Dynamic of specific activity of radioactive isotopes (137Cs, 40K, 226Ra, 232Th) in grey forest soil of the Right-Bank Forest-Steppe depending on mineral fertilizer application in Brassica napus L. oleifera сultivation

Abstract

The aim of the article is to determine the content of radionuclides 137Cs, 40K, 226Ra, 232Th in the main types of mineral fertilizers (nitrogen, phosphorus, potassium) and to assess the total radionuclide input of these fertilizers into grey forest soil during Brassica napus L. oleifera cultivation with varying target yields (30 c/ha and 35 c/ha). Methods. Gamma-spectrometric determination of the specific activity of radionuclides 137Cs, 40K, 226Ra, 232Th was carried out in samples of ammonium nitrate, double superphosphate, and potassium chloride. Based on the obtained data and the actual fertilizer application rates required to achieve the planned Brassica napus L. oleif- era yield, the total input of radioactive substances in Bq/ha into the grey forest soil was calculated. Results. It was established that mineral fertilizers are a source of radio- nuclide input into the soil. Potassium chloride shows the highest specific activity among all fertilizers due to the high content of the natural isotope 40K (up to 16 400 Bq/kg), which is the main dominant radionuclide. Phosphorus fertilizers (double superphosphate) have an increased content of 226Ra and 232Th. When applying fertilizers for Brassica napus L. oleifera cultivation (yield 30–35 c/ha), the total radioactive load on the grey forest soil is 3.7–5.2 MBq/ha. The largest contribution to the total con- tamination is provided by potassium chloride (63–66 %), and 40K constitutes the predominant share of the intro- duced radioactivity. Conclusions. Mineral fertilizers are a significant factor of additional radioactive load on the soil. Potassium and phosphorus fertilizers carry the greatest radionuclide risk. Potassium chloride is the largest source of 137Cs, 40K, 226Ra, 232Th input into the soil. It is necessary to mandatory consider the radionuclide content in fertilizers when planning agricultural measures to minimize their input into the soil-plant system.