Radioactive contamination of food has become a big concern since the Fukushima. This articles will explore how radioactivity finds it's way into the food chain.
Plants can take up radioactivity from the naturally occurring radioisotopes in the soil and from man-made radioisotopes from nuclear testing and releases from nuclear power plants. Soil contains natural uranium-238 and uranium-235, thorium-232, potassium-40, radium 226 and radon 222. Iodine-131, cesium-137 and strontium-90 come from man-made sources.
Where food is gathered from a natural environment such as mushrooms in a forest, the radioisotopes are easily taken up by the plant and fungi from the soil. Radioisotopes are more tightly bound to soil particles in agricultural regions and is less easily absorbed by growing plants. The type of soil used to grow food plants is important when considering absorption of radioactivity. In soil that has a lot of clay and low amounts of organic material, cesium-137 is locked up and immobilized by clay particles. In other soil where the concentration of clay is low and there is a lot of organic material, radioisotopes are mobile and readily available for absorption. Greater acidity of soil also favors the absorption of radioactivity by plants.
In plants such as red lettuce and other vegetables where the surface area is big compared to the weight, radioactive dust particles carried by winds and washed out of the air as rain can contribute to the contamination of food by radioactivity.
Milk and other dairy products are in danger of significant radioactive contamination when cattle eat grass that has been exposed to fallout in the wind and rain. The fact that cattle may consume a large amount of contaminated grass every day leads to concentration of radioisotopes such as strontium-90, iodine-137 and cesium-137.
Animals such as pigs and cattle as well as birds such as chickens which are raised for meat can absorb radioactivity from their feed as well as directly from fall out. Cesium-137 tends to concentrate in muscle meats and is a special concern. Strontium-90 will accumulate in bones and is not as dangerous unless the bones are ground up and use in food products.
Ocean water contains a small amount of natural radioactivity. The main concern with seafood is radioisotopes resulting from human activity such as Iodine-131, cesium-134 and cesium-137. The iodine is water soluble and has a short half-life. The cesiums have half-lives in years and can react or be picked up by particles. They are either suspended in the water or fall to the bottom. Cesium builds up in bottom feeding bivalves such as clams, oysters and gooey ducks. They are also consumed by crustaceans such as crabs and lobsters. The bivalves are either directly consumed by people or by larger fish which are consumed by people.
Iodine-131 is mainly a problem in the first few days after a nuclear accident because of its water solubility and short half-life. However, if exposed food is consumed in that short time period, the iodine-131 will concentrate in the thyroid gland and may lead to thyroid cancer.