三種印度芥菜對銅鋅鎘鉛污染土壤的生長反應及重金屬累積能力

Abstract

傳統的清除技術一般花費極大，而且通常會對污染區的土壤性質造成傷害，因此最近幾年以植物為主的土壤復育技術(植生復育)逐漸受到重視。其中植生萃取為利用植物對於重金屬的高累積能力，移除土壤中的重金屬，可免於傳統方法的大範圍開挖、昂貴處理費和表土大量損失。植生萃取的成功，與適當的植物產量和植物地上部的重金屬累積能力有關，此處適當的植物是指具有大生質量，可以累積高濃度重金屬。目前世界上使用最多的高累積性植物多為十字花科植物。此類植物除了可忍耐與累積高濃度的重金屬，並且還有極高的生質量。本研究所使用的十字花科植物為印度芥菜。但世界上印度芥菜的品種繁多，各品種之間的吸收能力與生長情形並不清楚。因此本研究目的為：比較三種不同地區(分別為印度、阿富汗、巴基斯坦)的印度芥菜對於銅、鋅、鎘、鉛污染土壤的生長反應與累積能力。 本研究試驗地點在台灣大學人工氣候室溫室進行，控制印度芥菜生長的溫度與溼度。種植期間從2004年11月到2005年4月。污染土壤經孵育後重金屬濃度分別為銅200、400 mg kg-1，鋅200、400 mg kg-1，鎘25、50 mg kg-1，鉛500、1000 mg kg-1。將三種不同地區(分別為印度、阿富汗、巴基斯坦)的印度芥菜種植於人為污染土壤中。利用重量法及添加去離子水控制盆栽水分含量為WHC的60%，於生長的第0、7、14、21、28、35天收集土壤溶液。生長35天後收穫植體，利用H2SO4/H2O2法將植體分解，以感應耦合電漿光學發射光譜儀(ICP/AES)分析植體中銅、鋅、鎘、鉛濃度。土壤於盆栽試驗結束後採集，並分別以0.05M EDTA (pH 7.0)、0.005M DTPA (pH 5.3)及王水法加以萃取分析，利用原子吸收光譜儀(AAS)分析萃取液中重金屬銅、鋅、鎘、鉛濃度。 研究結果顯示，三個不同地區印度芥菜對污染土壤中銅與鋅的忍受濃度分別低於200 mg kg-1與100 mg kg-1。對於土壤中鉛的忍受性，皆可生長於1000 mg kg-1鉛污染土壤，植體中鉛濃度最高為200 mg kg-1，並非鉛的超級累積植物。土壤中鎘的忍耐濃度可達25 mg kg-1，植體中鎘的濃度可以達到200 mg kg-1，為鎘的超級累積植物。印度與巴基斯坦品種之生質量明顯高於阿富汗品種(p<0.05)。植體中的鎘濃度比較，三個地區的印度芥菜並沒有明顯不同。植體中鉛濃度，以阿富汗品種明顯高於印度與巴基斯坦 (p<0.05)。添加EDTA後七天收穫植體，印度芥菜鎘含量由200 mg kg-1增加到330 mg kg-1，對鎘的總移除量由97μg 盆-1增加到157μg 盆-1。添加EDTA對印度芥菜植體中鉛濃度有顯著影響，三個不同地區印度芥菜中鉛的濃度由200 mg kg-1增加為700 mg kg-1，土壤鉛的總移除量由38μg 盆-1增加為250μg 盆-1。整體而言，三種印度芥菜對受重金屬污染土壤之植生萃取能力並沒有明顯的差別。而添加EDTA可顯著增加印度芥菜對於土壤重金屬的移除能力。

Conventional cleanup technology is generally too costly, and often harmful to desirable soil properties (i.e., texture, organic matter) for the restoration of contaminated sites. More recently, increasing attention has been given to the development of a plant-based technology (phytoremediation) to remediate heavy metal contaminated soils without extensive excavation, disposal costs, and loss of topsoil associated with traditional remediation practices.The success of a phytoremediation process is dependent on adequate plant yield and high metal concentrations in plant shoots. The largest numbers of hyperaccumulating species in the world belong to Brassicaceae. The optimum plant for phytoextraction would be able to both tolerate and accumulate high levels of heavy metals and also grow with a high biomass yield. But there are many different species of Indian mustard in the world, and the growth and uptake of those Indian mustard are not clear. Therefore, the object of this study is to compare the growth and heavy metal accumulation of three Indian mustard (Brassica juncea) grown in soils contaminated by Copper, Zinc, Cadmium and Lead. The study site was located at the green house of National Taiwan University. The investigation was conducted from July 2004 to April 2005. Four salt solution were added to the air-dried soil to control the total concentration of four metals at 200, 400 mg Cu kg-1, 100, 200 mg Zn kg-1, 25, 50 mg Cd -1kg, 500, 1000 mg Pb kg-1. Three kinds of Indian mustard (Brassica juncea) grown in soils contaminated by zinc, cadmium, lead or coppe. The soil moisture content was maintained at 60% of the water holding capacity, by weighing and adding deionized water. Soil solution were collected directly by RSMS after seeding 0 , 7, 14, 21, 28, 35 day. Test plants were harvested after seeding 35 days, then harvested plant were digested by the H2SO4/H2O2 digestion method. The concentration of Cu, Zn , Cd, and Pb in soil solution and plant digested solution were determinated by inductively coupled plasma optical emission spectrometry (ICP-OES)(Perkin-Elmer 2000 DV). The total and available concentration of Cu, Zn , Cd, and Pb in soil were digested by aqua regia and EDTA, DTPA extractable methods , then determinated by atomic absorption spectrometry (Hitachi 180-30 type). The results indicated that the soil limiting concentrations of Cu and Zn of the three different species of Indian mustard were lower than 200 and 100 mg kg-1. The soil limiting concentration of Pb of the three different species of Indian mustard was 1000 mg kg-1, and the maximum Pb accumulation of the three Indian mustards was 200 mg kg-1, which was much lower than the accumulation of the Pb hyperaccumulator . The soil limiting concentration of Cd of the three different species of Indian mustard was 25 mg kg-1, and the maximum Cd accumulation of the three Indian mustards was 200 mg kg-1. It reaches the standard level of the Cd hyperaccumulator .The biomass of India and Pakistan Indian mustard were significantly higher than Afghanistan specie (p<0.05). There were no significant different of Cd accumulation between the three Indian mustard species. The Pb accumulation of the three Indian mustard species, the species of Afghanistan of Indian mustard was significantly higher than the species of Indian and Pakistan (p<0.05). The total Cd removal , the species of India and Pakistan were significantly higher than that of Afghanistan species (p<0.05). There were no significant different between the Pb removal of the three Indian mustard species. Harvestd at 7th day after applying EDTA, the Cd concentration of Indian mustard were increased form 200 to 330 mg kg-1, and the total removal of Cd were increased form 97 to 157 μg pot-1. Harvestd at 7th day after applying EDTA, the Pb concentration of Indian mustard were increased form 80 to 700 mg kg-1, and the total removal of Cd were increased form 38 to 250 μg pot-1. In conclusion, the ability of phytoremediation of the three species of Indian mustard are not different, and adding EDTA solution can significantly increase the uptake of heavy metal in contaminated soil.