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, a
myriad 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, 20 km 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.