Physicochemical Characteristics and Heavy Metal Distribution in Agricultural Soils of Nasarawa State, Nigeria

Abstract

The baseline data of soil quality and trace metal distribution is essential to assess agro-environmental sustainability in highly cultivated areas. This research evaluated the physicochemical characteristics and spatial distribution of heavy metals in agricultural soils in the three senatorial areas of Nasarawa State, Nigeria, to explain the factors that are controlling and the likelihood of contamination. The samples of composite topsoil (0-30 cm) were taken at Awe (South), Nasarawa Eggon (North) and Kokona (West) and analyzed following standard protocols of pH, electrical conductivity (EC), organic carbon (OC), organic matter (OM), moisture content (MC), macronutrients, and trace metals. The soils were almost neutral to slightly acidic (pH 6.82-6.88) and non-saline (EC: 1.11-1.17 dS m -1), and were mostly sandy-textured, which means that they had low sorption capacity. The values of moderate OC and OM were found, and nitrogen and phosphorus were relatively enriched in the southern zone. Concentrations of trace metals were strongly spatially heterogeneous, with Pb and Zn always predominant, with Cd, Cr and Ni being local enriched. The patterns of distribution of metals were characterized by different zonal patterns: Nasarawa North (Zn > Pb >> Mg ≈ Cu ≈ Fe > Cr > Cd), Nasarawa South (Pb > Zn >> Fe > Mg > Cu > Ni), and Nasarawa West (Pb > Zn >> Fe). PCA showed that there was evident segregation of fertility related variables, soil texture, and metal related variables, which imply that there, were mixed lithogenic and anthropogenic controls. Whilst the general levels of metals were within the allowable range, localized enrichment of Cd in the south and Ni/Pb in the west hints at developing hotspots of contamination. These results enable important baseline data and the necessity of specific soil management and constant monitoring to reduce the threat of ecological and food safety risks in the long term.