Impact of a Mixed “Industrial and Domestic" Wastewater Effluent on the Southern Coastal Sediments of Sfax (Tunisia) in the Mediterranean Sea

Abstract

Concentrations of Zn, Cu, Cr, Cd, Pb and Fe in surface marine sediments of the southern coast of Sfax were studied in order to understand current metal contamination at the outlet of a mixed industrial and domestic wastewater effluent discharged into the seawater since 1953. We found that heavy metal concentrations (mg/kg dry weight) in surface marine sediments varied from 42 to 391 for Zn, 15 to 44 for Cu, 44 to 137 for Cr, 6 to 56 for Cd, 19 to 59 for Pb and 52344 to 54543 for Fe. The computed metal enrichment factors (EF) in the sediments showed that EF of Zn ranged from 0.49 to 9.13, EF of Cu from 0.35 to 3.04, EF of Cr from 0.3 to 3.05, EF of Cd from 0.63 to 9.37 and EF of Pb from 0.43 to 3. All heavy metals were characterized by maxima EF values greater than 1.5, indicating a considerable metallic pollution of the study area. The PCA analysis revealed two distinct groups: (i) the first group (G1) is representative of Fe selected as natural tracer and (ii) the second group (G2) is articulated around Zn, Cu, Cr, Cd and Pb. These metals which did not show any correlations with Fe of the first group imply a significantly impact of the selected wastewater effluent. The calculation of the geoaccumulation index (Igeo) showed that all analyzed metals (except for Fe) can be considered as moderate to extreme pollutants. The microbial analysis of seawater samples and also of both water and sediment samples collected from the Sfax solar saltern (placed at the vicinity of the outlet of the selected effluent) showed that no indicator germs of contamination (total coliforms, faecal coliforms and faecal streptococci) were detected.