Endocrine Disruptors Chemicals: Impacts of Bisphenol A, Tributyltin and Lead on Thyroid Function

The large-scale industrial production characteristic of the last century led to an increase in man-made compounds and mobilization of natural compounds, many of which can accumulate in the environment and organisms due to their bioaccumulation and biomagnification properties. The endocrine system is especially vulnerable to these compounds that are known as endocrine disruptor chemicals (EDCs). Thyroid hormones (THs) are essential for normal development and growth, besides being the main regulators of basal metabolic rate. Thus, compounds able to affect THs synthesis, transport, and action could produce important deleterious effects, impacting the development of metabolic and endocrine diseases. Herein, we will review the main effects of EDCs on the thyroid axis, with special emphasis on the widely used substances bisphenol A (BPA), employed in the synthesis of polycarbonate plastics and epoxy resins; tributyltin (TBT), an organotin chemical substance widely used in several agro-industrial applications; and lead (Pb), a ubiquitous environmental and occupational polluting heavy metal. Exposure to these EDCs occurs mainly from the ingestion of contaminated food and beverages. Furthermore, there are few epidemiological studies evaluating human risk, and experimental studies employ different exposure models, making it difficult to integrate results. However, even low doses of these EDCs warn of thyrotoxicity. Since THs homeostasis is essential for health and humans are increasingly being exposed to EDCs, it is important to clarify which substances might act as thyroid hormone system disrupting chemicals and how they act in order to try to overcome their deleterious effects and limit the exposure to these compounds.