Assessment of Heavy Metals Levels in Soils of Old Oyo National Park, Southwest, Nigeria

Soil contamination by heavy metals is a major environmental concern eliciting from both natural and anthropogenic factors, with the potential to disrupt the delicate balance of physical, chemical and biological processes which soil fertility and structure depends upon. The study therefore investigated the heavy metals levels and degree of contamination of soils sampl ed from three purposively-selected ranges (Oyo-Ile, Marguba, Tede) of Old Oyo National Park, Nigeria. Surface soil samples (0 -15 cm) were randomly collected along chosen topographical catenae for four seasons with the aid of a soil auger. The samples were analysed for copper, zinc, lead, nickel, cadmium, chromium, iron and manganese using standard methods. Data collected were subjected to descriptive and inferential (ANOVA) statistics using SPSS v.20 with statistical significance set at α0.05. The result of the mean concentration of the heavy metals showed that only cadmium was higher than the permissible limit. The ANOVA result showed that there were significant differences in the concentrations of all the analysed heavy metals except Ni (P=0.123) across the seasons of sampling. The quantitative indices used to assess the degree of heavy metal contamination showed that the studied soils had moderate degree of contamination while soil contamination was observed more during the wet season. This study observed cadmium toxicity as well as moderate degree of soil heavy metal contamination in Old Oyo National Park. There is need for continuous assessment of soil quality in Old Oyo National Park as a means of ensuring good ecological health.