In the UK most of the problems of contamination were caused by radioisotopes of Caesium (137) and Iodine (131).  

 In areas of heavy rain, approximately equal numbers of Bequerels of 137Cs and 131I were present. However, in dry areas more iodine was found.  This effect was also noticed in studies carried out near Zurich, where it was found that water played an important role in lowering the levels of radioactivity, and that iodine became proportionately more important in dry conditions.

Short term restrictions on milk consumption were needed due to the iodine and caesium. Caesium contamination was a long term problem in sheep meat. This is because upland areas where sheep graze tend to be on acidic soils. Here protons are absorbed onto the soil in preference to Cs. This means that the Cs remains near the surface and can easily be absorbed by plants, especially during periods of fast growth. 

In areas of clay rich soils (lowland pastures) the levels in meat from animals grazing on the land fell rapidly as the Cs was strongly adsorbed onto the clay particles.

Studies in Zurich also found that Cs was washed off the land into rivers more slowly than any other isotopes. In lakes, Cs was slower to precipitate than isotopes of ruthenium. This is because ruthenium is carried into the sediments by plankton and bacteria, Caesium is not.