Soil trace metal contamination and ecological risk in differently urbanized environments: insights from Kochi, Kerala

The study examines two contrasting settings in Kochi, Kerala: urban and peri-urban clusters that experience different levels of anthropogenic pressure. Surface soil samples were analysed for trace metals to quantify concentrations, map spatial patterns, evaluate ecological risk, and identify potential sources. Pollution indices, including the single-factor pollution index ( P i ), enrichment factor ( EF ), geo-accumulation index ( I geo ), Nemerow Integrated Pollution Index ( NIPI ), and ecological risk index ( NIRI ), were applied to assess contamination status. Urban soils showed elevated Zn (mean: 132.19 mg/kg), Cu (59.42 mg/kg), and Ni (53.62 mg/kg) relative to peri-urban areas. P i highlighted Cr (max: 3.07), Cu (2.87), and Ni (2.38) as dominant contributors, with EF and I geo indicating localized enrichment of Cu, Cr, Sr, V, and Ni. NIPI values ranged from 0.75 to 5.49 (mean: 2.32), indicating overall moderate contamination with localized severe pollution in southern and central urban sectors, while mild contamination dominated peri-urban zones. NIRI values ranged from <40 to 160, classifying ecological risk as low in agricultural and peripheral areas, moderate in peri-urban regions, and considerable in densely urbanized zones. Multivariate statistical approaches (PCA and APCS-MLR) indicated mixed geogenic and anthropogenic sources. V, Ni, and Cr were mainly lithogenic but amplified by industrial emissions and fossil-fuel combustion. Zn, Rb, and Y were associated with mixed anthropogenic inputs, including agriculture, traffic emissions, and urban activities, while Zr, Ga, Ba, and Cu reflected both lithogenic materials and localized human activities. These results underscore the influence of rapid urbanization, industrialization, and traffic on soil contamination and provide actionable insight for pollution control, land-use planning, and sustainable urban development.