What are the two radionuclides which concentrate on seafood?

1. Cesium-137 (¹³⁷Cs): This is a highly radioactive isotope of cesium that is produced during nuclear fission. It is readily absorbed by marine organisms and can accumulate in their tissues, particularly in muscle tissue.

2. Iodine-131 (¹³¹I): This is a radioactive isotope of iodine, also produced during nuclear fission. It is taken up by marine organisms through the thyroid gland and can concentrate in seafood, especially in species that have a high iodine content like seaweed and fish with large thyroid glands.

It's important to note that other radionuclides can also accumulate in seafood, but these two are among the most common and concerning due to their potential health risks.