PAH derivatives in sediments and fish from white Nile near Melut oil fields, South Sudan: bioaccumulation and source apportionment

Abstract

This study was aimed at determining the occurrence and distribution of Nitro-PAHs, Oxy-PAHs and Hydroxy-PAHs in three different fish species (Oreochromis niloticus, Lates niloticus and Clarias gareepinus) and sediments from White Nile in vicinity of Melut oil fields, South Sudan. Extraction of analytes in fish and sediment samples was done using accelerated solvent extraction and an ultrasonic extraction, respectively. Analysis of the concentrations of PAH derivatives was done using Gas Chromatography-Tandem Mass Spectrometry (GC-MS/MS). Hydroxy-PAHs were first derivatized by using BSTFA/TMCS,99-1 prior to instrumental analysis. Total concentrations of PAH derivatives (∑15NPAHs, ∑5OPAHs and ∑3 OHPAHs) in sediments were and (319.28, 312.68, and 184.21), (54.05, 34.31 and 30.85), (53.07, 47.02 and 17.81) ng g-1 dw at A, B and C, respectively. In Clarias gareepinus fish species, the mean levels NPAHs, OPAHs and OHPAHs were (215.7, 24.9 and 32.6), (340.1, 30.6 and 44.5), and (208.4, 22.3 and 18.6) ng g-1 ww at A, B and C, respectively. They were (347.7, 97.2 and 68.2), (392.5, 66.8 and 117.9), and (214.5, 78.2 and 105.2) ng g-1 ww at A, B and C, respectively in Lates niloticus and (276.5, 52.7 and 36.3), (241.3, 47.2 and 73.1), and (230.1, 59.3 and 94.7) ng g-1 ww at A, B and C, respectively in Oreochromis niloticus. Lower molecular weight (LMW) PAH derivatives (2-3 rings) were more abundant in the samples (77% of the ∑PAH derivatives for fish and 81% for sediments). 1-Nitronaphthalene was the most abundant congener (contributing 33% and 26% of the ∑LMW-PAH derivatives sediments and fish, respectively). The levels of PAH derivatives did not differ significantly in sediments of different sites, and this is indicative of a common source of pollution. Among fish species, O. niloticus had the highest concentrations of PAH derivatives. The total carcinogenic risk of PAH derivatives showed that, consumption of fish from White Nile could have an effect on human health. The major sources of PAH derivatives are petrogenic in nature, based on diagnostic ratios. Biota-sediment accumulation factor values ranging from 0.03-2138 g OC g-1lipid in fish, showed high bioaccumulation of lower molecular weight PAH derivatives compared to high molecular weight derivatives. The results further showed that, bioaccumulation of PAH derivatives decreases as the number of fused aromatic rings increases. This study makes suggestions and recommendations about data needs and future research on NPAHs, OPAHs and OHPAHs.