Radiation can affect the body in several ways.
Very high doses can cause skin burns and acute radiation syndrome, with symptoms usually present within 24 hours. Acute radiation syndrome arises from damage to organs and can be very severe. However, the doses high enough to cause these are extremely rare (numbering a handful of cases per year worldwide), and are usually related to direct involvement in some form of radiation accident. Symptoms that arise from a known high-dose exposure are easily traceable to specific events, so they are commonly called “deterministic effects.”
A more common concern is the longer-term health effects of habitual exposure to less-extreme levels of radiation. Specifically, such exposure could involve damage to DNA, leading to hereditary abnormalities and cancer. These effects are somewhat random and difficult to track, and are described as “stochastic effects.”
The random nature of stochastic effects is rooted in how ionizing radiation interacts with the body.
When radiation knocks an electron out of its atom’s orbital, that atom becomes an ion, which is electrically imbalanced. This means it is attracted to other molecules around it, and could undergo chemical reactions that leave it configured differently than before the ionization.
Each DNA molecule is a long chain of information that guides the body’s development. Ionization of an atom in that chain could essentially change the “code” by which a person is built. However, an incident of ionization is still unlikely to cause a tumour or defect: much of the information in DNA guides things that are not critical to life, such as hair texture or eye colour. Furthermore, damage to DNA often causes the chain to fail to replicate – meaning that it is damaged, but not passed along to another generation. So, DNA damage is generally of concern only when it happens to the genes that are responsible for tumour suppression, or are critical to child development.
Even so, both ionization and the resulting DNA damage are perfectly natural phenomena, which the human body deals with excellently. DNA damage naturally occurs at a rate of over 1,000 “lesions” per cell per day – more than 1,000,000,000,000 DNA-damage events in any human body every day, from natural processes. The natural defences of the cell and the body repair the vast majority of these without any illness. Radiation at normal exposure levels contributes less than 2% to the DNA damage taking place at all times in the human body.
Scientists have long understood the health effects of exposure to ionizing radiation, and Canada’s nuclear industry adheres to extremely safe practices, to ensure that exposure levels are kept well below limits set and enforced by radiation regulations.