Following atmospheric release, vegetation intercepts radionuclides from wet, dry or occult deposition19 and the remaining radionuclides are deposited to the ground surface. The fraction of radionuclides intercepted by vegetation is dependent on the developmental stage of the plant and the amount of above ground biomass, and consequently the time of year is important in determining how much radionuclide is retained initially on plant surfaces. Leafy vegetables, because of their large surface area, have a high interception of radionuclides which is currently being demonstrated around the Fukushima site where radioiodine and radiocaesium activity concentrations in spinach are high compared with other crops.66

For dry deposition, interception is more effective for small particles and reactive gases than for larger particles. Interception of wet-deposited radio­nuclides is a result of the complex interaction of the chemical form of the element and the stage of development of the plant.

The process of loss of radionuclides from plant surfaces is termed ‘‘weathering’’, which is influenced by a number of physical processes, including wash-off by rain (or irrigation in agricultural systems), surface abrasion, wind action, tissue senescence, leaf fall, herbivore grazing, growth, volatilisation and evaporation.20

Direct ingestion by animals of radionuclides intercepted by vegetation can be an important contributor to radionuclide intake.