Spatial distribution of contaminants in sediments of two rivers crossing Tangier (northern Morocco).

The distribution and accumulation of heavy metals in the sediments of two rivers which cross various agglomerations of Tangier city, Morocco, were investigated. Surficial sediment samples were collected during 2005 and characterized for metal content (Zn, Pb, Cd, Cu, Cr and Ni), organic matter, total nitrogen, and n-hexane extractable material (HEM). The organic components (organic carbon, total nitrogen and HEM) show a slightly increasing enrichment from the upstream to the downstream of the emissary. An evaluation of the heavy metal pollution status of both tributaries was carried out using the metal pollution index (MPI). The results revealed the importance of anthropic pressure and the zones influenced by industrial discharges, which keep the metals Pb, Cr and Ni at high levels. Comparison with international regulatory guidelines for sediments revealed serious contamination of Cr, Zn and Ni.

Evaluation of metal contamination in sediments from north of Morocco: geochemical and statistical approaches.

Concentrations of Fe, Mn, Cr, Cu, Ni, Pb, Zn, Cd and Hg were evaluated in surface sediments of two rivers from north of Morocco, known as Souani and Mghogha rivers. Significantly higher concentrations in mg kg(-1) dry weight (dw) of Mn (747.6 vs. 392.9), Cr (86.4 vs. 56.3), Zn (299.5 vs. 138.5) were found in sediment samples from Mghogha when compared with Souani river. Average concentrations of Cd and Hg in several sediment samples from both rivers were above the effect range median that predicts toxic effects to aquatic organisms. The calculation of enrichment factors showed that Mn, Cr, Cu and Ni were depleted, whereas Pb and Hg were enriched. The results of geoaccumulation index revealed that sediments of both rivers were unpolluted with most of the metals and moderately contaminated with Fe and Hg. Some of elevated concentrations of Hg, principally in Mghogha River, were due to anthropogenic sources including the direct discharges of industrial zone.