| Summary: | 博士 === 國立臺灣大學 === 環境工程學研究所 === 103 === 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.
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