Application of Pollution Load Index (PLI) and Geo-Information Techniques for Evaluating Heavy Metal Distribution in Soils of the Toro Mining District, Nigeria

Abstract

This study investigates the geochemical characteristics and spatial distribution of heavy metals in soils within the Toro mining district, Bauchi State, Nigeria, to evaluate the environmental impact of prolonged artisanal tin mining. A total of ten (10) composite soil samples were collected from depths of 10–15 cm across active, abandoned and control sites. Samples were analysed using Atomic Absorption Spectroscopy (AAS) at the Nigerian Geological Survey Agency (NGSA) Laboratory, Kaduna, with quality control protocols observed throughout the analytical process. The concentrations of Pb, Cd, As, Cr, Cu, Zn, Fe, and Mn were determined and compared with World Health Organization (WHO) soil quality standards. Results revealed elevated levels of Pb, Cd, and As in soils proximal to mining ponds and tailings, exceeding permissible limits and indicating significant anthropogenic enrichment. Pollution assessment models, including the Contamination Index (CI) and Pollution Load Index (PLI), confirmed moderate to high pollution intensities across the study area. Integration of geochemical data with geospatial analysis (ArcGIS 10.7.1) delineated contamination hotspots, predominantly within Badiko and Bakin Kogi, while Wonu remained relatively unpolluted due to favourable drainage conditions. The predominance of clay soil types further influenced metal retention and distribution patterns. Overall, the study demonstrates that tin mining activities are the primary contributors to soil contamination in Toro, with potential ecological and public health implications through bioaccumulation and groundwater infiltration. Remedial actions and improved mining waste management practices are strongly recommended to mitigate further environmental degradation.