How does natural radiation enter our body through the biosphere ?

Natural radiation enters the human body through three pathways. First, some natural radionuclides in the earth crust can be washed away and carried in underground water. They then enter into the human body through water intake. Secondly, the radionuclides on the soil surface can become airborne, in the form of dust or particulates, by wind action. They then enter into the human body through respiration. Thirdly, soluble radionuclides in deep soil can be absorbed by plant root and transported up the stem. The edible portion of the plant then becomes food for human or herbivore. Radiation present in the latter may eventually enter our body through ingestion.