Mobility of Contaminated Heavy Metals and Metalloids in Sediments Caused by Recent Industrial Activities

Sequential leaches (sequential extractions) experiment of 62 elements were carried out for assessing the mobility of contaminated heavy metals and metalloids contaminated in natural sediments; river sediments of Oued El Harrach (Algeria) and lagoon sediments of Bizerte (Tunisia), North African Mediterranean coast. Applied extractants for the sequential leaches are: (A) distilled water for extracting water soluble components, (B) 1M sodium-acetate for extracting exchangeable cations by clay minerals and co-precipitations of carbonates, (C) 0.1M sodium-pyrophosphate for extracting the elements bound with organic matter, (D) 0.1M hydroxylamine for extracting the elements bound with amorphous Mn hydroxides, and (E) 0.25M hydroxylamine for extracting the elements bound with amorphous Fe hydroxides and more crystallized Mn hydroxides. According to the results of sequential leaches experiment, contaminated heavy metals, metalloids, and other potentially toxic element (PTEs) in the sediments are mostly presented as exchangeable cations by clay minerals, co-precipitations of carbonate compounds, binding complexes with organic matter, and/or amorphous manganese hydroxides. Mobility of contaminated heavy metal and metalloids is relatively larger in Algerian river sediment than in Tunisian lagoon sediments. However the mobility of the PTEs in the sediments can be easily changed if the depositional environment is altered by civil