Distribution of natural and artificial radionuclides in soil and food plant crops with assessment of radiation risk in the population

Considering that radioactive substances reach the human through the food chain, in the past decades special attention has been dedicated to these problems, in terms of radiation safety of population. As material during this dissertation, soil samples and food crops have been analyzed, from locations in the surrounding of the city of Skopje, as well as from three larger cities from Republic of Macedonia. On the basis of the examinations performed for the selected radionuclides, the specific activities have been determined for the natural radionuclides ²²⁶Ra, ²³²Th and ⁴⁰K in cultivated soil at different depths, whereby it was determined that ²²⁶Ra has the highest mean value of 34.36 Bq/kg measured at a depth of 5- 10 cm, ²³²Th has the highest mean value of 45.22 Bq/kg at a depth of 10-15 m and ⁴⁰K has the highest mean value of 623.31 Bq/kg measured at a depth of O-5 cm. The mean values of the specific activities have been determined from all depths, for the same radionuclides, whereby it was calculated that ⁴⁰K has the highest specific activity which is 608,12 Bq/kg, than ²³²Th - 43.74 Bq/kg, while the calculated value for ²²⁶Ra is 34.09 Bq/kg. in order to make a comparison in regard to a specific activity for these radionuclides, samples of uncultivated soil from the same locations have been analyzed. lt was revealed the mean value of specific activities calculated from all depths for ²²⁶Ra, ²³²Th, and ⁴⁰K are 28,30, 35.70 Bq/kg, and 506.54 Bq/kg, respectively. From this comparison it was determined that the activity of all natural radionuclides in uncultivated soil is significantly lower than their value in cultivated soil, which is due to the application of various fertilizers that have been applied to the agricultural and may increase the level of radioactivity in soils, These data were the foundation for calculation of several parameters which are the base line for determination of the radiation safety of the population. Hence, from all calculated mean values the absorbed gamma radiation dose of ²²⁶Ra, ²³²Th and ⁴⁰K in the surrounding of Skopje, the total dose rate obtained in this research is 69.39 n Gy/h and it approximately corresponds to the value of the world average. ln regard to the other parameters that have been calculated for radiation risk estimation, in general, it may be concluded that they are all within the permitted limits. Hence, the mean value of the index of radiation risk H_eks is 0.40; the mean value of the annual effective dose D_ef,sp, is 85.09 μSv; the mean value of the annual gonad dose D_gon is 490.83 μSv, and the mean value of the cancer risk factor for the surrounding of the city of J Skopje is 3,28xl0^-4. From all data, the collective dose determined arising from natural sources in the surrounding of Skopje is 56.9 man Sv. In terms of increased radiation risk, important information is the level of ¹³⁷Cs which is 12.48 Bq/kg for cultivated soil in the surrounding of Skopje, while for uncultivated soil it is determined to be 10.37 Bq/kg. The mean value of the specific activities of ¹³⁷Cs for cultivated soil is by 24.23 % higher than the mean value of the specific activities of ¹³⁷Cs for uncultivated one. The dose that originates from the artificial radionuclide ¹³⁷Cs l is 0.08 n Gy/h. ln order to see whether there is a variation with other locations, a comparison of specific activities of the analyzed radionuclides has been provided. with three large cities in the Republic of Macedonia. On basis of the specific activity values revealed for the radionuclides investigated, an estimation of effective dose due to ingestion of certain plants containing ²²⁶Ra, ²³²Th, ⁴⁰K and ¹³⁷Cs, cultivated on the specific locations. was performed. For calculations facilitation an algorithm was designed whereby. by the determined specific activity for radionuclides and the statistical amount of certain plants ingested by the population, the dose may be estimated. The revealed data from this research may be used as base line for identification of a possible future environment and plant contamination with some natural and artificial radionuclides. As a consequence, an increased population exposure to radioactivity, as well as increase of the radiation risk index, could occur. For this reason, the necessity of continuous monitoring the natural and artificial radionuclides level in the environment has to be highlighted. (author)