Comparative Evaluation of the Levels of Selected Heavy Metals and Index of Pollution Status of the Sub-Soil of Bauchi Main Abattoir, Bauchi State, Nigeria

Abstract

Activities in abattoirs and direct release of its waste into the environment are on the increase due to the high protein demand and hence there is need for proper assessment of abattoir soil with the aim of evaluating its degree of contamination. This study evaluated the variation in the levels of heavy metals in soil impacted by wastes from Bauchi main abattoir. Soil samples from four different distances away from the abattoir were collected at a depth of 0-20 cm and at distances of: 0-40 cm, 40-80 cm, 80-120 cm and a control (60 m). Soil samples from each distance/location were separately collected, digested and evaluated for the levels of selected heavy metals at their respective wavelengths using Atomic Absorption Spectrophotometry. The observed ranges (mg/kg) are: cadmium (14.90-22.96), cobalt (9.13-11.96), copper (1.13-13.98), chromium (2.93-6.92), iron (556-739),manganese (42.43-71.43), nickel (5.97-11.96),lead (8.00 -30.30) and zinc (0.66-2.97 ) in the studied area, while  the control values (mg/kg) are: cadmium (8.80), cobalt (5.96), copper (0.97), chromium (0.96), iron(34.60), manganese (21.33), nickel (2.96), lead (7.97) and zinc(0.96). The study indicated that, the levels of heavy metals in the studied area decreased as the distance increases. The variations in the concentrations of all the heavy metals both in the studied and control soils were found to be significantly different as revealed by one- way ANOVA and Least Significant Different test (p ≤ 0.05).The contamination potential of heavy metals were all found to be within than the values stipulated by WHO (2007) and DPR (2022) except for cadmium and iron. This shows that the soil samples from Bauchi main abattoir are not contaminated with most of the heavy metals except for cadmium and iron. The enrichment factor (EF) follows the order: Mn ˃ Cu˃ Cr ˃ Ni ˃ Pb ˃ Cd ˃ Zn ˃ Co (0 – 40 cm), Co ˃ Mn ˃ Zn ˃ Cr ˃ Cu ˃Ni ˃ Cd ˃ Pb (40 -80 cm) while at 80 -120 cm the order was: Cr ˃ Mn ˃ Co ˃ Pb ˃ Ni ˃ Cd ˃ Cu ˃ Zn. The order of  the contamination factor (CF) was: Cd ˃ Co ˃ Cu ˃ Pb ˃ Ni ˃ Fe ˃ Mn ˃ Cr ˃ Zn  at the studied abattoir, while at the control location, the CF follows the order : Cd ˃ Co ˃ Pb ˃ Ni  ˃ Mn ˃ Cu ˃ Cr ˃ Fe ˃ Zn. Based on the indices of metal pollution, the soil are classified as very slight contamination to severe pollution. The I-geo index spread from practically uncontaminated to moderately contaminated,  the enrichment factor at all distances in all the abattoir soils studied were greater than 1.00 indicating that these heavy metals are from anthropogenic source, while  the pollution load index (PLI) in all the locations were found to range from 1.06 – 2.27. The PLI values in all the studied soils are within moderately polluted (1 < PLI < 2) category. according to (Olusola et al., 2020).The operations of Bauchi main abattoir are therefore not environmentally friendly based on the levels of iron and cadmium and  this can pose health and environmental threats to the residents.