Evaluating the Impact of Abattoir Wastes on Soil Properties in Benin City, Edo State, Nigeria

Abstract

Abattoir wastes is a major environmental concern to both urban and peri-urban areas in Nigeria. Therefore, its impact on soil properties in Benin City, Edo State, Nigeria was evaluated. Variations in the morphological, physicochemical and microbial properties of the abattoir soils were assessed while the heavy metals toxicity of the soils were evaluated. A total of 24 soil samples were randomly collected from the abattoirs in Oluku and Ikpoba slope areas as well as the non-abattoir site (control) at depths of 0-15 cm (topsoil) and 15-30 cm (subsoil) respectively. Each of the soil samples was evaluated in-situ for key morphological characteristics. The physicochemical and microbial properties of the soils were determined in the laboratory following standard methods, while the heavy metal concentrations were estimated using the atomic absorption spectrophotometer method. Results revealed that the abattoir soils were predominantly black in colour. Consistent anthropogenic disturbances may have caused the abattoir soils to be more compact with higher mean bulk density (BD) values (1.25 - 1.35 Mg/m³) than the control that had 1.15 Mg/m³. The abattoir soils which were slightly alkaline and rich in organic matter could serve as a good source of manure for agricultural purposes. There were increased fungi and bacteria counts in the abattoir soils. All the examined heavy metals - lead (Pb), cobalt (Co), chromium (Cr) and cadmium (Cd) were more concentrated in soils of the abattoir sites than the control site, but were within the toxicity limits established by World Health Organization and the Department of Petroleum Resources (Nigeria). However, these heavy metals could pose potential risks to the soil environment and health of nearby residents. The study also revealed that contamination factor, geo-accumulation index, enrichment factor, contamination degree and pollution load index of the heavy metals were all within the acceptable ranges. In the correlation matrix, the major significant positive relationships that were observed were between silt and total porosity, potassium, chromium, total heterotrophic bacteria count; while the significant negative relationships were between sand and silt, total porosity, potassium, chromium, total heterotrophic fungi count. The study concluded that Pb was the major heavy metal contaminant among the investigated heavy metals in the abattoir soils which could have devastating effects on public health if left unchecked.