Appraisal of Heavy Metals Uptake Capacities of 2 Edible Vegetables (Amaranthus caudatus and Amaranthus hybridus) from Natural, Heavy Metals and Urea Fertilizer-Enriched Soils: Towards Family Health Security

Abstract

Heavy metals uptake capacities of 2 edible vegetables (Amaranthus caudatus (soko) and Amaranthus hybridus (tete)) from natural,  metals and fertilizer enriched soils were evaluated to establish their safety for family consumption. Oxides of Fe, Cu, Pb and Zn giving  equivalents of 800 mg Fe kg^-1 , 500 mg Cu kg^-1 , 1500 mg Pb kg^-1 and 700 mg Zn kg^-1 respectively were measured into each of the 4 pots  containing 2.5 kg of soil. Two grams of urea fertilizer were weighed into 2 of the pots with added metals and mixed. Seeds of the 2  vegetables were planted inside the pots and labelled. Two pots served as controls. The pots were watered and germination occurred  within 5 d. Seedlings were thinned to one stand per plant. Vegetables were harvested after 34 d and each separated into shoot and root,  dried in the oven at 60^oC for 1 h and then at 110^oC for 5 h. Dry samples were crushed, weighed and ashed in the furnace at 600^oC. HNO₃  solutions of the ashes were analyzed using Buck Scientific 210 Atomic Absorption Spectrophotometer. Results showed that the shoots of  the vegetables contained less metal concentration the roots with Amaranthus hybridus having higher values. Fertilizer application  increased the metal concentrations in the shoot of Amaranthus hybridus with the levels of Pb (6.65 mg/kg) and Fe (10.54 mg/kg) being  higher than the FAO/WHO maximum limits of 0.3 and 2.5 mg/kg respectively for leafy vegetables. Amaranthus hybridus without applied  fertilizer is safer for consumption.