Integrated assessment of heavy metal contamination and human health risks in granitic soils of South India: A multi-index approach to pollution and ecological impacts

Abstract

Granitic soils in South India are increasingly vulnerable to heavy metal contamination arising from both natural (geogenic) and human-induced (anthropogenic) sources, posing ecological and human health hazards. This study aimed to assess the concentration, spatial distribution, and potential risks of 14 heavy metals (HMs)—As, Ba, Co, Cr, Cu, Mo, Ni, Pb, Rb, Sr, V, Y, Zn, and Zr—in 44 soil samples collected from granitic terrains across the region. X-ray fluorescence (XRF) analysis was conducted on powdered samples to determine metal concentrations. Multiple indices, including Geo-accumulation Index (I_geo), Contamination Factor (CF), Modified Pollution Index (MFPI), and Pollution Load Index (PLI), were applied to evaluate contamination levels. Ecological risks were quantified using the Potential Ecological Risk Index (PERI) and toxicity units. Sample S27 exhibited the highest PERI value (6.001756), primarily due to elevated Zn levels. Zinc (Zn) and Zirconium (Zr) were identified as major pollutants with strong anthropogenic signatures. As presented, the lowest ecological toxicity (0.189 ± 0.059). Human health risk assessments revealed dermal contact as the primary exposure pathway for both non-carcinogenic and carcinogenic effects, particularly for Zn, Cr, and Co. Ingestion and inhalation pathways posed relatively lower risks, with Cr_ingestion and Cr_inhalation averaging 0.041 ± 0.038 and 0.166 ± 0.051, respectively. Spatial analysis highlighted localized pollution hotspots. Overall, integrated pollution indices indicated moderate contamination, with areas of severe localized impact. This study emphasizes the urgent need for pollution mitigation strategies in granitic regions of South India, especially targeting Zn and Zr contamination and addressing dermal exposure pathways in human health risk management.