820 Indian Journal of Science and Technology Vol. 4 No. 7 (July 2011) ISSN: 0974- 6846 Research article “Heavy metals in groundwater Ifo Nigeria” H. Ayedun et al. Indian Society for Education and Environment (iSee) http://www.indjst.org Indian J.Sci.Technol. Assessment of groundwater contamination by toxic metals in Ifo, Southwestern Nigeria H. Ayedun 1 , A. M. Taiwo 2 , B. F. Umar 1 , O. A. Oseni 3 and A. A. Oderinde 1 1 Department of Science Laboratory Technology, Federal Polytechnic, PMB 50, Ilaro Ogun State, Nigeria 2 Dept. of Environ. Management and Toxicology, University of Agriculture PMB 2240, Abeokuta, Ogun State, Nigeria 3 Dept. of Science Laboratory Technology, Moshood Abiola Polytechnic Abeokuta, Ogun State, Nigeria hayedun2000@yahoo.com Abstract A study was carried out to assess groundwater contamination by toxic metals in Ifo community of Ogun state, Nigeria. Twenty two wells were sampled in this regard and analyzed for pH, temperature, redox potential (RP), alkalinity, salinity, toxic metals such as cadmium (Cd), lead (Pb), iron (Fe) and zinc (Zn) using standard procedures. High trace metal concentrations were observed in most of the well water samples. Results showed that 50 % of the wells recorded values greater than WHO standard for Fe (0.06-0.59 mg/L), 41 % have Cd (0.000-0.010 mg/L) level higher than WHO standard while 82 % recorded high Pb (0.00-0.23 mg/L) levels greater than WHO standard in drinking water. Zinc values of the well water samples were generally low. The high values of Cd and Pb in most of the groundwater samples is harmful to human health and calls for necessary cautions by the public before consuming the water. The study therefore, recommends proper purification methods that will remove the toxic metals and further minimize their nefarious ill-effects on humans. Keywords: Groundwater, trace metals, parameters, standard, contamination. Introduction Water is required by all living things for cell metabolism. Continuous existence of man on this planet will definitely depend on the availability of good quality water. It is a vital resource human activities depended upon in the areas like agriculture, industry, transportation, domestic uses and recreation (Awomeso et al. 2010). Water is considered a universal solvent due to its natural abundance (Nwosu & Ogueke 2004). It covers 71 % of the earth surface as oceans, groundwater and freshwater lakes, streams and rivers which occupy 97.2, 0.9, and 0.02 % of the earth’s water respectively (FAO, 1997). In Nigeria, only 48 % of urban and semi-urban dwellers, and 39 % of the rural dwellers have access to potable water (Federal Republic of Nigeria 2000). Underground reservoirs constitute major sources of fresh water. In terms of storage capacity, underground aquifers worldwide contain over 90 % of the total fresh water available for human use (Oluyemi et al., 2009). Groundwater contamination occurs widely from variety of sources like waste disposal facilities, industrial discharges and urban runoff from agricultural land among others. Industrial evolution in developing countries, most especially Nigeria in the last century, has resulted into geometrical increase in waste generation compared to management and disposal methods put in place. Wastes generated from industries have contributed immensely to water pollution especially when contaminants become leached into the ground water (Forster et al. 1998) or drifted by runoff to surface water (Taiwo 2010; Bariweni et al., 2001). Generally, water resources are under threat of metal pollution as a consequence of human activities. Metal toxicities in drinking water had been reported by many authors (Holynska et al. 1996; Garcia et al. 1999; Fatoki et al. 2002). The presence of trace metals in drinking water above the permissible limits could initiate deleterious health effects on human. In Ifo community, potable water from public water supply is inadequately and irregularly supplied. Rapid population growth in Ifo makes demand for potable water to increase. Since there’s a shortage in public supply, the residents depended absolutely on hand-dug wells and boreholes for daily water supply. Consequently, thorough water analysis for metals (plus other physical and chemical parameters) is essential for the establishment of baseline data for groundwater quality in the study area. This forms the basis of our objective as this study is concerned. Materials and methods The study area Ifo community is located in Ogun central senatorial district of Ogun state (Fig.1). The inhabitants are mainly Yoruba speaking people comprising of the Egbas, Yewa, Aworis, Hausas and other tribes (forming smaller proportion). There is a reasonably high level of economic and social activities taking place in the Local Government Area. The primary economic activity, however, remains agriculture, with crops such as maize, rice, cassava, melon and watermelon widely grown in the area. The population of Ifo local government has increased from 186, 000 in 1991 to 524,837 in 2006 (NPC 2006). Its closeness to Lagos had resulted in ‘paradigm shift’ of diverse peoples from Lagos relocating to Ifo and settling down on a daily basis due high cost of living in Lagos. Geology: Ifo is located on the Western coastal plain. It is underlain by recent sedimentary deposits of the Ilaro Formation. The Ilaro Formations consist of Continental Fluviatile sandstones. The sands are usually coarse, angular and poorly sorted containing significant clay fraction.