Tracking nitrate sources in groundwater and associated health risk for rural communities in the White Volta River basin of Ghana using isotopic approach (δ15N, δ18O[sbnd]NO3 and 3H)

Abstract

In this study, we present a first attempt on the use of integrated hydro-chemical and isotopic technique to trace the sources of groundwater nitrate contamination in the Upper East Region of Ghana to aid the sustainable management of this vital resource. The objectives of the study are (1) assess the present status and spatial distribution of the nitrate contamination (2) identify and distinguish the most likely sources of nitrate , (3) identify the relationship between 3H and NO3− and F−, and (4) ascertain the potential human risk from exposure to nitrate contamination. The results showed that, nitrate concentrations varied from 0.42 to 431.17, 0.83 to 143.94, 0.03 to 28.94mg/l with mean values of 36.09, 21.54 and 5.01mg/l for boreholes, hand dug wells and the surface water respectively. These values showed that, about 95% of boreholes and hand dug wells and 45% of the surface water have nitrate concentration above the baseline value in the area. The NO3−/Cl− ratio showed that, 98.4%, 95% and 64% of the NO3− in the borehole, hand dug wells and the surface water are from anthropogenic activities. The δ15NNO3 and δ18ONO3− data confirmed that NO3− in the samples was predominantly derived from manure (human and animal waste) and denitrification occurring in some areas. The isotopic data further affirms the hydro-chemical interpretation that, chemical fertilizer and atmospheric deposition are unlikely sources of NO3− in the area. The relationship between 3H and NO3− concentrations showed that, higher NO3− values are associated with younger waters. Non carcinogenic health risk for adults and children posed by oral ingestion of the NO3− contaminated water revealed some degree of health risk, especially to children whose risk is about 72% higher. The study provides a conceptual model of the NO3− dynamics and some recommendation for groundwater management in the area.