Sources identification, health risk assessment of potentially toxic elements (PTE) of Southern parts of NCR environs, Delhi, India.

The National Capital Region is characterized by high depletion and overexploitation with significant water table decline along with challenges related to pollution, including the presence of metal contamination. The urban water system of NCT Delhi requires an updated water infrastructure to meet the expanding population. Total 57 groundwater samples were collected from different sources of drinking water wells and measured for 11 metals concentration during pre-monsoon 2017. The results reveals that Ni (3%) and Pb (4%) exceeded World Health Organization (WHO) permissible limits, and Al (16%), Mn (3%), Ni (5%), Pb (4%) and Fe (42%) of samples exceeding Bureau of Indian Standards (BIS) acceptable limits. Spatial distribution of metals shows that there is a higher concentration towards Delhi area and the Southern parts of the study area. The pollution indices (HEI, NI and Cd) characterize high pollution zones except for HPI. HPI is high in the majority of groundwater samples in the southwestern side of the study area. The ecological risk assessment has also been computed and reported very low (0.80-86.48), that is much below the critical value indicating no ecological risk associated with metals. Children are more prone to risk assessment of both carcinogenic (CR) and non-carcinogenic risks than adults. Ingestion is the main pathway. Ni is the highest contributor for CR with the mean value of 2.95 × 10^-4 and 7.82 × 10^-4 in adults and children. Further, Cr and Cd have the mean values of 6.88 × 10^-5, 4.11 × 10^-5 and 4.08 × 10^-5 in adult and 1.82 × 10^-4, 1.09 × 10^-4 and 1.08 × 10^-4 in adults and children, respectively. Chemometric methods mainly Cluster analysis classifies all metals in 2 main clusters and 3 sub-clusters associated with each other, indicating anthropogenic and geogenic sources of contamination. 3 principal components (PC) have been identified through principal component analysis (PCA). 1 PC indicates main sources of Co, Ni, Cu and Zn are from anthropogenic sources. PC-2 signifies that Al, Mn and Fe are mainly from geo genic sources. However, Fe is also contributed from anthropogenic sources. In all, around 70% of the study identified with occurrence of contaminated groundwater and does not fit for drinking purposes, mainly from close vicinity of landfill area and south & south-Western parts. An effective remediation strategy can be planned based on the findings of the study.