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茶葉與稀土元素
茶葉與稀土元素
曾耀源
(廠商會檢定中心)
與茶葉有關的最常見食品安全問題，大家當然會想起除害劑殘餘和重金屬。除此之外，茶葉含稀土元素亦是近年引起關注的食品安全危害。
甚麼是稀土元素?
稀土元素是指17種特定化學元素，包括鑭系元素(共15種)、鈧和釳。
稀土元素與必要元素 (例如鈣和鐵) 不同，對人體沒有用處，還具有輕至中等程度的毒性。有研究報告指長期攝食含過量稀土元素的食物可嚴重影響健康，例如損害大腦功能、影響肝腎、心臟、免疫功能和女性生殖功能等。
茶葉被檢出稀土元素超標
在過去數年，中國的食品安全主管機關不時檢出多種茶葉的稀土元素超標。例如北京市食品藥品監督管理局曾公佈鐵觀音、龍井茶、紅茶、大紅袍、綠茶和普洱的稀土元素超標。
關於食物中稀土元素限量標準的爭議
中國國家標準GB 2762-2012 《食品中污染物限量》訂明茶葉中稀土元素限值(參照GB 2762-2005)，為每公斤茶葉不可含多於2毫克稀土元素 (以稀土氧化物總量計)。
該標準亦同時訂明稀土元素在其他植物源性食物的限值:
然而，設定這些限值的科學理據被質疑不夠充份。目前，國際食品法典委員會、美國、澳洲以及香港等地均沒有對食品設有稀土元素限值要求。
檢測食物中稀土元素的方法
電感耦合等離子體原子發射光譜法(ICP-AES)和電感耦合等離子體質譜法 (ICP-MS) 常被應用於檢測茶葉的稀土元素含量。這兩種方法均具有高靈敏度和特異性，並可同時分析食物中多種稀土元素。
建議
事實上，茶葉中稀土元素超標並不只出現在中國，其他國家/地區(例如台灣、印度和越南) 出產的茶葉亦曾出現同樣問題。因此，即使對稀土元素所造成的健康風險存疑，它還是一個值得關注的食物安全問題。
在香港，很多人都喜歡飲茶，而且茶葉亦多是進口的。因此，筆者認很值得調查市面各類茶葉的稀土元素含量，然後評估本地市民攝入過量稀土元素的風險。
根據調查結果，大家更可進一步判斷現時食物攙雜（金屬雜質含量）規例 (第132V章)是否需要作出修訂。這是因為現時法例只訂明七種金屬元素在指定食物類別的限值，但當中並不包括稀土元素。
