Reducing the risks associated with the ingestion of vegetables grown on soils contaminated with trace metal elements through the application of soil amendments: Results of experiments in Lubumbashi/Democratic Republic of the Congo.

Abstract

The expansion of mining companies in the province of Haut-Katanga in general, and in the city of Lubumbashi in particular, is one of the main causes of the very worrying environmental problems facing the city's inhabitants. These problems include contamination of agricultural and residential soils, river and well water, the atmosphere and vegetables. This study evaluates the effectiveness of organocalcareous soil improvers applied to heavy metal-contaminated soils in reducing the mobility and bioavailability of heavy metals. Trials were conducted under glass at the Faculty of Agronomic Sciences, University of Lubumbashi, using a randomized factorial design with four replications. Treatments included four plant species (Brassica chinensis, Amaranthus vulgaris, Beta vulgaris and Brassica carinata), five levels of amendment (D0: no amendment; D1: 150g sawdust; D2: 150g chicken droppings; D3: 75g sawdust and 15g agricultural lime; D4: 75g chicken droppings and 15g agricultural lime), and three types of urban market gardens (Chem-chem; Manoah Kinsevere and Kashamata). The results reveal that the soil and plant biomass of four vegetables are contaminated with metals, with the daily consumption index of vegetables produced on the soils of the Kashamata garden with low copper contamination exceeding the limits authorized by the World Health Organization (WHO) and the Food and Agriculture Organization of the United Nations (FAO) for daily vegetable consumption for a person of 60 kilograms body weight. The daily consumption index was not determined due to insufficient biomass linked to high soil contamination, inhibiting plant growth for the market gardens of Manoah Kinsevere and Chem-Chem, soils moderately and highly contaminated with copper, respectively. However, these vegetables remain unfit for human consumption, underlining the need to adopt new soilless production techniques such as conventional hydroponics or bioponics in areas heavily impacted by anthropogenic activities.