Characterization of tenorm and sediments of Kastela Bay and the influence of tenorm on the quality of sediments

The objective of this study was set on three goals: (i) Chemical and radiological characterization as well as leaching properties of the mixture of fly and bottom ash produced in thermo electric unit of former "Adriavinil" factory and deposited in Kastel Gomilica region, Croatia, (ii) Chemical, radiological and mineralogical characterization of the Kastela Bay sediments under the influence of past industrial activity and its waste by products, and (iii) Estimation of the influence of TENORM deposition on the quality of Kastela Bay sediments. Kastela Bay sediments are exposed to numerous sources of pollution like fly and bottom ash enriched in radionuclides and heavy metals, chemical plant, cement plant, iron plant, shipyard, electroplating facility, untreated industrial and domestic waste waters as well as to heavy traffic. High activity of naturally occuring radionuclides U-238, U-235 and Ra-226 present in the ash was the reason for its classification as TENORM (Technologically Enhanced Naturally Occuring Radioactive Material). Besides, this material was highly enriched in heavy metals. To obtain a preliminary data about the present state of researched area, 33 samples of the mixture of fly and bottom ash, 12 sediment cores ranging from 0 to 40 cm and nine surface sediment samples were analyzed. Enrichment with heavy metals in the mixture of fly and bottom ash ranged from 1.5 to 36 times compared to flisch soil while Ra-226 and 238U were up to 50 times enriched compared to average activities characteristic for surrounding soils developed on the Middle and Upper Eocene flisch. Most of the measured heavy metals in the ash were 3-4 times those in the surrounding soil. It was found that over 37% of the total U could be removed from the ash by the sea water. Bioavailable fraction of the ash was estimated by conducting different leaching tests. According to mean values of the elemental concentrations for each sediment segment, the elements could be divided into five groups with similar distribution patterns. The highest enrichment in sediment cores compared to background values were found for Zn (35.6 times), Pb (16 times), Cr (9.1 times) and Ni (4 times). The highest concentrations of total uranium were determined at positions 1 and 2 situated in the vicinity of the ash deposit site and under the constant influence of ash dumping into the sea and leaching from the ash deposit. Observed concentrations of Zr, Fe and Co point out a larger input of terrestrial material, like the mixture of fly and bottom ash and flisch material, into predominant carbonate sediments. Maximum concentrations of heavy metals were found in deeper sediment segments deposited in the period of the highest industrial production and the negligible care to the environment.