Ecological vulnerability: seasonal and spatial assessment of trace metals in soils and plants in the vicinity of a scrap metal recycling factory in Southwestern Nigeria

The concentrations of selected heavy metals in the soil and vegetation in the immediate vicinity of a metal scrap recycling factory were determined in the dry and wet seasons using the Atomic Absorption Spectrophotometer. The results showed that the soil pH in all the sites indicated slight acidity (from 5.07 to 6.13), high soil organic matter content (from 2.08 to 5.60 %), and a well-drained soil of sandy loam textural composition. Soil heavy metal content in the dry season were 0.84–3.12 mg/kg for Pb, 0.26–0.46 mg/kg for Cd, 9.19–24.70 mg/kg for Zn, and 1.46–1.97 mg/kg for Cu. These values were higher than those in the wet season which ranged from 0.62–0.69 mg/kg for Pb, 0.67–0.78 mg/kg for Cd, 0.84–1.00 mg/kg for Zn, and 1.26–1.45 mg/kg for Cu. Except for cadmium in the dry season, the highest concentrations occurred in the northern side of the factory for all the elements in both seasons. An increase in the concentrations of the elements up to 350 m in most directions was also observed. There was no specific pattern in the level of the metals in the leaves of the plant used for the study. However, slightly elevated values were observed in the wet season (Pb 0.53 mg/kg, Cd 0.59 mg/kg, Cu 0.88 mg/kg) compared with the dry season values (Pb 0.50 mg/kg, Cd 0.57 mg/kg, Cu 0.83 mg/kg). This study showed that the elevated concentrations of these metals might be associated with the activities from the recycling plant, providing the basis for heavy metal pollution monitoring and control of this locality that is primarily used for agricultural purposes.