Assessment of Physicochemical Characteristics and Spatial Distribution of Heavy Metals in Hand-Dug Wells near Septic Tanks in Ojo LGA, Lagos. Nigeria

Abstract

One of the most important environmental issues today is groundwater contamination, and between the wide diversity of contaminants affecting water resources, microbial quality and heavy metals receive particular concern considering possible outbreak of diseases. Thus, well water meant for consumption must meet the guidelines for drinking water quality to reduce possible health-risk associated with chemical hazards. In Nigeria, there is a scarcity of portable drinking water, hence many homes have wells dug around the house at a distance of about nine meters from the septic tank. The lack of drinkable water has prompted people to seek other sources of water. This study assessed the physicochemical quality and concentration of heavy metals in water samples drawn from fifteen hand-dug wells sited close to septic tanks in Ojo Local Government Area of Lagos State, Nigeria. Samples were collected in both the rainy and dry seasons, Temperature, Ph, Conductivity, Salinity, Total Dissolved Solid (TDS) were determined using standard procedures. Iron, Copper, Zinc, Manganese, Lead, Cadmium and Nitrate content of well water samples were evaluated by Atomic Absorption Spectrometer. The values of turbidity, conductivity and total dissolved solids obtained were higher than the WHO standard limit in some of the well sampled which shows that the well water may not be acceptable or recommended for human consumption due to the effect on human health such as gastro-intestinal irritation as well as fabric stains. The results also revealed that there were no heavy occurrences of Cu, Fe, Zn and Cd, in all the analysed water samples, their concentration values were below the desirable limits specified by World Health Organization while Mn concentration falls within the WHO desirable limit, lead has a concentration values (0.01 to 0.05 mg/L) higher than the permissible limit of 0.01 WHO standard in all the hand dug well water sampled. This implies that the well water in the studied location is unsuitable for drinking because of the possible poisoning effect of lead and the resulting health disorder even when consumed at a low concentration.