Radionuclide Uptake in Food and Consequences for Humans

The following sections are included:

• Preface
• About the Editors
• Contents

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.

The study of soil-to-plant transfer of radionuclides has attracted considerable attention from a large number of researchers because of the continuous pollution of soils and the effects of radionuclides on plants. In addition, it is one of the important routes for radionuclide entry into the food chain, leading to humans’ exposure to radiation. This chapter focuses on the influence of radionuclides on plant growth, with a particular emphasis on the ratio of these substances in soil and plants concerning nutrition. It is shown in this review that physical and chemical processes and biological accumulation influence the uptake and fate of radionuclides in plants. It is reported that soil contamination by radionuclides affects plant survival rates and inhibits their growth. The effects of radionuclides on plant growth depend on the type of plants, soil properties, initial radionuclide concentration in the soil, and the duration of exposure for the plants. However, some plants have developed radionuclide tolerance mechanisms and accumulate a significant amount of radionuclides, making them suitable for soil remediation.

In order to effectively address the optimization of remediating agricultural lands affected by nuclear accidents, thorough research on the parameters of radionuclide accumulation by crops and the factors that influence this process is necessary.

The mobility of radionuclides in soil is affected by a number of factors, including the granulometric composition of soils. Soils with high-dispersed particles are characterized by a high absorption capacity. Differences in the ability to fix radionuclides are associated with the mineralogical composition of the mechanical fractions of the soil. The ability of soils to fix ¹³⁷Cs is largely determined by the content of labile clay minerals in the soil.

The development of remediation techniques for contaminated soils relies on effectively regulating the processes of sorption/fixation of ¹³⁷Cs. These techniques involve the use of agromeliorants (sorbents) to minimize the mobility of the radionuclide in the soil–plant system. The physicochemical processes of the interaction between agromeliorants (sorbents) and soil, as well as the behavior of chemical analogues such as potassium (K), play a crucial role in understanding how these substances influence the transfer of radionuclides, particularly ¹³⁷Cs.

This chapter presents the findings of a series of comprehensive studies that examine how the mineral composition of soil’s clay fraction affects the behavior of ¹³⁷Cs, investigate the migration parameters of the isotopes ¹³⁷Cs and ⁴⁰K from soil to pasture grasses, and analyze the impact of agromeliorants on the biological mobility of ¹³⁷Cs in soil using radiocesium interception potential.

Almost four decades after the Chornobyl accident, the transuranium elements (TUEs), in particular plutonium (Pu) and americium (Am) isotopes, contribute significantly to the radioactive contamination pattern within a 30 km exclusion zone around the Chornobyl NPP. Nowadays, ²⁴¹Am has become the most important α-emitting contaminant in this area. Owing to ²⁴¹Am formation from ²⁴¹Pu decay, the permanent growth of the forest biomass in large uncultivated areas of the Chornobyl zone, and the enhancement of Am mobility in contaminated soils with time, a considerable increase in this radionuclide uptake by plant species in the local forest ecosystems is expected in the next decades.

The distribution of ^241,243Am and ^238,239,240Pu isotopes in the forest ecosystems of the Chornobyl exclusion zone and processes of radionuclide inclusion in biogeochemical cycles of migration were studied. Based on the obtained data on the productivity of the pine biogeocenosis components, the balance of the activity of Am and Pu isotopes in the forest biomass and soil cover was evaluated. It was demonstrated that only 6% of ²⁴¹Am bulk content in the forest ecosystem is involved in the biogeochemical cycles of migration. The obtained distribution of exchangeable forms of the radionuclides in the upper layers of the soil indicates a higher migration ability of Am compared to Pu.

In the decades since the Chernobyl NPP accident, ¹³⁷Cs has remained the primary radionuclide contributing to radiation exposure. Contaminated food is one of the primary sources of exposure for humans. Therefore, restricting the entry of this radioisotope into crops is a key measure of radiation protection for the population.

The behavior of ¹³⁷Cs in the soil–plant system changes over time due to redistribution between forms with varying degrees of biological availability and vertical migration, the effects of protective measures, and other factors. The “aging” of radioactive cesium in the soil leads to changes in the contributions of various factors affecting its accumulation in crops. Identifying patterns of ¹³⁷Cs accumulation at later stages of the Chernobyl catastrophe is essential for optimizing radiation protection measures during the transition to the existing exposure situation.

This study is based on the analysis of a dataset pertaining to ¹³⁷Cs transfer to crops during the years 2019–2020. The results of the study show a nonlinear relationship between the aggregated transfer factor of ¹³⁷Cs and the concentration of K⁺ in soil solution, soil moisture in the growing season, and the percentage of the ion-exchangeable form of the radionuclide. Furthermore, the contribution of transfoliar uptake of the radionuclide from atmospheric fallout in later stages of the Chernobyl catastrophe is identified in fields with a low level of contamination density.

Transfer factor (TF) is a parameter that has been investigated for a long time and has recently undergone several modifications. It depends on other factors; therefore, it is best to use its specific values for studies of specific forest ecosystems. Usually, TF is applicable for calculating the distribution of radionuclides in an ecosystem and for calculating the dose rate for parts of an ecosystem and for humans. There are a number of reference values which can be used or with which individual measurement values can be compared. In this work, some relevant TF values are presented for forest ecosystems, with particular attention given to edible species in temperate forests.

Radioactive contamination of natural and anthropogenic landscapes has become a significant factor in radionuclide uptake by humans since 20^th century. Contamination of soils by radionuclides occurs as a result of nuclear weapon tests, major radiation accidents, waste deposition, and using phosphate fertilizers with a high content of natural radionuclides. Various methods of rehabilitation of radioactively contaminated lands, such as plowing, liming, addition of sorbents, and addition of mineral and organic fertilizers, as well as phytoremediation techniques, have been developed. Among them, elimination of the upper soil layer and phytoremediation allow decreasing the real activity of a soil but generate secondary radioactive waste, whereas the other methods are focused on suppression of radionuclide transfer from soil to plants. Plowing the upper soil layer to deeper horizons and using ferrocyanide sorbents result in the maximum decrease in radionuclide transfer to plants among the developed methods.

Potential biological effects initiated by exposure to ionizing radiation are described in some detail, including the characteristics of radiation sources, radiation fields, dosimetry, and fundamental radiation protection quantities and units. Special attention is paid to exposure pathways and the risk assessment of radiation exposure to the human body in terms of relevant health risks reflecting biological effects resulting from external and internal radiation exposure. Some particulars are presented to illustrate the nature and severity of stochastic and deterministic effects caused by the exposure. The chapter then presents an overview of pertinent radiation protection requirements and monitoring methods for the evaluation of exposure of persons in regular and emergency situations, as well as the assessment of environmental radioactive contamination inflicted by releases of radioactivity from facilities where radioactive materials are used or stored, taking into account their possible damage or destruction resulting from accidents and potential terrorist attacks, sabotage, or other malevolent actions. In all these cases, discharges of radioactive substances from various sources, including those used in medicine, industry, and research facilities, should be considered to obtain reliable information about specific radiation routes. Radioactive materials, in the form of solid particulates, aerosols, and gases, disperse in several ways known as exposure pathways. It is essential that the description of both exposure pathways and their characteristics be expressed in officially recommended and generally accepted quantities and units. In general, the final part of an exposure pathway refers to how a person can come into contact with hazardous substances, including materials containing radionuclides.

On August 24, 2023, the Fukushima-1 nuclear power plant began dumping liquid radioactive waste into the ocean. It is planned to release water containing 22 TBq of tritium per year. This caused an outcry from the public and governments in many countries. A large amount of tritium is dumped into the ocean by nuclear fuel processing plants in France, Great Britain, and other countries. Tritium activity in fish near Cardiff reached 50,000 Bq/kg. Tritium differs from other technogenic radionuclides in that it is a part of tritium water. It can easily evaporate from the water surface and be carried by atmospheric currents to any distance. Therefore, any pollution of the ocean with tritium will quickly lead to contamination of soil, plants, and human food. In the Chelyabinsk region, unique conditions have developed for studying the process of atmospheric transfer of tritium from the surface of a technological reservoir to the surrounding area. The content of tritium in sediments and stagnant water bodies was estimated. We calculated the multiple correlation coefficients of tritium activity in water with the distance from the emission source and the deviation of the azimuth from the direction to the north. The transition of tritium into river and underground water was also studied. A regression equation was calculated for the dependence of the limiting level of ³H contamination of drinking water on the distance from the source of contamination. Correlation coefficients were calculated between the specific activity of radionuclides in river water and the amount of precipitation for the decade preceding sampling, activity and the sum of temperatures per decade, and activity and hydrothermal coefficient.

The chapter outlines the main provisions of the proposed model of competitive sorption of a microelement by a sorbent placed in a suspension of contaminated material. The simulation results were used to create a new sorption technique for cleaning radioactively contaminated material, in which competitive partitioning of microelements between material suspension and a selective sorbent is coupled with membrane separation of the contaminated material and sorbent. The above coupling is realized in the construction of a minireactor (MR), which consists of a closed container made of a semi-permeable membrane material, inside which there is a suspension of the adsorbent. As an example, the results of an experimental study of the statics and kinetics of material purification from trace amounts of Cs(I) ions pre-sorbed by the material are presented. Silica gel and soil samples in the form of an aqueous suspension were taken as materials contaminated with cesium ions. It was found that the limiting stage of sorption mass transfer of cesium ions from the material to the sorbent (particles of the suspension of Prussian blue, PB, separated from the suspension of the material by the wall of the membrane MR) is diffusion inside the pores of the membrane. The distribution of Cs(I) ions between the material, the aqueous solution, and the sorbent is determined using the difference in the chemical potentials of cesium ions in the material and the sorbent. It is found that the flow of Cs(I) ions from the suspension of the material inside the MR can be regulated by changing the pore diameter of the membrane, the size of the membrane surface of the MR, and the composition of the solution, including pH and the concentration of humic acids. The construction of the membrane MR allows its simple mechanical separation from suspensions. By using this property, it is shown that the ratio between the equilibrium concentrations of Cs(I) ions in an aqueous solution and in each of the solid phases represented by the material and the competing sorbent is additive in nature and can be described by the sum of two Langmuir isotherms for the material (silica gel, the soil reference sample, SRS) and for the sorbent (PB). In conclusion, the methods of controlling the mass transfer of sorbed ions inside a MR with a sorbent and the possibility of scaling up the technique of sorption purification of materials using sorbent-filled MRs as part of future technologies for directed and autonomous remediation of radioactively contaminated areas are discussed.

Radionuclides pose a serious threat to both human and environmental health if they are present in the environment. Radioactive waste is produced and released into the environment, both naturally and artificially. Exposure to this waste could lead to severe and potentially fatal illnesses in people. Radionuclide-contaminated habitats host several microbial species that develop a high degree of tolerance to these elements through mechanisms such as biosorption, biotransformation, biomineralization, and intracellular accumulation. These mechanisms involving interactions between microbes and radionuclides have the potential to be used in biotechnology for designing solutions to address various contamination problems through bioremediation. Bioremediation has been proven to be more ecofriendly than physical remediation for the environment. Microorganisms possess inherent genetic, metabolic, and physiological characteristics that render them highly suitable for the purpose of pollutant remediation in soil and groundwater. Microorganism-aided bioremediation can impact the solubility, bioavailability, and mobility of radionuclides. This study presents a comprehensive analysis of several reports in an attempt to understand how microorganisms interact with radioactive substances and how they withstand the effects of ionizing radiation. The review incorporates a multidisciplinary approach and provides an assessment of the current status of research in this field.

Radionuclides produced during nuclear fission or explosion in civil industries and research activities, such as isotopes of chromium, cesium, plutonium, radium, strontium, tritium, and uranium, could be released, contaminating the natural ecosystems, which can have serious impacts on living beings, causing carcinogenesis and mutagenesis, as well as on the environment. Therefore, proper management of radionuclide and heavy metal waste from potential sources is necessary through eco-friendly remediation methods. However, it is often very tedious to degrade radionuclides and heavy metals from contaminated sites; however, these can be effectively converted into less toxic forms, minimizing their hazardous effects. Radionuclide-contaminated environments are inhabited by various microorganisms resistant to such elements. The interaction of radionuclides and microbes represents a bioremediation strategy that includes biosorption, bioleaching, biomineralization, and biotransformation to withstand such stress conditions. This chapter provides a review of the sources of radionuclides and their effects on the environment, and it elucidates the microbial interaction with radionuclides. In addition, the advancement of biotechnological applications in bioremediation and approaches for environmental pollution control through detoxification and degradation of radionuclides are discussed.

Radionuclides are present in the environment or result from human activities, such as the use of radiation or nuclear technologies. The presence of radionuclides in foods can pose certain health risks, and their toxicity depends on several factors, including the intake of radionuclides, the type of radionuclide, its concentration, and the specific characteristics of the food. Under typical situations, the contributions of internal exposure to the human body from food or water, where only trace concentrations of usually natural radionuclides are present, are minor in most cases. Slightly different situations may occur when food, due to radionuclides from man-made sources used in various applications in industry and medicine or radioactivity induced during radiation sterilization of food, shows an increased level compared with the natural background concentrations. But even here, there is no reason to consider the impact on living organisms to be serious since the increase in exposure levels is only a fraction of exposure due to the natural background.

On the other hand, however, the concentration may be higher in some cases when the food is produced from plants or animals that are heavily contaminated. Specific aspects of radioactivity or, in general, ionizing radiation (hereinafter, simply, radiation), which can be detected even at particularly small levels thanks to the availability of very sensitive instrumentation, have to be stressed here. Radiation monitors are able to measure even extremely insignificant changes within the fluctuation level of natural radiation. When the instrument shows some results close to the background level or even up to several times this level, there is no need to be concerned since the impact of such exposure on a person is almost negligible in comparison with other, much more dangerous situations we face daily in our typical living or working environment caused by many other, much more hazardous agents. The chapter will present an overview of the health risks attributed to the toxicity resulting from exposure to foods contaminated by radionuclides of various origins.

The following section is included:

• Index