Nitrate concentration in drinking water supplies in selected communities of Ibadan Southeast local government, Ibadan, Nigeria

Abstract

Elevated levels of nitrate in drinking water have been associated with adverse health effects. Most susceptible to nitrate toxicity are infants under six months of age and pregnant women. This study assesses the nitrate concentration of 48 randomly selected wells in an urban-slum setting in Ibadan South East Local Government Area (IBSELGA), Nigeria. The coordinates of the wells were mapped with a hand-held Global Positioning System (GPS). The nitrate concentration ranged between 0.00 and 42.80 mgL^-1 with a mean of log₁₀ of 0.735 and a geometric mean of 5.43 mgL^-1; and 0.00 and 93.30 mgL^-1 with a mean of log₁₀ of 0.696 and a geometric mean of 4.97 mg L^-1 for the wet and dry seasons, respectively. During the wet season, the levels of nitrate in all the wells were within the WHO permissible limit of 45 mg L^-1 NO₃. However, during the dry season, few of the wells; six (12.5%) dried up completely. Out of the remaining 42 wells, six (14.3%) had nitrate concentration which exceeded the permissible limit. This same set of wells lacked sanitary features such as lining and cover. Out of the 48 wells, 30 (62.5%) and 24 (50%) were located at ≤10 m from the septic tank/pit latrine and refuse  dumps, respectively. Nitrate maps were developed using Georeferenced data for the water points. The nitrate exceedence map produced showed water sources within the study area with nitrate concentration exceeding the recommended limit and therefore requiring urgent intervention. The results of this study will serve as indicator for determining risk areas with respect to nitrate concentration in drinking water and therefore help in decision making activities.

Key words: Global positioning system, Ibadan, nitrate, nitrate exceedence, wells, urban slum.