Table 1.

Partial List of Environmental Agents That Interfere with Thyroid Function

Agent	Example of sources	Mode of action	Associated as a trigger or accelerating autoimmune thyroid disease
PCBs	Found in coolants and lubricants, multiple cogeners, lipophilic	TR agonist/antagonist, can alter levels of T4 and TSH	Possible increase in TSH, thyroid autoantibodies, thyroid volume
Organochlorine pesticides	Used as pesticide on crops	Induce hepatic UDPGTs and glucuronidate T4, accelerating metabolism	No human studies establishing association
PBDEs	Found in flame retardants	Bind to TRs, displaces T4 from binding proteins	Increase in HT in some studies
BPA	Used in plastic bottles	Antagonize TR	No human studies establishing association
Perchlorate, thiocyanate	Rocket fuel, fertilizer, smoking	Inhibits iodine uptake	No human studies establishing association
Triclosan	Antibacterial in soaps	Reduce serum T4, disrupt amphibian development	No human studies establishing association
Isoflavones	Soy products	Inhibits TPO activity	Possible increase in HT

PCBs, polychlorinated biphenyls; TR, thyroid hormone receptor; T4, thyroxine; TSH, thyrotropin; UDPGTs, uridine diphosphate glucuronyltransferase; PBDE, polybrominated diphenylethers; HT, Hashimoto's thyroitidits; BPA, Bisphenol-A; TPO, thyroid peroxidase.