E.F Ajagbe - Ecotoxicology and Conservation Unit, Department of Zoology, Faculty of Science,University of Lagos, Lagos, Nigeria
J.K Saliu - Ecotoxicology and Conservation Unit, Department of Zoology, Faculty of Science,University of Lagos, Lagos, Nigeria
S.O Ayoola - Department of Marine Sciences, Faculty of Science, University of Lagos, Lagos,Lagos. Nigeria
N.D Menkiti - Department of Chemistry, Faculty of Science, University of Lagos, Lagos, Nigeria.

Polychlorinated biphenyls (PCBs) are a health risk for high trophic level predators and the Stockholm Convention requires measures to reduce or eliminate their release into the environment. The study was conducted an ecological survey on River Ogun, Lagos, Nigeria, quarterly over a period of two years (March 2013-February 2015). Water physicochemistry and the levels of nine PCB congeners were analyzed in water and sediment samples from five river zones: Agboyi, Maidan, Owode Elede, Kara, and Akute. Water physicochemistry showed significant (p<0.05) increases in conductivity, turbidity, temperature, salinity, total dissolved solids, and dissolved oxygen in the dry season compared to rainy season across the zones, while there was an increase in pH, transparency and depth in the rainy season across the zones. Mean temperature in the range of 28.53 -28.95°C, the mean pH ranged between 5.58-7.74, mean total dissolved solid ranged between 0.67 -1.69 g/L, mean conductivity ranged between 0.77 mS/cm -0.94 mS/cm, mean salinity ranged between 0.05 -0.42%, mean turbidity ranged between 29.30-30.50NTU, mean Secchi-disc transparency ranged between 2.88-3.16m, mean depth ranged between 3.21-3.65m while meaning dissolved oxygen ranged between 14.54- 22.65mg/L.PCB congeners were analyzed in sediment and water samples. The analyzed categories were the IUPAC numbers: non-ortho PCBs (CBs 8, 18 and 58), mono-ortho PCBs (CBs 87, 128,170 and 195) and dl-PCBs (CBs 206 and 209). The mean concentrations of PCBs in the sediment samples for all zones ranged from 0.000078-0.01μg/kg, while the mean concentrations of PCBs in the water samples for all the sampled zones ranged from 0.00006-0.006mg/L. The total PCBs concentrations in all water samples in this study for the rainy and dry seasons were 0.0296 mg/L and 0.0299 mgL-1, respectively. The hazard quotient (HQ) values for the rainy season ranged from 0.0039 - 0.014 and between 0.0047 - 0.013571 for the dry season. The cancer risk for the rainy season ranged from 3.90 × 10-6 - 9.82 ×10-6, while that of the dry season ranged from 1.57× 10-7 - 3.17 × 10-7. There was no significant difference between the congeners when the samples were subjected to descriptive (mean and standard error) and analysis of variance statistics and P<0.05 was considered to indicate statistical significance. Means were separated using Bonferroni’s multiple comparison tests, p<0.05). PCB concentrations in all the zones were above US EPA limits in surface waters (0.0005 mg/L), which is a cause for environmental concern for River Ogun

Polychlorinated biphenyl congeners,Environmental contamination,Physicochemistry,Ogun River