In addition to uncontrolled growth, they migrate throughout the body and invade other tissues, destroying the ability of the healthy tissues to functio n. Death is often the result. It is known that the cells in a malignant tumor descended from a common ancestor cell. Further, the transformation of a healthy cell into a cancer cell is linked to changes in the genes. Mutations to a gene can perturb a cell, causing it to develop and grow uncontrollably. Excess exposure to radioactive substances is to be avoided because of the increased cancer risk such exposure creates.
Radioactive substances can enter the body through either of two pathways, air or water.
These two pathways are illustrated in Figures 1 and 2, shown on the next page. General scheme for pollutants to enter the food chain through water pathways. General scheme for pollutants to enter the food chain through air pathways. The fundamental issue with nuclear cleanup and nuclear waste storage is to prevent radioactive substances from entering the food chain through the pathways shown above. In the case of nuclear cleanup, the approach followed is to recover radioactive su bstances that have been dispersed in the environment so they are not able to enter the air or water.