engleski

DDT and PCB levels and long - term trends in sediments collected from the eastern coastal and open waters of the Adriatic sea

The Adriatic Sea, a semi-enclosed body of water, is of special interest for the evaluation of the entry, extent and fate of chlorinated hydrocarbon pollutants. Bottom sediment is often the best available medium for the long-term monitoring of many contaminants in aquatic recipients. From 1976 to 1990, sediment samples were collected from several areas at over sixty stations located in the eastern Croatian coastal and open waters of the middle and the northern Adriatic Sea. Chlorinated insecticide and polychlorinated biphenyl concentrations in the surface sediment samples ranged from <0.1 to 96.7 for DDT and from <0.5 to 294/ug kg-1 for PCB on the basis of dry weight. The DDT and PCB levels in the analyzed sediment samples collected from the eastern Adriatic coastal areas were lower than those from other Mediterranean areas. DDT and PCB concentration does not follow Gaussian distribution in the investigated area and collecting period. Therefore, it is necessary to be very careful in interpreting the concentration data using parametric statistics. The pollutant levels in sediment samples collected simultaneously at nearby stations frequently differ. This often has a significant influence on the means and confidence intervals. Using n onparametric Kruskall Wallis one-way analysis by rank, significant differences were found according to the collection period for DDT concentration levels but not for PCB concentration. Although the DDTs and PCBs concentration data in sediment samples collected from the open waters of the northern and middle Adriatic show statistically significant differences, neither the DDT nor PCB levels show any statistically significant annual trend. It is very important to stress that all these samples were analyzed from a single analytical group (mostly by the same analyst), using a uniform methodology that had been very successfully intercalibrated during twelve international intercalibration exercises.

PCB; DDT; sediments; Adriatic; levels; trends

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