Radioactivity and food safety in Serbia: Chernobyl accident and 4 decades later

Radioactivity occurs due to natural processes or as a consequence of various antropogenic activities such as nuclear power plants, military industry, etc. Food chain is one of the most important ways of contributing to the total radiation dose of an individual, as all types of food contain radionuclides. Continuous control of radioactivity levels in food, and inclusion of such data in publicly accessible databases is of great importance. Radioactivity occurs due to natural processes or as a consequence of various anthropogenic activities (nuclear power plants, military industry, etc.) (Cinelli et al., 2019; čulović et al., 2020). Radioactive contamination of the environment can arise in several ways: due to technological development, use of nuclear energy, experimental nuclear testing, as well as due to the use of nuclear weapons. Regardless of the origin, radioactive substances endanger living organisms. From the point of human population, food chain is one of the most important ways of contributing to the total radiation dose of an individual, as all types of food contain radionuclides (Figure 1). Therefore, it is essential to use food of plant and animal origin with the lowest possible amount of radionuclides, in order to minimize the exposure to radiation. However, it should be noted the levels of natural radionuclides in food and drinking water are rather low and their concentrations are considered safe for human consumption. Many laws and rulebooks are created and implemented with the aim of ensuring a high level of protection of life and health for people. Moreover, it is of high importance to protect consumer interests and ensure the production and trading of safe food, but also to protect plant and animal health and welfare, as well as the entire environment, when possible. Radionuclides that are of major interest in food monitoring programs are natural radionuclides 40K, 210Pb, 226Ra, 238U, and 232Th, and artificial radionuclides 90Sr, 131I, and 137Cs (Cinelli et al., 2019). Exposure of humans to natural and artificial radioactivity. After the Chernobyl accident (Ukraine) in 1986, large amounts of radionuclides were released in the atmosphere. Luckily, out of 200 radionuclides that were formed during nuclear fission, less than 10 could have impacted humans due to their participation in physiological pathways. The damaged Chernobyl reactor was estimated to have emitted 1.3 × 1018 Bq 131I, 3.0 × 1017 Bq 133I, 8.9 × 1016 137Cs, and 2.0 × 1016 Bq 134Cs into the environment. Besides them, 90Sr, 239Pu, and 241Am also had some impact. The territory of Yugoslavia deposited approximately 2.4% of all emitted radionuclides (without inert gasses), or approximately 5% of all 131I and 10% of 137Cs (Federal Committee for Labor, Health and Social Security, 1987). International Atomic Energy Agency (IAEA), European Atomic Energy Community (EAEC or Euroatom) and other professional bodies engaged in dealing with the situation, prescribing a number of regulatory rules with the aim to control the damage. Among the most important were regulations concerning the exposure of the population to radiation, directly or indirectly via consumption of food and drinking water. The first one was Council Regulation (Euroatom) Document 31987R3954 (Comission Regulation (Euroatom), 1987), issued on the maximum permitted levels of radioactive contamination of foodstuffs and feedingstuffs, followed by Commission Regulations: No 944/89 (Commission Regulation (Euroatom) 1989), No L:1990:083:TOC (Comission Regulation (Euroatom), 1990), No 770/90 (Comission Regulation (Euroatom), 1990), No 2013/51 (Comission Regulation (Euroatom), 2013) and No 2016/52 (Comission Regulation (Euroatom), 2016, in force). The import of goods from East Europe was forbidden and agricultural products from the so-called third world countries were permitted provided that they satisfied the allowed radionuclide content. The most important radionuclide for humans was 131I, quantities of which were significant and it was present in the environment both in its elementary form and as iodide (IAEA/EMRAS, 2004). The risk of its inhalation directly from the air (as radioactive aerosol) was lower than indirectly by the consumption of leafy vegetables considerably radio-contaminated by atmospheric precipitation. Physical half-life of 131I is 8 days, whereas its biological half-life varies between mammals and within the same species. After absorption from food, approximately 90% of 131I reaches blood, and 30%–50% is further accessible and fixed by the thyroid gland, reaching saturation. The remaining 131I is excreted via milk, urine, and feces. The Chernobyl accident imposed a serious challenge in food monitoring, classification, certification for consumption, and the official prescription of limits for radionuclide content. Immediately after the accident, limitations referred to 131I, in order to control the consumption of milk and dairy products, which were contaminated via leafy plants and grass on pasture. Animal meat and other parts used for human nutrition were subjected to rigorous radiological control before declaring their safety for consumption (at the market or for individual direct use). Introduced measures immediately after the nuclear accident ensured that the exposure of thyroid to radiation was less than 0.30 Sv in children, which was achieved by limiting the content of 131I in milk to 3.7 kBq/L. As time passed, the level of 131I activity decreased in all types of food; thus, the permitted limits for the food content of 131I were changed, taking into account that the entire body exposure had to be less than 50 mSv/year. Levels of 131I in tested samples from Serbia (water, food, air, and soil) were low enough, so the consumption of preparations containing stable iodine isotopes was not needed. According to Document 31987R3954 from 1987, the maximum permitted level of 131I in dairy products was 500 Bq/kg (or L) and 2 kBq/kg in other foodstuffs except minor foodstuffs, whose activity levels were regulated by documents issued before the Chernobyl accident. The second biologically most important radionuclide was 137Cs, which behaves as potassium homolog and is an organotropic radionuclide. 137Cs was ingested via food and water and its further faith depended on the solubility in the gastrointestinal tract, as it is pH-dependent. Physical half-life of 137Cs is 30.2 years and biological half-life in humans is 70–120 days. Investigations have shown huge genetic potential of radiocesium, as it is deposited in gonads and other organs exposing an organism additionally to internal irradiation (Melnikov notably 134Cs and 137Cs, in dairy products was 1 kBg/kg (or L) and 1.25 kBg/kg in other foodstuffs. The permitted levels remained the same in Commission Regulation No 2016/52 from 2016, with more strict limits for infant food: 150 Bq/kg (or L) for 131I and 400 Bq/kg (or L) for 134Cs + 137Cs. This document defined minor foodstuffs (certain plants, spices, seeds, truffles, some vegetable products, and essential oils) and their radioactivity limits: 20 kBq/kg for 131I and 12.5 kBq/kg for 134Cs + 137Cs. The maximum permitted levels for feed are 1.25 kBq/kg for pigs, 2.5 kBq/kg for poultry, lambs, and calves, and 5.0 kBq/kg for other animals. Institute for the Application of Nuclear Energy (INEP) in Belgrade, Serbia was officially involved in radioactivity monitoring immediately after the Chernobyl accident and is still doing so. Immediately after the accident, the total gamma radioactivity of grass and soil in Belgrade was measured to be 30.6 kBq/kg and 6.8 kBq/kg, while the activity levels of 137Cs were 5.3 kBq/kg and 1.6 kBq/kg, respectively. Animal feed was extremely contaminated - 137Cs in alfalfa flour was up to 6.2 kBq/kg. Consequently, high levels of radioactivity were measured in meat; the highest 137Cs was 537 Bq/kg in sheep meat. The activity of 137Cs in milk increased from 0.14 Bq/L in 1985 to 72.4 Bq/L on average in 1986, with an extreme sample having 292 Bq/L. High levels of 137Cs persisted until 1991 in snail meat (maximum was 521 Bq/kg), deer, and meat from other wild animals (up to 60 Bq/kg). Although much higher than before the Chernobyl accident, these levels were still much lower than in a similar samples measured in North European countries. Considerable contamination in terms of 134,137Cs was measured in 1986 and 1987 in sour cherry concentrate (maximum 273 Bq/kg), apple concentrate (maximum 261 Bq/kg), powder milk (maximum 220 Bq/kg), and chocolate (maximum 102 Bq/kg). Medicinal plants were significantly contaminated with 137Cs: Herba asperulae 4.2 kBq/kg and Sumitates crataegi 5.6 kBq/kg. Activity levels of 137Cs in bioindicators were up to 2.4 kBq/kg in (edible) fungi and 13.6 kBq/kg in lichen Cladonia fimbriata (Čučulović et al., 2020). Food chain is the main route to radionuclides exposure today. Certain plants and animals absorb radioactive material due to similar characteristics of radionuclides and essential elements. For example, humans accumulate radiocesium due to its chemical and metabolic homology with potassium. The concentrations of radionuclides taken in by plants and animals mainly rely on the radioactivity of source medium (soil or water). Additionally, the ability of plants to accumulate the element from the soil and transfer it from roots to different vegetative organs is a species-specific characteristic, which is associated with the distribution of elements within a food chain (Cinelli et al., 2019). Regulations concerning radioactivity levels issued successively after the Chernobyl accident, the last being No. 2016/52, remain valid in European Community (EC) countries, while a rulebook on population safety (Rulebook on radionuclide content limits in drinking water, food, animal feeds, drugs, items for general use, construction materials, and other goods put on the market (Official Gazette, 2018)), was issued in Serbia several years ago. According to this document, radionuclide limits were lowered for a number of foods and other items. New limit for milk and dairy products, infant food, vegetables, fruits, cereals, meat and meat products, eggs and other groceries such as lard, oil, sugar, sweets, alcohol and non-alcohol drinks is 15 Bq/kg (or/L). Higher limits (but still less than those in EC) are allowed for: powder milk, wild berry fruits, wild animal meat, fish, seafood, mushrooms (fresh and their products), medicinal plants, tea, and coffee, which is 150 Bq/kg (or L); whereas, the limit for dry mushrooms, aromas, spices, and other foods used less than 2 kg per year per individual is 600 Bq/kg (or L). The same rule book also prescribes permitted levels of natural radionuclides in mineral fertilizers: 238U 1.6 kBq/kg for market-ready phosphorus-based fertilizers or 3.2 kBq/kg for the components used for the production of phosphorus-based fertilizers, 226Ra 1.0 kBq/kg for both market-ready and raw material for phosphorus-based fertilizers, and 40K 27.0 kBq/kg, for both market-ready and raw material for the production of potassium-based fertilizers. Nowadays, the radioactivity levels of 137Cs are below 1.0 Bq/kg in meat (domestic and wild animals), milk, and dairy products originating from Serbia. Radioactive residues of 137Cs can still be detected in bioindicators: fungi (up to 20 Bq/kg), lichens, and mosses, but they are naturally expected and at the level before Chernobyl accident. Chernobyl accident and radioactivity spreading resulted in very high levels of radionuclides in foods and the entire environment, imposing a need to revise official regulations concerning the intake and exposure of the population. Four decades later, radioactivity levels mostly correspond to the pre-Chernobyl period. However, regular everyday gamma spectrometric monitoring can still be prescribed for the imported goods, preventing the arrival of items with higher activity levels of 137Cs that can be found in the region, thus protecting the local population. All the above-mentioned supports the importance of continuous control of radioactivity levels in food, and inclusion of such data in publicly accessible databases. Ana Čučulović: Investigation; resources; writing – original draft. Jelena Stanojković: Investigation. Olgica Nedić: Methodology; resources; writing – review supervision; visualization; editing. The authors would like to thank the Ministry of Science, Technological Development, and Innovation of the Republic of Serbia for financial support (Grant No. 451-03-66/2024-03/200019, 451-03-65/2024-03/200116). The authors declare that they have no conflict of interest. Ministry of Science, Technological Development, and Innovation of the Republic of Serbia, Grant/Award Numbers: 451-03-66/2024-03/200019, 451-03-65/2024-03/200116. The authors confirm that the study did not involve any human or animal subjects. Data sharing is not applicable to this article as no datasets were generated or analyzed during the current study.