Determination of levels of nutrients, organic matter and trace heavy metals in river Migori
Mbovu, Charles Chivatsi
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Migori is situated in a rich agricultural heartland and strategically placed on the Makuyu Isebania-Musoma highway. In recent times, and with the renewed East African Co-operation, the town has attracted rapid population and commercial growth, with the mushrooming of much small- scale industrial enterprises-the jua kali industries. The town is not served by clean piped water and the majority of the population depends almost entirely on the raw untreated water for their domestic use. This makes the general population vulnerable to any contaminants, either from natural or artificial sources. This study was undertaken to establish the concentration level of nutrients (as Nitrite-N, Nitrate-N and Phosphate-P), organic matter (as dissolve oxygen DO, biological oxygen demand BOD, and chemical oxygen demand COD) and the trace metals (cadmium, chromium, copper, lead and zinc), The study also attempted to relate the levels of these parameters in the river water with the agricultural and town's activities. The Nitrate-N levels were determined by the Brucine method, and those of Nitrite-N, by the Griess method. Phosphate-p levels were determined by the Molybdenum complexation method. DO and BOD levels were determined by the Winkler's titration method and the COD levels by the titration of the remaining potassium dichromate with ferrous ammonium sulphate after the oxidation of the organic matter. The levels of the trace metals were determined by Atomic Absorption Spectrophotometry. The averages of the mean levels of the parameters from the four stations on the section of the river, and within the period of study were as follows:- (1) The organic matter: DO, 7.03 mgO2/1;BOD, 5.98mgO2/1 and COD, 81.84mgO2/1. (2) The nutrients: NO3-N,0.213mg/1;NO2-N0.044mg/1 and PO4-P0.170mg/1. (3) The trace metals (mg/1): Cd (0.311), Cr (6.04), Cu(4.288), Pb (46.77) and Zn (32.52). This study established that: I. The levels of organic matter were low but still significant, with mean levels increasing in the wet season. II. The PO4-P levels were above the maximum allowed concentration (MAC) recommended by the World Health Organisation (WHO). NO3-N and NO2-N levels were low. The changes in the mean levels of the nutrients (PO4-P and NO3-N), and especially during the wet season decreased downstream from the potential agricultural region. III. The levels of the trace metals, except for lead were generally low. Lead and cadmium were comparatively higher in the dry season, whereas chromium and zinc levels seemed to increase during the wet season. The mean copper levels did not vary significantly between the dry and wet seasons. From the findings of this study, it was concluded that:- (1) The agricultural activities may have an influence on the quality of River Migori. (2) The activities in the town could also have an influence on the water quality of the river, in view of the fact that higher levels of lead and chromium were detected after the town. (3) The river water may not be safe for express domestic use.