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食物含納米顆粒？
食物含納米顆粒？
曾耀源
(廠商會檢定中心)
地球之友 (澳洲) 最近公佈一項有關食品含納米顆粒的調查1。結果顯示， 14種澳洲常見食品樣本含有 “納米二氧化鈦” 及 “納米二氧化硅”。澳洲新西蘭食品標準管理局對此作出回應，指現時沒有證據顯示人類進食含這兩類納米顆粒的食物後會出現健康問題。
1 Friend of the Earth, 2015 http://emergingtech.foe.org.au/independent-testing-finds-potentially-harmful-nanoparticles-in-common-food-products/
納米顆粒的毒性一直備受爭議，而且納米材料種類亦越來越多。很多國家已表示關注 “納米食品” 的安全性和會適時進行風險評估。
圖片來源：Food & Water Watch, 2009 http://www.foodandwaterwatch.org/reports/unseen-hazards-from-nanotechnology-to-nanotoxicity/
甚麼是納米食品？
首先，大家要知道納米是一個長度單位，一納米等如十億分之一米的長度。因此，納米材料尺寸非常微小，但其比表面積卻很大；這造成其性質 (如吸附性和擴散性) 與普通尺寸材料不同。由於納米顆粒 / 材料的性質獨特，納米技術已被應用於不同領域，包括食品行業。
一般來說，“納米食品”指食物成分經納米技術改造至尺寸約介乎1至100納米的結構的食物。此外，有人亦認為食物的包裝物料假如含有納米材料，該食物亦可視作“納米包裝食品”。
“非納米食品” 亦含有納米顆粒？
一些食物雖然成分沒有經過納米改造，但其包裝上的納米材料亦可能遷移至食物。此外，食物亦可在養殖或生產過程中受到 “污染”。例如，使用含有納米顆粒的農藥後可使農作物受到 “污染”。其他養殖用品 (如獸藥)、環境 (水、土和空氣) 及食品生產時用到的工具亦是潛在污染源。
納米食品有毒嗎？
要判斷一種納米材料是否有毒，各國一般需進行毒理學安全評估。簡單來說，首先要研究納米材料在試驗動物體內的吸收、分佈、代謝和排泄情況。另外，記錄動物進食納米材料一段日子後的反應，從而推算該納米材料對人體健康的影響。
在一些動物實驗中，某些納米材料被證明具有一定毒性。例如，有文獻2曾指出納米二氧化鈦可對多種哺乳動物細胞 (神經細胞、心肌細胞、肝細胞、腸細胞、生殖細胞等) 產生有害作用，例如降低細胞活力、誘導細胞凋亡等。有研究亦指出將納米二氧化鈦重覆灌胃給大鼠，幼鼠會出現肝臟水腫、心臟損傷等毒性反應；但成年鼠僅肝腎輕微損傷。
2 梁春來.賈旭東納米食品的毒理學研究及其風險評估與管理 [期刊論文] -中華預防醫學雜誌 2014(5)
然而，目前並無有力證據顯示人類進食含納米二氧化鈦(或其他納米材料)的食物後會出現不良健康反應。因此，納米材料的毒性一直存在爭議。
結語
對於納米食品 (及加入納米粒子的食物接觸材料) 的安全性，大家要記住不能一概而論。
因為現時各國對納米食物的安全評估方法並不統一，所作的評估亦存在一些不確定因素 (例如缺乏關於長期攝食納米顆粒的風險評估)。要進一步確定納米食品的安全性，還需要更多的科學依據和進行更全面的評估。
