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3 Health Effects of Radiation
damage is damage that has no effect on the cell—it may be in non-coding part of
the DNA, or to a gene that is not active in the particular cell that was damaged),
and harmful damage may be either lethal or sublethal to the cell. At this point, the
only DNA damage that concerns us is sublethal damage to the DNA in a part of the
genome that may be harmful. Although lethal damage is bad for the cell, the damage
does not get passed on to progeny cells, so a lethally damaged call cannot go on to
cause cancer.
However, the possibilities do not stop here, because our cells have DNA damage
repair mechanisms. Although these mechanisms are very effective, they are not
perfect. This means that any bit of DNA damage may be repaired properly, may
be repaired improperly, or might not be repaired at all. It is at this point that DNA
damage may become a mutation—a mutation is what happens when damage to our
DNA becomes “fixed” and is able to be passed on to the next generation of cells.
As with DNA damage, mutations may be good, bad, or neutral, and the detrimental
mutations may be lethal or sublethal. And, as before, it is only the sublethal damage
that is of interest to us, and then, only if it can cause the cell to become cancerous
(Fig. 3.1).
The preceding paragraphs are a quick summary of the various possibilities that
might follow exposure of a cell to radiation. Part of the reason for this summary
is for the sake of completeness, but it also helps to make an important point—
radiation is a weak carcinogen. If we sum up all the possibilities above, there are
over 20 pathways that can be followed. Of these, only one (sublethal damage that is
misrepaired or unrepaired and causes a cell to become carcinogenic) have a chance of
causing cancer. Radiation is a carcinogen, but not a very effective one—not compared
to many of the chemicals we work with.
In the next few sections, we will look at the effects of both acute and chronic
radiation exposure on the organism, instead of the individual cells. First, however, it
is important to distinguish between acute and chronic radiation exposure and between
deterministic and stochastic health effects.
Acute exposure occurs when an organism is exposed to a high dose of radiation
in a short period of time. This is characteristic of radiation accidents. Acute radiation
exposure causes deterministic health effects such as skin burns, vomiting, and so
forth. Deterministic health effect occur when a person is exposed to more than a
threshold dose of radiation, and the severity of the effects increase with increasing
dose. So, for example, radiation burns from 5 Sv to the skin are more severe than from
3 Sv to the skin, and 1 Sv is below the threshold dose and will not cause radiation
burns at all.
Chronic radiation exposure causes stochastic health effects; effects that are probabilistic and that might not have a threshold for induction. A person exposed to 1 Sv
of radiation over a lifetime has a greater chance of developing radiogenic cancer than
a person exposed to only 0.5 Sv—but if a cancer does ensue it will be neither more
nor less severe than cancer caused by a lower or higher radiation exposure.
3 Health Effects of Radiation
damage is damage that has no effect on the cell—it may be in non-coding part of
the DNA, or to a gene that is not active in the particular cell that was damaged),
and harmful damage may be either lethal or sublethal to the cell. At this point, the
only DNA damage that concerns us is sublethal damage to the DNA in a part of the
genome that may be harmful. Although lethal damage is bad for the cell, the damage
does not get passed on to progeny cells, so a lethally damaged call cannot go on to
cause cancer.
However, the possibilities do not stop here, because our cells have DNA damage
repair mechanisms. Although these mechanisms are very effective, they are not
perfect. This means that any bit of DNA damage may be repaired properly, may
be repaired improperly, or might not be repaired at all. It is at this point that DNA
damage may become a mutation—a mutation is what happens when damage to our
DNA becomes “fixed” and is able to be passed on to the next generation of cells.
As with DNA damage, mutations may be good, bad, or neutral, and the detrimental
mutations may be lethal or sublethal. And, as before, it is only the sublethal damage
that is of interest to us, and then, only if it can cause the cell to become cancerous
(Fig. 3.1).
The preceding paragraphs are a quick summary of the various possibilities that
might follow exposure of a cell to radiation. Part of the reason for this summary
is for the sake of completeness, but it also helps to make an important point—
radiation is a weak carcinogen. If we sum up all the possibilities above, there are
over 20 pathways that can be followed. Of these, only one (sublethal damage that is
misrepaired or unrepaired and causes a cell to become carcinogenic) have a chance of
causing cancer. Radiation is a carcinogen, but not a very effective one—not compared
to many of the chemicals we work with.
In the next few sections, we will look at the effects of both acute and chronic
radiation exposure on the organism, instead of the individual cells. First, however, it
is important to distinguish between acute and chronic radiation exposure and between
deterministic and stochastic health effects.
Acute exposure occurs when an organism is exposed to a high dose of radiation
in a short period of time. This is characteristic of radiation accidents. Acute radiation
exposure causes deterministic health effects such as skin burns, vomiting, and so
forth. Deterministic health effect occur when a person is exposed to more than a
threshold dose of radiation, and the severity of the effects increase with increasing
dose. So, for example, radiation burns from 5 Sv to the skin are more severe than from
3 Sv to the skin, and 1 Sv is below the threshold dose and will not cause radiation
burns at all.
Chronic radiation exposure causes stochastic health effects; effects that are probabilistic and that might not have a threshold for induction. A person exposed to 1 Sv
of radiation over a lifetime has a greater chance of developing radiogenic cancer than
a person exposed to only 0.5 Sv—but if a cancer does ensue it will be neither more
nor less severe than cancer caused by a lower or higher radiation exposure.