- 學位論文
塑膠類食品容器釋放微米以及次微米塑膠微粒之評估
Study on the Release of Microplastics and Sub-Microplastics from Food Contact Plastics
摘要
塑膠微粒(Microplastics)被定義為小於5 mm 不溶於水的塑膠碎片，其中小於1 μm 者被稱作次微米塑膠微粒(Sub-Microplastic)。目前塑膠微粒廣布在環境水體如海洋、河川或是湖泊中，此外，在日常生活所會食用的蜂蜜、啤酒、食鹽以及牛奶中也有塑膠微粒的蹤跡。這些環境所檢測到的塑膠微粒粒徑大多都落在幾百或是幾千微米，且數目通常每公斤幾十到幾千顆塑膠微粒。然而近年來的研究發現，我們日常生活中外帶或外送食品時所使用的塑膠類食品容器(Food contact plastics, FCPs)接觸到高溫後可能會釋放數十億顆的次微米塑膠微粒。以毒理學的觀點來說，在同樣的重量濃度下，越小的顆粒具有越大的總表面積，且更有可能造成健康上的風險。 在過往的研究中，大多使用電子顯微鏡(Scanning electron microscope, SEM)進行計數，此方法固然可以眼見為憑，然而前處理需要先將塑膠微粒的懸浮液體乾燥，可能會對樣本產生影響。此外所選取的範圍相較於塑膠微粒散佈的區域，存在一定的統計抽樣誤差，且顯微鏡的計數方法較為耗費時間。再者過往研究中對於各類FCPs的加熱方法各異，所顯示的單位與觀察的粒徑範圍亦不盡相同，且大多專注在某一種材質或用途，故對於台灣市面上眾多的FCPs並無法進行完善的比較。 在本篇研究中，檢測了市面上常見不同材質的塑膠袋、塑膠碗、塑膠杯以及塑膠茶包，探討其在溫度控制95、70、25℃ 以及自然降溫狀況下的釋出情形，以比較不同材質或用途的FCPs之塑膠微粒釋出情況之異同，以及對於不同溫度和溫度控制情況測試，以了解溫度對FCPs釋出塑膠微粒的影響。此外觀察這些FCPs於加熱前後容器表面是否產生變化，以及濾出液中所含的微米及次微米塑膠微粒的型態。為了在液相的狀況下進行高通量的分析，本研究選用流式細胞儀(Flow cytometer, FCM)以及奈米追蹤分析(Nanoparticle tracking analysis, NTA)分別對於大的顆粒(200~2260 nm)和小顆粒(20~1000 nm)進行FCPs釋出塑膠微粒的總釋出量以及粒徑分布進行檢測。使用高解析度的場發射掃描式電子顯微鏡(Field emission scanning electron microscope, FM-SEM)分別在微米等級(10000X)及奈米等級(100000X)對於加熱前後的FCPs表面進行觀察以及FCPs濾出液中的塑膠微粒進行型態的觀察。在成分鑑定的部分，對未加熱的FCPs使用衰減全反射傅立葉紅外線轉換光譜(Attenuated total reflection fourier-transform infrared spectroscopy, ATR-FTIR)進行成分的鑑定以及分組，對於FCPs的濾出液使用拉曼光譜(Raman spectroscopy)進行成分的鑑定。 除了非用於盛裝高溫物質的材質後，經流式細胞儀(FCM)分析，可以發現聚丙烯(PP)材質平均來說單位面積會釋出最多塑膠微粒(4.39 × 105 particles/cm2)。而單次的FCP使用則是塑膠茶包平均會釋出最多的塑膠微粒(2.41 × 108 particles)，其中又以聚乙烯混紡聚對苯二甲酸乙二醇酯(PE/PET)塑膠茶包的次微米塑膠微粒釋出量最高，經奈米追蹤分析(NTA)後，每次的使用可能會釋出1.03 × 1011 particles。此外高密度聚乙烯塑膠袋會釋出1.66 × 1010 particles，而聚丙烯的塑膠碗會釋出1.59 × 1010 particles。在FCM所檢測到的塑膠微粒九成以上為小於1 μm的次微米顆粒，而在NTA中又以小於200 nm 的顆粒占比較多，在塑膠袋中佔了52.42 %，塑膠碗81.41 %以及塑膠茶包93.20 %，此處顯示小顆粒重要性以及在分析上的必要性。而高低溫度的影響對於不同的FCPs來說不盡相同，但可以知道這些FCPs盛裝高溫物質的時候都會釋出大量的顆粒，且有溫度越高，所釋出的顆粒越多的傾向，其中塑膠碗雖不受溫度影響釋出量，但其在95、70及25 ℃的釋出量都相近，經FCM分析後，一次使用的情況下釋出量高達2.04 × 108 particles。在溫度控制與自然降溫的比較，除了塑膠袋在無溫度控制狀況下顆粒的釋出會減少，塑膠碗與塑膠茶包有無進行溫度控制的差別不大，顯示只要盛裝高溫物質就會有暴露塑膠微粒的風險。於加熱前後可以觀察到部分FCPs表面的裂縫增大或是扭曲變形，這可能導致塑膠顆粒因此釋出。而所釋出的顆粒型態大致上以碎片、顆粒狀的塑膠微粒為主。 總結來說，使用這些FCPs盛裝高溫物質會暴露幾千萬顆的塑膠微粒和幾十億顆的次微米塑膠微粒，且盛裝的溫度越高，所釋出的顆粒越多。在這些顆粒中，越小的顆粒占比越多。根據本研究的結果，不建議使用FCPs盛裝高溫的物質，且不建議使用聚丙烯(PP)材質的FCPs盛裝任何食物，以避免塑膠微粒暴露的風險。
並列摘要
Microplastics are small plastic fragments smaller than 5 mm. Besides this, plastics smaller than 1 μm are defined as sub-microplastics. The widespread distribution of microplastics has been found in many previous studies. Up to now, the traces of microplastics have been found in oceans, rivers, atmosphere, honey, beer, table salt and milk. Most of the microplastics detected in these environments were at the micro level, and the amount of microplastics were usually tens to thousands per kilogram. However, recent studies have found that the food contact plastics (FCPs) used in our daily life for takeout or food delivery may release billions of sub-microplastics when they contained high temperatures substances. At the same weight concentration, the surface area of sub-microplastics is much larger than the microplastics and they might have higher toxicity. In previous studies, scanning electron microscope (SEM) was used for calculating the number concentration of microplastics. However, the sample might be destroyed and caused sampling errors in sample preparation. Besides, the analysis process was very time consuming. Moreover, in previous studies, the heating methods for various FCPs were different, the concentration units and the observed particle size range were disaccorded. In addition, most of them focus on a certain material or use, so it is hard to make a suitable comparison with the different varieties of FCPs in the Taiwan. This study aimed to investigate the release of microplastics in FCPs (including plastic bags, plastic bowls, plastic cups, and plastic tea bags) of different materials and heating conditions. For high-throughput and liquid phase analysis, this study used flow cytometer (FCM) and nanoparticle tracking analysis (NTA) to investigate the total relese and particle size distribution of microplastics (FCM 200 to 2260 nm) and sub-microplastics (NTA 20 to 1000nm) respectively. Field emission scanning electron microscope (FM-SEM) was used to observe the surface changes of FCPs before and after heating and also the morphology of FCPs leachates at the micron level (10000X) and nanometer level (100000X). Attenuated total reflection Fourier-transform infrared spectroscopy (ATR-FTIR) was used for component confirmation and FCPs material classification. Leachates of FCPs were analysis with raman spectroscopy. Except for the materials that were not used to contain high-temperature substances, it can be found that polypropylene (PP) released the highest level of microplastics (4.39 × 105 particles/cm2) on average. The plastic tea bag released the highest of microplastics (2.41 × 108 particles) on average. Among the tea bags, polyethylene blended with polyethylene terephthalate (PE/PET) plastic tea bag had the highest release of sub-microplastics, each use of the teabag may released 1.03 × 1011 particles. More than 90% of the investigated particles were sub-microplastics with diameter less than 1 μm, and particles smaller than 200 nm accounted for 52.42% of plastic bags, 81.41% of plastic bowls, and 93.20% of plastic tea bags. From the proportion of sub-microplastics, we can know the importance and necessity of sub-microplastics investigation. The influence of temperature was different for different FCPs, but it can be known that when these FCPs contain high-temperature substances, they release large number of microplastics, and the higher the temperature, the more particles were released. Among them, although the release of the plastic bowl was not affected by temperature. The releases at 95, 70 and 25 ℃ were similar, however, it may released up to 1.59 × 1010 particles in once use. In the comparison of temperature control and natural cooling, apart from the plastic bags , most of the FCPs microplastics release were not affected by temperature control. It could been seen that as long as we use FCPs to contain high temperature substances, there is a risk of microplastics exposure. It can be observed that the loose structure and rough surface of FCPs after heating. And it may be the source of microplastics release. Besides, the morphology of microplastics were fragments and particles. In conclusion, the use of these FCPs that containing high-temperature substances will expose billions of sub-microplastics. And the higher temperature, the more microplastics will be released. And most of them are smaller than 200 nm. Based on the results, it is not recommended to the use of FCPs with high-temperature substances. In addition, it is not suggested to use polypropylene (PP) based materials for containing any food since there is a higher risk of exposure to the plastic particles.