Monitoring of radionuclide contamination of plants in the western part of Volyn Polissya (Ukraine) during 1994–2007

Abstract

We present the main results of our more than decade-long monitoring of 137 Cs content in berry plants and medical herbs growing in the Shatsk National Natural Park (Volyn Region, Ukraine). It is shown that the 137 Cs content for most of the medical herbs has significantly decreased during the monitoring time period and now it meets the demands of Ukrainian sanitary standards (less than 200Bq/kg d. w.). The decreasing rate is much higher than that for the corresponding soils. This is because the radionuclide available in the soil becomes less accessible for digesting by the plant rootage in the course of time. The 137 Cs content in the vegetative and generative organs of bilberry shows essential seasonal variations. The corresponding content for the foliage reveals almost double decrease during the period when the berries ripen and an increase occurring after fructification. Radiologic studies of flora have become especially urgent after the Chornobyl disaster. During more than twenty years, these studies have been attracting permanent attention of researchers, both from the countries that have suffered most of all from the post-Chornobyl fallouts (Ukraine, Byelorussia and Russia) and from many other regions of the world. This interest is caused by the fact that entrance of radionuclides via typical food chains represents a crucial point in contaminating human organisms and so their internal irradiation. In its turn, contamination of foodstuff is now associated mainly with transition of radionuclides from soil to plants. The processes of accumulation of radionuclides from the soils taking place in the plants depend on many factors (1). In particular, they are determined by specific kinds of radioisotopes, their amounts and states in the near-root layer of the soil (exchanging, non- exchanging or fixed). Again, the states mentioned above are dependent on the type of soil, its physical, chemical content and grading, acidity, amount and type of moistening, as well as availability in the soil of the closest chemical analogues of the radionuclide. Of importance are also some features of the depth distribution of radionuclide in the soil, together with species of the plant itself (2-4). All of those factors may lead to essential discrepancies in the experimental results derived for radionuclide contamination of representatives of a given plant in different regions. The same also refers to the plants that belong to different species, though grow in the same region (2-4). Of course, the radiologic studies enable estimating the level of radioactive contamination of the plants only in a specific place and under specific conditions. Nonetheless, they facilitate forecasting time evolution of the contamination. The mentioned studies are all the more important for the contaminated territories of Ukrainian Polissya, since about a quarter of radiocaesium amount entering into organisms of people living on those territories is caused just by the berries used for food (5). In general, the contribution of wild mushrooms and berries to the internal irradiation of the population of this region may reach 75-80% of the overall internal irradiation linked to the foodstuff (6). Our choices of the place (Shatsk National Natural Park abbreviated as ShNNP, which is situated in the Volyn Region) and the objects of inquiry (berry plants and medical herbs) are justified by the