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.
The European aquaponic sector started to develop and professionalize in the early 2010′s. This development and the subsequent challenges faced by early practitioners were investigated in various publications between 2015 and 2020. Although most of these studies were focused on educational and research institutions, only a few included commercial entities. The present survey is aimed at defining and assessing the recent evolution of the European aquaponic activities in professional structures. One hundred and forty professional aquaponic entities (non-profit organization, educational, and commercial) having an aquaponic system with more than 1 m3 of water in their recirculating aquaculture systems were identified in Europe. Among them, 46 responded to a survey about the technical and business aspects of their structures. In comparison to previous surveys, a much higher number of entities had larger systems (up to 14,000 m2), with higher yields (up to 20 t of fish or vegetables per year), whereas 59% of them declared making profits. This revealed a clear expansion and professionalization of the sector, which was found to be highly diversified, with systems varying greatly in size, design, and technology. Business models and activities were generally diverse, and included a combination of production, education, and/or services. Most entities also combined different customer segments. At the time of the survey, the aquaponic sector was still struggling to find its economic viability, as the business model of most entities did not only rely on fish and vegetable sales, but also largely relied on free labor through volunteers or internships. Acquiring knowledge as well as optimizing production and business models were perceived as the main challenges for the steady growth of the sector. Consequently, there is a clear need to increase training, to continue the research and development work, and create public support systems for aquaponics farms to further improve and expand the commercialization of aquaponics in Europe.
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