Estimation of 137Cs and 90Sr accumulation in the organism of dairy cows in the radioactive contaminated agro landscapes of the Central Forest-steppe in the remote period of the Chernobyl catastrophe

Abstract

Because of the Chernobyl catastrophe, almost all the territory of Polissya and a significant part of the Forest-Steppe south of Kyiv suffered radioactive contamination. More than three decades have passed since the Chernobyl accident, but despite the time since the disaster, the problem of radioactive contamination is still very relevant. In radioactive contaminated agro landscapes, plant fodder becomes a source of 137Cs and 90Sr in the body of cows. In the organism of an animal, radionuclides of cesium mainly accumulate in muscle tissue, and strontium in bone and excreted with milk, urine and feces. Milk plays an important role in human nutrition, which necessitates constant monitoring of the radio ecological situation, estimates of the accumulation of 137Cs and 90Sr, and the determination of the laws governing the transition of these radionuclides into products. The aim of the research was to evaluate the supply of 137Cs and 90Sr with feed in the body of dairy cows and the accumulation of these radionuclides in milk and barnyard manure mass in radioactive contaminated agricultural landscapes of the Central Forest Steppe. The research was carried out at LLC "Agro-Leader Ukraine" Ltd. and "Nadiya" Ltd and on the peasants’ plots of Yosypivka, Tarasivka villages of the Bila Tserkva district of the Kyiv region who suffered from the radioactive contamination because of the Chernobyl catastrophe. Samples of soils, fodder, milk and barnyard manure mass for conducting research were selected. The activity of 137Cs and 90Sr was determined at the USM "Gamma Plus U" with the "Progress 2000" software in the laboratory of the Bila Tserkva NAU, department of life safety. The activity of 137Cs was determined by the method of scintillation gamma spectrometry in a Marinelli vessel of volume 1L in native samples or after their physical concentration, and 90Sr – after radiochemical isolation by scintillation beta spectrometry. The results of the studies indicate that the content of 137Cs and 90Sr in feed is directly proportional to the level of soil contamination by these radionuclides. At the same time, the least accumulated 137Cs and 90Sr in the green mass of corn, and most of all in the green mass of alfalfa and oats mixture. The intensity of the accumulation of 90Sr in the green mass of corn is 20 times, the alfalfa – in 1,5-2 times, the use of oatmeal mixture – 4 to 6 times higher than 137Cs. It has been established that the concentration of 137Cs and 90Sr in milk of cows is directly proportional to their activity in the diet. In the daily hopes of milk from cows from the diet 7,6 ± 0,55 % of 137Cs and 1,7 ± 0,42 90Sr passed from their activity in the diet. The coefficient of transition of 137Cs in 1 liter of milk on average was 0.76 % and 0.17 % 90Sr. The activity of 137Cs and 90Sr in milk does not exceed the permissible levels. At the same time, in the milk of households, the activity of 137Cs and 90Sr in the spring-summer period was two to three times higher than that of autumn-winter due to the grazing of cows in natural pastures, where the level of soil contamination is much higher than that of arable lands. The determinants of the formation of 137Cs and 90Sr activity in cow’s milk are the amounts of these radionuclides with feed from the daily ration, which depend on the composition of the diet and the density of soil contamination on which the forage crops are grown. Studies have shown that the main proportion of 137Cs and 90Sr (up to 90 %), coming from plant foods in the body of cows, is converted into a barnyard manure mass. The accumulation coefficient of 137Cs and 90Sr in the cow barnyard manure is 0.87. The barnyard manure mass of cows, when introduced into the soil, becomes a source of secondary soil contamination and promotes the migration and redistribution of 137Cs and 90Sr in agro landscapes. Obtained in radioactive contaminated areas of the barnyard manure mass of cattle must be used only within the farms in which it is produced. Studies have shown that fodder crops can be grown on the radioactive contaminated forest-steppe areas and it is possible to get milk without any restrictions. Key words: agro landscapes,radioactive contaminated areas, radionuclides, 137Cs, 90Sr, grass, dairy cows, milk, cow’s manure, forest-steppe zone.