Testing the Impact of Contaminated Sediments from the Southeast Marine Coast of Tunisia on Biota: a Multibiomarker Approach Using the Flatfish Solea Senegalensis

Coastal marine areas are highly vulnerable to the exposure to various types of stressors and impact of chemical pollution resulting from increasing anthropogenic activities, namely pollution by metals and polycyclic aromatic hydrocarbons (PAHs). To assess ecosystem quality and functions, biomarkers can provide information about the presence and adverse effects of pollutants. Accordingly, the present study was conducted to evaluate the chronic (28 days) biologic effects of putatively contaminated sediments from the Zarzis area, located in the south of the Gulf of Gabes on the Southern Tunisian coast, on the marine flatfish Solea senegalensis. Sediments were collected at three sampling sites, impacted by wastewater discharges, aquaculture activities, and industrial contamination, and then surveyed for metals (Cd, Cu, Cr, Hg, Zn, and Pb) and organic contaminants (polycyclic aromatic hydrocarbons). The quantified biomarkers involved the determination of oxidative stress, phase II metabolism, and the extent of lipid peroxidation (catalase, CAT; glutathione peroxidase activity: total and selenium-dependent, T-GPx and Se-GPx; activities of glutathione-S-transferases, GSTs; levels of lipid peroxidation, by means of the thiobarbituric acid reactive substances assay, TBARS) and neurotoxicity (activity of acetylcholinesterase, AChE). S. senegalensis exposed to potentially contaminated sediments, collected near the aquaculture facility, presented the highest values for the generality of biomarkers tested, and a significant inhibition of AChE activity. A few lesions have been also recorded in the gills and liver tissues of S. senegalensis following chronic exposure. However, the observed lesions in gills (e.g., epithelial lifting, lamellar fusion, gills hyperplasia and hypertrophy, and leukocyte infiltration) and liver (cytoplasmic vacuolation, enlargement of sinusoids, foci of necrosis, and eosinophilic bodies) were of minimal pathological importance and/or low prevalence that did not significantly affect the weighted histopathological indices. Finally, the biological responses evidenced by this flatfish can be potentially caused by metal and PAH pollution occurring in specific areas in the southeast of Tunisia. The type and extent of the observed biochemical alterations strongly suggest that the contaminated sediments from the surveyed areas could cause early adverse biological effects on exposed biota.