Pathways of transfer of radionuclides to food

作者：admin  点击次数：15  发布时间：2025-04-24

(I) Human-caused radionuclide pollution in the environment
1. Human-caused radionuclide pollution in the environment
The human-caused radionuclide pollution in the environment mainly comes from four aspects:
①Atomic bombs and hydrogen bombs can produce a large amount of radioactive substances when they explode, which can cause serious radionuclide pollution to the environment;
②) Mining, smelting, fuel refining, enrichment, reactor component production and nuclear fuel reprocessing in nuclear industry production can pollute the environment through the discharge of three wastes;
③The wastewater discharged by scientific research, production and medical units using artificial radioactive isotopes contains 1 (iodine), H1, ”P (phosphorus) ’H (hydrogen) and C (carbon), etc., which can also cause water and environmental pollution;
52
Chapter II Food pollution and its prevention
④) Radionuclide leakage caused by accidents mainly causes local environmental pollution, such as the Windsgill atomic reactor accident in the UK and the nuclear accident in Chernobyl in the former Soviet Union, which caused serious environmental pollution.
2. Human-caused radionuclide pollution in food
The human-caused radionuclide pollution in food mainly includes the following:
(1) 1I I is the main fission product produced in the early stage of a nuclear explosion and during the operation of a nuclear reactor. It can be completely absorbed into the digestive tract and concentrated in the thyroid gland. The amount of stable iodine ingested through the diet can affect the concentration of radioactive iodine in the thyroid gland. Cows eat grass contaminated with I, which contaminates their milk. Therefore, in areas where dairy products are consumed more, milk is the main contaminated food with I. In addition, fresh vegetables also contain a large amount of I. The half-life of I is about 8 days, and the long-term contamination of food is relatively light.
(2) Sr (strontium) Sr is produced in large quantities in nuclear explosions. Because its half-life is very long (about 29 years), it can exist in the environment for a long time. Sr is widely present in the soil and is the main source of food radioactivity. According to surveys in European and American countries, the annual intake of Sr through diet can reach 0.148~0.185Bq, mainly dairy products, followed by vegetables, fruits, cereals and pasta products. After Sr enters the human body, most of it is deposited in the bones, and its metabolism is similar to that of calcium.
(3) "Sr" Sr is also a product of nuclear explosions. Although its production is higher than that of "Sr", "Sr" has a shorter half-life (about 50 days). Compared with "Sr", "Sr" has a lighter pollution to food.
(4) 1Cs (cesium) "" Cs has a half-life of up to 30 years. Its chemical properties are similar to potassium. It is easily absorbed by the body and can participate in the metabolism of potassium. "Cs is mainly excreted through the kidneys and partly through feces. Cs can also enter the human body through the special food chain of lichens (a plant) and reindeer. (II) The transfer pathways of radionuclides to food
Radionuclides in the environment can be transferred to plant foods through water, soil, and air, and to animal foods through contact with the external environment and food chains. The main transfer pathways are as follows.
1. Transfer to plant foods
After artificial radionuclides contaminate water, soil, and air, rainwater and water sources containing radionuclides can directly penetrate plant tissues or be absorbed by plant roots. Plant roots can also absorb radionuclides from the soil. Radionuclides in the air directly enter the plant body as precipitation or dust, or enter the plant body after contaminating the soil. The amount of radionuclides transferred to plants is related to the amount of air pollution. It is related to factors such as the weather conditions, the physical and chemical properties of radionuclides and soil, soil pH, plant species and the type of fertilizer used.
2. Transfer to animal food
When animals drink water contaminated by artificial radionuclides, breathe polluted air, and touch polluted land, radionuclides will enter their bodies. Through the food chain, herbivores also enrich radionuclides in plants, and animals that feed on herbivores will enrich radionuclides in herbivores. Therefore, the transfer of radionuclides to animals often shows a bioaccumulation effect.
3. Transfer to aquatic organisms
Radionuclides that enter water bodies can be dissolved in water or exist in a suspended state. Aquatic plants and algae have a strong ability to concentrate radionuclides. For example, the concentration of "Cs in algae can be 100 to 500 times higher than that in the surrounding waters. Radionuclides in fish can enter through the gills and mouth, or they can gradually penetrate into the human body through radionuclides attached to their body surface. Fish and aquatic animals can also enrich radioactive substances by ingesting lower aquatic plants or animals, showing a bioaccumulation effect through the food chain.
(III) Hazards of radioactive nuclide contamination of food to the human body The effects of ionizing radiation on the human body can be divided into two forms: external irradiation and internal irradiation. When the human body is exposed to a radioactively contaminated environment (mainly the atmospheric environment), ionizing radiation directly acts on the human body surface, which is called external irradiation. External irradiation mainly causes skin damage and even leads to skin cancer. Highly penetrating rays can also cause systemic damage and cause diseases of multiple organs and tissues. When food and water contaminated by radioactive substances are ingested, ionizing radiation acts on the human body, and the impact on the human body is called internal irradiation. Because radioactive nuclides are unevenly distributed in the body and internal irradiation is continuous at the deposition site, internal irradiation is often dominated by local damage, with progressive development and prolonged symptoms. The harm of food radioactive nuclide contamination to the human body is mainly due to the low-dose long-term internal irradiation effect of radioactive substances in food on various tissues, organs and cells in the body, which is mainly manifested as damage to the immune system and reproductive system and carcinogenic, teratogenic and mutagenic effects.
Low-dose radiation can cause suppression or enhancement (excitation) of immune function. Studies have shown that after irradiation of the spleen of mice with a dose of 0.25~0.5Gy, its anti-sheep red blood cell (SRBC) reaction can be enhanced and the number of plaque forming cells (PFC) can be increased. However, when the radiation dose is greater than 1Gy, it has the effect of inhibiting the formation of plaque cells. Low-dose long-term irradiation can also cause T lymphocyte proliferation reaction, so that the cell immune function shows stress enhancement, and the antibody production can be increased due to the enhanced activity of helper T cells, and the humoral immune response is also enhanced.
Irradiation has obvious damage to reproductive function. The testicle is one of the organs that is very sensitive to radiation damage. Irradiation can increase the number of sperm abnormalities, sperm production disorders, sperm count and testicular weight. Low-dose internal irradiation of 0.03~0.1Gy can cause temporary infertility, while doses above 2Gy can cause permanent azoospermia. Human ovaries are highly resistant to radiation damage. Doses above 2Gy can cause temporary infertility, while low-dose irradiation has a certain stimulating effect on the production of eggs.
Carcinogenic, teratogenic, and mutagenic effects are the main biological effects of low-dose long-term internal irradiation. Irradiation of 0.2~0.3Sv can cause a significant increase in the incidence of chromosome aberrations in animal and human cells, especially dicentrics and centromere rings are characteristic indicators of chromosome damage caused by radiation. Radiation can cause tumors such as leukemia, thyroid cancer, breast cancer, lung cancer, liver cancer, and osteosarcoma. For example, retention of Te (tellurium) and Co (cobalt) in the liver mainly causes cirrhosis and liver cancer; Sr2Ra, 29Pu (plutonium), etc. mainly cause osteosarcoma; C and Po, which are distributed in tissues, mainly cause soft tissue tumors. Low-dose long-term internal irradiation can also cause fetal reduction, stillbirth, fetal malformation, and intellectual development disorders.