Spatial and seasonal variations of heavy metal loads in Uyo urban drainage stream under PS and NPS pollution

The concentration of heavy metals (HM) in the 4km urban drainage stream in Uyo was studied using grab and composite sampling of water from six stations on the stream, and analyzed by a multipurpose atomic absorption spectrophotometer. The data were statistically analyzed using SPSS version 17 software at1d correlated between stations and runong samples. HM contamination was evaluated with the coefficient and rate of dispersion between stations and the Nom1alized Scatter Coefficient (NSC). The seasonal distribution of metal pollution varied individually amongst metals at stations. The Fe and Pb concentrations exceeded the sate drinking water standard, rendering the water quality not acceptable for drinking; however, the quality was within the safe limit for crop production along the river bank. The relative.dominance of heavy metals followed a different sequence in upstream leachate effluent from all downstream stations. The NSC in dry-wet season was higher than in wet season, and was in the order: Fe>Cu>Zn>Pb, showing that large but variable concentration of Fe from PS and NPS contaminated the stream at faster rate in the wet season while Pb contaminated at nearly constant rate. However, in the dry season, Fe and Pb depleted at downstream at rates far higher than Zn as Cu was increasing. Fe and Pb could be good pollution monitor for total maximum daily load (TMDL) pollution monitoring programme.Key words: Heavy metal loads, Urban drainage stream, Water quality, Seasonal variation,Normalized Scatter Coefficient