Seasonal Changes of PAHs in Water and Suspended Particulate Matter from Cross River Estuary, SE Nigeria in Response to Human-Induced Activity and Hydrological Cycle

Abstract

Profile assessment of the behavior of total polycyclic aromatic hydrocarbons (TPAH – sum of 16 US EPA priority PAHs) in water and suspended particulate matter (SPM) from Cross River estuary, SE Nigeria in response to hydrological cycles and human-induced activities as well as their sources were undertaken using gas chromatography-flame ionization detector (GC-FID). TPAH concentrations in water were in the range 0.23–3.98 ng/L, with a minimum and maximum values found in April and December, respectively (mean = 0.97 ± 0.65 ng/L) having higher concentrations in the dry season. The low PAHs levels recorded in water for the wet season were linked to dilution effect. On the other hand, TPAH concentrations in SPM (suspended particulate matter) ranged between 5.16 ng/g in February and 40.52 ng/g in June (mean = 17.77 ± 8.48 ng/g). Higher PAHs levels found in the wet season were associated with greater wash-in of terrigenous materials occasioned by intense rainfall events via river discharges/wet precipitation coupled with the high adsorption capacity of PAHs toward solid matrix as well as proximity to fish settlement. Seasonal changes in salinity, temperature and suspended sediment concentration (SSC or SPMC) somewhat influenced the PAH phase association. Higher SSC in the wet season accounted for the higher PAHs levels in SPM (r = 0.9295), whereas lower salinity aided desorption from SPM in the wet season, temperature did not show regular trend with PAHs levels in both seasons. Application of principal component analysis (PCA) and multiple linear regression (MLR) to both water and SPM data indicated a scenario predominated by petroleum and wood combustion PAHs with a moderate vehicular exhaust emission and coal tar inputs (11%).