Radionuclides, once deposited by rainwater or air onto the ground, will find their way through the ecosystem. We are already tracking its path from rainwater to creek runoff to tap water, but we would also like to monitor how much these isotopes that make their way into our food. For example, how much gets taken up by the grass and eventually winds up in our milk?
We have been collecting produce that is as local as possible to test for the radioactive isotopes. We might expect different kinds of plants to take up different quantities of cesium and iodine, so we are trying to measure as many different plants and fruits as we are able to. So far, we have measuredgrass, wild mushrooms, spinach, strawberries, cilantro, kale, and arugula. We have also measured local topsoil.
The topsoil, grass, and wild mushroom samples collected so far all come from the same place, so comparing grass samples to each other is a fair "apples to apples" comparison. For most of the produce, different samples came from different markets and different farms, so there will be many factors influencing the results. This variety of produce helps provide a picture of the food chain as a whole. But for understanding the time-dependence of the food chain results, the grass and soil is what to look at.
In the tables below, we are providing two numbers for each of the isotopes. The first is a standard concentration unit of Becquerel per kilogram (Bq/kg) which is the number of particles decaying per second in each kilogram of the sample. The number in parentheses after the activity is the number of kilograms that one would need to consume to equal the radiation exposure of a single round trip flight from San Francisco to Washington D.C. (0.05 mSv). For more information on how this equivalent dose is calculated, the details are here: How Effective Dose is Calculated
The experimental setup used for the food testing is the same setup used for the Rainwater Collection Experiment.