Pollution of well water with some nitrogenous pollutants and toxic micropollutants in the sixth district of Cotonou in South-Benin

Abstract

Difficulties of access to public water distribution sources in the suburbs of the sixth district of Cotonou create more resorts to the traditional water sources (wells). To assess the degree of chemical pollution of those waters, a study was conducted during the long rainy season of 2015 on thirty (30) traditional wells. Concentration of nitrogenous pollutants (nitrates and nitrites) was analyzed by cadmium reduction method and diazotization method, respectively. Micropollutants (lead and mercury) were respectively determined by the rapid extraction method of LeadTrak ™ column and by pre-concentration at cold vapor method. The results show that waters have a high level of nitrate and mercury pollution which are respectively 26.67%, (16.38 mg/l to 349.85 mg/l) and 13.33% (0.10 mg/l to 1.50 mg/l) and a low level of nitrite (0.02 mg/l to 2.63 mg/l) and lead (1 mg/l to 5mg/l). The Principal Component analysis helped to identify four groups (I-IV) of well waters: water with high degree of nitrogen pollution (NO3-) and high toxic metal and toxic metal (I: 20%); with low degree of nitrogen and toxic metal (II: 30%);water with high mineralization (III: 20%) and water rich in nitric pollutant (NO2-) (IV: 6.67%).The water pollution may be related to the low sanitation level and the improper conditions of well installation. Consumption of well waters may expose humans to health risks.