Evidence of heavy metal in soil, irrigation water and vegetable cultivated in peri‑urban area of Yaoundé-Cameroon

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Résumé

Environmental pollution by anthropogenic activities is of global concern. The levels of Heavy metal contamination were evaluated in the soil and irrigation water and their transferability to the cultivated plant were appraised in the locality of Nkolbisson, Yaoundé-Cameroun. The level of Zn, Cu, Cd, Ni, Pb, Cr and Mn contamination were evaluated using Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). The analysis of soils, waters and crops (Corchorus olitorius and Lactuca sativa) samples has shown high levels of heavy metal contamination. Cd, Ni and Cr concentrations in water samples (0.986±0.003f, 2.230±0.002a, and 2.635±0.002a mg/l) was above threshold set by FAO for irrigation water. In agricultural soils, the level of heavy metal (Zn, Cu, Cd, Ni, Pb and Cr) analysed on soils samples were below the European Union (EU) and the Canadian Council of Ministers for Environment (CCME) thresholds toxicity values except that of Mn (1013.090±102.126a mg/kg) one. The concentration of Zn (48.855±0.230b; 56.731±0.230a and 48.650±0.230b; 53.261±0.230a mg/kg MS), Cu (18.864±0.107b; 27.453±0.107a and 25.642±0.107b; 27.476±0.107a mg/kg MS), Cd (0.654±0.017b; 1.434±0.017a and 0.921±0.017b; 0.959±0.017a mg/kg MS), Ni (3.131±0.051b; 4.557±0.051a and 1.647±0.051b; 1.985±0.051a mg/kg MS) and Cr (3.162±0.048b; 3.942±0.048a and 6.133±0.048b; 4.875±0.048a mg/kg MS) analysed in plants samples was above the normal values in the edible parts of the two plants analysed, except those of Pb (0.361±0.033a; 0.394±0.033a and 0.043±0.033a; 0.041±0.033a mg/kg MS) and Mn (113.457±0.138b; 123.341±0.138a and 173.667±0.138b; 180.321±0.138a mg/kg MS). Thus, these plants pose a health risk. Market gardening in this city presents risks due to the presence of heavy metal in soils and irrigation waters. This is a public health hazard which should be controlled. Bioconcentration and translocation factors have shown that Lactuca sativa can be used for phytoextraction of Zn, Cu, Cd and Corchorus olitorius for phytomobilization of the same elements.

Mots-clés

heavy metal contamination, soil contamination, irrigation water quality, vegetable crops, bioaccumulation, bioconcentration factor, translocation factor, Corchorus olitorius, lettuce, cadmium, nickel, chromium, manganese, zinc, copper, lead, phytoextraction, market gardening, health risks, peri-urban agriculture, Yaoundé