The study of the long-term effects of radiation began in the 20s of the XX century. Studies have shown that ionizing radiation is the cause of chromosomal mutations. A study of the he alth of residents of the Japanese cities of Hiroshima and Nagasaki showed that 12 years after the nuclear bombing, the incidence of cancer in those people who were exposed to radiation increased. Moreover, the risk of developing cancer is not associated with the threshold model, when the disease occurs as a result of exceeding the "critical" value of the dose received. It increases linearly, even with short-term irradiation. These phenomena are associated with the stochastic effect of radiation. According to scientists, any dose of radiation increases the risk of malignant tumors and genetic disorders.
What is the stochastic effect of ionizing radiation?
Radiation has a destructive effect on biological tissues. In modern science, there are 2 variants of such consequences: deterministic and stochastic effects. The first type is also calledpredetermined (from the Latin word determino - “determine”), that is, the consequences occur when the dose threshold is reached. If it is exceeded, the risk of deviations increases.
Pathologies resulting from deterministic effects include acute radiation injury, radiation syndromes (bone marrow, gastrointestinal, cerebral), deterioration of reproductive function, cataracts. They are noted as soon as possible after receiving a dose of radiation, less often - in the long term.
Stochastic, or random, effects (from the Greek word stochastikos - "knowing how to guess") are such effects, the severity of which does not depend on the dose of radiation. Dose dependence is manifested in an increase in the incidence of pathology among a population of living organisms. The potential for negative effects exists even with short-term exposure.
Differences
The differences between the stochastic radiation effect and the deterministic one are described in the table below.
| Criterion | Deterministic effects | Stochastic effects |
| Threshold dose | Manifested at high doses (>1 Gy). If the threshold value is exceeded, the disease is inevitable (predetermined, determined). The severity of the injury increases with increasing dose | Observed at low and medium doses. Pathogenesis is dose-independent |
| Mechanism of damage | Cell death leading to dysfunction of tissues and organs |
Irradiated cells remain alive, but change and give mutating offspring. Clones can be suppressed by the body's immune system. Otherwise, cancer develops, and if germ cells are affected, hereditary defects reduce life expectancy |
| Spawn time | Within hours or days of exposure | After the latency period. The disease is random |
One of the features of stochastic phenomena is that they can simultaneously occur along with chronic radiation sickness.
Views
Stochastic effects include 2 types of changes depending on which type of cell is affected:
- Somatic effects (malignant tumors, leukemia). They are revealed during long-term observation.
- Inherited effects recorded in the offspring of exposed individuals. Arise due to damage to the genome in germ cells.
Both types of defects can appear both in the body of an exposed person and in his offspring.
Cell mutation
Mutational processes in a cell exposed to radiation do not lead to its death, but stimulate genetic transformation. There is a so-called radiation-induced mutation - an artificially induced change in structurescells that are responsible for the transmission of hereditary information. They are permanent.
Cellular mutations are always present in natural mechanisms. As a result, children are different from their parents. This factor is very important for biological development. Spontaneous cancerous and genetic pathologies are constantly present in the human population. Ionizing radiation is an additional agent that increases the likelihood of such changes occurring.
In medical science, it is generally accepted that even one transformed cell can initiate the development of a tumor process. DNA breakage and chromosomal aberrations can occur after a single ionization incident.
Diseases
A reliable connection between certain diseases and accidental effects of radiation was proven only in the 90s of the XX century. Listed below are the stochastic effects of ionizing radiation:
- Malignant tumors of the skin, stomach, bone tissue, mammary glands in women, lungs, ovaries, thyroid gland, colon. Neoplastic diseases of the hematopoietic system.
- Non-tumor diseases: hyperplasia (excessive cell reproduction) or aplasia (reverse process) of organs consisting of connective tissue (liver, spleen, pancreas and others), sclerotic pathologies, hormonal disorders.
- Genetic consequences.
Hereditary anomalies
In the group of genetic effects, 3 types of anomalies are distinguished:
- Changes in the genome (the number and shape of chromosomes), leading to the development of various abnormalities - Down syndrome, heart defects, epilepsy, cataracts and others.
- Dominant mutations that appear immediately in the first or second generation of children.
- Recessive mutations. They only occur when the same gene is mutated in both parents. Otherwise, genetic aberrations may not appear for several generations, or may not occur at all.
Ionizing radiation leads to genetic instability in the cell due to disturbances in the system of repair of damaged DNA. A change in the normal course of biosynthesis entails a decrease in viability and the appearance of hereditary diseases. Instability of the cell genome is also an early sign of cancer development.
Oncopathy level and latent period
Since stochastic effects are random in nature, it is impossible to reliably know who will develop them and who will not. The natural rate of cancer in the human population is about 16% throughout life. This figure is higher with increasing collective radiation dose, but there are no exact data on this in medical science.
Since the development of malignant tumors is a multi-stage process, oncopathologies due to stochastic effects have a rather long latent (hidden) period prior to the detection of the disease. So, with the development of leukemia, this figure averages about 8 years. After nuclearbombings in the Japanese cities of Hiroshima and Nagasaki, thyroid cancer was diagnosed after 7-12 years, and leukemia after 3-5 years. Scientists believe that the duration of the latent period for malignant diseases in a particular localization depends on the dose of radiation.
Consequences of genetic mutations
The consequences of hereditary mutations are divided into three groups according to the severity of the course:
- Major aberrations - death in the early embryonic and postpartum period, serious congenital malformations (craniocerebral hernia, absence of bones of the cranial vault, micro- and hydrocephalus; underdevelopment or complete absence of the eyeball, anomalies of the skeletal system - extra fingers, absence limbs and others), developmental delay.
- Physical disability (instability in relation to the storage and transmission of genetic material from generation to generation, deterioration of the body's resistance to adverse external factors).
- Increased risk of developing malignant tumors as a result of hereditary predisposition.
