PHYSICOCHEMICAL PROPERTIES AND HEAVY METALS IN AGRICULTURAL SOIL, WATER AND LEAFY VEGETABLE WITHIN AKURE METROPOLIS, NIGERIA

Abstract

The bioavailability and bio-enrichment of some heavy metals (Ni, Pb, Cd, Cu and Se) were investigated in African Spinach (Amaranthus hybridus) vegetable, cultivated soil, and irrigation water samples from seven vegetable farmsteads in sub-urban Akure, Nigeria. The sequential extractions were also performed on the metal in the cultivated soil. The results showed that the levels of metals in soil, water used for irrigation and plant samples were within range of the regulatory standards. The sequential extraction study showed that the residual fraction was the dominant proportion for Pb ( 6 - 90 %), Ni (51 - 61%) and Cd (38 - 49 %) in soils, Cu was found mainly in the organic fraction (45 %) whereas Se was found mainly in the organic and residual fractions (40 - 42 % of the total Se). The translocation coefficients of metals in leaf/root systems revealed that Cu and Ni were mainly accumulated in roots, whereas Pb and Cd were mainly in the leaves of the vegetable. The enrichment coefficients of metals in leaf/root systems indicated that Ni and Cu had the strongest capacity of accumulation from soils to vegetables among all the five elements under study. A positive correlation (p≤0.01) was found to exist between the metals in the soil and the organic matter; cation exchange capacity of the soil and organic matter; and Cu with its enrichment coefficient in the vegetable sample. However, the metals in the soil negatively correlated (p≤0.05) with soil pH and their enrichment coefficients in the vegetable sample. The health risk assessment was found to be less than one implying no health risk hazard to the consumers of the vegetable sample.