Soil and plant contamination with metals from concrete batching plant processes in Murchison Falls National Park, Uganda

Abstract

Concrete batching activities involving the use of cement are increasing especially in developing countries even though they are associated with pollutants to the environment. This study assessed the effect of concrete batching activities commissioned in October 2018 in Paara village on a gentle slope within Murchison Falls National Park, Buliisa District, Uganda, has on metal contamination in soils and vegetation. While the specific objectives were to: i) determine the level of metal contamination in soils and selected grass species along a distance gradient; and ii) identify the management practices employed to minimize metal contaminations. Sixty-two (62) grass species samples and eighteen (18) soil samples were collected at varying distances along transects radiating from the concrete batching plant. The grass species included Brachiaria brizantha (A. Rich.) Stapf, Sporobolus africanus (Poiret) Robyns & Tourmay, Hyperthelia dissoluta (Nees ex Steud,) Clayton, Hyperrhenia rufa (Nees) Stapf, Cynodon dactylon (L.) Pers and Panicum maximum Jacq. Metal concentrations in grass and soil samples were determined using Atomic Absorption Spectroscopy (AAS) and data on the management strategies collected using Key Informant Interviews (KII). Variation in metal concentration along the transects was analyzed using a One-way Analysis of Variance (ANOVA) and Pearson’s correlation coefficient (r). Data on management practices were analysed using descriptive statistics and thematic analysis. Soils had Cr mean concentrations was 9.525mg/kg at 100m, Mn 2.55mg/kg at 100m, Pb0.0055mg/kg at 100m and Ni 0.03 mg/kg at 100m. Mn mean concertation in grass species shoots was 19.83mg/kg at 500m and roots 17.99mg/kg at 500m. The shoot of Hyperthelia dissoluta (Nees ex Steud) Clayton presented Mn mean concentration of 25.5mg/kg at 500m, Cr 0.85 mg/kg at 1000m and Pb 0.04mg/kg at 1000m. There was a positive Pearson’s correlation coefficient observed for Pb (r = 0.087) and Ni (r = 0.097) and a significant positive correlation observed for Cd (r = 0.905*) between root and shoot. Significant variations in metal concentration with distance from the concrete batching were observed in soils and both roots and shoots of plant species of Brachiaria brizantha (A. Rich.) Stapf and Hyperthelia dissoluta (Nees ex Steud,) Clayton. Generally, there was no consistent decline of metal concentration over a distance gradient. Wastewater recycling, sedimentation pits, and dust control measures involving the sprinkling of working areas, were the management strategies employed at the batching site. The results reveal a metal contamination of soils and the selected grass species around the concrete batching plant. This predisposes the herbivorous wild animals to bioaccumulation of metal in their body tissues.