fluoridated water
chemical fertilizers
chemical pesticides
teflon pans
scotchguard
various medications including prozac, etc.
fluoride will accumulate in your thyroid and will be used instead of Iodine to make your hormones, which then wont work at the cellular level.
it is ubiquitous, but it is a killer and it is essential to avoid it as much as possible.
also, perchlorate will destroy your thyroid and is found in water supplies in california. even some organic veggies from california contain it. it is a rocket fuel and used in drycleaning processes!