Abstract:
Old Oyo National Park (OONP), a protected area in Nigeria, is threatened by anthropogenic activities (mining, charcoal production and farming) from surrounding communities. These activities have been reported as sources of Heavy Metals Contamination (HMC) with resultant toxic effects on the environment. For sustainable management of OONP natural resources, data on HMC characteristics and structures are crucial but not available. Therefore, HMC characteristics and structures in waterhole, soil, plant and wild animals’ faecal samples in OONP were investigated.
Three out of five ranges (Marguba, Tede, Oyo-Ile) in OONP were purposively selectedbased on availability of perennial waterholes and observed anthropogenic activities. Segmented transect belt (n=15, 1.2 km in length) was adopted for dry (November - March) and wet (April - October) season sampling. Composited surface water, topsoil (0-15 cm), plants (leaves) and faeces of wild animals were collected for 24 months using standard methods. Samples were analysed forheavy metals (mg/kg)using standard procedures. Soil contamination determinants: Contamination Factors [(CF): <1 (low contamination) to ≥6 (very high contamination) and Geo-accumulation index(I-geo): <0 (unpolluted) to ≥5 (extremely polluted) were calculated. Data were analysed using descriptive statistics, T-test and Principal Component Analysis (PCA) at α0.05.
The least and highest levels of heavy metals in waterholes were cadmium [0.01±0.01 (Tede), 0.05±0.03 (Marguba)]; lead [0.07±0.10 (Tede), 0.15±0.10 (Marguba)]; zinc [0.13±0.07 (Tede) and 0.24±0.32 (Marguba)]. In topsoil, cadmium varied from 0.62±0.52 (Tede) to 1.47±1.07 (Marguba), lead from 1.73±2.34 (Oyo-Ile) to 3.20±2.23 (Tede) and zinc from 6.81±1.77 (Tede) to 22.96±17.58 (Marguba). In plants, cadmium ranged from 0.11±0.21 (Tede) to 0.27±0.30 (Oyo-Ile), lead from 0.32±0.50 (Marguba) to 0.55±0.59 (Oyo-Ile) and zinc from 5.64±3.58 (Oyo-Ile) to 12.48±10.41 (Marguba). Highest mean level of zinc in faeces (30.41±42.20) was obtained in Marguba while other heavy metals were Below Detection Limit (BDL). In other ranges, cadmium, lead and zinc were BDL. Cadmium, lead and zinc in waterholes [(0.03±0.04; 0.05±0.04), (0.08±0.10; 0.16±0.09), (0.15±0.16; 0.16±0.06)], topsoil [(0.86±0.67; 1.06±1.31), (2.08±1.76; 3.17±2.47), (7.02±7.36; 22.59±17.44)] and plants [(0.18±0.26; 0.24±0.31), (0.44±0.57; 0.47±0.61), (8.87±7.77; 11.24±7.01)] were obtained in dry and wet seasons, respectively. Zinc level in faeces was 30.41±42.20 in dry season with cadmium and lead BDL while zinc, cadmium and lead were BDL in wet season. Significant seasonal variation existed only for zinc, in water and soil samples. Cadmium, lead and zinc had CF of 4.68±1.79, 0.63±0.08 and 0.33±0.18 while I-geo were 3.02±0.62, -2.63±0.17 and -3.20±0.87, respectively. Zinc had highest contribution of total variability of identified components (PC 1 and PC 2) of waterholes (50.97%), plants (34.66%) and faeces (39.47%) while lead (52.23%) had highest contribution of total variability of identified components in soils.
The Old Oyo National Park was considerably contaminated and strongly polluted with cadmium. Appropriate remediation efforts should be put in place to protect the park’s ecosystem health.
