Impact of a mixture of organic pollutants on the thyroid axis

Introduction

Endocrine disruptors (EDs) are widely recognized for their adverse effects on human and environmental health. Studies suggest that their ubiquitous presence impacts amphibian metabolism, contributing to their decline over several decades.

Materials and methods

A mixture of six obesogenic EDs (TBT, TCS, DDE, PBDE, BaP, and DEHP) was studied at concentrations corresponding to environmental quality standards (EQS) over short- and long-term exposure periods in Xenopus tropicalis at three developmental stages (NF 47, 62, and 65). Particular attention was given to the thyroid system, which plays a key role in metabolic regulation.

Results and discussion

The results show that short-term exposure induces increased proliferation and reduced cell mortality in the brains of exposed tadpoles. Additionally, a significant increase in mobility was observed in darkness during the active phase. At the molecular level, exposure to the mixture led to alterations in the expression of specific genes.

In the long term, histological analysis of the thyroid glands revealed structural changes, characterized by a reduction in colloid content, clusters of thyrocytes, and follicular disorganization.

Conclusion

These findings indicate that this obesogenic mixture is not inert at the tested EQS concentrations in exposed frogs, highlighting the importance of studying chemical mixtures rather than individual compounds.