Hydrochemical Assessment of Water Quality and Risks Related to the Use of Groundwater Resources in the Urban Area of Niamey and Nearby Rural Areas in the Regions of Dosso and Tillabery in Niger

Abstract

Groundwater continues to be useful as the main source of drinking water in semi-arid and arid regions of sub-Saharan Africa. The main goal of this work is to assess the health risks associated to the consumption of borehole water in urban and peri-urban areas of Niamey in Niger. Hydrochemical analyses were carried out from water samples of 16 boreholes using standard methods (AFNOR). The parameter measured are pH, Electric conductivity (EC), HCO3-, NO3-, NO2-, Cl-, SO42-, F-, Na+, K+, Ca2+, Mg2+, Fe2+ and Mn2+. 80% of the samples are very risky for the populations. About 56% of boreholes have a nitrate concentration < 30 mg/L and 44% of samples have more than 50 mg/L corresponding the limit standard set by the WHO. High nitrite contents (NO2-) were determined from the same borehole water samples and contain more than 10 mg/L, and are considered unfit. Main causes are the lack of good urban wastes  managements, and the uncontrolled use fertilizers in the agricultural sectors. The sites containing between 2 and 3 mg/L of Fe2+ are located in areas of lateritic soils. About 12% of samples contain Mn2+ above the WHO standard (0.4 mg/L). This study of few boreholes from Niamey and its close rural areas demonstrates that nitrate, nitrite and manganese contents may cause major risks, in particular gastric, cardiovascular, carcinogenic and neurological diseases. With the growing population and urbanization, the lack of sanitation and of good management of urban waste, monitoring of groundwater quality is urgently need to preserve human health. Regular,  rapid and less costly monitoring of the pH and electrical conductivity of urban borehole  waters can help to prevent the risk of poisoning by nitrate, nitrite and by heavy metals such as manganese.