Chapter 1: Distribution of Radionuclides in Soil and Their Entry into Food through Uptake by Plants

Radiocesium (Cs-137, t_1/2 = 30.2 years), a long-lived anthropogenic radionuclide, has been the subject of extensive research on soil-to-plant uptake factors due to the fact that it is widely released from global fallout and other nuclear catastrophes. However, other radionuclides in the environment are either anthropogenic (such as Sr-90 and Pu-239) or naturally occurring (such as ²³⁸U and ²³²Th), and their daughter nuclei in the natural radioactive decay sequence, as well as ⁴⁰K, can be absorbed by plants. Due to their presence in the soil, they have a chance of spreading to plants and contaminating the food supply. The primary method by which plants absorb radionuclides is through root absorption, and the soil-to-plant transfer factor (TF) is typically used to simulate radionuclide transfer from soil to plants. The primary objective of the research is to calculate the activity concentrations due to natural and man-made radionuclides in some soil and rice crops, including their soil-to-plant TFs. A total of 15 soil and 5 rice plant/grain samples were collected for the measurements of ¹³⁷Cs, ⁴⁰K ²²⁶Ra (²³⁸U), and ²³²Th. A high-purity germanium (HPGe) detector was used to measure the activity of these radionuclides. The average radioactivity for ²²⁶Ra (range: 21.13–23.52 Bq kg⁻¹), ²³²Th (range: 28.72–48.53 Bq kg⁻¹), ⁴⁰K (range: 274.78–374.52 Bq kg⁻¹), and ¹³⁷Cs (range: 0.19–1.23 Bq kg⁻¹) were found to be 31.69, 38.79, 319.07, and 0.88 Bq kg⁻¹, respectively. The total combined uncertainty (%) was found to be 15, 7, 8, and 10 for ¹³⁷Cs, ⁴⁰K, ²³²Th, and ²²⁶Ra, respectively. In general, these values are in good agreement with other literature or world average values. Multivariate statistical techniques, such as correlation matrices and cluster analysis, were applied to the radioactive datasets in order to comprehend the intricate correlations between the radioactive variables and their environmental categories. The following radiological indices were calculated: radium equivalent activity (Ra_eqv), absorbed gamma dose rate (D_g), yearly effective equivalent dose (Y_d), yearly gonadal equivalent dose (Y_gd), average yearly committed effective dose (A_cd), external hazard index (H_ext), internal hazard index (H_int), internal alpha radiation hazard indices (I_a), gamma radiation representative level index (I_ri), and lifetime cancer risk (L_rc). The collected data are crucial for mapping naturally occurring radioactivity and serve as a baseline for assessing radiation risk in the future caused by changes in radio-activity levels brought on by nuclear, industrial, or human activity. In continuation of earlier research, the TFs in some rice plants/grains from soil radioactivity for anthropogenic and naturally occurring radionuclides are also assessed. The background, methods, ideas, radioactivity measurement, dose calculation, and future direction on the soil–plants– food cycle are all thoroughly discussed in this book chapter.