The means by which radioactive materials can be transmitted to humans include ingestion of surface and ground water, fish and wildlife, and dairy products - primarily milk - passed through cows who have fed on crops exposed to airborne contaminants. Exposure to radioactive Iodine-131 released from Hanford has largely been in the latter form. Between 1944 and 1951 approximately 730,000 curies of radioactive Iodine-131 were released from the Hanford reactors, most of it in 19451.
Once consumed by humans, the thyroid gland receives the highest concentration of radioactive iodine. As a result, the question of thyroid related medical problems, hypothyroidism in particular, continues to be studied among Hanford downwinders and those exposed to the release of radioactive Iodine-131 around the world.