河海匯流區溶解態銀的轉化與遷移作用

Transformation and Remobilization of Dissolved and Colloidal Silver in an Urban Estuary

林佩俞(Pei-Yu Lin)

指導教授 ： 溫良碩

國立臺灣大學/理學院/海洋研究所/碩士(2019年)

https://doi.org/10.6342/NTU201903597

摘要

銀的毒性以及生物累積性，一直以來都是受到關注的議題。自從工業革命以來，因為銀極佳的導電性及光化學特性，所以被廣泛地應用在各項工業以及生活用品中。近年來又因為奈米銀獨特的抗菌效果，使得銀的使用量大幅提升，造成自然水體當中溶解態銀的濃度急遽增加。一般而言，因為銀的親顆粒性，溶解態銀在水體當中的滯留時間短，容易被移除且埋藏在沉積物當中，但是前人研究結果發現，淡水河關渡地區潮汐變化大，再懸浮作用容易發生，可能會讓這些埋藏在沉積物的金屬被重新釋放回水體當中，因此本次研究主要在關渡定點進行時序觀測，並搭配淡水河主河道採樣，希望探討再懸浮作用發生時，對溶解態銀的濃度變化及物種轉化的影響。
本次研究方法主要分為兩部分 溶解態銀在現場就以 0.45 μm的濾球過濾 得到總溶解態(< 0.45 μm)的樣品回到實驗室後再將總溶解態的水樣進行交流過濾得到真溶解態(< 1 kDa)的銀物種。這些 溶解態的樣品均使用 有機複合酸萃取法濃縮水中的銀，再以感應耦合電漿質譜(Inductively coupled plasma mass spectrometry，ICP-MS)分析。顆粒態銀則是將未過濾的水樣帶回實驗室後，以 0.45 μm PC濾紙過濾收集得到顆粒態 (> 0.45 μm)樣品 接著以序列酸解法分離及消化最後以石墨式原子吸收光譜儀（Graphite Furnace Atomic Absorption Spectrometer GFAAS）量測顆粒態銀的濃度。
研究結果顯示，淡水河主河道總溶解態銀的濃度比前人研究高出許多，濃度範研究結果顯示，淡水河主河道總溶解態銀的濃度比前人研究高出許多，濃度範圍在圍在46-298 pM之間，且分布趨勢與前人研究相同，都是移除型的變化。膠體態佔之間，且分布趨勢與前人研究相同，都是移除型的變化。膠體態佔總溶解態的比例為總溶解態的比例為10-90%，主要分布在低鹽度，主要分布在低鹽度位置；位置；之後隨鹽度增加，膠體的比之後隨鹽度增加，膠體的比例逐漸減少例逐漸減少。。此外，研究結果還發現膠體態銀與膠體態鐵的濃度兩者呈現正相關，此外，研究結果還發現膠體態銀與膠體態鐵的濃度兩者呈現正相關，顯示顯示水體當中水體當中溶解態銀的移除是受到氫氧化鐵產生沉澱所影響溶解態銀的移除是受到氫氧化鐵產生沉澱所影響。。真溶解態銀的濃真溶解態銀的濃度範圍在度範圍在11-66 pM之間，分布趨勢則是隨鹽度增加而增加，且與氯離子濃度呈現之間，分布趨勢則是隨鹽度增加而增加，且與氯離子濃度呈現正相關，此結果同樣也被熱力學平衡模式運算正相關，此結果同樣也被熱力學平衡模式運算(MINEQL + Version 5.0)所證明。不所證明。不同於主河道的分布趨勢，關渡測站時序觀測的結果顯示，當再懸浮作用發生時，水同於主河道的分布趨勢，關渡測站時序觀測的結果顯示，當再懸浮作用發生時，水中的懸浮顆粒會主導反應的進行中的懸浮顆粒會主導反應的進行(log Kd維持定值在維持定值在6.45 ± 0.15 cm3/g)，使得原本，使得原本被埋藏在沉積物中的銀會從懸浮顆粒上脫附，以真溶解態的形式釋放回自然水體被埋藏在沉積物中的銀會從懸浮顆粒上脫附，以真溶解態的形式釋放回自然水體當中，之後這些真溶解態的銀可能又因為膠體幫當中，之後這些真溶解態的銀可能又因為膠體幫浦作用，由真溶解態進入膠體態，浦作用，由真溶解態進入膠體態，再次從溶解態移除。同樣地使用熱力學平衡模式計算，但計算所得到的濃度與實測再次從溶解態移除。同樣地使用熱力學平衡模式計算，但計算所得到的濃度與實測值差距很大，此結果驗證了模式運算並不適用於再懸浮現象發生時，必須考慮膠體值差距很大，此結果驗證了模式運算並不適用於再懸浮現象發生時，必須考慮膠體凝絮作用以及顆粒的吸附與脫附反應，值得未來再繼續探究。凝絮作用以及顆粒的吸附與脫附反應，值得未來再繼續探究。

關鍵字

銀 ； 再懸浮作用 ； 物種轉化 ； 氯離子錯合 ； 膠體絮凝 ； 顆粒的吸附與脫附反應 ； 熱力學平衡模式

並列摘要

Silver (Ag) is one of the most toxic elements, and it can accumulate in aquatic organisms and cause lethal consequences. Since the Industrial Revolution, silver has been widely used for coins, electronics, metal fabrication, photography, and many other industries. In recent years, silver nanoparticles have been engineered and extensively used for its antimicrobial effects, which causes silver concentration in nature water is getting much higher than before and still rising.
As studies showed, silver can be removed to sediments at a fairly rapid rate in estuarine systems. However, little is known about releasing silver due to resuspension. The purpose of this study is to investigate the distribution and transformation of dissolved and colloidal silver during river-sea mixing, and the effects of sediment resuspension. Water samples were collected in fall 2017 from Danshuei river using ultra-clean sampling protocols, and sampling is categorized into two parts sampling at different geographic locations in Danshuei mainstream by a small boat and time series sampling at a fixed station at Guandu pier. Real time in-line filtration was achieved by a 0.45 μm capsule filter, and then the filtered waters were subsequently further processed with cross flow ultrafiltration by a 1 kDa spiral wound membrane. Ag in both filtered (< 0.45 μm) and ultrafiltered (< 1kDa) waters were extracted by Ammonium pyrrolidinedithiocarbamate(APDC)/Sodium diethyldithiocarbamate (DETC) complexed method and then measured by high resolution inductively coupled plasma mass spectrometry (HR-ICP-MS). Particles collected on 0.45 μm PC filters were digested and measured by graphite furnace atomic absorption spectrometer (GFAAS). Silver in each fractions are defined as total dissolved (< 0.45 μm), colloidal (1 kDa-0.45 μm), truly dissolved (< 1 kDa), and particulate (> 0.45 μm).
The results showed that total dissolved fraction ranged from 46 to 298 pM and exhibited a non-conservative estuarine removal mixing pattern as previous study. We also found that 10-90% of dissolved silver fraction was present in the colloidal phase, and the percentage decreased with salinity. Simultaneously, strong correlation between colloidal Ag and colloidal Fe was observed to prove the removal of Ag may be controlled by the generation of hydrous iron oxides. However, truly dissolved fraction increased with salinity because silver chloride complexes were dominant in saline water, which was proved by mixing and thermodynamic speciation model calculation. At Guandu pier station, dynamic changes and remobilizations were found in truly dissolved fractions, which were due to competition reactions of the formation of silver chloride complexes, desorption from re-suspended particulate matter, and colloidal pumping. All these processes may cause failure to access Ag species by the mixing and thermodynamic modeling (MINEQL+ Version 5.0). In conclusion, to accurately predict the fates of Ag in shallow estuary, the effects of sediment resuspension and colloidal pumping should be incorporated.

並列關鍵字

Ag ； resuspension ； transformation ； silver chloride complexes ； colloidal pumping ； particle desorption ； thermodynamic model (MINEQL+ Version 5.0)

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