First investigation of seasonal concentration behaviors and sources assessment of aliphatic hydrocarbon in waters and sediments from Wadi El Bey, Tunisia

The contents, composition profiles, and sources of aliphatic hydrocarbons were examined in surface sediment and water samples collected from Wadi El Bey, in Tunisia, during different year seasons in 14 stations receiving domestic effluent, industrial discharge, and agricultural drainage wastes. The target substances were analyzed by gas chromatography coupled with mass spectrometric detection (GC/MS). Total concentrations of n-alkanes (n-C14-n-C38) ranged from 0.08 ± 0.01 to 18.14 ± 0.1 µg/L in waters and 0.22 ± 0.04 to 31.9 ± 24.6 µg/g in sediments, while total aliphatic fraction ranged from 0.08 ± 0.01 to 196 ± 140 µg/L in waters and 0.22 ± 0.04 to 1977 ± 1219 µg/g in sediments, which means that almost all sites were affected by hydrocarbon contents in sediments exceeding the recommended limit (100 µg/g). Various diagnostic indices (ADIs) were used to identify the hydrocarbon sources, namely the concentration ratios of individual compounds (n-C17/pristane, n-C18/phytane, pristane/phytane, n-C29/n-C17, n-C31/n-C19) as well as cumulative quantities (Carbon Preference Index, natural n-alkanes ratio, terrigenous/aquatic compounds ratio, unresolved complex mixture percentage, low molecular weight vs. high molecular weight homologues, Alkane Proxy and Terrestrial Marine Discriminants). In general, these indexes indicated that the origin of aliphatic hydrocarbons affecting sediments and waters of Wadi El Bey were linked to both biogenic and petrogenic inputs, attesting the impact of plankton and terrestrial plants and of oil contamination, respectively. The average carbon chain length computation (ACL), used to further index the chemical environment, ranged from 25.5 to 31.1 in sediments and 47.9-116 in waters. This finding could depend on the severe disturbances suffered by the ecosystem as a consequence of heavy anthropogenic inputs. Petroleum contamination associated with high eutrophication rates in Wadi El Bey must be strictly controlled, due to possible harmful effects induced on ecosystem and humans.