Summary

The Deutsches Hydrographisches Institut, since the accident has investigated
 with even more intensity the radioactive contamination of
the North Sea and the Baltic Sea. Thereby, the input of the radioactive
 Fallout from Chernobyl could be detected not only from the rise
of the measurement values in the radiological measurement network,
but also by the analysis of the water samples which were taken at
the corresponding moments in time. The temporal and spatial investigations
 indicated that the input took place differently in intensity
and local distribution.

Mixing processes effected a rapid decrease in activity concentration
already during the first hours after the input. The direct Gammaspectroscopical
 determination of individual nuclides without chemical
 enrichment was no longer possible after a few days. For that
reason, the concentration in the following period was essentially
determined from the tracer isotopes Cs 134 and Cs 137. A series of
Samples for Gamma-spectroscopy was concentrated by evaporation.
The Fallout from Chernobyl, according to its characteristic nuclide
composition, can be clearly differentiated from the contaminations
of the North Sea and the Baltic Sea which derive from the nuclear
fuel reprocessing plants Sellafield Works and La Hague. The concentration
 decrease observed as the result of mixing processes also apply
 exemplarily for other toxic substances entering the sea from the
atmosphere«

In spite of the time-consuming methods of analysis, a series of
Sr 90, Pu 239, Pu 238, Am 241, and Cm 242 determinations were
carried out. For the time being, Tritium was not determined further,
after the analysis of an intensively radioactive rainwater sample
indicated no significant increase of the Tritium concentration.
The data gained, permit the recognition of no immediate hazard by
external radiation burden from the biosphere for the marine environment
 as a whole. To what extent enrichments of nuclides in the sediments
 and suspended matter, and enrichment in biological systems can
lead in the long term to relevant effects, must be clarified in the
future by extended {investigations. The further investigation projects
 are aimed in that direction.