Monsoon-Driven Seasonal Variability of Potentially Toxic Metals in Hard-Rock Groundwater of Natham Taluk, South India: Pollution Indices and Human Health Risk Assessment

Abstract

The recharge process triggered by the monsoons can influence the mobility and dispersion of potential metal contaminants in hard rock aquifers, thus making the groundwater seasonally variable in terms of its quality. The current study focuses on the assessment of the seasonal variability of eight metals (Cu, Zn, Pb, Cd, Cr, As, Hg and Fe) and fluoride (F⁻)in 102 groundwater samples in the premonsoon (n=51) and postmonsoon (n=51) periods in Natham Taluk, Dindigul district, Tamil Nadu state, India. Metal content and threshold exceedances were analyzed in conjunction with the heavy metal pollution index (HPI), heavy metal evaluation index (HEI), Spearman rank correlation, principal component analysis (PCA) and screening level human health risk assessment. The findings show the seasonal difference with postmonsoon maximum metal concentrations of 0.07 mg/L for total Cr. The respective proportion of excess relative to the study threshold levels was 11.8%. The mean Fe concentration changed from 0.054 to 0.135 mg/L, while the respective zinc (Zn) concentration changed from 0.002 to 0.013 mg/L. However, the mean HPI and HEI values stayed within their low pollution classes. Chromium speciation sensitivity revealed possible risks based on the presumption that all the detected chromium was in the form of Cr(VI), where the hazard quotient values for children were greater than one for six samples after the monsoon period. This reveals the need for periodic groundwater quality assessment with respect to the season and checking of metal concentration, species of chromium, and contamination sources.