||Heavy metals are one of the most important environmental pollutants. In recent years, many low cost stretages of bioremediation for contaminated sites by heavy metals, such as fungi, bacteria and plants have been investigated for their biosorption capacity towards heavy metals. The uses of plant species for remediate contaminated sites by heavy metals are so called phytoremediation. The purpose of the first parts of this study are to (1) evaluate bioavailability of Cadmium (Cd) in contaminated soil and phytoremediation potential by three plant species, Vetiveria zizanioides, Pteris multifida, and Alternanthera philoxeroides (Mart.), and (2) realized the influence of photosynthetic bacteria (PSB) on the uptake of Cd in the three species. The results showed that the Alternanthera philoxeroides (Mart.) could accumulate the highest concentration of Cd among the three species, in which the Cd concentration of plant tissue increased with the concentration in soil. The highest concentration of Cd (164.9 mg kg-1) was found in the below-ground parts of Alternanthera philoxeroides (Mart.) at the 8th week of culturing period. However, the species of Vetiveria zizanioides could accumulate the largest total Cd, up to 547.5 μg/ plant, which thus extracted the greatest amounts of Cd from the soil. Therefore, in the first part of this study the species of Vetiveria zizanioides was concluded to be the best accumulator among the three plant species. In addition, the concentration of Cd in the species of Pteris multifida was found significantly increased after PSB was added into the soil, but the plants died later due to Cd stress. The experimental results also showed that PSB seemed to be not suitable for each species used in this study to accumulate Cd from Cd-contaminated soil.|
In the second part of this research, both pot and field experiments were conducted to (1) evaluate bioavailability of copper (Cu), lead (Pb) and zinc (Zn) in contaminated soil and phytoremediation potential by domesticated plants, Bidens pilosa and Passiflora foetida inoculated with arbuscular mycorrhizal (AM) fungi, and to (2) compare the results of pot and field experiments. The plant species of Bidens pilosa inoculated with AM fungi had significantly higher Cu concentrations in the shoots and roots than non-inoculated plants. The plant species of Passiflora foetida inoculated with AM fungi also had significantly higher Cu and Pb concentrations in the roots than non-inoculated plants. When we found that the root dry weight of Passiflora foetida inoculated with AM fungi dramatically increased, the concentrations of Cu, Pb and Zn in the root of the plant species increased by 9-14 times, comparing with the plants without inoculation of AM fungi. The AM fungi have potential either to promot plant growth or to increase heavy metal accumulation. The values of element translocation proportion from root to shoot was Zn>Cu>Pb for the plant species in both pot and field experiments. For both experiments, the results of pot test and field test were significantly different. The concentrations of pot tests were found higher than the field tests, and some values of pot tests were even found significantly greater than those in the field tests.
In the third part of this study, the field experiments were conducted to test the feasibility of using domesticated vegetations for phytoremediation of the contaminated farmland. The objectives of this study were (1) to acquire information about the ability of five plant species growing wild in the polluted area to accumulate Cu, Pb and Zn, (2) to investigate the season effects on phytoremediaton of five plant species and evaluate the total uptake of heavy metal, and (3) to run both pot tests and a field trial of phytotremediation to compare their differences. The experimental results showed that three maximum toxic elements in a pot were 3020 mg kg-1 Pb, 232 mg kg-1 Cu and 1012 mg kg-1 Zn respectively. The Cu concentrations of the five plant species collected from the polluted plots ranged from 0.7 to 17.43 mg kg-1. The range of variation of Pb in plant tissues was measured varied from 2.29 to 81.65 mg kg−1, while a wide range of Zn concentrations was found from 12.84 to 192.85 mg kg-1 among the plants collected at the contaminated plots. In comparison to winter season, the Zn concentrations in Broussonetia papyrifera, Passiflora foetida and Saccharum sinensis collected in summer season was significantly higher. The higher Cu concentrations were obtained in both plant species of Bidens pilosa and Mimosa diplotricha in summer season. However, Pb concentrations in Saccharum sinensis collected in winter were significantly higher than those in the same plant species collected in summer. Bidens pilosa was also found having the highest total amount of Cu and Zn. The highest total amount of Pb was found in Mimosa diplotricha. For both plant species, both of the pot and field tests were different.