Radioactivity, radiological risk and metal pollution assessment in marine sediments from Calabrian selected areas, southern Italy

Abstract.

The two most significant categories of physical and chemical pollutants in sediments (radionuclides and metals) were investigated in this article, in order to evaluate pollution levels in marine sediments from eight different selected sites of the Calabria region, south of Italy. In particular samples were analyzed to determine natural and anthropic radioactivity and metal concentrations, in order to assess any possible radiological hazard, the level of contamination and the possible anthropogenic impact in the investigated area. Activity concentrations of ²²⁶Ra, ²³²Th, ⁴⁰K and ¹³⁷Cs were measured by High Purity Germanium (HPGe) gamma spectrometry. The obtained results show that, for radium (in secular equilibrium with uranium), the specific activity ranges from ($14 \pm 1$) Bq/kg dry weight (d.w.) to ($54 \pm 9$) Bq/kg d.w.; for thorium, from ($12 \pm 1$) Bq/kg d.w. to ($83 \pm 8$) Bq/kg d.w.; for potassium, from ($470 \pm 20$) Bq/kg d.w. to ($1000 \pm 70$) Bq/kg d.w. and for cesium it is lower than the minimum detectable activity value. The absorbed gamma dose rate in air (D), the annual effective dose equivalent (AEDE) outdoor and the external hazard index ($H_{\rm ex}$) were calculated to evaluate any possible radiological risk, mainly due to the use of marine sediments for the beach nourishment. The results show low levels of radioactivity, thus discarding any significant radiological risk. Some metals (As, Cd, Cr_tot, Hg, Ni, Pb, Cu, Zn, Mn and Fe), that could be released into the environment by both natural and anthropogenic sources, were investigated through inductively coupled plasma mass spectrometry (ICP-MS) measurements and compared with the limits set by the Italian Legislation, to assess any possible contamination. Experimental results show that they are much lower than the contamination threshold value, thus excluding their presence as pollutants. The degree of sediment contaminations were quantified using enrichment factor (EF) and geoaccumulation index ( I_geo) for some potential hazardous elements. Results show that EF and I_geo values of As, Pb and Mn were the greatest among the studied metals. Data of this preliminary study could be helpful in the future to obtain background levels in marine sediments of the investigated region and to develop environmental regulatory frameworks.