Assessment of the Heavy Metals’ Levels, Phytochemical Profiles, Mineral and Proximate Compositions of Four Commonly Consumed Vegetables in Lagos State, Nigeria

Abstract

Safety of the environments (land, air and water) including plants and animals inhabiting it is a concern for many ecologists nowadays and this is due to human ecosystems' exploration. Thus, this study aimed at assessing the heavy metals' levels, phytochemical profiles, mineral and proximate compositions of four commonly consumed vegetables in Lagos State. Leaves of Vernonia amygdalina, Telfairia occidentalis, Gnetum africanum and Parquetina nigrescens were obtained in some major markets in Lagos State; the leaves of the vegetables were subjected to laboratory analysis for the determination of phytochemical, mineral, proximate and heavy metals' concentrations using standard procedures. Data obtained were subjected to analysis of variance (ANOVA). Proximate analysis revealed appreciable amount of protein, carbohydrate, fat, moisture and ash contents in the vegetables. The phytochemical profiling revealed the presence of some vital secondary metabolites viz: tannins, phenols, saponins, flavonoids, cardiac glycosides, steroid, phlobatanin, alkaloid and sugar except terpenoids within the four vegetables sampled. However, it was observed that T. occidentalis lack saponins; P. nigrescens contain no tannins and phenols while, G. africanum show no steroids and phlobatannins. Also, the analysis of metals revealed the range of minerals-K (27.51-68.09mg/100g), Mg (25.68-27.60mg/100g), Mn (0.31-1.06mg/100g), Zn (0.45-1.42mg/100g), Fe (2.20-6.65mg/100g), P (1.10-1.19mg/100g) and Na (1.36-2.15mg/100g) and heavy metals-Pb (0.10-0.28mg/100g), Ag (0.04-0.57mg/100g), Cd (.01-0.90mg/100g), Cu (2.95-3.35mg/100g), Cr (0.075-2.60mg/100g), Co (0.45-0.95mg/100g) and Ni (1.16-2.60mg/100g) and all these elements were within or below the World Health Organization's permissible limits for toxicity. Hence, these four vegetables commonly consumed in Lagos are good and toxic free for consumption and continuous check on the consumed vegetables in Lagos to avoid toxicity since it's a mega city with industrialization is recommended.