Research article

Eco-Nutritional Risk Assessment of Maize Cultivated in Post-Mining Landscapes: A Case Study of Soil-Plant Heavy Metal Dynamics and Nutrient Composition at the Kilembe Copper Belt, Uganda.

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This article is a preprint and is currently undergoing peer review by UCL Open: Environment.

Abstract

The cultivation of crops around the considerable copper mining site in Kilembe, Western Uganda, has become a huge concern especially about the environment and the safety of food crops grown herein, including maize. The study therefore aims to investigate whether contamination of soil linked with mining activities at the Kilembe mining site may be a contributing factor to diet related risks through assessing the physicochemical characteristics of the soils, the heavy metal concentrations in the soils and maize grains, and the nutritional analysis of maize. Soil samples were obtained from maize farms at varying distances from the Kilembe mining site (0, 1, 3 and 5km) and a control site in Bushenyi (95 km) serving as group 1 – 5 respectively. The physicochemical properties and heavy metal content of the soil were determined before planting. At harvest, the heavy metal levels and nutritional properties of the maize fruits were determined. Soils were mostly sandy or sandy-loamy and changes in soil pH, electrical conductivity, exchangeable acidity, moisture content, and water holding capacity were significant in groups near the mining site compared to the control. Total nitrogen was lower (p<0.05) in 0km; K and Na varied in 0– 3km from the site, while Total Organic Carbon and Total Phosphorus showed no significant change. Heavy metal levels (lead; Pb, copper; Cu, cadmium; Cd, chromium; Cr, and nickel; Ni) were higher (p<0.05) in soils 0–5 km from the site while cobalt; Co, silver; Ag, and mercury; Hg were undetectable. Maize grown at 0–3 km had elevated levels of Cd, Cu, Pb, and Cr, as well as increased moisture and essential minerals (Zn, Mn, Ca, Mg, Na, K, P, Fe) while no differences in mineral content were found at 5 km (p<0.05). Nutritional quality declined except for riboflavin, which increased at 5 km while Tocopherol and ascorbic acid increased in all sample sites except for ascorbic which decreased at 5 km. These findings raise concerns about human health risks from heavy metal ingestion from the consumption of maize in this mining catchment. There is therefore need for nutrient supplementation in this area as well as formulation of guidelines for public health safety in farmland within 0 – 3 km of mining activities.

Keywords: Zea mays, Maize, Physicochemical, Proximate, Minerals, Vitamins, Heavy metals, Kilembe Mining Site