生物易降解性螯合劑對促進五彩石竹吸收土壤中鎘之評估

Abstract

植生萃取(phytoextraction)可施用螯合劑以增強地上部對重金屬的吸收能力，本研究以一鎘污染坋質黏土，鎘濃度分別為0.42, 8.98及20.2 mg/kg，以代號Cd 0.5, Cd 10, Cd 20稱之，利用盆栽試驗種植五彩石竹(Dianthus chinensis Linn.)50天，並分四次施用經計算後足量之1 mmol/kg的四種生物易降解性螯合劑乙二胺二琥珀酸(Ethylenediamine-N,N'-disuccinic acid, EDDS)、羥基亞氨基二琥珀酸( 3-hydroxy-2,2'-Iminodisuccinate, HIDS)、檸檬酸(Citric acid, CA)、琥珀酸(Succinic acid, SA)，以評估這些螯合劑對土壤溶液鎘濃度的影響、植株生長狀況與植體鎘含量變化。結果顯示，在Cd 0.5條件下，土壤溶液中鎘濃度不隨著施用天數與施用螯合劑種類而有顯著差異，但在Cd 10條件下，以EDDS處理組在收穫前土壤溶液鎘濃度最高且可達367 μg/L，其次依序為HIDS, CA, SA，但各處理間未達顯著差異(P≦0.05)，不過都明顯高於控制組。在Cd 20條件下，四種螯合劑處理的土壤溶液鎘濃度均在1000 μg/L以上，不過各處理間未達顯著差異，但可明顯高於控制組。五彩石竹產量、株高、葉綠素含量、脯胺酸含量及根部triphenyltetrazolium chloride(TTC)還原性等，各螯合劑處理間均無顯著差異，但由地上部鎘累積濃度顯示，Cd 10條件下，以EDDS在地上部累積的鎘濃度最高52.8 mg/kg，其次依序為CA、SA與HIDS，而控制組僅 31.7 mg/kg。在Cd 20條件下，仍以EDDS所累積地上部鎘濃度最高，其次為CA, SA與HIDS。因此EDDS是四種螯合劑增強效果最好的，可增加土壤鎘有效性，不會影響植物生長狀況，又可增進五彩石竹植生萃取。

Phytoextraction is a technique by harvesting the plants which can remove large amounts of heavy metals from comtaiminated site. Considering that metal uptake is related to the availability of metals in soils, addition of natural and synthetic chelators has been used to increase uptake and translocation of metals and to achieve high removal rates. Rainbow pink (Dianthus chinensis Linn.) has been proved to accumlate relatively high amounts of Cadmium. In this study, cadmium accumulation in Dianthus chinensis treated with different biodegradable chelators cultivated in Cd contaminated soils for 50 days were studied. The pot experiments were conducted in the phytotron of National Taiwan University. The studied soil texture was silt clay loam and the three levels of Cd concentration are 0.42(Cd 0.5), 8.98(Cd 10) and 20.2 (Cd 20) mg/kg. The objectives of this study were to: (1) investigate the effect of the application of the biodegradable chelators N,N'-disuccinic acid (EDDS), 3-Hydroxy-2,2'-Iminodisuccinate (HIDS), citric acid (CA) and succinic acid (SA) on growth and physiology of Cd-stressd Dianthus chinensis, (2) assess the effect of the chelators on the solubility of cadmium in the Cd-contaminated soils, and (3) explore the potential of EDDS, HIDS, CA and SA for ehnanced phytoextraction of Cd-contaminated soils. The results showed that the soil solution under the Cd 0.5 condition had no significant difference between time and treatments. Under Cd 10 condition, the Cd concentration was the highest in the EDDS treatment and reached 367 μg/L, followed by HIDS, CA, SA, but there was no significant difference between the treatments (P≦0.05). However, all chelator treatments were significantly higher than control. Under Cd 20 condition, Cd concentration of all chelating agents exceeded 1000 μg/L, but there was no significantly difference between chelators in spite all chelator treatments were significantly higher than control. Application of biodegradable chelators had no significant effect on growth situation, biomass, chlorophyll, proline content, and TTC reactivity in roots. There was no significantly difference between treatments. The maximum Cd concentration in the shoot was 52.8 mg/kg, followed by CA, SA and HIDS, while the control was only 31.7 mg/kg. Under Cd 20 condition, Cd concentration of EDDS was the highest, followed by CA, SA and HIDS. Application of biodegradable chelators has significant effect on Cd concertation in soil solution and Cd accumulation in plant. The results showed adding biodegradable chelators can be used for promoting phytoextraction and the effect of EDDS is the best.