DEvans has it spot-on.
-- here is a little more detail:
http://lpi.oregonstate.edu/mic/minerals/iodine
This references data about iodine food content. Marine food sources
are very constant in terms of sampling at different times and places.
So seafood and algae have a pretty much known iodine content.
Many places in the world have iodine-depleted soils. India for example.
Rice imported from most places in India has low to very low iodine levels.
For this reason among others, the gold standard for learning about the
nutrient content of foods:
http://ndb.nal.usda.gov/ndb/search/list
does not have iodine listed for any food. The iodine content of food
plants varies a lot. Swine and beef production depends on micronutrient
supplements to increase production. Iodine is listed on Purina pig chow.
FWIW pickling salt never has added iodine in it. Pickles are made by
brining cucumbers in hot brine. Iodine in the salt used to make 30%-35%
changes color of the finished product. So it is not used there.
If you want high iodine try iodized salt or seafood. Multi-vitamin and
mineral pills usually have iodine as well. A North American diet even from
fast food places will have sufficient iodine.
Unless directed by a physician do not try to avoid iodine - aside from the
fact that in the Western world it is difficult to do - it is a required
nutrient. Its absence in the diet can lead to goiter in adults, and a dimished mental
capacity in children.