Thyroid disrupting chemicals: mechanisms and mixtures

Area of Science:

• Environmental Science
• Endocrinology
• Toxicology

Background:

• Environmental contaminants can function as thyroid disrupting chemicals (TDCs).
• TDCs are xenobiotics that disrupt thyroid gland structure/function, thyroid hormone (TH) homeostasis, or TH concentrations.
• Thyroid hormones are critical for nervous system development, increasing concern over TDC exposure.

Purpose of the Study:

• To review the complexities of assessing TDC mixtures.
• To highlight uncertainties in extrapolating animal data to humans.
• To emphasize the need for understanding how diverse TDC mechanisms impact THs and nervous system development.

Main Methods:

• Literature review of TDC mixture studies.
• Analysis of uncertainties in TDC research.
• Examination of different biological levels for effect assessment (molecular vs. downstream consequences).

Main Results:

• Limited TDC mixture data suggest dose addition can predict effects on serum T4 concentrations.
• Significant uncertainties exist in interpreting and extrapolating TDC mixture data, especially across species.
• TDC mechanisms of action vary, complicating the assessment of cumulative effects.

Conclusions:

• Assessing health risks of environmental TDCs requires understanding their impact on THs and nervous system development.
• Improved methods are needed to address uncertainties in TDC mixture studies.
• Further research should focus on how divergent TDC mechanisms affect THs and downstream neurodevelopmental outcomes.