Final report of the research projects sponsered by Association EURATOM - C.E.A. under the No. SC 007/61 PSTD. Pt. 1

Field experiments for determining the deposition and desorption of elemental iodine on vegetation are being presented. For dry surfaces, theoretical reflections in conjunction with experimental results have led to a simple semi-empirical equation, defining the deposition velocity as proportional to the dry matter of vegetation per area unit, relative air humidity, atmospheric friction velocity and a biological quality factor. The biological quality factor, which could not be determined by any direct measurement, is more or less constant at the beginning and at the end of the growth period and increases by about the factor five during the period from end of May to end of August. Measurement of the biological half-life of iodine on grass has yielded a mean value of 7.5 d. A similar value is found for clover. Any influence on biological half-life by meteorological parameters such as the duration of sunshine and precipitation per day should be ruled out. In the event of the grass being cut after contamination, no decrease of the iodine contamination could be measured. This is indicative of the fact that the reduction of the iodine content of vegetation is closely linked with the processes taking place in living plants. Furthermore, the deposition velocity of methyl iodide was measured in a closed system. Although it only amounts to 0.5% of the deposition velocity for elemental iodine, it is not low enough to justify a neglection of the ingestion exposure caused by methy iodide besides the inhalation exposure. (orig./HP)