An Assessment of the Levels of Heavy Metals, Nitrates and Nitrites in Three Leafy Vegetables from Selected Rural and Urban Markets in Kwara State, Nigeria

Abstract

The concentration of some heavy metals, nitrates and nitrites in leafy vegetables sold in selected markets in Ilorin and its environment were investigated. Three leafy vegetables (Amaranthus hybridus, Celosia argentea and Corchorus olitorious) were used in this study. The concentration of selected heavy metals (cadmium, lead, copper, zinc and arsenic), nitrates and nitrites in the leaves were analyzed using standard methods and compared with the permissible limits recommended by the Food and Agricultural Organization (FAO)/WHO Expert Committee on food additives. The concentration of cadmium was significantly higher than the permissible limits (0.20 mg/kg) for all the vegetable types across locations. However, the concentrations of lead, copper, zinc and arsenic which ranged from 0.06 to 0.13 mg/kg, 0.09 to 0.18 mg/kg, 0.05 to 0.16 mg/kg and 0.08 to 0.17 mg/kg were lower than the permissible limits for all the vegetables and in all locations. The concentration of nitrates in the leafy vegetables ranged from 0.09 to 0.37 mg/kg and was within the safe limit (< 3.70 mg/kg) as recommended by (FAO)/WHO Expert Committee on food additives while nitrite was not detected. In conclusion, monitoring of vegetables for toxic heavy metals is essential for food safety in Nigeria. Although lead and arsenic were below safe limits they have the tendency to accumulate to toxic level in consumers. There is the need to increase the essential micronutrient content of soils around the study area given the low concentration of Cu and Zn in the leafy vegetables.

Keywords: Food safety, toxicity, micronutrients and concentrations.