Identification, Source Forensics, and Risk Assessment of Heavy Metals in the Groundwater of Tannery Area in Bangalore, India

This study involves the identification and risk assessment of heavy metals in groundwater of tannery area in Bangalore, India, where leather and a few allied industries are responsible for severe contamination. Groundwater-dependent residents report health disorders, underlining the need for planned studies and mitigation measures. Groundwater samples were collected from 30 locations during the pre-(dry) and post-monsoon (wet) seasons of 2024 and analyzed for chromium, copper, lead, cadmium, and iron. Risk indices such as contamination factor (CF), degree of contamination (CD), pollution load index (PLI), index of geo-accumulation (Igeo), enrichment factor (EF), quantification of contamination (QoC), and ecological risk index (ERI) were evaluated. Forensic and source identification confirms anthropogenic origin linked to tanning, metal processing, and associated industrial activities. During pre-monsoon, 70%, 36.67%, 33.33%, 53.33%, and 56.67% of samples exceeded BIS limits for Cd, Fe, Cu, Pb, and Cr, respectively, while in post-monsoon, 60%, 33.37%, 33.33%, 53.33%, and 46.67% exceeded limits in the same order. Pre-monsoonal metal concentrations were marginally higher, though variations were negligible. Based on CF, 53.33%, 33.33%, 30%, and 26.67% of samples were in very high contamination zone for Fe, Cd, Cr, and Pb; 6.66%, 23.33%, 13.33%, and 3.33% were in considerable contamination zone for Fe, Cr, Cu, and Pb. CD index shows 43.33% and 13% of samples under high and considerable contamination range. PLI indicated extremely heavy contamination in 40% and heavy contamination in 13.33% of samples. EF showed most samples in background rank and minimal enrichment; only one sample each showed very high enrichment for Pb and Cd, and extremely high enrichment for Cu, Cr, and Cd. Igeo values revealed 10, 6, 5, 6, and 10 samples fell under the heavily to extremely contaminated category. ERI indicated Cd contributed to 30% of samples under very high ecological risk, along with 3 due to Pb, 2 due to Cu, and one each due to Pb and Cd, showing high ecological risk. Overall, ERI showed low to moderate risk. QoC revealed human activities as the primary contamination source. These findings provide a critical foundation for policymakers to reduce contamination, mitigate risks, and ensure sustainable groundwater management.