A Survey of Concentrations and Source Characterization of Polycyclic Aromatic Hydrocarbons in Surface Waters of the Imiringi River System

Ten water samples were collected along the Imiringi water channel, cutting across several sub-communities of the upstream to downstream sections of the river. All samples were collected in the month of August 2019, reflecting increased tidal movement of water and aggravated pollutants redistribution which is typical of the rainy season. Analysis was carried out using the HP 6890 Plus gas chromatograph – flame ionization detector (GC-FID). The rate of ionization of each PAH component was directly proportional to the obtained concentration. The total concentrations of 14 PAHs ranged from <0.01 to 300.1 µgL-1, with the high molecular mass PAHs (4-6 ring HPAHs) observed as the most important fractions showing 82.4% distribution. Also, the low molecular mass PAHs (2-3 ring LPAHs) were found in trace concentrations, accounting for 17.6% of total PAH mass. The application of PAH source diagnostic ratios revealed vegetation and coal combustion as primary sources, followed by petroleum combustion, and then, petroleum sources. Correlation cluster analysis (CCA) and principal component analysis (PCA) showed discrete localization for samples of stations OL1, OB2 and OS4. The pyrogenic inputs are most likely from runoffs of seasonally burnt vegetation at near-coastal farmlands as well as leachates from surrounding waste-dumpsites. Petroleum sources may have resulted from neighbouring oil installations and illegal oil bunkering sites. Overall, the study is aimed at identifying the most important contributing sources of polycyclic aromatic hydrocarbon (PAH) micro-pollutants in the aquatic environment.