Geochemical and quality assessment of groundwater in some Nigerian basement complex

Abstract

Fifty samples from hand dug wells and boreholes were collected at Ijebu Igbo and its environs within the basement complex of some part of southwestern Nigeria. The purpose was to establish preliminary baselines for constituents in the groundwater and also to determine the quality for both drinking and irrigation purposes. Physical parameters were determined in situ using the appropriate digital meters, while the analysis of trace elements and cations in water was carried out using inductively coupled plasma optical emission spectrometry at Actlabs, Ontario, Canada. The order of relative abundance for major elements is Na > Ca > K > Si > Mg > P > Fe > Al > S. Al, Fe, Na, K and P were above the EPA 2012 recommended standard for drinking water in 79, 23, 3, 37 and 6 % of the water samples, respectively, and geochemical process is being influenced by both man activities and weathering of silicate minerals. Sodium absorption ratio ranges between 0.12 and 10.43 and falls within excellent and good for irrigation purpose. Only 78 and 22 % of water samples were suitable for irrigation based on the soluble sodium percentage and magnesium adsorption ratio, respectively, while all the water samples were good for irrigation purpose based on Kellys ratio. Concentration of Te and Ti was below the detection limit for all the samples. As, B, Cd, Cr, Cu, Mo, Ni, U and Zn though present in water were below recommended standards for all the samples. Ni and Sb exceeded recommended standard only in sample W24, and Ba exceeded recommended standard in W20 with value as high as 909.76 ppb. Mn and Pb were higher than recommended standard in 12 % of the samples, respectively. The pollution index varied from 0.09 to 1.66 with 8 % of the water samples showing pollution index above 1. Generally, groundwater in the study area is suitable for both domestic and irrigation uses except samples W4, W20, W24, W47 and W49. However, since heavy metals are not biodegradable, they tend to bioaccumulate and biomagnify in the body and eventually become harmful to human health.