Effect of municipal effluent on the water quality of Pece Stream and on selected vegetables along its shoreline in Gulu Town, Northern Uganda

Abstract

The restoration of peace in Northern Uganda has caused a rapid population growth in Gulu Municipality, which in turn has elevated anthropogenic pollution over the recent past. Pece stream being the only drainage system in the Municipality has over the years been contaminated with effluent emanating from the various activities in town. This study, carried out in both rainy season (Sep-Oct, 2015) and dry season (Jan- Feb, 2016) aimed at determining the seasonal variation, levels of heavy metals and nutrients in water from Pece stream and in Amaranthus dubius grown along its shoreline. Some physico-chemical parameters such as temperature, pH, electrolytic conductivity, total dissolved solids, turbidity and hardness were also determined. The analysis of heavy metals was done by Flame Atomic Absorption Spectrophotometry. The mean concentrations of metals in the water in the dry season were 0.1051±0.0576, 0.0331±0.014, 0.0037±0.0005 and 0.0031±0.0007 mg/L for Zn, Pb, Cd and Cu respectively. During rainy season, the mean concentrations were 0.1865±0.0755 mg/L for Zn, 0.1253±0.0621 mg/L for Pb, 0.0049±0.0009 mg/L for Cd and 0.0038±0.0006 mg/L for Cu. It was observed that the concentrations for Cd and Pb exceeded the WHO guideline values in drinking water of 0.003 mg/L and 0.01 mg/L, respectively. Statistical analysis of the results obtained in both seasons using the paired sample t-test showed a significant difference for all metals (p<0.05). The concentration of Zn, Cu and Cd in Amaranthus dubius were 48.55±2.96, 2.96±1.14 and 0.349±0.098 mg/kg respectively. The values of these metals were below the recommended maximum tolerable levels proposed by Joint FAO/WHO Expert Committee on Food Additives. The mean concentrations of nitrates, phosphates and nitrites were 0.0825±0.02, 0.34±0.02 and 0.074±0.002 mg/L respectively. The nitrates were the most predominant among the three probably because of the bacterial conversion of the other forms of nitrogen such as nitrites and ammonia into nitrates. The average values for temperature, EC and pH were 24.6°C, 453.4 µScm-1 and 8.4 respectively, whereas hardness, turbidity and TDS registered 120.6 mg/L, 42.8NTU and 246.3 mg/L respectively. There was no significant difference in most of the results for physico-chemical parameters (Appendix D). The high levels of Cd and Pb as indicated could pose very serious human health risks once ingested. Therefore, early pollution control measures are advisable.