Assessment of metals contamination in sediments from the Mediterranean Sea (Libya) using pollution indices and multivariate statistical techniques

Total metals concentrations, Geoaccumulation index (Igeo), Pollution load index (PLI), degree of contamination (DC) and sediment quality guidelines (SQGs) were used to assess heavy metals contamination status and ecological risk in the sediments from the Libyan Mediterranean coast. The distribution pattern of heavy metals in the sediment follows the sequence: Fe>Pb>Mn>Ni>Zn>Cr>Cu>Co>Cd. Over than 100% of the samples were lower than the Cr and Zn thresholds effect level (TEL) of SQGs, 79% percent of sediments would be expected to occasionally be associated with the toxic adverse effects on aquatic organisms because of Pb. While, cadmium exceeded the probable effect level (PEL) value at 100% of the sediment samples. In general, the results revealed very high contamination factor (Cf > 6) for Cd. This was supported by CF (>6) for Cd. The modified degree of contamination was (4 ≤ mCd < 8), reflecting high degree of contamination. The calculated PLI were less than 1, indicating only baseline levels of pollution. Multivariate statistical analyses (Principal component analysis, cluster analysis) and correlation matrix were used in this study. Highly significant correlations were found between the concentrations of Cd, Co, Cu, Mn, Ni and Zn, suggesting similar sources and/or similar geochemical processes controlling the occurrence of these metals in the sediments. The study point out that although there were slight variations in the results of the three indices, the combination of the three indices gave us a comprehensive understanding of heavy metals risks in the surface sediments of the Libyan Mediterranean coast.