PHYTOACCUMULATION OF HEAVY METALS IN AN OIL-SPIKED SOIL BY Vernonia amygdalina AFTER EXPOSURE TO SODIUM AZIDE SOLUTIONS

Abstract

This study investigated the effects of sodium azide pre-treatment of Vernonia amygdalina stem cuttings on the bioaccumulation of heavy metals in a waste engine oil-contaminated soil. Top soil was collected and sun-dried to constant weight. Soil was then mixed thoroughly with waste engine oil (WEO) on weight basis, to obtain a constant 4% w/w concentration. Soils were then left to attenuate for 1 week (WAP). Sodium azide solution was prepared to obtain concentrations of 0.125, 2.50 and 5.00 % w/v respectively. The control solution was distilled water. At 1 WAP, equally-cut stem cuttings of Vernonia amygdalina that had originally been entirely immersed in sodium azide solutions for one hour were transferred into the oil-polluted soil. Results showed that at 150 days after sowing, pretreatment of stem cuttings with azide had significant impact on plant growth development with respect to height (58.0 – 78.4 cm) and chlorophyll index, which ranged from 16.8 – 24.3 CCI in the oil polluted soil, compared to 17.8 CCI in the control. Although Cr, V, Mn and Cu were never detected in the plant leaves and stems, Pb and Ni were both detected in treated plants. The 5% NaN3-treated plant accumulated 13.80 mg/kg of Pb and 0.32 mg/kg of Ni in the leaves, as well as 13.84 mg/kg of Pb and 3.98 mg/kg of Ni in the stems. Upon pretreatment with azide, V. amygdalina significantly bioaccumulated Ni, compared to other metals.