Leafy Vegetables as Potential Pathways to Heavy Metal Hazards

Abstract

The effect of anthropogenic activity relating to industrial and economic development has had a detrimental impact on the environment and human health, and hence the need for continued research. Five common African vegetables—Murraya koenigii, Ocimum gratissimum, Amaranthus hybridus, Capsicum annuum and Moringa oleifera were used to study absorption of Lead, Cadmium, Cobalt and Zinc from soils inoculated with metal ions. 0.1M and 0.5 M solutions of the metal ions were used in the inoculation. Each of the plants was collected in the first instance at 8 weeks, and then at 10 weeks of inoculating. Atomic Absorption spectrophotometer was used to determine the metal ions concentrations absorbed in the plants. Cd2+ was most and Moringa oleifera the least absorbed of the four metal ions, with a highest value of 34.801 ± 0.805 mg/kg occurring in Capsicum annuum. Co2+ was the least absorbed of the four metal ions, Amaranthus hybridus showed highest absorption of Co2+ with mean absorption values of 5.566 ± 0.324 mg/kg and 5.670 ± 0.210 mg/kg for 0.1 M and 0.5 M solution of Co2+ respectively. Ocimum gratissimum absorbed Pb2+ most with the highest mean absorption of 5.290 ± 0.180 mg/kg and 6.354 ± 0.366 mg/kg for 0.1 M and 0.5 M respectively. Ab-sorption increased as the concentration of the inoculant solution increased for all the plants, and decreased on moving from 8 weeks’ to 10 weeks’ for all the plants except Moringa oleifera. This could as a result of Phytovolatilization against the report of Padmavathiamma and Li, 2007 [1] that phytovolatilization occurs in As, Hg and Se. Ocimum gratissimum showed highest absorption with the mean value of 9.334 ± 0.312 mg/kg, when the inoculants concentration increased to 0.5 M, Capsicum annuum showed highest absorp- tion with mean absorption value of 9.916 ± 0.614 mg/kg at 10th week. Also absorption increased as the concentration of the inoculant solution increased, and also on moving from 8 weeks’ to 10 weeks’ for all the plants. From the results obtained, all the vegetables absorbed significant amounts of the metalions. This raises a lot of health concern about the vegetables consumed in most developing countries like Nigeria where vegetables are grown anywhere, without any consideration of the environment.