Source Apportionment and distribution of Polycyclic Aromatic Hydrocarbons in Imo River Sediments near Afam Power Station, S.E. Nigeria: Molecular index and Multi-Variate Approaches

Abstract

Surface sediments from Imo River near Afam Power Station were analysed for quantitative determination of polycyclic aromatic hydrocarbons (PAHs) using gas chromatography-mass spectrometry (GC-MS). The total PAH concentrations (excluding perylene) were in the range 1.60 – 67.70 ng/g dry weight (dw).The degree of anthropogenic impacts were considered relatively low when compared to other urban Asian / American coastal sedimentary environments. PAH compositions were dominated by 3 – and 4 – ring types with phenanthrene, anthracene, fluoranthene and pyrene being the dominant species. Relatively high levels of PAHs were found in sediments near the fish settlement while minimum amounts were observed for the remote upstream location. Utilization of five selected PAH molecular ratios such as Fluoranthene/(Fluoranthene + Pyrene) (0.3- 0.5), Anthracene/(Anthracene +Phenanthrene) (0.19 – 1.19), Benzo(a)Anthracene/(Benzo(a)Anthracene+ chrysene) (0.35 – 1.0), Low molecular weight PAHs/High molecular weight PAHs (0.20 – 1.10) and 1,7/(1,7 +2,6 – Dimethylphenanthrene) (0.34 – 0.84) enabled apportionment of sample to source to be made with an observed mixed source dominance scenario. The complication in the molecular ratios may be associated with short/long range transport weathering, and differences in microbial or photo-degradation effects. Cluster analysis employed classified the study area into specific regions and distinguished two main cluster groups with great dissimilarity that are site and source specific. Factor analysis showed that four factors (sources) accounted for 85.1% of total variability.

KEYWORDS: PAHs, source, distribution, molecular ratios and multivariate analysis.