Ecotoxicological and Carcinogenic Risks of Nickel and Cadmium in Wastewater-Irrigated Soils of the N-Choe Drainage System, Punjab, Northern India

Abstract Intensive irrigation with untreated wastewater significantly increases soil heavy metal contamination and associated environmental hazards, thereby exacerbating public health risks in peri-urban regions worldwide. This study presents an integrated spatial-toxicological assessment of heavy metal contamination in peri-urban soils of northern India irrigated with untreated wastewater (SWW) and groundwater (SGW). Soil samples were analyzed for nine toxicologically significant metals (As, Cd, Cr, Cu, Fe, Mn, Ni, Pb, Zn) using Inductively Coupled Plasma-Mass Spectrometry (ICP-MS). The results showed that SWW-irrigated soils exhibited very high contamination factors (CF) for Cd (11. 91) and Ni (7. 99), with a pollution index (PI) of 30. 34, indicating heavy pollution, while SGW samples showed considerable Cd contamination (3. 01) but lower overall pollution (PI 7. 83). Moreover, enrichment factors for Cd (36. 81) and Ni (24. 58) in SWW contribute to a modified pollution index (MPI) of 92. 00, signifying severe enrichment, compared to significant Cd enrichment (10. 68) and MPI of 26. 92 in SGW. Cd presented a very high ecological risk (Ei 367. 24), and the overall risk index (RI 408. 05) classified soils irrigated with SWW as significantly hazardous. Statistical analysis indicated that Cd displayed weak or negative correlations with most metals (Cr, r = -0. 56; Cu, r = -0. 36; Ni, r = -0. 34), suggesting an independent origin or distinct mobility within the soil matrix, potentially influenced by wastewater-induced geochemical alterations such as elevated alkalinity, pH variability, and interactions with Zn 2 ⁺ and Ni 2 ⁺ ions. Human health risk assessment revealed critically elevated non-carcinogenic hazard indices (HIchild = 29. 63; HIₐdult = 7. 47) and an alarming carcinogenic risk for children (CR = 7. 00 × 10⁻ 1), well above USEPA safety limits.