Released radioactivity is dispersed into the environment and is deposited in the soil and in plants. The nuclides can reach edible foodstuffs and animal feeds via various routes (surface of leaves, roots). By feeding on or consuming these goods, they can enter the bodies of humans and animals. Depending on the half-life and type of nuclide, the danger can persist for long periods of time. In order to establish the level of danger and to be able to take the necessary measures to protect the population, it is important to estimate the behaviour of individual nuclides in the biosphere.The radio-ecological model CHECOSYS, developed in Germany and adapted to Swiss conditions, is used for these forecasts. Starting with the existing radioactivity in the air or deposited in the soil and in plants, the model calculates the resulting concentrations in foodstuffs and animal feed. The dose contributions to be expected are then assessed, using assumptions on particular human consumption behaviour. If the values are too high, a ban on harvesting crops or restrictions on certain foodstuffs may be introduced .