Environmental impacts and distribution of polycyclic aromatic hydrocarbons (PAHs) in soils and sediments in Ilaje area, southwestern Nigeria

Continuous oil exploration and exploitation activities in the Niger Delta region have led to the area being plagued by oil pollution. Baseline and detailed studies have been reported in the southeastern part of the region; however, in the southwestern part, some authors have ascribed the pollution in the area with oil production activities, with no empirical evidence to justify the claim. This present work is a baseline study utilizing polycyclic aromatic hydrocarbons (PAHs) extracted from soils and sediments in four (4) localities within the southwestern part of the Niger Delta region, with the aim of determining the sources and level of pollution in the area. A total of fifteen (15) samples, made up of four (4) sediments and eleven (11) soil samples, were collected. Identification and quantification of PAHs were performed using a Shimadzu GC/MS QP 2010 model. In all soil samples analyzed, 15 PAHs were identified (naphthalene (Nap), acenaphthylene (Acy), acenaphthene (Ace), fluorene (Flu), phenanthrene (Phe), anthracene (Ant), pyrene (Pyr), benz(a)anthracene (BaA), chrysene (Chr), benzo(b)fluoranthene (BbFl), benzo(k)fluoranthene (BkFl), benzo(a)pyrene (BaP), dibenz[a,h]anthracene (DahA), benzo[g,h,i]perylene (BePe), and indeno[1,2,3-c,d]perylene (InP)) while 6 were detected in the sediments (Nap, Flu, Phe, Ant, BaP, DahA). The concentrations of PAHs identified in the soil and the sediment samples ranged from 0.056 to 52.640 ng/g (∑PAHs 57.998 ng/g) and from 0.188 to 0.932 ng/g (∑PAHs 2.052 ng/g), respectively. The ranges of different diagnostic ratios used indicated more of pyrogenic sources, with the exception of low molecular weight polycyclic aromatic hydrocarbons to high molecular weight polycyclic aromatic hydrocarbons ratio (LMWPAH/HMWPAH), which indicated a petrogenic source. Generally, the PAH concentration in the samples was relatively low and below standard thresholds of toxicity. However, the presence of some carcinogenic PAHs, though at lower concentrations, may pose threat to the ecosystem if not monitored.