Polychlorinated biphenyls and thyroid function: a scoping review

Area of Science:

• Environmental Toxicology
• Endocrinology
• Comparative Pathology

Background:

• Polychlorinated biphenyls (PCBs) are persistent environmental pollutants with known endocrine-disrupting properties.
• Existing evidence on the association between PCB exposure and thyroid hormone disruption is conflicting.
• A comprehensive understanding of PCB impacts on thyroid function across species is crucial.

Purpose of the Study:

• To conduct a scoping review and meta-analysis to clarify the association between PCB exposure and thyroid hormone disruption.
• To evaluate the effects of specific PCB congeners on thyroid hormones in animal models.

Main Methods:

• Systematic literature search on PubMed, Scopus, Web of Science, and Google Scholar (2010 onwards).
• Inclusion of animal studies investigating PCB effects on thyroid function.
• Meta-analysis using a random-effects model to assess TSH, TT4, TT3, and FT4 levels, with subgroup analyses by PCB type.

Main Results:

• Significant increases in TSH were observed with Aroclor 1260 and PCB 126 exposure.
• Exposure to Aroclor 1260, PCB 118, PCB 126, and PCB 153 significantly reduced TT4 levels.
• PCB 118 and PCB 153 exposure increased TT3 levels, while Aroclor 1254 and PCB 126 decreased TT3 levels. PCB 126 significantly reduced FT4.

Conclusions:

• PCB exposure is associated with hypothyroidism in various animal models, including rodents, fish, and chicken embryos.
• The findings underscore the thyroid-disrupting potential of PCBs across different species.
• Further large-scale human cohort studies are warranted to investigate the association between PCB exposure and thyroid dysfunction in humans.