The word “safe” means different things to different people. For
many, the idea of being safe is the absence of risk or harm.
However, the reality is that there is a level of risk in almost
everything we do.
For example, speed limits on roads are set to maximize safety.
Nevertheless, accidents occur even when drivers are obeying the
speed limit. Despite the risks, we make a conscious decision to
drive.
Similar conscious decisions are made when radiation is used.
Radiation exposure carries a health risk. Knowing what the risks are
helps the CNSC and other regulatory bodies set dose limits and
regulations that limit exposure to an acceptable or tolerable risk
(some may even say a safe limit).
How radiation affects cells
The primary way radiation affects our health is through breakage of
DNA molecules. DNA consists of two long chains of nucleotides
twisted together into a double helix; it is the molecular compound
in the nucleus of a cell that forms the blueprint for the structure
and function of the cell. Radiation is able to break these chains.
When it does, three things can happen:
1) The DNA is repaired properly
In this case, the cell is repaired properly and it continues to
function normally. DNA breakage occurs normally every second of the
day and cells have a natural ability to repair that damage.
2) The DNA damage is so severe that the cell dies (deterministic
effects)
When the DNA or other critical parts of a cell receive a large dose
of radiation, the cell may either die or be damaged beyond repair.
If this happens to a large number of cells in a tissue or organ,
early radiation effects may occur. These are called deterministic
effects and the severity of the effects varies according to the
radiation dose received. They can include burns, cataracts, and in
extreme cases, death.
The first evidence of deterministic effects became apparent with
early experimenters and users of radiation. They suffered severe
skin and hand damage due to excessive radiation dose. More recently,
this relationship was observed at the 1986 Chernobyl nuclear plant
accident where more than 130 workers and firefighters received high
radiation doses (800 to 16,000 mSv), and suffered severe radiation
sickness. Two of the people exposed died within days of exposure.
Close to 30 more workers and firefighters died within the first
three months.
The CNSC and other international regulators put measures in place,
including stringent dose limits and radioactive source tracking
databases, to mitigate the chances of the public or workers
receiving doses of radiation high enough to cause deterministic
effects. The CNSC also has strict regulations on how nuclear
substances and devices must be handled in Canada.
3) The cell incorrectly repairs itself, but it continues to live
(stochastic effects)
In some cases, the DNA of the cell may be damaged by radiation, but
the damage does not kill the cell. The cell may continue to live and
even reproduce itself, but the cell and its descendents may no
longer function properly and may disrupt the function of other
cells. The probability of this type of detrimental effect is
proportionate to the dose and it is called a stochastic effect –
when there is a statistical probability that the effects of exposure
will occur. In such cases, the likelihood of the effects increases
as the dose increases. However, the timing of the effects or their
severity does not depend on the dose.
This process happens all the time in everyone. In fact, people are
exposed to about 15,000 such events every second of every day.
Sometimes, the cell structure changes because it repairs itself
improperly. This alteration could have no further effect, or the
effect could show up later in life. Cancer and hereditary effects
may or may not take place.
Epidemiological evidence
Studies on survivors of the atomic bombings of the cities of
Hiroshima and Nagasaki in 1945 indicate that the principal long-term
effects of radiation exposure have been an increase in the frequency
of cancer and leukemia.
Similar results have been found in:
people who have been medically treated or diagnosed with radiation;
early uranium mine workers;
workers who manufactured atomic weapons;
people exposed to radiation as a result of the Chernobyl nuclear
accident; and,
people exposed to radon gas in their homes.
Studies have shown that radiation will increase the frequency of
some cancers that already occur naturally and that this increase is
proportionate to the radiation dose – i.e., the greater the dose,
the greater the risk of cancer. However, studies to date have not
been able to show any excess cancers or other diseases in people
chronically exposed to radiation at doses lower than about 100 mSv.
(The lowest dose for excess cancers in atomic bomb survivors was
about 80 mSv).
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New Zealand
Morocco, Rabat
Chile, Santiago
Orange, California
Uruguay, Montevideo
Solomon Islands, Honiara
El Salvador, San Salvador
Maryborough, Queensland St. Petersburg, Florida, USA
Antigua and Barbuda, St. John's
