Effect of anthropogenic activity on the levels of metals in surface sediments of the Gabes Gulf (Tunisia)

Abstract The Gabes Gulf, recognized for its marine productivity, is the subject of high anthropogenic pressure. The aim of this synthesis work is to present a global view of metal contamination in marine sediments in the Gabes Gulf and its relationship with anthropogenic sources. The study is based on descriptive and chemometric methods, where contamination indices were used (Enrichment Factor and Geoaccumulation Index). The examined sites, classified in an increasing order of contamination are: southern coast of Sfax, northern coast of Sfax, and Gabes coast. Contamination is mainly explained by the industrial activity of phosphate treatment. Phosphogypsum, which is the main product enriched with metals, is evacuated directly into the sea along the Gabes coast, while small quantities were evacuated into the sea in the northern coast of Sfax. In the southern coast of Sfax, only a part of the phosphogypsum leaching water is drained into the sea. The contamination indices were calculated using two different methods. The first is based on regional natural concentration of metals while the second uses mean continental crust concentrations. The first method was shown to better characterize sediment contamination. However, the second was shown to be more adequate in comparing results against those of other areas around the world.