Widespread contamination of cultivated lands with heavy metals increase human exposure to contaminated agricultural products. The study investigated soil levels and transfer of Cu, Pb and Cd into leaves and barks of different citrus species in 35- and 11-year old orchards in north-central region of Nigeria. Heavy metals concentrations in soils were below permissible limits but greater than background concentrations (Cu = 2.27 mg kg-1, Pb = 0.25 mg kg-1 and Cd = 3.9 mg kg-1). Geo-accumulation index (Igeo) indicated that the 35-year orchard (orchard I) soil was uncontaminated with Cu (Cu-Igeo = -0.43), uncontaminated to moderately contaminated with Pb (Pb-Igeo < 0.39) and moderately contaminated with Cd (Cd-Igeo = 1.65). The 11-year old orchard (orchard II) soil was uncontaminated to moderately contaminated (Igeo for Cu, Pb and Cd was ≤ 1). Bioavailability of the heavy metals soil of orchards I and II were ≥ 30%. Levels of Cd and Pb in bark and leaf tissues were above the maximum permissible limits whereas Cu concentration was within the recommended nutritional status (10 - 50 mg kg-1) for fruit trees. Soil-to-tissue transfer (bioaccumulation) of all heavy metals into the citrus species was ≥ 1.0 and higher in orchard II. High concentration of heavy metals in the leaves and barks of the different citrus species is related to their high bioaccumulation factors despite the relatively low soil concentration of heavy metals in the orchards.

bioavailability, citrus, metal pollution, orchard, heavy metals

Published by University of Zagreb, Faculty of Agriculture, Zagreb, CROATIA
Sponsored by Ministry Science and Education of the Republic of Croatia