Sustainability Linked Assessment of Tropical Soils in Kuppam River Basin, India: Insight into the Geochemistry of Potential Toxic Elements, Source Apportionment and Associated Human Health Risk

Abstract Soil geochemistry in tropical agricultural catchments reflects interactions among parent material, weathering, land use, and seasonal hydrological processes. This study examined soil geochemistry, contamination levels and sources, and potential human health risks in the Kuppam River Basin. This tropical watershed is prone to contaminant buildup and downstream transport as it transitions from lateritic midlands to mangrove-fringed estuarine lowlands. Soil samples were collected from 42 sampling locations during each season (monsoon and non-monsoon) and analyzed for major oxides and potentially toxic elements (PTEs) using X-ray fluorescence (XRF) spectrometry. Contamination was determined using the geoaccumulation index (Igeo), contamination factor (CF), and the pollution load index (PLI), and the possible health risks were assessed through a human-health risk assessment framework. Soil geochemistry reflected potential contributions from the weathering of Precambrian crystalline parent materials, with possible additional influences from agricultural and other local anthropogenic activities. Positive matrix factorization (PMF) identified potential source signatures consistent with lithogenic and pedogenic processes, along with possible agricultural and other local anthropogenic contributions. The USEPA screening-level risk assessment identified cobalt as the principal contributor to the estimated non-carcinogenic risk and arsenic as the primary carcinogenic concern, with lifetime cancer risks exceeding 10⁻⁴ for both adults and children. Nickel risks remained between 10⁻⁶ and 10⁻⁴, while Pb ingestion risk remained below 10⁻⁶ for both receptors across seasons. Ingestion, dermal contact, and inhalation pathways were considered for As and Ni. Results indicate that small tropical catchments can serve as useful indicators for identifying potential contamination hotspots and prioritizing areas for further assessment and targeted environmental management.