Evaluation of metal contamination in a changed sedimentary environment: Ghar El Melh Lagoon, Tunisia

Abstract

Three cores were collected in the lagoon of Ghar El Melh (Northern Tunisia) and the sediments were analysed for trace and major elements, sulfides acid volatile sulfides (AVS) and pyrite and total organic carbon (TOC). The sediments are composed of black-mud in the upper layer (0 -10 cm depth) and greymud underneath. Based on the lagoon history, it was believed that the black-mud is endogenic, while the grey-mud is exogenic (derived from old contributions of the Mejerda River before its diversion). The concentrations of TOC and AVS decrease with depth, while the redox potential (Eh) is negative in the black-mud and positive in the grey-mud. The Eh measurements thus revealed the singularity of the sedimentation mode in this lagoon. The North American Composite Shale (NASC) normalisation indicated that Cd, Zn and Pb were enriched through the entire profiles, indicating that this sediment was contaminated for a long time by mining activities and human pollution. Trace metal profiles of Fe, Cd, and Cu approximated that of TOC, while the profiles of Mn, Co, Pb, Ni and Zn followed the Eh. These results, confirmed by the principal component analysis (PCA), suggested that some metals can accumulate in the reduced sediment, while others accumulate in the sub-oxic sediment. Such inference is supported by the metal chemical speciation, which showed these metal -sediment component associations: Mn, Co, Ni, Pb and Zn to the Mn-oxi-hydroxide fraction, Fe to the residual and organic -sulfide-fractions, Cu to the organic -sulfide fraction and Cd to carbonates and sulfides.

Fractionation of metals in the Sa1/2 sediment core from Lake Sarbsko (northern Poland) and its palaeolimnological implications

“…Lithology and bulk chemical composition of the samples are summarised in Tables 1 and 2. Sequential extraction of Fe, Mn, K, Mg, Cu, Zn and Pb was performed on material dried at 60ºC and homogenised in an agate mortar according to the protocol described by Walna et al (2005). Air or oven drying of the samples at temperatures up to 105 ºC have been applied to remove interstitial water from sequentially extracted aquatic (lake and marine) sediments by many authors (Steiberg and TayaraniDastmalian, 1993;Kiratli and Ergin, 1996;Clark et al, 1998;Donahoe and Liu, 1998;Pempkowiak et al, 1999;TokalioÈlu et al, 2000;Ribeiro et al, 2008, Adekola et al, 2010and Oueslati et al, 2010.…”

Accumulation of trace metals in sediments in a Mediterranean Lagoon: Usefulness of metal sediment fractionation and elutriate toxicity assessment

“…Next, the lagoon's water mass requires several months to completely renew, thus facilitating Zn and Pb accumulation (B ejaoui et al, 2008; B ejaoui, 2009). Such metal accumulation has been detected in several Mediterranean Lagoons, namely Ghar El Melh Lagoon (northern Tunisia) and Nador Lagoon (Morocco) where Pb and Zn accumulation rates were the highest in the twentieth century sediments (Oueslati et al, 2010;Gonz alez et al, 2007). Moderate enrichment was observed for Cr, mainly Fig.…”

Assessment of oxidative stress, genotoxicity and histopathological responses in the digestive gland of Ruditapes decussatus collected from northern Tunisian lagoons

“…A narrow channel enables a restricted water exchange with the open sea (water residence time in the lagoon: 35 days; Rasmussen et al 2009). Ghar El Melh Lagoon receives various discharges from the Mejerda River, which delivers 17 million t of sediment annually (Oueslati et al 2010). The lagoon ecosystem has suffered progressive deterioration and is considered hypereutrophic (Rasmussen et al 2009) because of human activities within the lagoon itself and in the surrounding area (such as discharges of domestic wastewater, industrial waste from the drainage system and fishing activity) (Moussa et al 2005).…”

“…According to Nourisson et al (2013), Ghar El Melh is considered a moderately polluted site, because it is one of the world's wetlands awarded the Wetland City Label accredited by the international Ramsar Convention for the protection of wetlands (Ben Haj 2012). Thus, it was selected as the LCA site in the current study on the basis of other published works (Oueslati et al 2010).…”