This study was carried out to investigate seasonal variations of polycyclic aromatic hydrocarbon (PAHs) in sediments of Ala River, South-west, Nigeria. The total amount of PAHs (∑PAHs) concentration ranged from 4.6 μgg-1to 10.1 μgg-1 dry weights during wet season and from 3.8- 10.3μg.g-1dry weights during the dry season. The total concentrations of PAHs were higher in most of the sites during wet season 80 % and 20 % during the dry season. The result showed that the contaminants in Ala river were mainly mixture of pyrogenic, petrogenic and few sources from vehicular emission using PAH diagnostic ratio. The ΣPAHs are between Effect Range Low (ERL) and Effect Range Median (ERM) did not exceed ERM in all samples both in wet and dry season. The results of the present study showed ΣPAHs were below 1 μgg-1 dw at all sampling locations. Principal component analysis was used to determine the origin of the PAHs. Analysis of PCA indicated that the PAH variables could be reduced to six components, which accounted for 82.97 % of the total variance for the data. The cluster analysis confirmed two major clusters arrangement of PAH concentration and this confirmed that Ala river contaminants were both from petrogenic and pyrolytic source.

Keywords: Polycyclic Aromatic Hydrocarbons (PAHs), Pyrolytic, Petrogenic, Ala River, Sediment PAHs = Polycyclic Aromatic Hydrocarbon