Radioactive Plutonium is virtually non-existent in nature. Plutonium metal reacts and burns in the air producing deadly minute particles which can be inhaled into the lung, and it absorbs or clings to soil particles in its soluble and insoluble forms. In large amounts, plutonium will simply corrode in air like rusting iron.
Inhalation is the major source of plutonium exposure.
Ingestion is not considered a major source because the uptake of plutonium by plants is very low and the further uptake by humans through the gut is also very low, because it is insoluble. Plutonium is known to be the most carcinogenic or cancer producing substance on earth and it is man made. Plutonium also lodges in the testicle where it can both damage the genes of future generations and it can induce testicular cancer. It freely crosses the placenta where like the drug thalidomide, it can damage a genetically normal embryo, to produce a deformed baby. Lung cancer has been observed in animal tests.