Phytoremediation Of ～(134)Cs And Cu Contaminated Soils

Soil pollution by heavy metals and radionuclides has been a problem in our society and the situation is deteriorating with increasing human activities. Phytoremediation, with the advantage of low cost and environmental friendliness, is one of the important techniques in removing inorganic contaminants from soils. Screening of hyperaccumulators, plants that accumulate high levels of heavy metals, is prerequisite for the technique. It is also critical for effective phytoremediation to explore ways to increase the content of contaminants in the hyperaccumulators by means of, for example, promotion of uptake, growth and hence biomass, especially of shoots. The present research was focused on the investigation of capability of plants from Amaranthaceae and Pteridophyte in removing radiocesium 134 and/or copper from soils respectively. Both field and greenhouse studies were carried out in order to characterize the tolerance, uptake, translocation and accumulation of these two inorganic contaminants in the two respective families of plants. Furthermore, we examined the effect of soil amendment and elevated CO₂ concentration on the uptake of ¹³⁴Cs and Cu by plants so as to make phytoremediation more effective. Major results are generalized as follows:1. Six species of plants from the Amaranthaceae — Amaranthus cruentus L., Amaranthus tricolor L., Amanranthns paniculatus L, Celosia argentea L., Gomphrea globasa L. and Gomphrea globosa cv. Alba — previously known to be capable of hyper-accumulating potassium, were grown in nutrient solution for 42 days before treatment with ¹³⁴Cs at 3 different levels of radiaoactivities (2.775×10⁵ Bq/pot, 5.55 × 10⁵ Bq/pot and 1.11 × 10⁶ Bq/pot). Plants were harvested 7 days after treatment and different plant parts analyzed for ¹³⁴Cs specific activities. All six plant species exhibited comparatively high ability in ¹³⁴Cs uptake and accumulation. Most of ¹³⁴Cs were found to accumulate in shoots and the shoot ¹³⁴Cs specific activity was positively correlated with the ¹³⁴Cs activity in nutrient solution. Amaranthus cruentus L., with the highest shoot biomass but a lower activity of ¹³⁴Cs among the six species, resulted in the highest removal rate in terms of total activities of ¹³⁴Cs in shoots. In addition, both Amaranthus tricolor L and Celosia argentea L. displayed high values of Bioconcentration Factor (BF; the ratio of heavy metal content in plant to that in medium) in leaves, therefore they could also be valuable for use in phytoremediation of ¹³⁴Cs- contaminated soils.2. A. tricolor and A. cruentus, which were shown to remove ¹³⁴Cs from solutionefficiently, were sown in soil contaminated artificially with 3 levels of 134Cs activities (5.55 × 10⁵ Bq/pot and 1.11 × 10⁶ Bq/pot and 1.665 × 10⁶ Bq/pot). Plants were harvested 49 days after sowing and analyzed for 134Cs specific activities. In accordance with hydroponics, plants grown in soils with increasing Cs activities showed increasing 134Cs activities in shoots. Experiments were also carried out to determine the effect of 26 chemicals on 134Cs desorption from soil. (NH4)2SO4 was found to have the highest efficiency to enhance the desorption of 134Cs. (NH4)2SO4 application reduced the biomass production of both species and caused a decrease of the total 134Cs removal by A. tricolor shoot but had no significant effect on the total 134Cs removal by A. cruentus shoot, implicating that (NH4)2SO4 might play quite different roles in different plant species with respect to 134Cs removal by shoots.3. Field study revealed that Petridium revolution was one of the predominant plant species grown vigorously on the copper mining spoils in Yunnan province. The soils where P. revolution was growing contained 201-7554 mg kg-1 of Cu, whereas the above ground part of P. revolutum 30⁵67 mg kg-1, and the remaining parts of P. revolutum accumulated 36¹723 mg kg-1 of Cu. The BFs of P. revolutum fronds varied from 0.03².96, and those of the underground part varied from 0.06³.67. The Translocation...