DOI: 10.14457/tu.the.2015.32
title: PHYTOEXTRACTION OF CADMIUM FROM CONTAMINATED SOIL

description: AbstractPHYTOEXTRACTION OF CADMIUM FROM FROM  CONTAMINATED SOILbyNonglak Rungruang Bachelor of Science (Public Health), Mahidol University, 1995.Master of Science (Environmental Technology and Management), Asian Institute of Technology, 1998.Phytoremediation is one of the green alternative and cost effective approaches used to clean up large areas of contaminated soil.  Contamination of agricultural soil by toxic heavy metals is a major environmental problem. Among these, cadmium (Cd) is one of the highly toxic heavy metals and causes chronic and acute effects on health and the environment. Cadmium in soil can accumulate in plants and can be transferred to animals through the food chain. In this study, in the first investigation, the cadmium hyperaccumulator potential of four species; marigold (Tagetes erecta L.), cosmos (Cosmos sulphureus), sunflower (Helianthus annuus) and Guinea grass (Panicum maximum) was investigated in pot culture experiments using artificially Cd spiked soil by spiking Cd solution onto heavy acid Rangsit soil. Experiments in triplicate were conducted in greenhouse and the concentration of cadmium was varied from 50 to 400 mg/kg of soil. Samples of different parts of plants after reaching flowering stage were harvested for cadmium analysis. Plant growth; flower diameter, height, leaf and stem size; were observed throughout the study period. Based on shoot Cd, translocation factor (TF), bioconcentration factor (BCF) and total uptake, marigold showed a greater ability to accumulate Cd in its biomass. The TF and BCF values of Guinea grass were lowest compared to those of other species, due to the higher biomass produced the total uptake at higher Cd concentration (200 and 400 mg/kg) was higher compared to other plants. Thus, marigold and Guinea grass were used for further experiments.Marigold and Guinea grass selected from the first experiment were used in the second experiment to investigate the effects of Zn (Cd:Zn of 1:0, 1:10, 1:30 and 1:50), pH (5.0, 6.3, 7.0, 7.5), Cd:EDTA treatments (1:0, 1:0.5 and 1:1) on Cd uptake; under various Cd concentrations of 50, 100 and 200 mg/kg. Based on the TF, BCF, total uptake per pot, and total biomass, marigold showed higher potential to uptake Cd from the soil compared to Guinea grass. Moreover, it was noticed that marigold had a greater ability to accumulate Cd in the aboveground parts and met one of the criteria for Cd hyperaccumulation (100 mg/kg dry weight in shoot). The translocation factor and bioaccumulation factor were greater than one. The present study demonstrated that the maximum shoot Cd, total Cd in whole plant tissues, TF and BCF of marigold were highest at the pH around 5. The maximum shoot Cd, total Cd in whole plant, BCF were obtained at 1:10 and 1:0 of Cd:Zn at Cd of 50 and 100 mg/kg, respectively and then decreased as Zn concentration application was increased to 1:30-1:50 of Cd:Zn treatment. At higher Cd concentration (100 mg/kg), the addition of Zn to soil did not promote Cd uptake by marigold. For Guinea grass, the maximum shoot Cd, Cd in whole plant, total uptake and BCF were achieved at the pH around 5.0. Shoot and root Cd, Cd in whole plant of Guinea grass increased with increasing Cd concentration in soil. EDTA application in soil promoted the transfer of Cd from roots to shoots in marigold but did not show any impact in Guinea grass. The highest Cd uptake was achieved at Cd:EDTA treatment of 100:50 mg/kg for both marigold and Guinea grass, but at the treatment of 50:25 mg/kg, only maximum Cd uptake was obtained in Guinea grass. Speciation of Cd in soil samples used for growing marigold and Guinea grass revealed the same trend that the highest fraction of Cd in soil was exchangeable fraction (F1) (72.3-83.03% in marigold and 74.54-82.01% in Guinea grass) and the lowest portion  was the  residual fraction (F5) (1.22-3.09% in marigold and 1.11-3.68% in Guinea grass). The Cd: EDTA of 50:25 and 100:100 mg/kg provided more bioavailable Cd fraction in the soil solution. However, the influence of the application of EDTA to the soil on the stimulation of Cd transfer from roots to shoots was only pronounced in marigold, but it did not show any effects in Guinea grass. The correlation analysis between Cd in whole plant tissues of four species (marigold, cosmos, sunflower and Guinea grass) and Cd in soil was highly positive, showing the positive linear relationship between Cd accumulation in whole plant tissues and Cd applied in the soil. The correlation between Shoot Cd of marigold and soil pH was negative, indicating negative linear relationship. Shoot Cd of marigold decreased with increasing soil pH.Overall, marigold possesses a greater ability to accumulate Cd in plant tissues but less biomass production could lower the total uptake. In both marigold and Guinea grass, Cd treatment of 100 mg/kg provided higher uptake than that at Cd 50 mg/kg, under all pH treatments. At Cd 50 and 100 mg/kg, the pH 5.0 provided maximum Cd uptake for both species. To increase phytoremediation efficiency of Cd removal from contaminated site, the proper selection of cultivars and adjustment of its cultivation practice such as repeating growing the same crop on the soil as well as substantial soil amendment to stimulate Cd solubility and enhance plant uptake (pH around 5.0-5.5 is preferable as Cd become more solubilized) are recommended to improve the efficiency of this green technology.