淡水河流域汞之空間分布

Abstract

本研究分別夏季﹝2003年5月及2004年7月﹞、冬季﹝2008年12月及2010年1月﹞採集淡水河的表水研究微量金屬汞在淡水河之濃度分佈、影響機制及估算季節性通量變化，其中2010年1月利用物理分離方法來分析淡水河在各相態中Hg分佈：總溶解態（total dissolved, ≤0.45 μm）、真溶解態（truly dissolved, ≤1 kDa）、膠體（colloidal,1 kDa ~ 0.1 μm & 0.1 μm ~ 0.45μm）與顆粒態（particulate, ≥0.45 μm）。夏季總汞濃度範圍介於1.7~34.3ng/L，溶解態總汞濃度範圍介於1.5~5.1 ng/L；冬季總汞濃度介於1.8~40.9ng/L，溶解態總汞濃度範圍介於0.6~29.8ng/L。 溶解態總汞與溶解性有機碳有顯著之相關性(R2=0.88)，且懸浮顆粒中有機碳(%)越高其顆粒態總汞濃度相對越提高(R2=0.55)，表明有機碳在淡水河中影響汞之濃度分佈。在河口區域具有強烈的氧化還原作用，導致微量金屬汞於河口地區表現出明顯的移除作用，為非保守性的混合型式。所以汞在淡水河中分佈受到有機物質及其缺氧環境所影響。汞在淡水河中之顆粒體與溶解態之間的分布係數(log Kd )約為5.4±0.2，顯示出Hg對於顆粒體有高度的親合力。藉由分離溶解態各種粒徑分析，基隆河、新店溪上游各溶解相態以真溶解態為主，大漢溪上有以大型膠體為主，當進入台北市都會區人為汙染影響，導致溶氧降低，溶解態汞大多轉變成大型膠體，進而形成顆粒態移除。 利用混合曲線簡單地計算出河口內的輸入與輸出通量，主要發現汞在河口有75%~90%移除率。夏季河口區域移除之通量約為冬季河口區域移除之通量的兩倍。

The distribution, partitioning and fluxes of Mercury (Hg) with its controlling factors had been investigated in surface waters of the Danshuei River estuary and nearby coastal areas of Taiwan in summer (May 2003 and July 2004) and winter (December 2008 and January 2010). Additionally, in January 2010 the Hg in different size phases of physical separation in the Danshuei River was analyzed such as filter-passing total dissolved (HgD≤ 0.45μm, ≤ 0.45 μm), truly dissolved (HgD ≤ 1kDa, ≤ 1 kDa), colloidal (HgLC, 1 kDa ~ 0.1 μm & HgHC, 0.1 μm ~ 0.45μm) and particulate (HgP, ≥ 0.45 μm) Hg. The distribution and concentration of Hg species varied spatially and temporally. Total Hg (∑Hg) concentration in summer overall ranged from 1.7 to 34.3ng/L and ∑Hg from 1.0 to 5.1 ng/L; in winter concentrations of ∑Hg and HgD≤ 0.45μm ranged from 1.8 to 40.9 and 0.6 to 29.8 ng/L, respectively. HgD≤ 0.45μm and dissolved organic carbon significantly correlated each other (R = 0.94), and a good correlation between HgP and particulate organic carbon (mg/g) was observed also (R= 0.66). These indicate that organic matter has a significant influence on the concentration distribution of the Hg in the Danshuei River estuary. Moreover, there was a significant Hg removal as a non-conservative mixing pattern at a low-salinity upper estuary（salinity 0~10）, in which a strong redox condition took place. Therefore, the Hg distribution was significantly affected by the organic matter and redox changes in Danshuei River estuary. Higher particle-water partition coefficients (log Kd = 5.4± 0.5, n = 43) were observed between particulate and dissolved Hg, and significantly affected by TSM concentration (total suspended matter) and DO (dissolved oxygen level). Through analyzing dissolved Hg in different size fractions, the Hg in the upstream of the Keelung River and Hsing-Dian Steam was mainly in the truly dissolved form and in the upstream of the Dai-Han Steam largely the colloidal in macro-molecule weight. Most of the riverine dissolved Hg were turned into particulate through colloidal pumping processes and then removed in the upper Danshuei River estuary at Taipei metropolitan areas, in which the hypoxia took place as a result of high human-derived pollutions. To estimate the first-order Hg budget within the estuary, ca. 83% ~ 91% (n=4)of the Hg removal rates were found by using mixing patterns of Hg versus salinity. The estuarine removal flux (about 22 g/day/m2) in summer was approximately two times of that in winter (about 10 g/day/m2). Keywords: Hg, speciation, spatial distribution, Danshuei River esturary, flux