V2I8P43

Bioindicator-Based Approach to Deposition of Heavy Metals in Roadside Vegetation: A Case Study of Benin-Auchi Road, Edo State, Nigeria

Ugah Chukwuemeka S^1*, Nwite Emmanuel C², Blessing U. Nnadi³

Abstract

The study investigates the deposition of atmospheric heavy metals in roadside vegetation using a bioindicator-based approach along the Benin-Auchi Road in Edo State, Nigeria. Two commonly occurring plant species Mangifera indica and Chromolaena odorata were selected as bioindicators due to their widespread presence and morphological suitability for capturing airborne pollutants. Vegetation samples were collected at three distances from the roadside (0–5 m, 5–10 m, and >10 m) in urban, peri-urban, and rural segments of the expressway. The concentrations of lead (Pb), zinc (Zn), copper (Cu), cadmium (Cd), and nickel (Ni) were analyzed using Atomic Absorption Spectrophotometry (AAS) after wet acid digestion. The results revealed significantly higher concentrations of all tested metals in vegetation within 0–5 meters of the road, particularly in urban areas. Pb ranged from 15.2 mg/kg in urban roadside vegetation to 9.3 mg/kg in rural areas; Zn ranged from 22.6 mg/kg to 15.5 mg/kg across the same gradient. Similar declining patterns were observed for Cd (3.6–2.1 mg/kg), Cu (9.4–6.5 mg/kg), and Ni (6.7–3.4 mg/kg). Statistical analysis indicated strong positive correlations between Pb and Zn (r = 0.89), and between Cu and Ni (r = 0.76), pointing to shared sources, mainly vehicular emissions. No significant differences were found between the two plant species in terms of heavy metal accumulation, confirming their effectiveness as bioindicators. These findings highlight the utility of roadside vegetation in monitoring airborne heavy metal pollution and suggest that proximity to vehicular traffic strongly influences the degree of atmospheric deposition. The bioindicator-based approach proves effective in environmental assessment, offering a cost-efficient and reliable method for air quality surveillance along major transportation corridors like the Benin-Auchi Road.

Keywords:

Bioindicator, heavy metals, roadside vegetation, mangifera indica, chromolaena odorata, environmental monitoring atmospheric deposition