3. Behavior and evolution over time of cesium-137 mass and volume activities

In soils

Caesium-137 mass activities in soils, as a result of the tests and accidents mentioned above, have fallen over the years, more rapidly than would have been the case had radioactive decay been the only factor. In fact, this decrease has been accelerated by the action of water, which carries the cesium down into the soil and into waterways [BN 3 907] . Between 1991 and 2016, caesium-137 mass activities measured in French soils decreased by a factor of 2 every 15 years on average for ploughed soils, and every 12 to 22 years...