聚氯乙烯管釋出塑膠微粒潛勢之研究：以臭氧、自由餘氯以及熱進行加速試驗老化

Abstract

塑膠微粒（microplastics）已被確認存在於大多數水體，包括海洋、河水以及自來水等等, 其中自來水與人類的生活最相關。淨水場內部之塑膠元件及配水系統中之塑膠管被認為是自來水中塑膠微粒的潛在來源，而在台灣塑膠管中又以聚氯乙烯（PVC）管為最大宗，幾乎可在所有建築物中見到。本研究透過以淨水程序中常出現的臭氧、氯消毒程序以及熱水進行PVC塑膠管的老化，並研究PVC管釋放塑膠微粒的潛在風險。實驗結果發現PVC管之塑膠微粒釋出量隨著臭氧、自由餘氯以及加熱暴露的條件提升而增加，各參數對應之最大釋出量可達1,058、1,256以及1,303 # L-1。在臭氧以及高溫暴露量提升下，雖說塑膠微粒釋出量提升，但並不影響所釋出塑膠微粒的尺寸組成比例，相對於自由餘氯的暴露，所釋出的塑膠微粒隨著自由餘氯曝露量提升而有變大的趨勢，代表著在餘氯暴露下，大尺寸的塑膠微粒較小尺寸的塑膠微粒更容易釋出。本研究同時也透過羰基指數（Carbonyl index, CI）估算羰基產物在PVC管表面上的生成量，配合掃描電子顯微鏡在微觀的尺度下觀察表面，發現到羰基指數在各條件下隨著臭氧、自由餘氯以及熱的暴露提升而變高，與此同時，也發現到孔洞大量生成在PVC管的表面，這些孔洞的生成可能與塑膠微粒的脫落有關。孔洞特性在不同條件老化亦有所不同。臭氧傾向於在表面生成孔洞後，持續攻擊孔洞內部使得孔洞尺徑比起較低濃度的臭氧老化更大；餘氯老化傾向於持續生成孔洞，孔洞數量隨著曝露量提升而提升，且表面有明顯受損；而PVC管在80°C高溫的老化下，表面粗糙度明顯提升，而且相較於臭氧、餘氯老化所生成的孔洞，高溫老化所生成的孔洞更小。儘管各機制對於孔洞生成條件不同，在CI隨著老化程度提升而提升的狀況下，可以推斷羰基產物（Carbonyl products）的生成可能與塑膠微粒的掉落有關。

Microplastics have been detected in most aquatic systems, including ocean, river and even drinking water. In the drinking water system, plastics pipes used in the water treatment facility and distribution system are potential sources of microplastics. In Taiwan, polyvinyl chloride (PVC) pipe is the most widely used plastic pipe. The potential hazard of microplastics release due to aging should be investigated. In this study, the effects of ozonation, chlorination and heating on the aging and release of microplastics from PVC pipes are investigated. The highest release of microplastics was found to be 1,058, 1,256 and 1,303 # L-1 after aging in 30 mg O3 L-1, 260 mg Cl2 L-1 and 80oC, respectively. The release of microplastics with a size in the range of 10-50 and >50 µm increased with increasing exposure of chlorine while those in size of 1-10 µm was not significantly changed. On the other hand, the size composition of released microplastics due to exposure of ozone and heat tended to maintain constant. The carbonyl index (CI) of PVC pipes generally increased with enhanced aging with ozone, chlorine and heating. Meanwhile, scanning electron microscope (SEM) images showed that hole structures developed on the surfaces of PVC pipes after aging. After the initial hole structures appeared, ozone tended to continuously attack the same sites resulting in bigger hole structures after enhanced ozone exposure. The exposure of chlorine tended to increase the hole structures in their abundance and damage the surface. For thermal aging, smaller hole structures and rougher surface were observed after aging at an elevated temperature. Although different surface morphologies were observed under different aging conditions, the formation of carbonyl functional groups on the surfaces may result in the surface roughness and ultimately lead to the detachments of microplastics from aged PVC pipes.