Bioavailability and assessment of heavy metal pollution in sediment cores off the Mejerda River Delta (Gulf of Tunis): How useful is a multiproxy approach ?

International audienceThree core samples were taken from zones offshore from the Mejerda River Delta (Tunisia) and analyzed formajor and trace elements to assess their relationships with organic matter, monosulfides and carbonates, aswell as for pollution and bioavailability. Chemical speciation,ΣSEM/AVS, the enrichment factor (EF) and thegeo-accumulation index (I-geo) were used. Iron, cadmium, lead and zinc – the most frequently mined metalsin the Mejerda catchment – were found as contaminants in the offshore areas. Estimations of trace elementaccumulation using the EF and the I-geo index show that lead, and to a lesser extent zinc, are the most pollutingmetals off the Mejerda outlet. According to their bioavailability, these metals are also the most toxic. Only cadmiumis heavily present in delta sediment (EF N 100) though deeply sequestrated (100% bound to the residualfraction) and thus presents no toxicity