- 學位論文
腐植酸對河川底泥/氧化鐵吸附全氟辛酸之影響
Effects of Humic Acid on Perfluorooctanoic Acid Adsorption onto River Sediments/Iron Oxide
摘要
全氟辛酸（perfluorooctanoic acid, PFOA）對人體具危害性且廣泛存在於自然水體環境中，已成為顯著的環境議題，由於不同的環境條件會影響吸附分配方式，進而影響PFOA在環境中的流布傳輸，本研究目的為瞭解溶解性有機物（dissolved organic matter, DOM）對PFOA與客雅溪底泥間吸附行為之影響，研究中DOM以腐植酸（humic acid, HA）為代表。 客雅溪底泥之礦物成分多達數十種，主要為Si（約佔14%）和Fe（約佔2%），粒徑大小分布為210~590 μm，屬粗顆粒細砂，比表面積約1.30 m2/g，pHzpc＜4。 以pH = 5、7、9及離子強度I = 無添加及0.1 N進行實驗，底泥對PFOA的吸附密度介於0.59~3.57 µg/g，改變溶液中pH和離子強度對PFOA的吸附密度影響並不顯著，但低pH值-高離子強度和高pH值-低離子強度的組合，對於水相中的PFOA分配到底泥上比較有利；而HA存在的情形下，HA-PFOA-底泥之吸附平衡時間為12天，且HA的存在會降低底泥對PFOA的吸附行為。 另以底泥主要礦物成分之氧化鐵作為吸附劑進行吸附實驗，研究使用之氧化鐵結構為α-Fe2O3，粒徑約1.5 μm，比表面積約6 m2/g，pHzpc約為8。 研究設計HA和PFOA分別以不同順序加入氧化鐵懸浮溶液中進行吸附實驗，並結合本研究室之氧化矽、氧化鋁實驗結果，共同探討HA對PFOA與底泥吸附行為的影響。研究發現HA和PFOA加入反應順序的不同，會明顯改變PFOA吸附密度，整體而言在酸性環境下，HA會增加PFOA吸附密度，除了原本PFOA和底泥礦物層表面的吸附作用外，HA和PFOA兩者間還會因為疏水性交互作用而發生共沉降的吸附現象，因此增加了底泥表面對於PFOA的吸附強度。例外的情形是HA先與吸附劑表面達平衡再加入PFOA，因可吸附位置皆被佔滿導致PFOA幾乎不被吸附，此結果與客雅溪的情況相符，自然水體中過多的DOM會包覆底泥表面，將導致PFOA僅有少部分會被底泥吸附而滯留，大多數仍會存在於水相中並經由傳輸擴散到下游，因此探討底泥有機碳層吸附行為時，必須將水中DOM的影響納入考量。
並列摘要
It has been recognized that the presence and persistence of Perfluorooctanoic Acid (PFOA) in the environment due to its toxicity and bioaccumulation potential. PFOA has increased the concerns of the public for the environment and human health. The fate of PFOA transported in water was governed by the adsorption from different medium that could be affected by the environmental conditions to another. The purpose of this study is to understand the effects of the dissolved organic matter (DOM) on PFOA adsorption behavior onto sediment and iron oxide, and DOM was represented by humic acid (HA). Sediment in Keya River consisted of dozens of different mineral materials. The dominant components found were silica (about 14%) and iron (about 2%). The particle size ranged from 210 to 590 μm, the specific surface area was relatively low at 1.3 m2/g, and the zeta potential was smaller than 4. The sorption density of PFOA to Keya River sediment ranged from 0.59 to 3.57 µg/g at three pH (5, 7, and 9) and at two ionic strength conditions (ambient and 0.01 N). The result showed that PFOA was not significantly affected by solution pH and ionic strength. The combinations of low pH-high ionic strength and high pH-low ionic strength favored partitioning of the PFOA to sediment. It revealed that the HA might be an important solution-specific parameter in sorption, with the presence of HA in the aqueous phase reducing the affinity of PFOA toward the sediment. Another experiment has been conducted by iron oxide. The particle size of iron oxide was about 1.5 μm with the specific surface area about 6 m2/g, and the zeta potential was about 8. We studied the adsorption of PFOA by introducing adsorbents in different orders to realize how HA affected the adsorption of PFOA to the mineral surface. The results suggest that in low pH condition (pH = 6), HA might enhance PFOA sorption to the mineral surface when both are introduced to the aqueous phase. However, an exception occurs when PFOA was introduced to the mineral surface that has already been exposed to and extensively coated with HA. The result implies that PFOA released to a river rich in DOM might not adsorbed on sediment and therefore be transported downstream. DOM thus can play a significant role in the transport and fate of PFOA in the natural water system.