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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