Heavy metal contamination may alter the chemical composition of plants with consequent effect on their growth and possible transmission of potential toxic metals to animals and humans along the food chain. The study was carried out to quantitatively assess the levels of heavy metals in plant species in Old Oyo National Park, Southwest, Nigeria. The Segmented Transect Belt Method was adopted for matured plant (leaves) sampling in Marguba, Tede and Oyo-Ile ranges of Old Oyo National Park, purposively selected based on the observed anthropogenic activities by the surrounding local communities. Sampling was done within four seasons during the wet and dry seasons for two consecutive years (between 2017 and 2018). Heavy metals such as copper, zinc, lead, chromium, cadmium, nickel, iron and manganese were analysed in the samples using standard methods. Data collected were subjected to descriptive and inferential (ANOVA) statistics with statistical significance set at α0.05. The result showed that the mean concentrations of cadmium (except dry season, 2017), iron (during wet season, 2017) and chromium (during wet season, 2017) levels in the plants were above the comparable recommended limit while the mean concentrations of copper, zinc, lead, nickel and manganese across the four seasons of sampling were below comparable recommended limits. The sampled plant species were more contaminated with heavy metals during the wet season than the dry season. Statistically, there were significant differences in the values of all the analysed heavy metals in the plant samples across the four seasons at P≤0.05. There is need for continuous monitoring of heavy metal deposition, accumulation and contamination in the park.
Key Words: Heavy metals, Plant samples, Wildlife, Old Oyo National Park