"...There are scores of environmental toxins that interfere with every aspect of thyroid metabolism and cause the mitochondria to malfunction. These include petroleum and petroleum byproducts; pesticides, herbicides and fungicides; heavy metals, among them mercury, arsenic, lead, aluminum, barium, and cadmium; organic solvents, including benzene, toluene, trichloroethylene, and dichloromethane; and numerous other synthetic chemicals. Fat-soluble toxins lodge in the fat cells that lie beneath the skin and surround internal organs. Women, whose bodies contain more fat than men's, hold proportionately more toxins in their systems and thus, one might assume, suffer from hypothyroidism in much greater numbers than do men. Statistics show this to be true..."
"Most thyroid diseases, whether they cause hypothyroidism, hyperthyroidism or thyroid eye disease (TED), are autoimmune disorders. Here, a defect in the immune system's response leads to diminished or excessive thyroid function or characteristic eye changes. The specific disorder that someone develops depends on the particular thyroid antibodies produced during this faulty immune response. The particular disorder can change over time and it can also improve, stabilize, or resolve when the immune system heals....
...Known triggers include cigarette smoke, stress, low selenium levels, seasonal and food allergies , sex steroids particularly estrogens, excess dietary iodine, and trauma. Thyroid cells may also be injured by oxidative stress related to the immune system's response to low antioxidant levels. Suspected environmental triggers include retroviruses, Yersinia and other enteric bacteria, and Aspartame in artificial sweeteners. The immune mechanisms that contribute to disease from environmental agents include: increased cell destruction or apoptosis, thyroid autoantibody production, inflammation as white blood cells invade thyroid tissue, and the production of cytotoxic (destructive to cells) immune system chemicals known as cytokines.
And Guy abraham, facts about Iodine and autoimmune thyroiditis(follow link for complete text):