Assessing severity in groundwater contamination by arsenic, iron and manganese and deciphering its heterogeneity in a sub-tropical monsoon region

Abstract

The present study examines groundwater contamination in a sub-tropical monsoon region relying heavily on groundwater. The region lacked assessments of metal pollution and health risks associated with it. The investigation, therefore, was mainly focused on the pollution impact and potential health risks associated with the heavy metals analyzed, namely arsenic, iron, manganese, zinc, aluminum, lead, and cadmium. While concentrations of zinc, aluminum, lead, and cadmium were within their respective permissible limits, arsenic, iron and manganese showed elevated levels in 76 %–94 % of sampling sites, during post-monsoon and pre-monsoon. Pollution indices including Heavy Metal Pollution Index (HPI) and Contamination Index (CI) classify 80 %–90 % of sampling sites as heavily polluted across both seasons. While ecological impact of heavy metals on the area is minimal, non-carcinogenic and carcinogenic risks associated highlight severe concerns. Over 60 % of sampling sites in 70 % of the study area surpassed the acceptable Total Hazard Index (THI) limit for adults, while all sites exceeded the limit for children. A similar trend was observed in Carcinogenic Risk (CR) values with over 60 % of sites in the entire study area exceeding acceptable limit. Arsenic was identified as the primary contributor to both non-carcinogenic and carcinogenic risks. Multivariate statistical analyses were instrumental in identifying the primary source affecting groundwater chemistry as geogenic sources. Further, the identification of hydrogeological factors including lithology, geomorphology, sand to clay ratio and hydraulic conductivity provided an answer for the notable diversity in assessments across the area. This optimization is beneficial for developing countries like India, highlighting the importance of groundwater monitoring to attain sustainability while aligning with the One Health approach for public and environmental well-being.