Abstract

Levels of some heavy metals (As, Cd, Cu, Fe, Mn, Pb and Zn) were investigated in edible portions of Amaranthus caudatus and Lactuca sativa grown in Maiduguri. These heavy metals were similarly investigated in the soils in which the vegetables were grown. The metals were analyzed using atomic absorption spectrophotometer. The levels of the heavy metals in the vegetable and soil samples obtained from the sample areas were higher than their corresponding levels in the control samples. The results ranged from 0.26 ± 0.02 μgg^-1 Cd to 10.28 ± 0.61 μgg^-1 Fe in A. caudatus and 0.34 ± 0.06 μgg^-1 Cd to 40.11 ± 0.16 μgg^-1 Fe in L. sativa. In the soils, the results ranged from 0.56 ± 0.05 μgg^-1 Cd to 60.20 ± 0.70 μgg^-1 Fe. The order of the metals contamination in the soils and vegetables was: Fe > Mn > Pb > Zn > As > Cu > Cd. The data were analyzed with t-test and ANOVA. There were significant differences (p < 0.05) between the levels of the heavy metals in the vegetables obtained from the sample sites and those of the controls. The elevated levels of the metals in the soils and vegetables could be attributed to excessive usage of fertilizers and other agro-chemicals, as well as the use of waste water in irrigating the soils and of course, the environmental factors in the areas. The results were however lower than the published threshold values considered toxic for mature plant tissue, except L. sativa in which the Fe level was higher. Consumption of these vegetables as food may not pose possible health hazards to humans at the time of the study.

Key words: Amaranthus caudatus, Lactuca sativa, soil, heavy metals, wastewater, fertilizers.