developmental stages of gonadal cells were examined through histological analysis. We found that PET fibers bioaccumulated in the intestine and liver of zebrafish. ROS generation significantly increased at 100 mg/L of PET fibers, the expression of oxidative stress-related genes decreased in female and increased in male zebrafish. Exposure to 100 mg/L of PET fibers did not affect 17-beta estradiol, but significantly decreased the testosterone levels in male zebrafish. Sex hormone-related genes significantly decreased in both female and male zebrafish, except for androgen receptor in female zebrafish. However, these changes were exacerbated by the removal of NOM, suggesting a protective effect of NOM against PET fibers toxicity. We demonstrated that the accumulated PET fibers may lead to oxidative stress and sex hormone alteration, and disrupt the development of gonadal cells. Additionally, the NOM coating did not alter bioaccumulation considerably, but mitigated the adverse effects at the hormone level in PET fiber-exposed zebrafish. Thus, this study provides a basis for further research on the toxicity assessment of PET fibers and interactions between NOM and PET fiber-related toxicity.