EFFECTS OF CADMIUM, CHELATES AND PLANT GROWTH STAGE ON THE PHYTOEXTRACTION OF CADMIUM-CONTAMINATED SOIL BY MORNING GLORY (Ipomoea lacunosa)

Abstract: Phytoextraction is gaining acceptance as a cost-effective and environmentally friendly phytoremediation strategy for reducing toxic metal levels from contaminated soils. Cognizant of the potential of this phytoremediation technique as an alternative to expensive engineering-based remediation technologies, this experiment was conducted to (a) evaluate the suitability of morning glory as phytoextraction species and (b) to determine whether the addition of synthetic chelates, ethylene glycol bis (betaaminoethyl ether)-N,N,N,N-tetraacetate (EGTA) and acetic acid (HAc), can further enhance the shoot uptake of cadmium (Cd). Seeds were planted in plastic tubes containing top soil and peat (2:1, v:v) spiked with various levels (0, 250, 500 mg Cd/kg dry soil) of cadmium nitrate. At 6, 8, and 10 weeks after emergence, aqueous solutions of EGTA and HAc were applied to the root zone, and plants were harvested at 0, 5, and 7 days after chelate addition to coincide with the duration of maximum Cd availability as determined from a corollary chelate-induced metal solubility study. Results revealed that morning glory was relatively tolerant to moderate levels of Cd as shown by non-significant differences in root and shoot biomass among treatments. Root Cd concentration increased with increasing levels of soil-applied Cd. Further increases in root Cd concentrations were attributed to chelate amendments. Translocation index, which is a measure of the partitioning of the metal to the shoots, was significantly enhanced with chelate addition. Overall, this study demonstrated that depending on the nature and type of Cd-contaminated soil being remediated, the efficacy of phytoextraction can be further improved through the addition of synthetic chelates especially at a growth stage when the plants had attained maximum biomass.