Markers of Environmental Health: Nickel and Chromium Levels in Soil and Vegetation around a Steel Recycling Facility in Southwest Nigeria

Aims: To mark the environmental health status in the vicinity of a steel recycling facility in southwestern Nigeria using Nickel and Chromium levels in the top soil and leaves of Chromolaena odorata.
Methodology: Conventional methods were used to determine some soil parameters (pH and electrical conductivity in 1:1 soil: deionized water; percentage organic carbon using chromic acid oxidation method and particle size analysis using hydrometer method). The metal content in the soil and plant samples were analysed using the Atomic Absorption Spectrophotometer after digestion and extraction.
Results: The results of the soil within the factory showed pH values of 7.50 – 8.80 and reduced organic matter content indicating alkaline conditions. Electrical conductivity values were comparatively higher for soils within the factory (423 – 1550 µs/m) than soils outside the factory (146 – 226 µs/m) showing presence of some soluble salts in the soil. The levels of Ni and Cr in the soil were higher within the factory than outside of the factory. Nickel concentrations of the soil increased with increasing distance from the factory up to 200 m. Similar trends occurred for Cr in the eastern side of the factory where the detectable concentrations (2.29±0.05 – 33.26±0.02 mgkg –1) was observed. The Ni content in the soil around the factory ranged from: North (0.76±0.01 – 1.46±0.06 mgkg –1); East (0.19±0.05 – 2.68±0.04 mgkg –1); West (0.21 ± 0.01 – 1.46±0.07 mgkg –1) and South (0.22±0.02 – 1.89±0.01 mgkg –1). Within the factory however, the scrap yard contained high concentration of Cr 24.15±0.04 mgkg –1 while the soils from the dumpsite for sorted wastes contained elevated concentrations of Ni (73.17±0.02 mgkg –1). Nickel and chromium content in the plant leaves in this study ranged from 1.40 – 3.60 mgkg –1 and 0.40 – 1.5 mgkg –1.
Conclusion: Further increase in the Cr and Ni levels in the soil and plants of the study site poses a potential health hazard to animals that graze the area and man through consumption of forage and agronomic crops cultivated around the factory by peasant farmers.