Advanced Utilization of Rhizosphere Functions for Phytoremediation of Heavy Metal Contaminated Soils.

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To develop effective and environmentally clean phytoremediation technologies, basic researches were conducted concerning about 1)biodegradable chelate-assisted phytoremediation, 2)survey of metal accumulating plants and the mechanism of their metal accumulation, and 3)utilization of soil amendments for reducing As movement from rhizosphere to crop shoots. The main results were listed below :1.Addition of biodegradable chelating agents (S,S-ethylenediamine-N,N'-disuccinic acid, EDDS) to Cu contaminated soils significantly increased Cu uptake by brown mustard, compared with the plants grown without EDDS. Environmental risks, such as leaching of Cu and Cu-chelate and the impact on the soil microorganisms were smaller than the case of EDTA addition. However, biodegradable chelate-assisted phytoremediation should be carried out under isolated condition because complete reduction of leaching of Cu and chelating agents during plant cultivation was difficult.2.Soil and plant survey around the … More closed silver mine at Ikuno-cho, Hyogo Prefecture, Japan revealed that Arabis flagellosa is a new Zn and Cd hyperaccumulating plant. It was also found that well-known heavy metal accumulating fern, Athyrium yokoscense can accumulate As and heavy metals, simultaneously. More than 80 and 55% of Zn and Cd in the leaves of Arabis flagellosa were soluble forms, respectively. It was suggested that malic acid contributed to detoxify high concentrations of Zn in the leaves. When the plant was treated with high Cd, increase of SH compounds such as phytochelatins in the roots were confirmed, which suggested the detoxification of Cd by these compounds.3.As toxicity symptoms and As uptake of sunflower grown on As contaminated soils were significantly reduced by the application of arbuscular mycorrhizal inoculum, compared with the plants supplied with P fertilizers. On the other hand, application of amorphous Fe hydroxides to paddy soil significantly reduced As uptake by rice plants irrigated with As contaminated water. Less