Source characterization and human health risk assessment of nitrate in groundwater of middle Gangetic Plain, India

Nitrate (NO3-) pollution is a global concern as it affects the whole ecosystem: human, livestock, economy, and environment. The elevated levels of nitrate in groundwater can directly pose risks to population. A total of 156 representative groundwater samples were collected from groundwater sources such as hand pumps and bore wells across the study area. To identify the source of nitrate with its associated attributes, multivariate statistical methods (factor analysis (FA), sparse principal component analysis (SPCA)) were used in this study. In addition, empirical Bayesian kriging (EBK) modeling was used to predict the nitrate at ungauged locations of the study area. From the analysis of results, it was found that 5% of the groundwater samples exceeded the acceptable limit (50 mg l(-1)) of nitrate as specified by the World Health Organization (WHO). The first principal component (PC) indicated by the SPCA was salinity factor, which was significantly contributed by electrical conductivity followed by sulfate. The fourth PC represented the nitrate as a factor and positive loading of nitrate was strongly associated with chloride, sulfate, and calcium. The associated loading of nitrate with water quality attributes indicated that elevated level of nitrate in groundwater may be due to external sources that came through anthropogenic activity. A similar conclusion was drawn from factor analysis as well, indicating that SPCA can be applied as a new method for groundwater geochemistry. Hazard index calculations showed that infants of the study region were at a higher risk compared to the adults and children.