What are the biological effects of ionizing radiation?
Characteristics
One characteristic of ionizing radiation on human body is that the energy absorbed is low but the biological effects are serious. For example after receiving a lethal dose of 10 Gy, the body temperature will only increase by 0.02 °C but the dose may lead to death of all the exposed entities.
The second characteristic is the latent biological effects of radiation. Acute biological effects can occur within several hours to several days while the long term effects usually appear several years after the exposure.
Type of effects
Generally speaking, the biological effects of ionizing radiation can be classified according to the characteristics of effects, occurring times and the object that shows the effects.
| Characteristic of effects | Occurring time | Object | Effects on organs |
|---|---|---|---|
| Tissue Reactions (Deterministic effects) | Acute effects | Somatic effects |
|
| Tissue Reactions (Deterministic effects) | Latent effects | Somatic effects |
|
| Stochastic effects | Latent effects | Somatic effects |
|
| Stochastic effects | Latent effects | Genetic effects |
|
The effects of critical organs
Different organs have different sensitivity to ionizing radiation. For example, the thyroid in children, the female breast and the bone marrow have a relatively high sensitivity for the induction of solid cancer and leukaemia whereas the muscle and connective tissue have a relatively low sensitivity.
| Organs | Effects on organs |
|---|---|
| Gonad | The probability of cancer induction in this organ is comparatively low. The main concern is the genetic effects due to irradiation of this organ and the probability is proportional to the absorbed dose. |
| Bone marrow | Bone marrow have a relatively high sensitivity to radiation. Leukaemia(excluding chronic lymphocytic leukaemia) and multiple myeloma were included in the bone marrow category when estimating cancer risk. Besides, the threshold absorbed dose which leads to depression of blood-forming is about 0.5 Gy. |
| Bone | The radiosensitive cells in bone are endosteal cells and epithelial cells on the bone surfaces. The sensitivity of bone is less than that of the breast, red bone marrow, lung and thyroid. |
| Lung | Cancer of the lung has been observed in miners exposed to high concentration of radon and its decay products. External irradiation can also induce lung cancer. |
| Thyroid | Radiation can induce thyroid cancer. However, the mortality of this type of cancer is much lower than that of leukemia primarily because of the success in the treatment of thyroid cancer. |
| Breast | Studies suggested that the female breast cancer risk increases linearly with radiation dose but decreases with age at radiation exposure. |
| Skin | The effects on skin depend on absorbed dose and the area of irradiation. Major effects are erythema and ulceration of the skin. The probability of induction of skin cancer is less than the above organs. |
| Lens | Cataract is a heath effect that can be caused by ionising radiation. In the “Statement on Tissue Reactions (2011)”, International Commission on Radiological Protection (ICRP) considers the threshold in absorbed dose for the lens of the eye to be 0.5 Gy, below which tissue reactions(deterministic effects) are unlikely to occur. |
| Fetus | Effects depend on the stage of pregnancy at the time of exposure. At the early stage of pregnancy when the cells are still not differentiated, it usually causes death of the embryo. It is generally believed that exposure of fetus at the first 3 weeks of pregnancy should not cause any deterministic and stochastic effect to the embryo. Later stage irradiation of the fetus may leads to malformation of body organs and increase in cancer risk of the child. |