Di-(2-ethylhexyl) phthalate (DEHP) has the potential to disrupt the thyroid endocrine system, but the underlying mechanism is unknown. In this study, zebrafish (Danio rerio) embryos were exposed to different concentrations of DEHP (0, 40, 100, 200, 400 μg/L) from 2 to 168 hours post fertilization (hpf). Thyroid hormones (THs) levels and transcriptional profiling of key genes related to hypothalamus-pituitary-thyroid (HPT) axis were examined. The result of whole-body thyroxine (T4) and triiodothyronine (T3) indicated that the thyroid hormone homeostasis was disrupted by DEHP in the zebrafish larvae. After exposure to DEHP, the mRNA expressions of thyroid stimulating hormone (tshβ) and corticotrophin releasing hormone (crh) genes were increased in a concentration dependent manner, respectively. The expression level of genes involved in thyroid development (nkx2.1 and pax8) and thyroid synthesis (sodium/iodide symporter, nis, thyroglobulin, tg) were also measured. The transcripts of nkx2.1 and tg were significantly increased after DEHP exposure, while those of nis and pax8 had no significant change. Down-regulation of uridinediphosphate-glucuronosyl-transferase (ugt1ab) and up-regulation of thyronine deiodinase (dio2) might change the THs levels. In addition, the transcript of transthyretin (ttr) was up-regulated, while the mRNA levels of thyroid hormone receptors (trα and trβ) remained unchanged. All the results demonstrated that exposure to DEHP altered the whole-body thyroid hormones in the zebrafish larvae and changed the expression profiling of key genes related to HPT axis, proving that DEHP induced the thyroid endocrine toxicity and potentially affected the synthesis, regulation and action of thyroid hormones.

Silver nanoparticles (AgNPs), the most prevalent commercial nanomaterial products, are widely released into the environment. AgNPs are toxic to various aquatic organisms, but their influence on the aquatic organism’s gut microbiota remains unknown. Here, we characterized the bacterial communities in the guts of adult zebrafish treated with AgNPs (10, 33 or 100 μg L⁻¹) for 35 days and also measured the concentration of AgNPs in the zebrafish digestive tract. As expected, dose dependence of AgNP accumulation was observed in the digestive tract, accompanied by decreased overall microbial richness and diversity. To our surprise, however, the effects of the AgNP treatment on the gut microbiota of male and female fish were not the same; furthermore, AgNPs significantly altered the relative composition of the bacterial species in the community harbored in male zebrafish but not in females. This research investigates and compares zebrafish intestinal microbiota after AgNP exposure, pointing to the potential health risk to aquatic organisms from alteration of gut microbiota.