Compound risk of cadmium, copper, manganese and zinc in canal-fed communities, South India: linking physical and social vulnerability
Abstract
Heavy metal contamination in drinking water canals poses an unquantified health risk to the socially vulnerable communities of the Western Godavari Delta, India. This study quantifies the non-carcinogenic health risk associated with heavy metals, cadmium (Cd), copper (Cu), manganese (Mn), and zinc (Zn) across 10 monitoring stations on Gostani Velpuru Canal (GVC), sampled on a single day (29 March 2022) across six diurnal time-points per station and analyzed by flame atomic absorption spectrophotometry (AAS) with standard QA/QC verification, characterized into Hazard Index (HI), evaluated for an adult exposure scenario. HI derived from Targeted Hazard Quotient (THQ) ranged from 1.46 to 13.62, exceeding the threshold (HI > 1) at all stations. Cadmium emerged as a dominant carcinogen with negligible concentration in the upstream to a maximum concentration of 0.203 mg/L at the downstream, 67.7 times the drinking-water guideline (0.003 mg/L). Spatial analysis and metal correlations show a combination of distributed agricultural and aquaculture/poultry-feed inputs (Cu) and a probable shared point source near the paper mill industry (Cd and Mn) as the dominant contributing sectors. Physical Vulnerability Index (PVI) formed with the normalized HI values of all 10 stations are integrated with a census-derived Social Vulnerability Index (SVI) based on people’s socio-economic status, children aged 0–6 years, canal water-dependent agricultural labourers, and households lacking a functional tap connection (FHTC deficit) to form a Critical Compound Risk Score (CRS = (PVI_norm + SVI_norm)/2). Station ‘J’ and ‘I’ attained a critical CRS of 0.734 and 0.609 respectively, jointly defining the lower GVC reach as the major priority corridor for the targeted water safety interventions for public safety. The CRS framework demonstrated that peak physical hazard and maximum social vulnerability co-occur spatially, making it a blended tool applicable for canal water management safety in the deltaic ecosystems addressing Sustainable Development Goals (SDGs) 6 and 3.