Enhanced airborne radioactivity during a pine pollen release episode

A single episode of pine pollen release in the highly contaminated area of Novozybkov, Russian Federation, which led to enhanced atmospheric concentra tions of Cs-137 is discussed. The pollen grains were sampled by a rotating arm impactor and analysed by gamma-spectrometry for Cs-137 activity and by image analysis for their size. In the vicinity of a forest, a maximum conce ntration of 4.5+/-0.4 mBq m(-3) was measured, and a mean activity per polle n grain of 260+/-80 nBq was determined. The emission rate of the Novozybkov mixed pine forest was estimated to be approximately 400 Bq m(-2) per year. Because of the large size of pine pollen grains (about 50 mu m) and the sh ort emission period of 5-8 days per year, the estimated potential annual in halation doses are very low. Biological emissions including pollen release may be a source of increased airborne radionuclide concentrations at larger distances from the source areas as well.