POLLUTION STATUS OF WATER AND SEDIMENTS OF ASA RIVER EXPOSED TO INDUSTRIAL EFFLUENTS IN ILORIN, KWARA STATE, NIGERIA

Abstract

River Asa water is used for household and irrigation purposes and it receives wastes from both municipal and industrial sources. Previous studies on the pollution status of the river were focused on sediment and water samples from few locations, in spite of intense urbanisation and industrial activities within its catchment. Hence, there is a need to ascertain the current pollution status of the river. Therefore, this study was designed to determine the impact of industrial activities on and to establish the pollution level of water and sediments of Asa River.

Water (104) and sediments (104) samples were purposively collected seasonally for two years (February, 2013–April, 2015). Industrial effluents (32) were also sampled. Sampling points for effluents were point of discharge into the river, upstream and downstream of the discharge point, respectively. Control water and sediment samples were collected from Asa dam (located before the sampling points). Turbidity, Total Suspended Solids (TSS), Dissolved Oxygen (DO), Biochemical Oxygen Demand (BOD) and Chemical Oxygen Demand (COD) were determined using standard methods, while heavy metals were analysed using atomic absorption spectrophotometer. Results were compared with the National Environmental Standards and Regulations Enforcement Agency (NESREA) effluents and WHO drinking water guidelines. Overall Pollution Index (OPI) was used for the assessment of heavy metals in water, while sediment pollution indices were determined using Contamination Factor (CF) and Geo-accumulation Index (Igeo). Data were evaluated using descriptive statistics, Pearson’s correlation and ANOVA at α0.05.

Turbidity (9.3-15.3 NTU), TSS (53.8-76.8 mg/L) and DO (3.5-7.2 mg/L) were higher than NESREA effluent guidelines (5.0 NTU, 25.0 mg/L and 4.0 mg/L). For upstream and downstream water samples, the results were: Turbidity (19.1-20.0 and 21.0-22.8 NTU), TSS (87.0-91.0 and 91.0-98.3 mg/L), DO (5.3-6.4 and 4.4-4.8 mg/L), BOD (4.6-5.3 and 3.6-4.1 mg/L) and COD (5.4-6.2 and 6.2-6.7 mg/L). Downstream samples had higher concentrations compared to upstream except for DO and BOD and were above NESREA and WHO guidelines except COD and BOD. Metals (mg/L) in effluents, upstream and downstream were: 1.7±0.9, 3.1±0.2 and 3.7±0.2 (Iron); 0.6±0.5, 0.7±0.3 and 0.8±0.5 (Lead); 0.3±0.1, 0.5±1.0 and 0.6±0.1 (Chromium); 0.4±0.1, 0.7±0.2 and 0.8±0.1 (Copper), and 3.0±0.8, 3.3±0.1 and 3.6±0.1 (Zinc), respectively. Lead and Chromium in effluents and water were above the NESREA and WHO guidelines. Metal (mg/kg) in sediments were: 21.3±2.1 (Iron), 0.3±0.1 (Lead), 54.6±7.1 (Chromium), 38.3±2.6 (Copper) and 41.1±2.3 (Zinc). Metals in all the samples were significantly higher than the control. The OPI of metals in effluents and water ranged from 3.0 to 3.3, which were above the acceptable range in drinking water (0.0 to 1.0). Sediments CF for Iron (0.01), Lead (0.03) and Chromium (0.79) signified low contamination (CF<1), while Copper (1.34) and Zinc (1.72) showed moderate contamination (1≤CF<3). The Igeo ranged from unpolluted (0-1 for Iron, Lead and Chromium) to moderately polluted (1-2 for Copper and Zinc). Iron (1.00), Lead (0.87), Chromium (0.94), Copper (0.85) and Zinc (1.00) were positively correlated in water and sediments.

Asa River Ilorin is moderately polluted by the industrial effluents it receives with deteriorating physico-chemical properties. Proper monitoring of Asa River is important to safeguard public health.