Trace metal accumulation in different grain size fractions of the sediments from a semi-enclosed bay heavily contaminated by urban and industrial wastewaters

Cluster analysis was applied to identify granulometric similarities between sediment samples from a heavily contaminated semi-enclosed bay (the Ka tela Bay in the Middle Adriatic). Concentrations of Mn, Cr, Pb, Cd and organic matter were determined in four grain-size fractions (A, >300 μm; B, 54–300 μm; C, 20–54 μm; and D, <20 μm) of the sediment samples. The finest sediment fractions (C and D) contained the highest concentrations of Cr, Pb and organic matter. The concentrations of these metals were generally four times greater than in coarse grained-fractions. Cadmium is also accumulated in less extent in fine-grain fractions, while Mn distribution was quite irregular. The vertical distribution of the studied trace metals shows Pb enrichment in upper sediment layers, while Cd concentration was increased only in the samples from the most polluted part of the Bay. This indicates anthropogenic origins of these metals. Principal Component Analysis was used to interpret the variations of trace metals and organic matter concentrations in the sediment samples.