- 學位論文
新興污染物鎵與銦在不同土壤中之動態及其對水稻幼苗生長之影響
The fate of emerging contaminants gallium and indium in different soils and their effects on the growth of rice seedlings
摘要
新興汙染物鎵跟銦為廣泛被應用在半導體與光電產業相關製程之微量元素。根據近期的調查報告指出，在鄰近新竹科學園區區域之地下水鎵與銦之平均濃度都有高於非工業區的現象，顯示其在環境介質中之分布也越來越普遍，因此，評估鎵與銦對於作物生長之影響及其在環境中的動態也成了相當重要之議題。然而，現今國內外有關鎵與銦之研究仍處在起步階段，為了能夠進一步去釐清含鎵與銦之廢水可能對環境造成之潛在衝擊。本研究透過人為方式，分別添加 50、100、200與 400 mg kg-1 的鎵或銦於平鎮系、將軍系及彰化系三種試驗土壤中，以盆栽試驗的方式栽培水稻，選用台稉 9 號作為試驗材料，觀察水稻在不同試驗土壤及鎵與銦濃度處理下之生長情形，以分別評估鎵與銦在不同土壤系統中對水稻幼苗生長可能造成之影響，此外，也經由土壤孵育試驗與孔隙水之分析結果，探討其在不同土壤之動態差異。由水稻生質量之實驗結果顯示，鎵與銦的暴露下均會造成水稻幼苗之生長勢受到抑制，其程度會受不同土壤特性及添加濃度所影響。在鎵處理中，因平鎮系土壤陽離子交換容量較低，使土壤膠體上缺少能夠吸附鎵的位置，導致鎵較容易被釋出於土壤溶液，故其有效性較將軍系和彰化系高。至於對水稻幼苗生長之抑制情形以平鎮系最為明顯，當土壤鎵處理濃度為 50 mg kg-1 時，水稻幼苗之生質量即出現顯著下降的情形，但在先前之水耕試驗中，即使鎵暴露濃度達 15 mg L-1，對水稻仍不具明顯之毒害效應，然而，對照本研究平鎮系中，孔隙水鎵濃度最高僅為 0.5 mg L-1，水稻幼苗的生長即受顯著抑制，造成此差異的原因可能與鋁的動態改變有關。因鎵的添加間接與土壤膠體上之鋁產生置換反應，提高鋁在土壤溶液中的濃度，進而使水稻幼苗受到毒害。至於在銦處理中，由於銦在中鹼性的環境中容易形成沉澱，因此，在土壤 pH 值較高的將軍系與彰化系土壤，推測土壤中的銦主要受沉澱所致，導致其有效性相當低，進而也緩解銦對水稻造成之毒害效應。即使當土壤中銦的處理濃度高達 400 mg kg-1，水稻幼苗生長受抑制的情形較仍較不明顯。而雖然在平鎮系銦處理中同樣觀察到銦有置換土壤膠體上之鋁的現象，整體而言土壤溶液中之鋁濃度均低於水稻之鋁毒害臨界濃度，且植體累積之鋁濃度與對照組相比也並未明顯上升，又考量到孔隙水銦濃度已高於先前水耕試驗得到的銦毒害濃度，故推測被銦由膠體上所置換出的鋁並非影響種植於平鎮系土壤水稻幼苗生長之主因。水稻幼苗生長勢應主要是受高濃度銦的暴露影響而受到毒害，當土壤銦處理濃度為 100 mg kg-1 時，水稻幼苗之生長勢即受到明顯抑制。
並列摘要
Emerging contaminants gallium (Ga) and indium (In) are trace elements extensively used in semiconductor manufacturing and electro-optical industry. With the vigorous development of high-tech industry in Taiwan, a great amount of wastewater derived from the manufacturing process may be a potential contamination sources. Recent studies have shown that the concentration of Ga and In in the environment are soaring. Assessing the potential effect of gallium and indium on the plant growth and the fate of Ga and In in soils are indispensable, whereas related research is still in it’s infancy. To better understand the impact of Ga and In on the environment, pot experiments with rice seedlings (Oryza sativa L.) were carried out. Rice seedlings were grown in three different kinds of soil spiked with 50、100、200 and 400 mg kg-1 of Ga or In, respectively. In Ga treatment, low CEC and lack of O.M in Pinchen series made Ga more easily to be released into porewater, which enhanced the availability of Ga in soil solution. However, based on previous studies, the exposure of Ga did not cause significant toxic effect on rice seedlings in hydroponic experiments, which was contrary to this study. Owing to similar chemical properties, the aluminum (Al) rich in Pinchen series would be replaced by Ga, which can be verified by the increase of Al concentration in porewater with higher Ga application rate. Since the Al concentrations in porewter was higher than the toxicity levels of rice, we assumed that the Al replaced by Ga is the dominant factor caused growth inhibition on rice seedlings when the Ga concentration in soil was reach 50 mg kg-1. As for In treatment, affected by precipitation, the availability of indium is relative low in neutral and alkaline soils (Chengchung and Changhua series), which mitigated the toxic effect of indium on rice seedlings even though the soil concentration of In was up to 400 mg kg-1. Although the substitution of Al for In is also observed in Pinchen series, the concentrations of Al in porewater was still below the toxicity levels of rice seedlings, which indicated that Al may not be the factor affected the growth of rice seedlings. High concentrations of In exposure is the main cause inhibited the growth of rice seedlings.