The most common food safety problems associated with tea leaves that you have heard of should be pesticide residues and heavy metals. On the other hand, rare earth elements (REEs) present in tea leaves is another growing food safety concern.
What are Rare Earth Elements?
REEs refer to a specific group of 17 chemical elements including lanthanides (comprising 15 elements), scandium and yttrium.
Unlike essential elements (e.g. calcium, iron, etc.), REEs are not essential for human and with low to moderate toxicity. It is reported that long term consumption of food contaminated with excessive REEs can affect human health e.g. causing damage to brain, liver, kidney, heart, immunity, female reproductive function, etc.
Detection of REEs in Tea Leaves
In the past few years, Mainland food safety authorities found excessive REEs in several types of tea leaves from time to time. For example, Tieguanyin, Longjing tea, Black tea, Da Hong Pao, Chinese Green Tea and Pu-erh were problematic tea leaves once reported by the Beijing Food and Drug Administration.
Controversy Surrounding Tolerance Levels of REEs in Foods
In China, GB 2762-2012 National Food Safety Standard - Maximum Levels of Contaminants in Foods stipulates that REEs in tea leaves (in accordance with GB 2762-2005) must not exceed 2 mg/kg (measured as total amount of REE oxide).
The GB standard also specifies the permitted levels of REEs in the following plant-origin foods:
However, the scientific justification for setting the maximum levels is controversial. To date, Codex and developed countries like United States, Australia, as well as Hong Kong have not stipulated permitted levels of REEs in foods.
Measurement of REEs in Food
ICP-AES and ICP-MS are commonly used to measure the levels of REEs in tea leaves. Both methods are very sensitive and specific, and allow simultaneous measurements of different REEs in food.
REE problem is indeed not limited to China, but also found in tea leaves from other countries / territories like Taiwan, India, Vietnam, etc. Therefore, REEs is a potential food safety problem worth for concern even though the actual health risk remains undetermined.
In Hong Kong, the local citizens love drinking tea while tea leaves are mainly imported from different countries. Therefore, it is worth to find out the levels of REEs present in different types of tea leaves sold in Hong Kong, and then assess the risk level of local population exposing to REEs.
Based on the findings, we can tell if there is need to revise the existing Cap 132V Food Adulteration (Metallic Contamination) Regulations which only covers 7 metal elements in specified food commodities, but not REEs.