Contamination of market garden soils by metals (Hg, Sn, Pb) and risk for vegetable consumers of Ngaoundéré (Cameroon)

The objective of this work is to study the contamination risks of market garden soils by metals using combustion debris (CD) as fertilizers. Therefore, two parcels of land usually used by farmer for market gardening have been rented on two sites. Soils were plowed, amended with CD and three plants species were grown. Samples of non-amended soils, amended soils and leaves of three species plants such as Amaranthus hybridus, Corchorus olitorius and Lactuca sativa were treated and then metals were analyzed by ICP-MS. The results obtained revealed the presence of several metallic elements such as Hg, Sn and Pb in soils with maximum concentrations of 15.03 ± 0.52, 6.16 ± 0.07 and 307.20 ± 16.30 mg/kg, respectively. The highest concentrations were found on amended soils. This means that a significant amount of metals found in amended soils would come from either direct or indirect CD. The same metals were identified in the leaves of three plants species, with concentrations which in some cases exceeded the recommended limit values. The L. sativa species is also one that has the most accumulation of Hg and Pb with average concentrations of 3.12 ± 1.18 and 3.1 ± 0.57 mg/kg, respectively, on the two sites. The results of the risk index also indicate the existence of a real risk of ingesting metals by consumers of vegetables grown on these soils.