Critical Analysis of Polycyclic Aromatic Hydrocarbons Ring Size Distribution in Marshy Soils and Sediments in Warri City and Its Environs, Southern Nigeria
Industrialization and urbanization have advanced socio-economic development. As a consequence, amyriad of environmental problems have become prevalent in urban areas, including contamination by polycyclic aromatic hydrocarbons (PAHs) via various pathways. PAHs are ubiquitous environmental pollutants and are released into the environments via various routes. They have been largely detected in various environmental media, such as organism,atmosphere, water, soils and sediments. This study was carried out to analyze the ring size distribution of PAHs in marshy soils and sediment samples in Warri City, Southern Nigeria. The samples were collected during dry and rainy seasons from four locations within Warri and a control location in Agbarho, 20km away. Levels of 16 priority PAHs listed in United States Environmental Protection Agency (USEPA) were determined using Gas Chromatography coupled with Flame Ionization detector (GC-FID). This study was carried from January to March and June to August, representing the dry and wet seasons respectively. It was observed that PAHs concentration was generally higher in dry than rainy seasons for soil and sediment samples. The two-ringed PAHs analysed were naphthalene, 2-methyl naphthalene and 1-methyl naphthalene while the three-ringed PAHs were acenaphthylene, acenaphthene, fluorine, anthracene and phenanthrene. The four-ringed PAHs were fluoranthene, chrysene, pyrene and benzo(a)anthracene. The five-ringed PAHs were benzo(a)pyrene, benzo(b)fluoranthene and benzo(k)fluoranthrene while the six-ringed PAHs were indeno (1,2,3-c,d) pyrene and dibenzo(a,h)anthracene, and benzo(g,h.i)perylene. Moreover, the ring size analysis revealed that for soils, two to three-ringed as well as four-ringed PAHs were more predominant in Ugboroke location, five-ringed PAHs in Okotie and six-ringed PAHs in Ogunu location. Overall, five-ringed PAHs were more predominant in Okotie location in the dry season. However, for sediments, two to three-ringed as well as four-ringed PAHs were more predominant in Okotie location, five-ringed PAHs in Ogunu and six-ringed PAHs in Ugboroke location. Overall, two to three-ringed PAHs were more predominant in Okotie location in the dry season for sediment samples. Furthermore,in the marshy soil samples, the ring size distribution is as follows; 5-ring PAHs ˃ 2-3 ring PAHs ˃ 6-ring PAHs ˃ 4-ring PAHs. Considering the dominance of 5-ring PAHs; high lipophilicity, low water solubility and low volatility PAHs are prevalent in the study area. As a result, they are predominantly in solid state, decreasing their mobility and increasing their persistence in the environment.In the marshy sediment samples, the ring size distribution is as follows; 2 to 3-ring PAHs ˃ 5-ring PAHs ˃ 4-ring PAHs ˃ 6-ring PAHs. The dominance of 2 to 3-ring PAHs indicates that the PAHs found in the study area may have low lipophilicity, high water solubility and high volatility. As a consequence of their high volatility, they may readily appear in the atmosphere predominantly in gaseous form. Furthermore, being highly soluble in water, they are readily available for biological uptake and degradation. Hence, they are less toxic with decreased carcinogenic, mutagenic and teratogenic potential.
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