Radiocesium (Cs-137) does not occur naturally on earth, it is exclusively anthropogenic in origin for example through nuclear fission.
They have long half-lifes (Sr-90 = 28 years, Cs-137 =30 years)
They behave physiologically like the important bio-elements calcium and
Through atomic bomb testing since 1945 radioactive fission products have
artificially entered and spread worldwide throughout the atmosphere. Each test produces ca 200 fission products of which many are not identifiable due to their very short physical halflife. Of the
remaining fission products the isotopes Strontium-90 and Cesium-137 have a special significance:
They occur in large amounts after every atomic test (ca. 3 – 7% fission yield)
In the above ground atomic bomb testing the radioactive fission products were spewed into the atmosphere and were then deposited worldwide between the tropo- and the
stratosphere by exchange reactions. Precipitation is the main agent for these deposits, but they also occur on a dry basis.
As a result of the
atmospheric atomic bomb testing in the 1950’s and 1960’s the radioacitve isotope Cs-137 is even today present in the environment worldwide. With an increase in nuclear weapons testing the global contamination with Cs-137 has increased continuously.
Due to international pressure the USA, the former USSR, and Great Britain decided to impose a limited nuclear test ban treaty in 1963.
This treaty only permitted underground testing of atomic weapons. In the following 3 decades global contamination with Cs-137 has slowly decreased.
The reactor incident in Cchernobyl happened on April 26, 1986.
As a result of this accident a quantity of 2 x 1018 Bq radiation was released into the atmosphere (ZIFFERO 1988). That is the greatest amount of radioacitvity that has ever been released over the
short term from a radioactive source (IAEA 1991). About half of this amount settled out within 60 km of the accident site, while the remainder was spread unevenly over all of Europe (Fig. 1).
total of 40 different radionucleids were released into the atmosphere. Of these iodine-131 (I-131), Cs-137, and strontium-90 (Sr-90) are significant for long term radiation pollution.
gasses the radioactive substances were expelled to a height of more than 1500m from the reactor nucleus. In the following days depending on the weather they were distributed over Scandinavia, Finland, the Baltic,
and southern Germany.
The agent of fallout was mainly precipitation so that deposition occurred inhomogenously over the area affected; areas with a great amount of fallout were adjacent to those with very little.
Fig 2 presents the CS-137 areal activity measured in the soil (expressed in Becquerel/sq.m) in the Federal Republic of Germany in 1996. It is clearly evident that the soil
contamination in southern Germany is much higher than elsewhere in the country.
This inhomogenous distribution is primarily due to the regionally irregular distribution of heavy rains which wash the Cs-137 out of contaminated air masses.
Fig. 1: Distribution of Cs-137 radioactivity after the Tschernobyl Fallout (from European Union Brussels 1998)
In the Federal Republic of Germany the fallout of the radionucleids mainly took place through rain showers between April 30 and May 5, 1986. About 2/3 of the deposited radioactivity was
due to the isotopes Iodine-131 and Tellurium-132, which, however, decayed within a very short period of time (half-life of respectively 8 and 3 days). Of the long lasting nucleids Cs-137 makes
up the greatest proportion (8%) of total radiation. The long term radiation contamination through this reactor incident is almost exclusively caused by this nucleid. The quantity of Cs-137
fallout in the Federal Republic of Germany amounted to 300 g.
Fig. 2: Soil contamination with Cs –137 in the Federal Republic of Germany 1986 according to
the Department of Federal Health (2000)
During the months directly after the Chernobyl fallout food sources growing or raised outside as
well as meat from herbivorous wild animals was contaminated at a higher rate with radiocesium. While the radiocesium contamination in agriculturally produced plant and animal
foods has declined since the last few years to pre-Tschernobyl levels, comparatively high levels of Cs-137 can still be found in berries, mushrooms and the meat of game animals from certain
These differences in Cs-137 contamination are caused by the fact that the transfer of radiocesium from Cs ion fixing clay minerals in the soil to the crops growing there is low and the
high nutrient content, and the high pH-value of agriculturally used soils also inhibit transfer. In contrast this transfer to plants in forests, esp. on forest soils with thick humus layers is
relatively high. In addition dynamic biological processes (deposition of litter, decomposition, etc.) occur in forest ecosystems along with purely physical processes (adsorption, fixation,etc.),
both of which have a complex influence on the vegetation and wild animals.
We have been investigating the long term behaviour of radiocesium in undisturbed ecosystems
with emphasis on “forest products” since 1986.
IAEA International Atomic Energy Agency, 1991: The international Chernobyl projekt. An
overview. Assessment fo radiological consequences and evalution of protective measures. Report by an international advisory committee.
M. De Cort
, G. Dubois, Sh. D. Fridman, M.G. Germenchuk, Yu. A. Izrael, A. Janssens, A. R. Jones, G. N. Kelly, E. V. Kvasnikova, I. I. Matveenko, I. M. Nazarov, Yu. M. Pokumeiko, V. A. Sitak, E. D.
Stukin, L. Ya. Tabachny, Yu. S. Tsaturov and: "Atlas of Caesium Deposition on Europe after the Chernobyl Accident", EUR report nr. 16733, Office for Official Publications of the European
Communities, Luxembourg, 1998, Plate 1.
Ziffero M., 1988: A post-chernobyl view. in: Harley J.H., Schnidt G.D., Silini G. (eds.):
Radionuclides in the food chain. ILSI Monographs. Springer-Verlag; Berlin, Heidelberg: 3-9.
Top of Radiocesium in the environment page