Abstract
The activity concentrations and the distribution of manmade 137 Cs and naturally occurring radionuclides 40 K, 238 U and 232 Th 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 137 Cs 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 137 Cs in this transitional land-sea environment. The sediment accumulation rates, estimated from distribution of 137 Cs 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 40 K and 232 Th radionuclides indicates their distinct association with fine-grained sediments. The interrelation of 238 U 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.
Highlights
Environmental radioactivity has become a subject of scientific interest in recent decades, due to possible risks to human health, and because radionuclides have been recognized as tracers of many complex biogeochemical processes (PORCELLI & BASKARAN, 2011)
This paper reports on a study of the activity concentrations of 137Cs, 40K, 238U and 232Th radionuclides in the sediments of the Neretva Channel
Granulometric and mineralogical characteristics of sediments Considering the ratio of different grain size fractions (SHEPARD, 1954), surface sediments from the Neretva Channel were classified as clayey silts (Fig. 2)
Summary
Environmental radioactivity has become a subject of scientific interest in recent decades, due to possible risks to human health, and because radionuclides have been recognized as tracers of many complex biogeochemical processes (PORCELLI & BASKARAN, 2011). The mobility of radionuclides in aquatic environments is governed by their geochemical characteristics, such as solubility, complexation ability and affinity for adsorption onto mineral surfaces (CHABAUX et al, 2003). River-dominated coastal areas of the Adriatic region are characterized by complex physico-chemical interactions and transformations of dissolved and particulate organic and inorganic compounds (SONDI et al, 1994; SONDI et al, 1995; SONDI et al, 2008). In such environments, the transport and deposition of radionuclides is governed by dispersal processes affecting fine-grained sediments, direct precipitation of oxides and oxyhydroxides and coagulation of inorganic and organic colloidal materials (ANDERSSON et al, 1998; LIGERO et al, 2001)
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