| 摘要: | 迅速的經濟發展，環境污染問題也隨之而來，過去灌排未分離導致重金屬廢水排放到農地，使重金屬成為農田污染最普遍的污染物。目前已發展多種處理方法，其中現地穩定化因其低成本、高效率和對環境影響小，已成為減少農田和水體中重金屬風險的重要策略。此種方式主要以添加土壤改良劑至重金屬污染土壤中，透過改變重金屬的型態分布，讓重金屬變為不易被釋出的型態；或以吸附在土壤改良劑表面等方式降低重金屬的移動性。台灣每年產生大量牡蠣殼廢棄物，多數牡蠣殼被不當棄置堆放，引發了環境污染和異味問題。牡蠣殼之主成分為碳酸鈣，目前被應用於酸性污染耕地中，用以提升土壤 pH 值，增加羥基 (-OH)，在改善土壤酸度的同時使重金屬生物有效性下降。錳氧化物，特別是二氧化錳 (MnO2)，由於其優異的吸附能力，已逐漸成為固定土壤重金屬的有效方法。過去的研究表明，錳氧化物在復育重金屬污染土壤方面，能顯著降低重金屬的生物有效性。因此本研究透過鹼洗以及水熱法製備錳改質的牡蠣殼，藉由盆栽試驗種植小白菜，評估牡蠣殼及錳改質牡蠣殼之整治效益，並驗證是否具有減少土壤中重金屬移動性及生物可利用性的潛力。盆栽試驗條件設定二種材料，分別為未處理牡蠣殼及錳改質牡蠣殼，添加比例分別為1%、3%及5%；研究結果顯示，牡蠣殼及錳改質牡蠣殼的添加能夠改善土壤環境，使植體重量有顯著的上升，最多6倍，且使土壤pH值顯著的上升。然而施用牡蠣殼及錳改質牡蠣殼會增加鎘 (Cd) 及鉛 (Pb) 在根部的累積，且使鉛的移動性更大，讓地上部累積了比對照組更多的鉛，推測是由於根部區域土壤微酸性，導致根部碳酸鹽結合態的重金屬溶解進入根部。在序列分析中觀察到顯著的鍵結型態變化，材料的添加使有機物鍵結型態顯著下降，而使碳酸鹽鍵結態的比例顯著上升。綜合以上結果，在高濃度鎘及鉛污染土壤中施用牡蠣殼以及錳改質牡蠣殼雖會使植體重量顯著上升，但亦可能會使鉛的移動性上升，使植體地上部當中吸收較多的鉛，且都不能使植體當中的鎘及鉛達到合乎我國法規所制定標準 (0.2 ppm)。但本研究觀察到，在添加材料後與對照組相比轉移係數 (Translocation factor, TF)顯著下降，且錳改質牡蠣殼比未處理牡蠣殼下降得更多。;Rapid economic development has led to environmental pollution, with heavy metal contamination becoming a common issue in farmland due to the discharge of untreated wastewater. In situ stabilization, a cost-effective and environmentally friendly method, has gained attention for reducing heavy metal risks. This approach involves adding soil amendments to immobilize heavy metals by altering their forms or reducing their mobility through adsorption.
Taiwan produces significant amounts of oyster shell waste, most of which is improperly disposed of, causing pollution. Oyster shells, primarily composed of calcium carbonate (CaCO₃), are used to increase soil pH in acidic soils, reducing heavy metal bioavailability. Manganese oxides, especially manganese dioxide (MnO₂), are also effective in heavy metal immobilization due to their strong adsorption properties.
This study prepared manganese-modified oyster shells using alkali treatment and hydrothermal methods and evaluated their remediation efficiency in cadmium (Cd) and lead (Pb)-contaminated soils through pot experiments with Brassica chinensis. Treatments included oyster shells and manganese-modified oyster shells at 1%, 3%, and 5% application rates. Results showed that both materials improved soil conditions, increased soil pH, and significantly enhanced plant biomass (up to sixfold). However, they also increased Cd and Pb accumulation in plant roots and enhanced Pb mobility, leading to higher Pb levels in aboveground parts compared to the control.
Sequential extraction analysis revealed a shift in metal binding forms, with organic-bound metals decreasing and carbonate-bound metals increasing. Despite improving plant growth, neither amendment reduced Cd and Pb levels in plants to meet Taiwan′s regulatory standard (0.2 ppm). Furthermore, manganese modification did not significantly enhance heavy metal immobilization compared to unmodified oyster shells. |
