Integrated Geo-environmental Assessment of Heavy Metal Contamination in a Municipal Landfill System: A Case Study from Aluu, Obio-Akpor Local Government Area

Abstract

Background: Unregulated dumpsites driven by poor waste management infrastructure facilitate the release and leaching of persistent, toxic heavy metals into soils and groundwater, posing significant long-term environmental and public health risks, particularly in regions such as Nigeria’s Niger Delta. Aim: This study evaluates the extent, spatial distribution, and environmental risk of heavy metal contamination in soils at the Aluu municipal landfill, Obio-Akpor Local Government Area, Rivers State, Nigeria a rapidly urbanizing Niger Delta community characterised by high groundwater vulnerability and inadequate solid waste management infrastructure. Study Design: A field-based, cross-sectional analytical study integrating geochemical assessment, spatial analysis, and human health risk evaluation. Place and Duration of Study: Aluu municipal landfill, Obio-Akpor, Rivers State, Nigeria; sampling and laboratory analysis were conducted over a six-month study period. Methodology: Sixteen soil samples were collected from eight locations representing four contamination zones landfill core (A), near-field (B), far-field (C), and control/background (F)  at depths of 1.0 m and 1.5 m. Samples were analyzed for arsenic (As), nickel (Ni), chromium (Cr), cadmium (Cd), and lead (Pb) using atomic absorption spectrophotometry (AAS) following aqua regia digestion (ISO 11466:1995). Contamination levels were quantified using the Contamination Factor (CF), Geo-accumulation Index (Igeo), and Pollution Load Index (PLI), calculated relative to locally derived geochemical background concentrations from control sites. Spatial distribution patterns were mapped using Surfer 20.0, and human health risks were assessed using the USEPA hazard index (HI) approach for ingestion, dermal, and inhalation exposure pathways. Results: All measured heavy metal concentrations remained below WHO and DPR/NESREA regulatory thresholds for example, maximum arsenic (0.112 ppm) and lead (1.040 ppm) were well within permissible limits indicating no immediate regulatory exceedance. However, when assessed against the very low local geochemical background concentrations (As: 0.004 ppm; Ni: 0.020 ppm; Cr: 0.012 ppm; Cd: 0.039 ppm; Pb: 0.042 ppm), pollution indices revealed significant anthropogenic enrichment. CF values indicated very high contamination for arsenic (CF = 5.25) and considerable contamination for nickel (CF = 3.90) and lead (CF = 4.43). Igeo values classified soils as moderately polluted for arsenic (Igeo = 1.81), lead (Igeo = 1.56), and nickel (Igeo = 1.38). The overall PLI of 3.17 indicated considerable multi-metal pollution across the study area. It is important to note that these elevated index values reflect the degree of anthropogenic departure from natural background conditions not proximity to health-based regulatory limits and therefore serve as sensitive early-warning indicators of progressive contamination. Spatial analysis revealed a pronounced arsenic hotspot within the landfill core and a distinct lead anomaly in the far-field zone (C2: Pb = 1.039 ppm), suggesting multiple contamination sources and complex transport pathways. The high permeability of the Benin Formation was identified as a key hydrogeological factor enhancing contaminant mobility. Despite the evidence of anthropogenic enrichment, cumulative human health risk indices remained low (HI < 0.1 for all receptors), indicating no significant non-carcinogenic health risk under current exposure conditions. Conclusion: Although current heavy metal concentrations are within regulatory limits and associated health risks are low, the significant anthropogenic enrichment above natural background levels  as evidenced by elevated CF, Igeo, and PLI values and the spatial variability of contamination patterns highlight the urgent need for continuous environmental monitoring, source control, and improved waste management strategies at the Aluu landfill to prevent future environmental degradation in this vulnerable Niger Delta setting.