本研究以現有文獻中所知對重金屬具有高萃取潛力且擁有高生物質量產率及高蓄積量之芥菜（Brassica juncea），在不同培育期程條件下，對土壤污染管制標準值之重金屬(鉛、銅及鎘)污染土壤，進行植物萃取試驗。另外，也添加螯合劑EDTA來評估是否能增加上述植物對重金屬之萃取量。此外，本研究也以逐步萃取法(sequential extraction procedure, SEP)分析並探討單一和複合重金屬在土壤中，經芥菜萃取後土壤中重金屬各鍵結型態(可交換態、與碳酸鹽鍵結態、與錳氧化物鍵結態、與鐵氧化物鍵結態、有機物鍵結態及殘餘態)之轉移及變化之情形。
本研究結果顯示，在植物萃取試驗中，芥菜對土壤中重金屬之吸收量，隨著芥菜的培育期程增加而增加，亦隨著EDTA添加量增加而增加，但因土壤中各重金屬不同，而芥菜之吸收量有所差異。芥菜對土壤中重金屬之吸收量，大部份與土壤中可交換態呈正相關，且相關性非常高。
當芥菜的培育期程增加時，芥菜之生物質量隨之增加，但不成相對比例之增加；芥菜的培育期程大於四週以上，芥菜之生物質量相當大，而對於重金屬的耐受程度也相對提高。 EDTA添加量為0.5g/Kg-soil於單一和複合重金屬污染土壤中時，對於土壤孔隙水中重金屬含量明顯增加，且隨著EDTA添加量增加而增加；然而鉛污染土壤則除外，EDTA添加量需達1.0 g/Kg-soil時，於土壤孔隙水中鉛含量才有顯著的增加。土壤中鉛、銅和鎘含量相近且三者同時存在時，芥菜對複合重金屬污染土壤進行萃取，芥菜中各重金屬之含量的多寡如下:銅含量＞鎘含量＞鉛含量。
隨著EDTA添加量增加，土壤中易吸附性與易交換性重金屬也隨之增加，而其它鍵結型態之含量則逐漸減少，顯示EDTA易將土壤中重金屬釋出至孔隙水或形成易釋出之易交換性型態。此轉移現象非常有利於芥菜對土壤中鉛、銅及鎘之萃取吸收。
在土壤中重金屬移除量相同情形下，提高芥菜的培育期程，可減少EDTA添加量，可能達到相同甚至更好的移除效果，且可節省螯合劑之成本。 The aim of this study focuses on the enhanced uptake of Pb, Cu and Cd in to the soil-grown Brassica juncea with EDTA from polluted soil. In addition, sequential extraction procedure was used to find the variation of binding fractions of metals in contaminated soils spiked with single and multiple heavy metals before and after phytoextraction.
Results indicate that the uptake of heavy metals by B. juncea increased with the increase of both planted time and dosage of EDTA. The accumulation of heavy metals in B. juncea significantly correlated with the content of exchangeable fraction of heavy metals in soil.
Biomass of B. juncea increased with the increase of planted time. When planted time was greater than four weeks, the tolerance capacity of B. juncea against the poisoning of heavy metals gradually increased. Except for Pb, other heavy metals released into pore water increased with the increase of dosage of EDTA when the dosage of EDTA was greater than 0.5 g/Kg-soil. The order of accumulation amount in B. juncea from the soil spiked with multiple heavy metals was as follows: Cu, Cd, Pb.
It can be noted that the content of exchangeable fraction of heavy metals increased with the elapsed time of phytoextraction whereas other binding fractions decreased. This variation of binding fractions indicates that the adding of EDTA was helpful for the release of heavy metals into pore water or to form the easily releasing binding fraction.
Increasing planted time could reach high phytoextraction effect which could also be found by adding less amount of EDTA.
