Toxic Pollution 155
processes, half the quantity of the absorbed dose of a radioactive substance
or other pollutant. Half-life and biological half-life are of great importance
when a radioactive substance has entered the organism. The capacity for
emitting radioactive radiation is not affected by any chemical reaction
undergone by the radioactive substance during the biological processes
within the organism or along a food chain. Therefore the only way to get
rid of radioactive radiation is a short half-life or rapid elimination of the
radioactive substance from the organism. Radioactive substances (but not
the radioactive radiation) have the character of persistent pollutants, such
as metals and stable toxic organic compounds (Section 7.1), that is, they
display bioaccumulation and biomagnification.
The BHL is the same for an element and all its isotopes. A greater BHL
means that the radioactive isotope stays longer in the body and therefore more
radioactive radiation is absorbed. Uranium (alpha and gamma radiation )
has a BHL of 100 days in the human body as a whole, and 300 days in
the bones. Plutonium (alpha and gamma radiation) would have a BHL of
200 years, if human life were long enough. Caesium (beta and gamma
radiation) has a BHL of 70 days in the body as a whole and 140 days in
the muscles. Strontium (beta radiation) has a BHL of 35 years in the body
as a whole and 50 years in the bones. Iodine (beta and gamma radiation)
has a BHL of 138 days in the body as a whole including the thyroid gland.
Tritium (beta radiation) has a BHL of 12 days.
7.5.2 Effects of radioactive radiation
A common feature of radioactive radiations is that they cause ionisation
of the matter they encounter on their path, hence they are called ionising
radia tions. The effect on matter caused by alpha, beta or gamma radioactive radiation is due to its energy content. When its kinetic energy is
exhausted, the effect ceases. Alpha and beta particles, on their way through
matter, collide with the electrons of atoms and knock them out of their
orbits, thus creating ionised atoms or radicals as well as free electrons.
The free electrons often acquire enough energy from the collision to enable
them to then cause ionisation of other atoms. Gamma radiation causes
ionisation through various mechanisms, such as excitation of the atoms of
the matter through the absorption of the respective energy, resulting in the
dislodgement of a peripheral electron.
Ionising radiation causes severe damage to the whole spectrum of organisms. Its effect on living matter and the water it contains results in the
formation of a large number of ionised molecules, many of which have high
chemical potency. They react with proteins, deactivate enzymes, prevent cell
division, destroy cell membranes and in general damage cell function in the
short or the long term. Large doses of ionising radiation cause human death
shortly after exposure, as was demonstrated in Hiroshima and Nagasaki.
processes, half the quantity of the absorbed dose of a radioactive substance
or other pollutant. Half-life and biological half-life are of great importance
when a radioactive substance has entered the organism. The capacity for
emitting radioactive radiation is not affected by any chemical reaction
undergone by the radioactive substance during the biological processes
within the organism or along a food chain. Therefore the only way to get
rid of radioactive radiation is a short half-life or rapid elimination of the
radioactive substance from the organism. Radioactive substances (but not
the radioactive radiation) have the character of persistent pollutants, such
as metals and stable toxic organic compounds (Section 7.1), that is, they
display bioaccumulation and biomagnification.
The BHL is the same for an element and all its isotopes. A greater BHL
means that the radioactive isotope stays longer in the body and therefore more
radioactive radiation is absorbed. Uranium (alpha and gamma radiation )
has a BHL of 100 days in the human body as a whole, and 300 days in
the bones. Plutonium (alpha and gamma radiation) would have a BHL of
200 years, if human life were long enough. Caesium (beta and gamma
radiation) has a BHL of 70 days in the body as a whole and 140 days in
the muscles. Strontium (beta radiation) has a BHL of 35 years in the body
as a whole and 50 years in the bones. Iodine (beta and gamma radiation)
has a BHL of 138 days in the body as a whole including the thyroid gland.
Tritium (beta radiation) has a BHL of 12 days.
7.5.2 Effects of radioactive radiation
A common feature of radioactive radiations is that they cause ionisation
of the matter they encounter on their path, hence they are called ionising
radia tions. The effect on matter caused by alpha, beta or gamma radioactive radiation is due to its energy content. When its kinetic energy is
exhausted, the effect ceases. Alpha and beta particles, on their way through
matter, collide with the electrons of atoms and knock them out of their
orbits, thus creating ionised atoms or radicals as well as free electrons.
The free electrons often acquire enough energy from the collision to enable
them to then cause ionisation of other atoms. Gamma radiation causes
ionisation through various mechanisms, such as excitation of the atoms of
the matter through the absorption of the respective energy, resulting in the
dislodgement of a peripheral electron.
Ionising radiation causes severe damage to the whole spectrum of organisms. Its effect on living matter and the water it contains results in the
formation of a large number of ionised molecules, many of which have high
chemical potency. They react with proteins, deactivate enzymes, prevent cell
division, destroy cell membranes and in general damage cell function in the
short or the long term. Large doses of ionising radiation cause human death
shortly after exposure, as was demonstrated in Hiroshima and Nagasaki.