Seasonal Distribution, Source Identification, and Toxicological Risk Assessment of Polycyclic Aromatic Hydrocarbons (PAHs) in Sediments from Wadi El Bey Watershed in Tunisia

Surface sediments were collected from the Watershed of Wadi El Bey in Tunisia to evaluate the degree of polycyclic aromatic hydrocarbons (PAHs) contamination. Sediments were collected during different seasons in 14 sites that received wastes from domestic effluent, industrial discharge, and agricultural drainage wastes. Twenty-six individual PAHs were analyzed. The total PAH contents (Σ PAHs) in surface sediments showed wide variability, ranging from 6.89 ± 0.05 to 340 ± 0.1 ng g−1. The 4-, 5-, and 6-ring compounds were the most abundant PAHs detected at the majority of sites. Diagnostic concentration ratios between pairs of PAHs and molecular indices, calculated with the purpose of drawing information about pollution sources, indicated that PAHs were of both petrogenic and pyrolytic origins. Toxic contaminants concentrations were determined according to the numerical effect-based sediment quality guidelines (SQGs). PAH levels did not exceed the SQGs, indicating that PAHs seem to pose low and occasional toxicity risks. Total carcinogenicity and mutagenicity (TEQBaP and MEQBaP) ranged from 0.08 to 65 ng and from 0.02 to 135.0 ng g−1 of dry weight, respectively. Among the seven carcinogenic PAHs, BaP accounted for the majority of the potency and could potentially be used as a unique indicator of PAH toxicity. This study provides a baseline to promote environmental protection programs and pollution monitoring/control in Watershed and coastal areas.