Long-core profiles of 137Cs, 134Cs, 60Co and 210Pb in sediment near the Rhone River (Northwestern Mediterranean Sea)

Various anthropogenic radionuclides and Pb-210 were analyzed in a 4.3-m-long core, sampled near the Rhone River mouth in March 1991, to evaluate the extent of industrial releases that accumulate in this area. The whole core was significantly marked by radionuclide inputs from the nuclear facilities located along the river (Cs-137, Cs-134, Co-60). Irregular profiles in natural and artificial radionuclides should be related to variations in their respective inputs from the Rhone River to the Mediterranean Sea. Minimum concentrations were found during high flow periods. Using both the Cs-137/Cs-134 profile in the core and the range of this ratio in Rhone waters, mean apparent accumulation rates were estimated to range between 37 cm yr(-1) and 48 cm yr(-1). This core would then represent a sedimentary record over a 7-10 year period. However, the presence of a signal from the Chernobyl accident, which occurred on April 26, 1986, was not clearly observed in the core. Inventories of both artificial and natural radionuclides were greater than expected from atmospheric inputs. The increased sedimentation occurring in close vicinity to the mouth of the Rhone River is thus responsible for trapping of elements transported by the river to the Mediterranean Sea. In this area, inventories of artificial radionuclides are well in excess of aerial deposition from Chernobyl and atmospheric weapons tests and are linked primarily to industrial releases.