explosions an additional radiation exposure of 0.1-1.8 Ilrad/h has to be considered.
For smaller animals the radioactive exposure is considerably higher and assuming the
model calculation is correct, natural radiation and fall-out radiation are of about
equal dimension as regards the effect on plankton; fish eggs are just as small. Incidentally such radiolaria that have a skeleton of strontium sulfate may be exposed to a
higher radiation dose.
The radioactivity of marine sediments, too, can vary. On beaches, where due to the
sorting effect of wind and water, placer-type accumulations develop from especially
heavy, dark mineral granules, uranium-238 and thorium-232 can accumulate together
with zirconium. On the beach of Norderney Island on the German North Sea coast,
a local dose of up to 500 mrem per year was measured in such places. Higher doses
were measured in the monazite sands of India and Brasil (Bonka 1980).
The discussion about the level of the radiation dose a human being can endure, continues. At first 500 mrem per year were considered acceptable by the International
Commission on Radiological Protection, later 5 rem per generation (that means
167 mrem per year), or a dosage that is as high as the natural radiation exposure, was
considered. Now, a maximum of 30 mrem per year are considered acceptable, as stated
in the Radiation Protection Regulation of the Federal Republic of Germany of 1976.
This is a low amount compared to the radiation doses used for medical reasons, especially for X-ray treatment, for which in the Federal Republic of Germany an average of
50 mrem a year, and in the U.S.A. even 100 mrem a year may be guessed. This too, is
little compared to natural radiation levels. For a human being living at an altitude of
3000 m on a granite ground the natural radiation dose is made up of 100 mrem/year
of cosmic radiation, 90 mrem/year of radiation from the mineral sub-soil and 20 mrem/
year from potassium-40 in his own body; added together this amounts to 210 mrem
per year. For a human being living at sea level on sediment ground the result is more
favorable: 30 mrem/year of cosmic radiation, 23 mrem/year of radiation from the
sub-soil and 20 mrem/year from potassium-40, together 73 mrem per year. The exposure to natural radiation of the population of the Federal Republic of Germany can
be assessed at an annual average of roughly 110 mrem.
It does not look as though the increase of man-made radioactivity in the water of the
North Sea up to now, contributes essentially to the permissible radiation dose.
While freshwater fish caught in rivers near nuclear plants may contain 1-200 pCi/kg
of artificial radioisotopes in their flesh, and while on the other hand in fish from the
North Sea the natural radioactivity, mainly based on potassium-40, amounts to 10002500 pCi/kg, the artificial radioactivity in plaice and sole amounts to 2 pCi/kg of
strontium-90 and 60 pCi/kg of caesium-I 37 . There is less in the North Atlantic redfish
(Sebastes marinus) with 0.2 pCi/kg of strontium-90 and 10 pCi/kg of caesium-I 37
(Deutsche Forschungsgemeinschaft 1979). For the fish eater this seems not to be
hazardous to his health.
In the vicinity of Windscale on the Irish Sea, the additional radioactivity originating
from the reprocessing plant is regularly being checked, as percentage of a dose of
5 rem per generation which is regarded as permissible. For a person who stands
on contaminated mud for a longer period this amounts to 7% of the permissible
dose, for a fisherman who regularly eats fish from the contaminated area (Table 24)
up to 14%, and for an inhabitant of South Wales who regularly eats "laver-bread"
118
For smaller animals the radioactive exposure is considerably higher and assuming the
model calculation is correct, natural radiation and fall-out radiation are of about
equal dimension as regards the effect on plankton; fish eggs are just as small. Incidentally such radiolaria that have a skeleton of strontium sulfate may be exposed to a
higher radiation dose.
The radioactivity of marine sediments, too, can vary. On beaches, where due to the
sorting effect of wind and water, placer-type accumulations develop from especially
heavy, dark mineral granules, uranium-238 and thorium-232 can accumulate together
with zirconium. On the beach of Norderney Island on the German North Sea coast,
a local dose of up to 500 mrem per year was measured in such places. Higher doses
were measured in the monazite sands of India and Brasil (Bonka 1980).
The discussion about the level of the radiation dose a human being can endure, continues. At first 500 mrem per year were considered acceptable by the International
Commission on Radiological Protection, later 5 rem per generation (that means
167 mrem per year), or a dosage that is as high as the natural radiation exposure, was
considered. Now, a maximum of 30 mrem per year are considered acceptable, as stated
in the Radiation Protection Regulation of the Federal Republic of Germany of 1976.
This is a low amount compared to the radiation doses used for medical reasons, especially for X-ray treatment, for which in the Federal Republic of Germany an average of
50 mrem a year, and in the U.S.A. even 100 mrem a year may be guessed. This too, is
little compared to natural radiation levels. For a human being living at an altitude of
3000 m on a granite ground the natural radiation dose is made up of 100 mrem/year
of cosmic radiation, 90 mrem/year of radiation from the mineral sub-soil and 20 mrem/
year from potassium-40 in his own body; added together this amounts to 210 mrem
per year. For a human being living at sea level on sediment ground the result is more
favorable: 30 mrem/year of cosmic radiation, 23 mrem/year of radiation from the
sub-soil and 20 mrem/year from potassium-40, together 73 mrem per year. The exposure to natural radiation of the population of the Federal Republic of Germany can
be assessed at an annual average of roughly 110 mrem.
It does not look as though the increase of man-made radioactivity in the water of the
North Sea up to now, contributes essentially to the permissible radiation dose.
While freshwater fish caught in rivers near nuclear plants may contain 1-200 pCi/kg
of artificial radioisotopes in their flesh, and while on the other hand in fish from the
North Sea the natural radioactivity, mainly based on potassium-40, amounts to 10002500 pCi/kg, the artificial radioactivity in plaice and sole amounts to 2 pCi/kg of
strontium-90 and 60 pCi/kg of caesium-I 37 . There is less in the North Atlantic redfish
(Sebastes marinus) with 0.2 pCi/kg of strontium-90 and 10 pCi/kg of caesium-I 37
(Deutsche Forschungsgemeinschaft 1979). For the fish eater this seems not to be
hazardous to his health.
In the vicinity of Windscale on the Irish Sea, the additional radioactivity originating
from the reprocessing plant is regularly being checked, as percentage of a dose of
5 rem per generation which is regarded as permissible. For a person who stands
on contaminated mud for a longer period this amounts to 7% of the permissible
dose, for a fisherman who regularly eats fish from the contaminated area (Table 24)
up to 14%, and for an inhabitant of South Wales who regularly eats "laver-bread"
118