Concentration, enrichment and distribution of heavy metals in surface sediments of the Tangier Bay, Morocco

Abstract

The distribution, enrichment, and accumulation of heavy metals in the surface sediments of the Tangier Bay, Morocco, were investigated. Surface sediment samples from eleven locations in the Bay of Tangier were collected in 2007 and characterized for grain size, organic matter and metal content (e.g. Fe, Mn, Cr, Cu, Ni, Pb, Zn and Cd). The evaluation of the heavy metal contamination status of the bay showed minor enrichment by the enrichment factors (EF) calculation, corroborated by the metal pollution index (MPI). The results of a Pearson correlation showed high positive correlations among organic carbon and most metals (0.788 < r < 0.939) and cluster analysis grouped the stations inside the harbour (stations 1, 10 and 9) and in the vicinity of the principal rivers in the bay (stations 3 and 11), which showed the highest concentrations of metal content. The main sources of contamination are domestic and industrial effluents, which arise due to the lack of sewage treatment. However, these areas could not be classified as polluted when the data were compared with sediment quality guidelines (USEPA, 1997).