EFFECTS OF DUMPSITE ENVIRONMENT ON THE PHYTOCHEMICAL AND HEAVY METAL CONTENTS OF SOME EDIBLE PLANT SPECIES

Abstract

Municipal waste which is the most common source of waste contain heavy metals which are eventually leached out from the site into the soil and water. Plants and soil samples from Rinsayo dumpsite, Osogbo, Osun state, Nigeria were analysed to determine their heavy metals (Cd, Fe, Pb, Cu, Ni, Mn, Cr and Zn) concentrations. Five random plant samples growing at the dumpsite were collected: Bitter leaf (Vernonia amygdalina Del.), Tomato (Solanum lycopersicum L.), Neem (Azadirachta indica A. Juss.), Cassava (Manihot esculenta Crantz) and Pawpaw (Carica papaya L.) and soil samples from the dumpsite were retrieved as well. The heavy metal concentration in both plants and soil samples were determined using Atomic Absorption Spectrophotometer (AAS). The concentration of heavy metals in the dumpsite soil samples ranged from 7.21 ± 0.02 mg/kg (Ni) to 107.75 ± 0.02 mg/kg (Fe) while that in the plant samples ranged from 0.27 ± 0.01 mg/kg (Fe) to 26.16 ± 0.01 mg/kg (Cd). The decreasing order of heavy metal concentration in the dumpsite soil samples ranges: Fe > Mn > Pb > Cd > Zn > Cr > Cu > Ni. While that of the selected plants growing at the dumpsite is as follows: Cd > Cr > Cu > Ni > Pb > Zn > Fe > Mn. The susceptibility of heavy metal accumulation in the selected plants is as follows from highest to the least; Tomato (Solanum lycopersicum), Pawpaw (Carica papaya), Cassava (Manihot esculentus), Neem (Azadirachta indica) and Bitter leaf (Vernonia amygdalina) respectively. The phytochemical analysis of the plants shows the presence of alkaloid, flavonoid, terpenoid, saponin, tannin, phenols and cardiac glycosides. Neem leaf have the highest yield of phytochemicals in terpenoid (40.01 ± 0.07 mg/g) while tomato leaf has the lowest yield in steroid (0.00 ±0.00 mg/g). The decreasing order of the contamination factor cut across all the heavy metals studied from moderate to very high contamination. In view of the outcome of this research finding, farmers are strongly advised against cultivating near dumpsites.