Evaluation of Heavy Metal Contamination and Excess Lifetime Cancer Risk in Soil Samples Around Some Selected Dump Sites in South-South, Nigeria

Abstract

Atomic absorption spectrophotometry (AAS) was used to determine the total concentrations of heavy metals (Pb, Ni, Zn, Fe, Cd, and Cr) in soil samples from Rumuolumini, Aluu, and Igwuruta communities in Rivers State, Nigeria. The study evaluated metal concentrations, contamination status, potential human-health risks, and Excess Lifetime Cancer Risk (ELCR) using mathematical models and regulatory guidance from the World Health Organization and the U.S. Environmental Protection Agency. A total of fifteen (15) soil samples were collected at a depth of 1 m below ground level and assessed using the Contamination Factor (CF), Pollution Load Index (PLI), Geo-accumulation Index (Igeo), Hazard Quotient (HQ), Hazard Index (HI), and ELCR. The results showed spatial variation in metal concentrations, with the overall heavy-metal burden following the order Aluu > Rumuolumini > Igwuruta. Most metals exhibited low contamination (CF < 1), whereas Cd showed considerable contamination at Aluu (3.79 ± 2.35) and Rumuolumini (3.23 ± 2.93). Mean PLI values were 0.248 ± 0.049, 0.156 ± 0.037, and 0.038 ± 0.013 for Aluu, Rumuolumini, and Igwuruta, respectively. The Igeo values similarly indicated generally unpolluted conditions, except for localised Cd enrichment. Mean HI values were 0.0299, 0.0204, and 0.0038, respectively, all substantially below unity. Mean total ELCR values were 2.87 × 10⁻⁵, 1.28 × 10⁻⁵, and 3.55 × 10⁻⁶, respectively, with Aluu recording the highest potential carcinogenic risk. Overall, the soils showed low general heavy-metal pollution and non-carcinogenic risk; however, localised Cd enrichment and the contributions of Ni and Cd to carcinogenic risk warrant continued environmental monitoring.