Environmental Pathway Modeling Part 2

I've touched upon the transfer of radionuclides through air, ground, and water, and in the last part we discussed how organizations like the EPA use pathway models to factor in all three to estimate damage from a contamination (accidental or otherwise), and help direct their most effective course of action in containing, controlling, and removing the contamination. Reading through some of my classmates' blogs brought up an aspect I had not considered, however: the spread of nuclear contamination through organic matter, especially food. 

Radioactive atoms can stay around for a long time. A really long time. We're talking "the Earth has only existed (4.543 billion years) for as long as one half-life of uranium-238 (4.468 billion years)" level of long time. Now, uranium-238 is mostly harmless, as that long half-life makes it essentially stable and not enough to harm humans except in rather large quantities. But the half-lives of all radioactive isotopes make a pretty decent spectrum--ranging from infinitesimally small to unfathomably large--and many fall in the range of months to a few years. This time frame is what we would be most worried about when it comes to food: active enough to give off dangerous levels of radiation, but with enough longevity to stick around and be transferred through food.

When the radiation from a contamination (spill in transport, facility accident, dirty bomb, etc.) gets into the soil and groundwater, it can be absorbed by plants along with their usual nutrients from the soil and water. [1] Of particular note are tritium (hydrogen-3), carbon-13 and -14, technetium-99, sulfur-35, and iodine-129 and -131, among a few lesser others, as all of them are easily absorbed into organic material and by the biological processes of plants and animals. 

The organic material that absorbs these isotopes can have a much higher quantity of radioactive material than the water or soil that supplies it to them, due to the "Bioaccumulation  Factor"[2]. These plants could be in a farm meant for human consumption, or even in a food not typically associated with humans (such as grass) and passed up the food chain into an animal that we will eat (such as a cow), These radionuclides aren't filtered out of the body very quickly or efficiently, especially if it's an isotope of an atom normally expected to be in the body in at least a small quantity (such as carbon, sulfur, and iodine). When these isotopes then decay, the radiation they release can be absorbed by some of the most sensitive parts of the body, like the lungs, brain, or intestines. Parts that normally expect to be protected from radiation exposure by the epidermis. 

Modeling the spread of radioisotopes through the food chain proves to be even more difficult than through the geography of the environment, and the exposure caused can be an even larger danger to humans. As such it is of equal if not greater importance to the EPA for research and development of proper predictions and responses. 

[1]http://www.who.int/foodsafety/fs_management/radionuclides_and_food_300311.pdf

[2]http://www.nap.edu/read/5803/chapter/6#74