Activity concentrations and distribution of radionuclides in surface and core sediments of the Neretva Channel (Adriatic Sea, Croatia)

The activity concentrations and the distribution of manmade 137Cs and naturally occurring radionuclides 40K, 238U and 232Th in surface and core sediments of the semi enclosed, river-dominated marine environment of the Neretva Channel were investigated in relation to the sedimentological characteristics and the content of the total organic carbon (TOC). The activity concentrations of radionuclides were determined by gamma spectrometry. Distinct interrelations between sediment properties and spatial distribution of radionuclides were established. The highest accumulation of 137Cs was found close to the river mouth, in the region of intensive deposition of organic matter of terrestrial origin. This finding implies that the river-borne organic material and its deposition processes should be considered as the most important factor controlling distribution of 137Cs in this transitional land-sea environment. The sediment accumulation rates, estimated from distribution of 137Cs in core sediments, were approximately 6 mm y-1 in front of the Neretva River mouth and 4 mm y-1 in the channel area. The spatial distribution of natural 40K and 232Th radionuclides indicates their distinct association with fine-grained sediments. The interrelation of 238U with fine-grained particles was somewhat weaker but still present. The results obtained indicate that the accumulation pattern of natural radionuclides in the Neretva Channel sediments is mainly governed by the deposition of fine-grained material. This study scrutinizes the baseline level for occurring radionuclides and should be used for monitoring and assessing the radionuclide pollution record in the investigated transitional land-sea environment of the Adriatic