The CRIIRAD laboratory (Commission for Independent Research and Information on Radioactivity) has collected 152 soil samples (0 to 40 centimeters deep) all over France. Sampling sites were carefully selected in order to ensure a precise evaluation of the initial 137 Cs Chernobyl fallout (selection criteria : flat ground, undisturbed by human activities, with small vegetal cover). Samples were analyzed by gamma spectrometry on a EG&G ORTEC germanium detector. Sampling took place between 1987 and 1993. 134 Cs from Chernobyl was still measurable so that the use of a typical 137/134 Cs ratio allowed to distinguish the amount of 137 Cs associated with Chernobyl from that due to fallout from the fifties and sixties nuclear tests.
A 137 Cs Chernobyl fallout map of the French territory has been drawn up. The fallout levels are closely correlated with both the trajectory of the radioactive cloud and the amount of rainfall between the first and fifth of May 1986. The fallout intensity lies between our detection limit (120 Bq/m2) and a maximal figure of 34 600 Bq/m2 for 137 Cs. Many levels recorded in the eastern part of France exceed 7 300 Bq/m2, a value originally considered by the French authorities as the upper level registered in France. These data show that in one third of the French territory countermeasures should have been taken in order to reduce doses from ingestion of contaminated food.
Since the Summer of 1996, the CRIIRAD laboratory has undertaken a specific soil sampling programme in the French, Italian, Swiss and Austrian Alps, in order to study Chernobyl associated contamination of soil at high altitudes (above 1 600 m).
In situ radioactive monitoring of gamma radiation and laboratory analysis of 40 collected soil samples show a 137 Cs contamination exceeding 10 000 Bq/kg and sometimes 100 000 Bq/kg. The extreme heterogeneity of soil contamination requires a new radioprotection approach, very different from that appropriate to low altitude situations. Gamma spectrometry analysis of mushrooms has demonstrated that in 1997 some species still exceeded the 600 Bq/kg limit established in Europe for 137 Cs contamination of food after the Chernobyl accident.
Americium-241 contamination as high as 154 Bq/kg in Alpine soils highlights the problem of transuranian contamination. The study opens new approaches in the field of specific air pollutant behavior in a high altitude mountainous environment.
Read the 2002 article of the International Journal of Radiation Medecine
