"Animal studies have also demonstrated that a number of chemicals, including but not limited to PCBs, PBDEs, some phthalates, and perchlorate, can reduce circulating levels of thyroid hormone. Interestingly, not all of these chemicals also cause an increase in serum TSH."
From: Executive Summary to EDC-2: The Endocrine Society’s Second Scientific Statement on Endocrine-Disrupting Chemicals, page 7.