Phytochemical and Heavy Metal Analysis of Gongronema Latifolium, Talinum Triangulare and Amaranthus Hybridus

Heavy metals contamination of soil has continued to increase globally as a result of increase in anthropogenic actions. The phytochemical and heavy metals (Zn, Cu, As, Pb, Cd, Hg) content of three edible plant species grown in southern Nigeria and the health implications were evaluated. The heavy metal concentrations of Gongronema latifolium, Talinum triangulare and Amaranthus hybridus as well as the top soil were determined using Atomic Absorption Spectrophotometer. The consumption of vegetables is a very vital path to food chain by which toxic metals are transferred from the soil to human as well as other animals. Geo-accumulation index and Transfer factor were the parameters used to evaluate the extent of contamination of top soil and exposure by human via the food chain respectively. The results of phytochemical analysis of plants revealed the existence of some bioactive constituents and their corresponding concentrations are presented in increasing order of magnitude: anthocyanin˂ carotenoid ˂ flavonoid ˂ tannin ˂ steroid ˂ alkaloid. The soil analysis for heavy metals were performed and results demonstrated that zinc had the maximum concentration (103.1 – 174.0 mg kg-1) while mercury had the lowest levels (0.01 – 0.20 mg kg-1). The heavy metal concentrations in the soil samples are in the order; Zn ˃ Pb ˃ Cu ˃ Cd ˃ Ni ˃ As ˃ Hg. Geo-accumulation index analysis revealed that Pb and Cd were implicated in overall contamination of the soil samples but the control soil remained uncontaminated. The concentrations of heavy metal in the plant samples varied greatly with Zn having the maximum values (10.80 – 21.10 mg kg -1) whereas arsenic had the minimum concentration (0.01 – 0.03 mg kg -1). The heavy metal concentration in the plant samples are in the order; Zn ˃ Cu ˃ Pb ˃ Cd ˃ Ni ˃ Hg ˃ As. The concentrations of heavy metals in the selected plant samples evaluated were within the recommended standard limits apart for lead which was higher than the recommended value. Results revealed moderately high transfer factors and capacity of the vegetables investigated to accumulate copper, mercury and arsenic.