Assessment of Heavy Metal Pollution of Agricultural Soil, Irrigation Water, and Vegetables in and Nearby the Cupriferous City of Lubumbashi, (Democratic Republic of the Congo)

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Lubumbashi (DR Congo)—the capital of copper mining—has been considered as one of the richest mining regions of the world for more than a decade. These riches have brought along multiple mining companies responsible for soil, river water and vegetable pollution, as in many African cities. The aim of the present study was to quantify and evaluate the pollution levels and the potential sources of soil, irrigation water and vegetable contamination by the metals As, Cd, Cr, Cu, Pb, Co and Zn in the urban gardens of Lubumbashi (DR Congo). The contamination, pollution and enrichment levels of the gardens were determined based on different indices in order to rank the soils. The results show that soils, waters and vegetables present contamination levels that represent a serious concern for human health. All soils presented contamination indices ranging from low (72% of the soils) to very high (3.4% of the soils) metal (copper, lead, zinc) contamination. The Cu and Cd contents varied between 1355 mg/kg et 236 mg/kg, much higher than the World Health Organisation (WHO) thresholds (100 mg/kg for Cu and 2 mg/kg for Cd). Moreover, the water used for crop and garden irrigation presented high Pb (57% of the waters), Fe (52%), Cu (19%) and Cd (10%) contamination levels, above the Association Française de Normalisation (AFNOR) U4441 toxicity thresholds (2 mg/kg for Cu; 0.1 mg/kg for Fe and 0.01 mg/kg for Pb) for crop irrigation. Finally, the vegetables produced in these gardens and sold in the local markets had very high metal content (47% contained Cu; 100% contained copper and cobalt) above the WHO standard (10 mg/kg for Cu, 2 mg/kg for Cd and 1 mg/kg for Co) for human consumption. In the face of these issues, it would be preferable to consider cheaper, more sustainable techniques that reduce soil-to-plant metal transfer.