個人奈米採樣器的設計及驗證

Abstract

奈米物質具有獨特的物化特性而被廣泛的應用在不同領域，其產量持續地成長當中，人們也因此開始關注暴露在奈米微粒中對健康所造成的潛在影響。由於奈米物質具有粒徑小和表面積大的特性，許多研究均顯示奈米物質相較於相同化學成分的塊材物質對生物有較大的影響。2005年NIOSH建議勞工在每日工作8小時、一週工作40小時的情況下，TiO2細微粒及超細微粒的暴露時量平均濃度應分別小於1.5 mg/m3和0.1 mg/m3。然而目前市面上尚未有合適的採樣器可供個人奈米微粒的暴露評估。因此本研究主要目的為研發了一組可用於作業場所採集奈米微粒的個人採樣器。 本採樣器(IOSH-NCTU PNS)重250 g、高105 cm、直徑6.3 cm，包含一個旋風器和一個微孔衝擊器，分別用來分離可呼吸性微粒(respirable particulate matter , RPM)及奈米微粒(NPs)，且在2.0 L/min的操作流量下，產生的壓損為125 cm H2O。此微孔衝擊器(含137個直徑55 μm噴嘴)具有一個可旋轉且塗敷矽油的鋁箔衝擊基質的衝擊板，使微粒可均勻分布在衝擊基質上並降低微粒彈跳的發生。最後在衝擊器下方設置有一片用來採集奈米微粒的終端濾紙。 本研究先於實驗室利用液體和固體微粒進行本採樣器的微粒收集效率曲線校正，再進行微粒負載測試，之後與微孔均勻沉積衝擊器(MOUDI) 進行實驗室內比對以驗證本採樣器校正曲線的準確性。 校正結果顯示當S/W為13.8，旋風器和微孔衝擊器的截取氣動直徑分別為3.98±0.1 μm和101.4±0.1 nm。而S/W由3.13增加至16.2，微孔衝擊器的截取直徑會由72.5 nm上升至111 nm。由微粒負荷測試結果可知，本採樣器在高微粒濃度負荷下壓損幾乎不會改變且微粒最大負荷量為0.65 mg。此外實驗室比對測試的結果顯示本採樣器採集的的RPM及NPs濃度和MOUDI均十分接近。因此，本研究設計的採樣器已可用於評估作業人員RPM及NPs的暴露量。

Production of nano-materials has increased continuously because of their unique physicochemical characteristics and extensive applications. There is a great concern for the potential health effects due to exposure to nanoparticles. Because of small size and large surface area, many studies have shown that the biological effects of nano-materials are greater than bulk materials of the same chemical composition. In 2005, the NIOSH recommended the exposure limits of 1.5 mg/m3 for fine TiO2 and 0.1 mg/m3 for ultrafine TiO2, in terms of time-weighted average concentrations (TWA) for up to 8 hr/day during a 40-hour work. However, there are no active personal sampling devices to assess the exposure levels of workers to engineered nanoparticles (NPs). To meet the demand, a novel IOSH-NCTU personal nanoparticle sampler (IOSH-NCTU PNS) was designed and tested. The PNS operates at 2 L/min with a pressure drop of 125 cm H2O by a SKC XR 5000 pump. The PNS consists of a respirable cyclone and a micro-orifice impactor (with 137, 55 μm in diameter nozzles) in series for classifying respirable particulate matter (RPM) and NPs, respectively. The impactor plate is rotated by a stepper motor to deposit particles uniformly on the substrate. A final filter is used to collect NPs. The sampler is light weighted (250 g) and compact (H-10.5 cm, D- 6.3 cm). Both liquid and solid particles were used to calibrate the sampler for the collection efficiency. The effect of heavy particle mass loading on performance of the PNS was evaluated. For assessing its accuracy, the measured RPM and NPs concentrations by the PNS were compared with those of a collocated MOUDI. Calibration results show that the cutoff aerodynamic diameter (dpa50) of the respirable cyclone and the micro-orifice impactor is 3.98±0.1 μm and 101.4±0.1 nm, respectively, with the S/W of 13.8. A decreasing S/W from 16.2 to 3.13 in the micro-orifice impactor results in a decreased dpa50 from 111 to 72.5 nm. The particle loading tests reveals that the PNS has a maximum loading of 0.65 mg with a less than 5 % shift of dpa50 and a negligible solid particle bounce. The change in the pressure drop was less than 5 cm H2O after heavy particle loading, and the RPM and NPs concentrations agreed well with those of the MOUDI. Therefore, the present IOSH-NCTU PNS sampler is capable of assessing personal exposure levels of RPM and NPs in workplaces.