An Analysis of Heavy Metal Contamination in Vegetables and Herbs Growing in Water Hyacinth Manure, Case of Lake Chivero

The primary goal of this study was to determine concentrations of heavy metals in water hyacinth compost manure (Pb, Cd, Cu, Cr, and N) and their bioavailability in Brassica oleracea var acephala and mentha organs. Analysis also focused on the physiological responses of Brassica oleracea var acephala and mentha to water hyacinth compost.The target was to find if water hyacinth have high nutritive to enhance plant growth and act a an alternative solution for controlling water hyacinth if harvested from eutrophic Lake Chivero. Rhizofiltration ability of water hyacinth makes it potential source of fertilizer to plants since it accumulates all excess nutrients from hyper-eutrophic water sources. Before planting Mentha herb and Brassica oleracea var acephala, soil samples and compost were taken to the laboratory. The experiment was carried out in uncontaminated soil. For eight weeks, mature plants were harvested and their roots, stems and leaves were collected and plant materials were tested for heavy metal concentration to determine total metal concentration. The Bio-concentration Factor was used to calculate the concentration of heavy metals in Brassica oleracea var acephala and Mentha. The heavy metal accumulation rate in Brassica oleracea var acephala was calculated using a translocation factor. Heavy metal concentrations of Pb, Cd, Cu, Cr, and Ni were measured in compost treatments as well as Covo vegetables and mint herbs. Metal concentrations were greater than 1 mg/kg for Pb, Ni, Cu, and Cr, but not for Cd, which was below detection levels. The metals Pb, Ni, Cu, and Cr all had a BCF >1 mg/kg in Brassica oleracea var acephala and Mentha exceeded the WHO food safety guidelines. During the exposure experiments, the concentrations of Pb, Cd, Cu, Cr, and Ni in brassica oleracea var acephala vegetables and Mentha herbs increased. In decreasing order, Brassica oleracea var acephala and Mentha roots and leaves had the highest accumulation and total heavy metal concentration of Pb > Ni > Cu > Cd > Cr. In summary, water hyacinth from Lake Chivero cannot be used as a biofertilizer for food crops hence more research is required on other non-food crops and other uses like biofuel.