Evaluation of 137Cs fallout from the Chernobyl accident in a forest soil and its impact on Alpine Lake sediments, Mercantour Massif, S.E. France

Abstract The Boreon area in the Mercantour Massif, S.E. France, was contaminated by radionuclides after the Chernobyl accident in the first days of May 1986. Sediments from a small mountain lake in this area were collected, as well as forest soils in its vicinity, in order to obtain 137 Cs and 210 Pb profiles. Calculated from the 210 Pb inventory in a soil of a horizontal area, the flux is high in the area (0.06 Bq cm −2  y −1 ) probably because of the great frequency of rain and uranium ores outcropping in the massif. The comparison of the 137 Cs soil inventories and the unsupported 210 Pb suggests that the 137 Cs fallout due to the Chernobyl accident in the study site (Boreon) was at least 3.5 Bq cm −2 , more probably the double. The recent lake sediments still undergo a rather strong contamination by 137 Cs and the sediment profiles show that the residence time of 137 Cs in the catchment area is long. The study area is frequented by many inhabitants of the city of Nice and other cities at the Mediterranean coast during week-end and during summer and winter holidays. Thus the 137 Cs external exposure impact was evaluated at 2 mSv y −1 for 2002 in the most contaminated point.