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  • 學位論文

嘉南平原含水層中砷與腐植質之鍵結

The binding nature of arsenic with humic substances in the aquifer of Chianan Plain

指導教授 : 許正一 陳庭堅

摘要


臺灣嘉南平原曾經在1960年代發生嚴重的烏腳病疫情,其病因為當地居民長期飲用含砷地下水所導致,雖然目前嘉南平原地區之含砷地下水並不再被飲用,但仍做為灌溉用途,最後會經由食物鏈對人體造成潛在性危害。 本論文探討含砷地下水中各物種砷之含量,以瞭解地下水層中砷之氧化還原物種型態。利用物理分離地下水不同分子量範圍之溶解性有機質(DOM)及瞭解其所結合的砷濃度以及利用樹脂分離土壤樣品不同親疏水性有機質及瞭解其所結合的砷濃度。同時以紫外光/可見光分光光度與螢光光譜激發/放射光譜指標來探討有機質特性,並由螢光衰減法探討腐植質與砷之吸附能力(KDOM)。研究結果顯示,2013年9月、11月及2014年3月、5月共四季中,地下水砷濃度皆超出飲用水管制標準,並以五價砷為主。而且總砷濃度隨著溶解性有機碳(dissolved organic carbon, DOC)含量增加顯著(p < 0.05)(R2=0.6843)。模擬由地下水灌溉所產生之土壤水中發現,砷濃度約5-10 μg/L,比原地下水之濃度低,原因是受土壤中鐵氧化物或腐植質吸附所影響。另外,由地下水所分離之大(0.45μm-10 kDa)、中(10-1 kDa)及小分子量(< 1 kDa)有機質發現砷主要分佈在小分子及中分子量有機質中。由土壤萃取之親水性有機質砷濃度較高,原因為腐植質中的-COOH及-OH基,易與砷形成複合物之故。由KDOM得知,地下水DOM對三價及五價砷之吸附能力以小分子量及中分子量者較佳。由螢光圖譜可發現本論文地下水中的腐植質以黃酸為主,而傅立葉紅外線光譜分析得知地下水中DOM確實與砷產生鍵結作用。

並列摘要


In Taiwan, a peripheral vascular gangrene disease, known as Blackfoot Disease (BFD), was first reported in Chianan Plain where many people consumed well water with high arsenic content in 1960s. Although this As-contaminated groundwater is no longer used for drinking, it is still used for irrigation and thus arsenic may enter the food chain from crops cultivated in this region. In this study, It was confirming if the arsenic-humic substances complex in groundwater of Chianan plain and identifying the dominant arsenic species in order to understand the type of arsenic redox status. It was simulated groundwater pumping for irrigation to the soil to understand the changing of total arsenic. A resin separation method was used to separate the humic substance constituents to understand the binding concentration of arsenic in the groundwater from Chianan Plain. An UV/Vis and fluorescence spectrophotometer collected UV/Vis absorbance values and excitation/emission matrix to explore the characteristics of humus. The fluorescence quenching method was used to obtain the partition coefficient (KDOM) between the humic substance and arsenic. Furthermore, it was confirming different molecular weight or separation with DAX-8 and XAD-4 of concentration of arsenic in the soil humic substances. The results showed that the concentration of the arsenic linearly and significantly (p < 0.05) correlated well with dissolved organic carbon (DOC) (R2=0.6843) in the groundwater samples collected in September, November, 2013 and March and May, 2014. The concentration of the arsenic exceeded the drinking water limit of Taiwan (10 μg/L). Additionally, the arsenic speciation in the groundwater confirmed that As(V) was the predominant species. However, the concentration of arsenic was only 5-10 μg/L in the soil solution generated from groundwater simulated irrigation, because that arsenic from groundwater partly was adsorbed by iron oxides or humic substances in the soil. It is found that most arsenic was concentrated in the fractions of humic substance with the molecular weights of 1 kDa and 1-10 kDa through the contribution of binding capacity by COOH and OH groups. This binding tendency of arsenic and humic substance supported the arsenic concentration trend among the humic fractions separated by the resin method.. Excitation–emission matrix (EEM) spectra indicated that the dominant humic fraction in the groundwater was fluvic acid, elucidating the binding of arsenic with fulvic acid by Fourier transform infrared spectroscopy.

參考文獻


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