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The impact of an oil refinery process wastewater on the levels of mercury, lead, nickel, vanadium and cadmium in water and the associated sediment were investigated in order to determine the physicochemical quality of the receiving water. Samples were collected at two-monthly intervals from ten locations for a period of one year. Trace metals samples were prepared by acid digestion using 1:3:1 mixture of HC1O4, HNO3 and H2SO4 acids and those in water by solvent extraction using ammonium pyrrolidine dithiocarbamate (APDC) and methyl isobutyl ketone (MIBK). Buck scientific model 200A Atomic Absorption Spectrophotometer and airacetylene flame were used for the analyses, except for mercury which was by cold vapour technique using sodium borohydride in a mercury kit. Organic matter content was determined by the method of Walkey and Black. River water and the process wastewater quality parameters were determined using appropriate meters and various standard methods. The results of trace metals analyses in water with mean concentrations (ppb) were: Hg (BDL); Pb (21.66±11.65); Ni (38.84±32.15); V (0.15±0.29) and Cd (4.45±2.43), while those of sediment (ppm, dry weight) and organic matter (%) were as follows: Hg (0.273 ± 0.016); Pb (23.218 ± 13.427); Ni (57.194 ± 16.929); TOC (1.135 ± 0.401) and TOM (1.990 ± 0.703). These results revealed largely anthropogenic trace metal enrichment by organic loading most likely from land-driven waste brought in by runoff water and industrial wastes. Phosphate, which is particularly highest in the process wastewater, implicates the Port Harcourt refinery as an important source of this anion. The mean level of Ni in sediment (57.19 ppm) exceeded acceptable limits for sediment quality in Netherlands, and those of Pb and Cd in water also surpassed the background limits of <1.0-7.0) ppb for Pb and <0.2-2.8 ppb set by USA EPA for marine/brackish and freshwater.

Impact of Discharged Process Wastewater from an Oil Refinery on the Physicochemical Quality of a Receiving Waterbody in Rivers State, Nigeria