Plant Composition and Edaphic Assessment of Heavy Metals in a Waste Effluent Receiving Wetlands in Uyo, Nigeria

Heavy metals, once released into the environment, are problematic pollutants due to their harmful effects on living organisms. This study assessed the heavy metal composition in plants and soil in a wetland receiving waste effluents. Vegetation was sampled using a 5 m x 5 m quadrat through systematic sampling at regular intervals to determine density and frequency. Soil samples were taken at two depths (0 - 15 cm and 15 - 30 cm) using a soil auger, and their physicochemical properties were analyzed using standard methods. Shoots of dominant plant species were also collected for heavy metal analysis. The results showed that Alchornea cordifolia had the highest density (2800 ± 100.32 st/ha), while Caladium bicolor had the lowest (33.00 ± 1.20 st/ha). The mean heavy metal concentrations (mg/kg) in the soil were Fe (571 ± 48.36), Zn (78.24 ± 8.52), Cu (10.74 ± 0.30), Ni (8.42 ±0.98), Pb (4.95±0.70), and Cd (2.21±0.19), while the plant’s shoot was Fe (15.26±1.85), Zn (11.30±1.36), Ni (8.50±0.61), Cu (6.82±0.85), Pb (5.81±0.50), and Cd (2.51±0.11). The translocation factor threshold of heavy metals in the wetland exceeded 1 for Cd, Ni, and Pb, while Fe, Zn, and Cu had values < 1. The soil of this wetland was moderately contaminated with Cd, Ni, Fe, and Cu and was very highly contaminated with Pb and Zn. The degree of contamination obtained in this wetland was 42.25. This study has demonstrated that the ecosystem was polluted by heavy metals to varying degrees, thus, necessitating urgent management and protection measures to ensure its future sustainability.