Much of what we know about the link between cancer and radioisotopes released during nuclear disasters is from the studies in the aftermath of the 1986 nuclear disaster of Chernobyl.
The disaster at Chernobyl released 4 different isotopes including Strontium-90, Plutonium-239, Iodine-131 and Cesium-137. Of these, I-131 is particularly of concern as it accumulates in the body just like non-radioactive Iodine. I-131 can be ingested from the environment as well as through food and can stay in the body for a long time despite its 50% degradation rate of 8 days in the environment.
The National Cancer Institute also found that the likelihood of thyroid cancer increased with each dose of I-131, with the risk doubling with each unit of radiation. In this context, the butterfly shaped organ wrapping around your windpipe, the thyroid can become a deadly cancer. The Fukushima accident, where three of nuclear reactor cores melted due to a failure of the cooling systems caused by a 15m tsunami (Read more on Fukushima disaster and its effect on nature).
The main radionuclide among the volatile fission products in the Fukushima disaster was I-131. Since March 2011, 370,000 children have been given routine ultrasound checkups in the Fukushima prefecture. The screening is a proactive step taken by the government of Japan to ensure the early detection of thyroid cancer among evacuees and vulnerable population.
A recent study led by Toshihide Tsuda based on the data from Fukushima Medical University shows that among those screened, 137 children have been detected positive for Thyroid cancer with an increase of 25 cases from last year. This is a sharp contrast from other regions where the disease occurs in 2 out of every million kids.