Cadmium, lead and mercury in fresh and boiled leafy vegetables grown in Lagos, Nigeria.

Vegetables, eaten fresh or boiled, are an important diet relished in many local Nigerian cuisines and delicacies. Increasing their production has therefore become a prime focus of governments in Nigeria. In the process of production, metals capable of impairing the health of consumers are inadvertently picked up. Studies were therefore conducted to determine the presence of cadmium (Cd), lead (Pb) and mercury (Hg) in fresh and boiled leafy vegetables grown in farms close (proximal) to highways (PS) and those distant from highways (DS). Composite samples of fresh lettuce (Lactuca sativa), fresh Amaranthus (Amaranthus speciosa), boiled A. speciosa, soil, irrigation water, and manure from farms located at the two sites were analyzed by Atomic Absorption Spectrophotometry (AAS). The results show that the fresh vegetables grown on sites close to highways (PS) had higher levels of Cd and Pb (0.313 microg g(-1), 16.933 microg g(-1) for Cd and Pb respectively in fresh Amaranthus, and 0.877 microg g(-1), 16.833 microg g(-1) for Cd and Pb respectively in Raw Lettuce) than those from DS farms (0.20 microg g(-1), 8.33 microg g(-1) for Cd and Pb respectively in fresh Amaranthus and 0.266 microg g(-1), 8.00 microg g(-1) for Cd and Pb respectively in Raw Lettuce). The irrigation water at the PS farms contained more Pb but similar levels of Cd and Hg. Soil from the PS was slightly more acidic (pH = 6.32 + 0.08) than those from the DS (pH = 6.49 + 0.02). Soils of PS farms gave very high Pb levels (4.13 microg g(-1)). Boiling had an effect on the levels of Cd and Pb but not Hg in Amaranthus, irrespective of the site of production. Cadmium (Cd) increased from 0.2 microg g(-1) to 1.036 microg g(-1) before and after boiling respectively in DS samples, while it increased from 0.3131 microg g(-1) to 1.037 microg g(-1) in samples from PS farms before and after boiling respectively. The level followed similar trend. Pb increased from 8.33 microg g(-1) to 5.667 microg g(-1) before and after boiling respectively in samples from DS whereas it decreased from 16.933 microg g(-1) to 14.20 microg g(-1) before and after boiling respectively in samples from the PS.