Translocation of metals in two leafy vegetables grown in urban gardens of Ntoum, Gabon

Abstract

The aim of this study was to investigate the properties of cultivated urban soils and metal concentrations in these soils and in roots and leaves of the crops Amaranthus cruentus (amaranth) and Hibiscus sabdariffa (roselle). The soil physicochemical properties showed a poor fertility rate of cultivated soils. The metal concentrations in soils were in the range of concentrations for uncontaminated agricultural soils. The ranges of concentrations of metals were as follows: Aluminium (Al), 239-1222 mg/kg; cadmium (Cd), < 0.3. mg/kg; copper (Cu), 9.3-31.7 mg/kg; iron (Fe), 166-617 mg/kg; manganese (Mn), 18.1-187.5 mg/kg; lead (Pb), < 2.36 mg/kg; zinc (Zn), 25.2-66.9 mg/kg. The accumulation of metals was as follow: In leaves, Fe > Al > Mn > Zn > Cu >Pb; in roots, Al > Fe > Zn > Mn > Cu > Pb. Al and Fe were weakly bioaccumulated but their concentrations were high. Cu and Mn were more accumulated in leaves than roots for amaranth and roselle. The leaves of amaranth were found to accumulate soil Cu and Zn more efficiently than other tissues of both vegetables. The translocation factor was in the order: Mn > Cu > Fe > Zn > Al, and when this value was compared between amaranth and roselle, it was observed to be higher in amaranth than in roselle. The concentrations of the essential elements Cu and Mn in roselle, and Cu, Fe, Mn and Zn in amaranth indicate that these leafy vegetable are a good nutrient sources.