Investigation of the impact of brewing parameters on toxic element and rare earth element contamination in oolong tea

Sixuan Wu¹Ziming Peng²Yijun Ou¹Florence Mhungu³Yanyan Wang¹Yuhua Zhang¹Lan Liu¹Lei Jiangbo¹Lili Huang¹Rongfei Peng¹Zhijun Bai¹Weiwei Zhang^1*

• ¹Guangzhou Center for Disease Control and Prevention, Guangzhou, China
• ²Guangzhou University School of Economics and Statistics, Guangzhou, China
• ³Horizon Health Network, Fredericton, Canada

With the growth of oolong tea consumption, the risk of leaching toxic elements and rare earth elements (REEs) during its brewing process has raised concerns. In this study, 108 oolong teas of different origins and varieties were collected, and the concentrations of 7 toxic elements including lead (Pb), cadmium (Cd), aluminum (Al) and 15 REEs were measured by ICP-MS, and the effects of the water temperature (90 ℃/100 ℃) and brewing time (5 seconds-2 hours) on the leaching rate were investigated. The results showed that high temperature and long brewing time significantly increased the leaching of most elements (P<0.05), among which Tieguanyin tea had the highest content of Pb, Al and REEs, and the Pb and Al of Fujian tea exceeded the standard significantly. The anomaly was that the leaching rate of Cd at 100°C was lower than that at 90°C, while the release of scandium (Sc) increased with increasing temperature. Consumers are advised to shorten the brewing time to minimize the intake of harmful substances, and are called to strengthen the regulatory standards of toxic elements and REEs in tea. The study reveals the key role of brewing conditions on elemental migration and provides a scientific basis for safe tea drinking.