The radioactive contamination of food is a growing problem. It’s useful to know which food plants are affected more than others, and which radionuclides different plants absorb more than others. I found an interesting and very large document “Radiological assessment: A textbook on environmental dose analysis”, which was prepared for the NRC in 1983.
The table which can be downloaded here contains the ratio of radioactive materials found in edible portions of plants, to that of radioactive materials found in the soil. If the amount of a radionuclide in soil is X, the table shows how much is in the plant relative to X. For example, the value of 3.1 in the row “strontium-90” and column “alfalfa” means that 3.1 as much strontium-90 is in the alfalfa than in the soil, per unit weight.
The first thing that is obvious from the table is how much higher the values are for strontium-90 than other isotopes. This shows how dangerous Sr-90 is, how pervasive it is in the environment. This isotope, which causes bone cancer and leukemia, concentrates in bones and bone marrow. Note that 8 times as much collects in wheat, versus corn and rice. Also 33 times as much Sr-90 is absorbed into alfalfa than cesium-137. Alfalfa is fed to dairy cows. Trying to gauge the safety of milk and dairy products by cesium alone is misleading.
Iodine-129 is also very high in alfalfa (20 times the ratio of Cs-137). We can see that the highest risk in milk is in Sr-90 and I-129 (which causes thyroid cancer). These two isotopes are also found in grasses, which is the food source for beef cattle.
Note that the ratio of plutonium-239 is very low. The main risk for exposure to Pu-239 is in air and drinking water. Plutonium binds tightly to clay soil. But note americium-241 has a much higher ratio. Pu-241 decays to Am-241 with a half-life of 14 years. Americium is a bone seeker like strontium and plutonium.