Radioactive radiation does not only directly have a toxic effect on physiological processes, it also affects the genes in the chromosomes or breaks up the chromosomes,
so that they either remain in the form of fragments or coalesce in an unnatural order:
genetic changes and deformations are the consequence. In embryos of the scorpionfish (Scorpaena porcus) 6%-14% of all the chromosome sets are already fragmented
as a result of natural radioactivity and other natural influences, but if the embryos
are put into seawater with an artificial strontium-90 activity of 100,000 pCi/I, the
amount of chromosome fragmentation rises noticeably. But this is a concentration
level 1 million times higher than the strontium-90 concentration (approx. O.l pCi/l)
in the ocean originating from nuclear testings. In experiments with carbon-14 as a
radiation source, a dose ten times higher was needed to bring about the same effect
of chromosome fragmentation (Tsytsugina et al. 1973). There are also reports stating
that additional artificial radioactivity of just 100 pCi/1 is harmful to the development
of fish eggs, whereas in other experiments much higher radiation doses have not had
any harmful effects at all. So no final judgment can be given about the minimum
level of harmful radioactivity in the ocean water (Ravera 1978).
Radioactivity is emitted from the various isotopes in different qualities: alpha-radiation consists of positively charged helium atomic nuclei, that only penetrate 0.06 mm
deep into normal tissue. Beta-radiation penetrates 20 mm deep and consists of negatively charged electrons, the K-radiation consists of electrons of the inner atomic
shell. The photons of gamma-radiation penetrate practically every tissue unhindered.
Radioactivity does not only affect marine organisms from the outside, it is also
emitted by isotopes that are incorporated in the body tissue of the organisms themselves. This is the reason why organisms of different forms and sizes are differently
affected by radiation. Referring to human beings these complicated standards have
already been examined long ago and have been given the unit termed "rem" 4, a radiation equivalent applicable to human beings. First attempts are being made to set up
a differentiated rating applicable to marine organisms (Woodhead 1973).
A pelagic fish can be regarded as a cylinder with a diameter of 10 cm and a length of
50 cm. To begin with, it is exposed to the natural radioactivity contained in its own
body, from potassium-40 and polonium-21O, of 3-4Ilrad/h 5 .
Added to this is a slight radiation exposure of 0.1 IJrad/h from potassium-40 contained in the seawater. Cosmic radiation is only of importance to organisms living
near the water surface. For the model fish, cosmic radiation would here amount to
4 Ilrad/h; at 20 m below the water surface it would already be reduced to 0.5 Ilfad/h
and at· 100 m below the surface it can be dismissed. Instead radiOisotopes in the sediments become more important the more one approaches the sea bed. For a fish living
near the surface of the sediment the radiation dose would be 1.5-16 Ilrad/h of
gamma-radiation and 1.6-21 Ilrad/h of beta-radiation. If the fish were buried into
the sediment, the dose would be twice as high.
Altogether the exposure to natural radiation amounts to 5-21Ilrad/h for fish living
near the sediment at a depth of 20 m. For the fall-out caused by nuclear weapon
4 1 rem = 0.01 J/kg, equivalent dose from a mixture of different emitters of radioactivity , applied
to human beings; 1 mrem = 10- 3 rem
5 1 rad = 0.01 J/kg, unit of the absorbed radiation dose; 11lrad = 10- 6 rad
117
so that they either remain in the form of fragments or coalesce in an unnatural order:
genetic changes and deformations are the consequence. In embryos of the scorpionfish (Scorpaena porcus) 6%-14% of all the chromosome sets are already fragmented
as a result of natural radioactivity and other natural influences, but if the embryos
are put into seawater with an artificial strontium-90 activity of 100,000 pCi/I, the
amount of chromosome fragmentation rises noticeably. But this is a concentration
level 1 million times higher than the strontium-90 concentration (approx. O.l pCi/l)
in the ocean originating from nuclear testings. In experiments with carbon-14 as a
radiation source, a dose ten times higher was needed to bring about the same effect
of chromosome fragmentation (Tsytsugina et al. 1973). There are also reports stating
that additional artificial radioactivity of just 100 pCi/1 is harmful to the development
of fish eggs, whereas in other experiments much higher radiation doses have not had
any harmful effects at all. So no final judgment can be given about the minimum
level of harmful radioactivity in the ocean water (Ravera 1978).
Radioactivity is emitted from the various isotopes in different qualities: alpha-radiation consists of positively charged helium atomic nuclei, that only penetrate 0.06 mm
deep into normal tissue. Beta-radiation penetrates 20 mm deep and consists of negatively charged electrons, the K-radiation consists of electrons of the inner atomic
shell. The photons of gamma-radiation penetrate practically every tissue unhindered.
Radioactivity does not only affect marine organisms from the outside, it is also
emitted by isotopes that are incorporated in the body tissue of the organisms themselves. This is the reason why organisms of different forms and sizes are differently
affected by radiation. Referring to human beings these complicated standards have
already been examined long ago and have been given the unit termed "rem" 4, a radiation equivalent applicable to human beings. First attempts are being made to set up
a differentiated rating applicable to marine organisms (Woodhead 1973).
A pelagic fish can be regarded as a cylinder with a diameter of 10 cm and a length of
50 cm. To begin with, it is exposed to the natural radioactivity contained in its own
body, from potassium-40 and polonium-21O, of 3-4Ilrad/h 5 .
Added to this is a slight radiation exposure of 0.1 IJrad/h from potassium-40 contained in the seawater. Cosmic radiation is only of importance to organisms living
near the water surface. For the model fish, cosmic radiation would here amount to
4 Ilrad/h; at 20 m below the water surface it would already be reduced to 0.5 Ilfad/h
and at· 100 m below the surface it can be dismissed. Instead radiOisotopes in the sediments become more important the more one approaches the sea bed. For a fish living
near the surface of the sediment the radiation dose would be 1.5-16 Ilrad/h of
gamma-radiation and 1.6-21 Ilrad/h of beta-radiation. If the fish were buried into
the sediment, the dose would be twice as high.
Altogether the exposure to natural radiation amounts to 5-21Ilrad/h for fish living
near the sediment at a depth of 20 m. For the fall-out caused by nuclear weapon
4 1 rem = 0.01 J/kg, equivalent dose from a mixture of different emitters of radioactivity , applied
to human beings; 1 mrem = 10- 3 rem
5 1 rad = 0.01 J/kg, unit of the absorbed radiation dose; 11lrad = 10- 6 rad
117