Assessment of some Heavy Metals on Lettuce (Lactuca sativa L.) Grown along Badagry Expressway, Lagos, Nigeria

Vegetables grown at environmentally contaminated sites in Lagos could take up and accumulate metals at concentrations that are toxic to human health. This study was conducted to analyze the heavy metal in a selected vegetable (Garden Lettuce) in Lagos, Nigeria. Recently matured plant samples of Garden Lettuce (Lactuca sativa L.) from roadside farm, Badagry Expressway, Lagos, Nigeria were assessed using Atomic Absorption Spectrophotometer and underwent pressurized digestion with HCL, H₂SO₄ and HNO₃ to determine the heavy metals. Three composite samples on each bed at each distance were used. The distances were 5m, 10m and 15m.The concentration of heavy metals which include, Cu, Zn, Fe, Cr, Cd, and Pb, were determined using Analyst Perkin-Elmer 300 Atomic Absorption Spectroscopy (AAS). The mean concentration for each heavy metal in the samples were obtained and compared with the permissible levels set by the FAO and WHO. The results of this analysis revealed that Fe showed the highest concentrations in the stem (14.681±11.621mg/kg), second to Zn in the leaf (0.062±0.047mg/kg) while Cr shows the lowest levels (0.001±0.000mg/kg) in the whole plant organ .When compared with standards, heavy metal levels were found to be within safe limit.
Metal uptake differences by parts of the plant (Lactuca sativa L.) is attributed to plant differences in tolerance to heavy metals. The intake of all the six metals constitutes less than 100% of the TMDI (Theoretical Maximum Daily Intake) at present and hence, health risk is minimal. But with the increase in vegetable consumption by man, the situation could worsen in the future.