Abstract Weeds have negative effects on human activities but can be used as food, feed, medicine or metal-accumulator. The objectives of this work were to assess the safety level of some useful weeds grown at market gardening sites in Ngaoundere and identify some plants with accumulative characteristics from the weed plants that can contribute to the detoxification of the market gardening soils. Eight weeds used as vegetable, medicinal plant or forage grass (Ageratum conyzoides, Commelina benghalensis, Acanthospermum hispidum, Setaria barbata, Brachiaria lata, Bidens pilosa, Amaranthus spinosus, and Galinsoga parviflora) were analysed to determine heavy metals levels. The heavy metals analysed were Fe, Cu, Ni, Zn, Cd and Pb. Results showed that the concentrations of heavy metals in plants varied according to sites, plant species, and plant parts. Plants were more contaminated in urban site than in peri-urban site. For plants used as feed (Setaria barbata and Brachiaria lata), all the heavy metal concentrations in edible parts (aerial parts) were below the limits according to the National Research Council. For the weeds used as medicinal plant or food, the Cd concentrations exceeded WHO/FAO maximum recommended limit by 2 to 5 times in Commelina benghalensis, Acanthospermum hispidum and Amaranthus spinosus, while Pb concentrations exceeded WHO/FAO maximum recommended limit by 4 to 62 times in Ageratum conyzoides, Commelina benghalensis, Acanthospermum hispidum, Bidens pilosa and Galinsoga parviflora. So, these plants are not suitable for human consumption. Base on Translocation Factor (TF) values, the results showed accumulation and exclusion of various metals by different weeds. These uptake characteristics suggested that they can be used in the clean-up of the market gardening soils.
Keywords market gardening soils, useful weeds, heavy metals, translocation factor.