環境水體及淨水流程中二氧化鈦奈米微粒濃度及粒徑分佈先驅研究

Abstract

奈米科技是一項全新的研究領域，眾多奈米材料中以奈米二氧化鈦(TiO2)最常被使用，應用範圍從光催化、環境整治到消費性產品，如食品漂白劑和紫外線阻擋劑等。由於二氧化鈦奈米微粒在消費性產品的高使用率及普及性，二氧化鈦微粒透過工業設施中的洩漏及排放、水上休閒活動等途徑，很容易暴露到環境水體中。然而，環境水體中二氧化鈦奈米微粒濃度可能落在ng/L等級的低濃度範圍，因此欲分析環境水體中二氧化鈦奈米微粒是具有挑戰性的。故本研究目的在於驗證水體中二氧化鈦奈米微粒之檢測方法，並以此檢測方法分析地表水水源與飲用水系統水樣本中二氧化鈦奈米微粒之質量濃度、數目濃度及粒徑大小。 本研究使用單粒子感應耦合電漿質譜儀(single-particle inductively coupled plasma-mass spectrometry, sp-ICPMS)分析二氧化鈦奈米微粒，並以儀器分析準確度及儀器分析穩定度驗證水體中二氧化鈦奈米微粒檢測方法。另外，本研究採集大臺北地區地表水水源及國內主要飲用水系統水樣進行水中二氧化鈦奈米微粒分佈。地表水水源採樣點選自淡水河系的上游北勢溪坪林段、中游新店溪直潭段及下游淡水河士林段，飲用水系統樣本則取自A、B、C及D等淨水處理場的原水、沉澱、過濾、清水等。採集之水樣以sp-ICPMS分析水體中二氧化鈦奈米微粒。 研究結果顯示，以sp-ICPMS分析水體中二氧化鈦奈米微粒，其質量濃度偵測極限為2.71 ng/L、粒徑大小的偵測極限為2.32 nm。另外，以sp-ICPMS分析二氧化鈦奈米微粒的準確度及穩定度皆介於80 %-120 %間。大臺北地區地表水水樣以淡水河下游水樣中二氧化鈦奈米微粒質量濃度及數目濃度最高，分別為31.7 μg/L及479×103顆/mL。飲用水系統水樣中，以D淨水處理場原水池水樣所含二氧化鈦奈米微粒質量濃度及數目濃度最高，分別為8.69 μg/L及297×103顆/mL，且其二氧化鈦奈米微粒粒徑大小也最大，為112 nm。而A淨水處理場原水池水樣所含二氧化鈦奈米微粒質量濃度最低，為1.29 μg/L，可能與新店溪青潭上游處為水質水量保護區有關。另外，A淨水處理場及B淨水處理場相比於C淨水處理場及D淨水處理場，過濾池水中二氧化鈦奈米微粒數目濃度更低，可能與前者過濾池多一道無煙煤過濾層的處理方式有關。本研究結果可提供更具體的二氧化鈦奈米微粒分佈資訊，供後續人體暴露健康風險評估及水質管制之依據。

Nanotechnology is an emerging research field. One of the most commonly used engineered nanomaterials (ENMs) is titanium dioxide (TiO2), with applications ranging from photocatalysis, environmental remediation to consumer products for food -whitening and ultraviolet radiation-blocking. As being widely used in consumer products, titanium dioxide nanoparticles (TiO2 NPs) are readily released into environment resulting from industrial manufacture processes and human recreational activities. However, the detection of TiO2 NPs in environmental medium is challenging because of the expected extremely low concentrations at the ng/L level. Therefore, the objectives of this study were set to validate the methodology for characterizing TiO2 NPs in aqueous samples and to profile the TiO2 NPs distribution in aquatic environment and drinking water system in terms of mass concentration, number concentration and particle size. In this study, TiO2 NPs in study samples was measured using single-particle ICP-MS (sp-ICPMS), which was validated through accuracy and reliability check for TiO2 NPs measurement. Aqueous samples were collected from the surface water of the Tamsui River Basin at Pinglin of Bei-Shi Creek, Tzetan of Hsindien River, and Shi-Lin of Tamsui River, and from four water treatment plants, i.e., A, B, C, and D water treatment plants, for raw water, sedimentation tank water, filtration tank water, and finished water samples. Results showed that sp-ICPMS was capable for quantitative determination of TiO2 NPs at low concentrations with mass concentration detection limit of 2.71 ng/L and particle size detection limit of 2.32 nm. In addition, both the accuracy and reliability for TiO2 NPs determination by sp-ICPMS were between 80 % and 120 %. For the surface water samples, those from the downstream of the Tamsui River presented the highest mass concentration and number concentration of TiO2 NPs, i.e., 31.7 μg/L and 479×103 particles/mL, respectively. For the drinking water system samples, the raw water in D Water Treatment Plant showed the highest mass concentration, number concentration and particle size of TiO2 NPs, which were 8.69 μg/L, 297×103 particles/mL and 112 nm, respectively. However, the raw water in A Water Treatment Plant showed the lowest mass concentration of TiO2 NPs (1.29 μg/L), which might be attributed to the stipulation for water conservation in the upstream of the Hsindien River. As compared to the C Water Treatment Plant and the D Water Treatment Plant, the filtration tank water in A Water Treatment Plant and the B Water Treatment Plant showed lower mass concentration of TiO2 NPs, which might be ascribe to the use additional anthracite coal as a part of filtration in these tow water treatment plants. Overall, results of this study provided more specific information on the distribution of TiO2 NPs in aquatic environment for subsequent human health risk assessment and water quality control.