孔雀草與非洲鳳仙對污染土壤鎘及美女櫻對污染土壤鉛累積吸收之研究

Abstract

植生復育(phytoremediation)意指使用植物移除土壤中的污染物，可大量累積重金屬於植體中的植物，稱為超級累積植物。目前發現的超級累積植物大多有一共同缺點，生質量小及移除量低。國外雖有許多相關研究，但國外的植物不易取得，且不一定可以適應國內的自然環境，種植在台灣是否可達預期的效果。本研究目的為選用臺灣污染區試種過之物種，分別為繁星花(Star cluster, Pantas lanceolata Deflers.)、孔雀草(French marigold, Tagetes patula Linn.)、非洲鳳仙(Impatiens, Impatiens walleriana Hook.f.)、美女櫻(Garden verbena, Verbena bipinnatifida Nutt.)及一串紅(Scarlet sage, Salvia splendens Ker-Gawl.)，種植於人工鎘、鉛污染土壤中，測試其對鎘、鉛污染土壤的生長反應及吸收累積重金屬之能力。 試驗土壤採集自桃園新屋一塊未污染農田，於國立臺灣大學人工氣候室溫室進行試驗，調控日/夜溫度為30℃/25℃。土壤重金屬處理濃度分別為對照、鎘10 mg kg-1與20 mg kg-1及對照、鉛500 mg kg-1與1000 mg kg-1，三重覆，種植35天後收割。將植物幼苗移植至人工污染土壤後，以重量法添加去離子水，維持土壤水分約為最大容水量之60％。於種植期間第0、7、14、21、28及35天以土壤水分採樣器(RSMS)收集土壤溶液，探討土壤溶液中重金屬溶出量之變化。植體收割後，以土壤萃取劑0.05M EDTA (pH 7.0)、0.005M DTPA (pH 5.3)及0.01M CaCl2萃取土壤中植物有效性重金屬含量，探討其與植物地上部累積重金屬濃度之相關性。植體以H2SO4/H2O2法分解，樣品溶液皆以原子吸收光譜儀(AAS，Hitachi 180-30型)測定重金屬含量。 研究結果顯示孔雀草及非洲鳳仙於鎘20 mg kg-1處理時地上部累積鎘濃度分別為66.3±6.5 mg kg-l及100±11 mg kg-l，非洲鳳仙更達到超累積植物之標準(100 mg kg-l)，生長狀況及乾物重並無有明顯的減少，鎘移除量分別為799±106 μg plant-1及815±18 μg plant-1，建議可繼續測試受更高鎘濃度污染之累積現象。美女櫻種植於鉛1000 mg kg-1處理時累積鉛濃度達65.1±9.1 mg kg-l，其鉛移除量為651±128 μg plant-1，雖然累積鉛濃度未達超級累積植物之標準(1000 mg kg-l)，鉛移除量也不如預期的高，但已比一般植物有明顯偏高之鉛濃度與吸收量。土壤萃取劑(0.05M EDTA、0.005M DTPA及0.01M CaCl2)可萃取之重金屬濃度與繁星花、孔雀草、非洲鳳仙及一串紅地上部累積之鎘濃度及繁星花、孔雀草、非洲鳳仙及美女櫻地上部累積之鉛濃度具顯著相關性(p<0.05)。

Phytoremediation is a technique by selecting special plants to remove heavy metals from contaminated soil. Plants which can accumulate heavy metals more than the threshold of hyperaccumulation are regarded as hyperaccumulators. Hyperaccumulators have the limitation on small biomass and low total removal of metals from soil. There are many studies on the phytoremediation in the world. However, hyperaccumulators from abroad are not obtained easily and not suitable for the natural environment of Taiwan in some cases. According to some studies on the contaminated sites of Taiwan, some highly potential species of phytoextraction are selected for this study. The objective of this study is to compare the growth condition and heavy metals accumulation of these species for growing in the soils artificially contaminated by cadmium and lead. The selected plants are star cluster (Pantas lanceolata Deflers.), french marigold (Tagetes patula Linn.), impatiens (Impatiens walleriana Hook.f.), garden verbena (Verbena bipinnatifida Nutt.), and scarlet sage (Salvia splendens Ker-Gawl.). The studied soil was collected from uncontaminated soil in Taoyuan, Taiwan. The pots experiments were conducted in the phytotron of National Taiwan University, which the air temperature was controlled at 30℃ in day and 25℃ in the night, respectively. The treatments of heavy metals are control, 10 mg Cd kg-1, 20 mg Cd kg-1, 500 mg Pb kg-1, and 1000 mg Pb kg-1. Three replicates were conducted for each treatment. All plants were harvested at 35 days after transplanting. The soil moisture content was maintained at 60% of water holding capacity by weighing and adding deionized water. Soil solutions were collected directly by RSMS (Rhizon Soil Moisture Sampler) after transplanting at 0, 7, 14, 21, 28, and 35th day for monitoring the changes of metal concentrations in the soil solution. The bioavailability of Cd and Pb in soil were extracted by 0.05M EDTA (pH 7.0), 0.005M DTPA (pH 5.3), and 0.01M CaCl2, respectively, to evaluate the relationships between heavy metal accumulation in the plants and soil solution’s concentration extracted by different extractors. Samples of harvested plants were digested by the H2SO4/H2O2 digestion method, and heavy metal concentration in all solution samples and plants were determined by atomic absorption spectrometry (Hitachi 180-30 type). The results indicated that Cd accumulation of french marigold and impatiens growing in the soil contaminated by 20 mg kg-1 were 66.3±6.5 and 100±11 mg kg-l, which can remove 799±106 and 815±18 μg plant-1, respectively. The maximum Cd accumulation of impatiens reached the threshold value, 100 mg kg-l, of hyperaccumulators, and impatiens did not have any toxicity effect on the growth. This result indicate that impatiens is a superaccumulator of Cd and can grow in higher Cd concentration of the soil. The Pb accumulation of garden verbena growing in 1000 mg kg-1 were 65.1±9.1 mg kg-l, and it can remove 651±128 μg plant-1. Although Pb accumulation of garden verbena did not reach the threshold concentration of 1000 mg kg-l of hyperaccumulator, but the concentration of Pb in the plant are much higher than that of general plants. There are good relationships between Cd or Pb concentrations of soil extracted by 0.05M EDTA, 0.005M DTPA, and 0.01M CaCl2 and Cd or Pb concentrations in shoots of star cluster, french marigold, and impatiens (p<0.05). These results indicated that 0.05M EDTA, 0.005M DTPA, and 0.01M CaCl2 are good extractants to predict the uptake of heavy metals in soil medium.