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Strontium 90 in Finnish Grass and Cow’s Milk
Of the long-lived fission products found in agricultural produce as a
result of atmospheric fallout, Sr and 1’Cg are generally considered to present the major hazard to the consumer. Therefore we have started a research
project to gain preliminary information on the amounts of these nuclides
in the most important phases of the food-chain soil-plant-animal-man in
Finland.
In this paper results are reported on the Srin the first series of samples.
Most of these samples have also been analysed for 18’Cs; the results of these
analyses will be published separately (1).
In most western countries, in which 65—85 % of the calcium in the
average diet derives from milk and milk products (2), the most important
links in the above-mentioned food-chain are grass and milk. In Finland,
the proportion of the dietary calcium provided by milk and milk products
is among the highest in the world, 85 % for the urban (3) and 84.5 % for
the rural population (4). This percentage is of the same magnitude in the
other Scandinavian countries — e.g. in Norway also 85 % (5), whilst in
England it is 75 % (6, 7), and in Germany (West) 75.9 % (8).
To obtain information both on the general level of Sr in the milk and
on the magnitude of the local variation in a country, two kinds of survey
should be made (6): a »country-wide» survey, in which samples are collected
and mixed to represent the milk consumed bya large part of the population,
and a »special area» survey, in which samples are taken from individual
farms in which the Sr content of the milk is suspected to be higher than
the average. The »country-wide» survey of the British Radiobiological Laboratory (6) comprises milk samples taken fortnightly from over 200 milk depots,
which represent more than 40 % of the total milk produced in the United
Kingdom. The»special area» survey made by the same laboratory comprises
6 farms in regions having a high annual rainfall, three of the farms even
being located at an altitude higher than 400 m. Both British (6, 13) and
Norwegian (11) investigations have shown a good correlation between the
amounts of annual rainfall and of Sr deposited per km? or present in grass
and milk. Recent studies in different countries have also shown a pronounced seasonal variation in the Sr contents of grass and milk (6, 9, 10, 11,
12). The peak values of 1958 were found in England (6, 12) and Germany
(9) in June-July, in Norway in July-August (11).
In this survey our aim has been to obtain preliminary information both