long term accumulation of potentially biologically active substances in the body is an increasing concern and is becoming more recognized as a major health threat not only to humans, but also other animals
cesium-137 in the food chain - 80% of ingested amounts accumulate in muscle with a radio-active half-life of 30yrs
iodine-131 does not accumulate as it has a radio-active half life of only 8 days and is generally cleared from the body within 6 days, but it can cause issues with the thyroid in acute high doses and cause delayed onset thyroid cancers
persistent pathogenic infections which remain potentially active in the body after they have been acquired with potential to cause harm or re-activate