WATER QUALITY ASSESSMENT OF OSUN RIVER: STUDIES ON INORGANIC NUTRIENTS A. A. OLAJIRE ∗ and F. E. IMEOKPARIA Department of Pure and Applied Chemistry, Ladoke Akintola University of Technology, Ogbomoso, Nigeria ( ∗ author for correspondence) (Received 4 June 1999; accepted 22 February 2000) Abstract. The present investigation provides data of some ions, namely Na + , Ca 2+ , NH + 4 , Cl − , NO − 3 , CN − and PO 3− 4 on water samples of river Osun, selected rivers in the region and groundwa- ters. The pH, temperature, electrical conductivity (EC), total dissolved solids (TDS), total hardness (TH) and total carbon (IV) oxide (TCO 2 ) have also been determined to asses the chemical status and pollution levels of these water sources. The higher values of certain parameters with respect to the acceptable standard limits for drinking water indicate the pollution in both groundwater and river water samples of the study area, and make the waters unsuitable for various applications. The high pollution river water source showed higher levels of phosphate, nitrate and ammonium ions (P < 0.05). There is no significant difference (P < 0.05) between the mean concentrations of other inorganic nutrients in the high and low pollution water source types. The correlation coefficient between quality parameter pairs of river water and groundwater samples are determined and the significance of these parameters in both types of water sources are discussed. Keywords: atomic absorption spectrophotometer and flame photometry, inorganic nutrients, rivers, technicon’s autoanalyzer, water quality assessment 1. Introduction The importance of environmental quality in Osun State (Southwestern Nigeria) generally, and in Osogbo (an urban area) in particular has recently attracted a great deal of interest. The population density of the study area in 1991 was about 183,223; in 1996 about 209,139 and in 1998 about 557,707. By the next millen- nium, it may exceed 1 million [NPC, 1991]. Water and land, the vital resources of life, are increasingly being polluted in the wake of popular growth, poor land use system, agricultural activities, industrialization and anthropogene impact on the study area. The effect of poor water quality on human health was noted for the first time in 1854 by John Snow, when he traced the outbreak of cholera epidermic in London to the Thames river water which was grossly polluted with raw sewage. Since then, the science of water quality progressed. In the third world countries, 80% of all diseases are directly related to poor drinking water and unsanitary conditions (Sharma et al., 1995). The industrial units located at the outskirt in cities, intens- Environmental Monitoring and Assessment 69: 17–28, 2001. © 2001 Kluwer Academic Publishers. Printed in the Netherlands.