ASSESSMENT OF POLYCYCLIC AROMATIC HYDROCARBONS (PAHs) AND HEAVY METALS IN THE SEDIMENTS OF ALA RIVER, AKURE METROPOLIS, NIGERIA

Abstract

Carcinogenic, teratogenic and bioaccumulation tendencies of PAHs and heavy metals are a great concern these days because they are discharged into the environment. Ala River, a major water body that transverses the entire Akure metropolis is now at the receiving end, thus, there is need to evaluate the level of PAHs and heavy metals in this water to prevent possible health consequences. Sediment samples were taken at ten different locations along the course of the river between April 2013 and October 2014, covering both dry and wet seasons. Polycyclic Aromatic Hydrocarbons (PAHs) in the sediments samples were determined using Gas Chromatography-Mass Spectrometry technique (GC-MS) after extraction, while heavy metals were analysed by Inductively Coupled Plasma- Optical Emission Spectrometry (ICP- OES). Geo-accumulation index (lgeo), Enrichment Factor (EF), Degree of Contamination (Cd), Pollution Load Index (PLI), and Potential Ecological Risk Index (PERI) were used to evaluate the level of heavy metal pollution quantitatively while PAHs diagnostic ratio was used to identify the sources of the polynuclear aromatic hydrocarbons. Some sediments physicochemical parameters as indices of pollutant were determined using standard methods. The physicochemical parameters of the sediments in the two seasons showed that the sediments were slightly acidic with pH values ranging from 5.43 to 6.20 and had total organic carbon, total organic matter, sand, clay, and silt ranging from 0.03 to 0.22%, 0.08 to 0.49 %, 89.9 to 95.2 %, 4.50 to 9.10, and 0.17 to 1.40 %, respectively. Sixteen United State Environmental Protection Agency (USEPA) priority PAHs analysed showed concentration (μgg-1) as follows: Naphthalene (0.03 to 0.67); Acenaphthene (0.03 to 0.35); Acenaphthyene (0.03 to 0.70); Fluorene (0.02 to 0.42); Phenanthrene (0.02 to 0.84); Anthracene (0.02 to 0.34); Fluoranthene (0.21 to 0.61); Pyrene (0.02 to 0.90); Benzo[a]Anthracene (0.03 to 0.41); Chryene (0.02 to 0.45); Benzo[b]Fluoranthene (0.01 to 0.52); Benzo[k]Fluoranthene (nd to 0.050); Benzo[e]Pyrene (nd to 0.13); Benzo[a]Pyrene (0.02 to 0.52); Dibenz[ah]Anthracene (nd to 0.31); Benzo[ghi]Pyrene (0.03 to 0.43); Indeno[1,2,3-cd]Pyrene (0.01 to 0.36). The total PAHs (ΣPAHs) concentration ranged from 1.70 to 5.73 μg/g dry weights during the wet season and from 2.93 - 6.05 μg/g dry weight during the dry season. There were significant difference (p ≤ 0.05) between Naphthalene (NAP), Phenanthrene (PHEN), Anthracene (ANT), Pyrene (PY), Benzo[b]Fluoranthen (BbF) and Benzo[e]Fluoranthene (BeF) concentrations for the two seasons while there was no significant difference between the two seasons for the concentrations of the remaining PAHs analysed. Applying the PAH diagnostic ratio, the result showed that the PAHs in Ala river sediments were mainly a mixture of pyrogenic and petrogenic. The total concentrations of PAHs were higher in most of the stations (80 %) during the wet season. The ΣPAHs were between the Effect Range Low (ERL) and the Effect Range-Median (ERM) in all samples both in the wet and dry season and did not exceed Effect Range-Median (ERM) in all samples. For individual PAH, the values were between ERL and ERM and none was higher than the values of the Effect Range-Median which indicate that the biological effects would occur occasionally. The nine heavy metals determined were: Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, and Zn. The range of metals concentration (mg/kg) of each metal was: for both seasons ranged from Cd (bdl to 0.06); Co (0.27 to 10.00); Cr (4.33 to 34.70); Cu (0.37 to 8.43); Fe (4198 to 14823); Mn (16.60 to 376); Ni (0.2 to 10.40); Pb (1.50 to 23.03) and Zn (4.67 to 10.16). In the studied sites, most of the studied metal shows a higher concentration in the dry season than in wet season.The seasonal variations of heavy metals were observed and it was discovered that there was a significant difference (p < 0.05) in some metals Cd, Mn and Pb levels in both seasons while other metals showed no significant difference (p < 0.05) at this confidence interval.