Trace elements in successive tea infusions made via a brewing method widespread in China: Implications for human exposure

Abstract

Tea is a globally popular drink with many associated health benefits, although tea plants can also accumulate potentially toxic metals from industrial and agricultural contamination of soil and water. This study determined 10 trace elements present in tea leaves and successive tea infusions made using a brewing method widespread in southern China. The levels of aluminium in tea infusions were the highest (range: 32.0–6130 μg/mL), followed by zinc (5.76–92.6 μg/mL), nickel (1.97–17.7 μg/mL), copper (1.49–14.9 μg/mL), cobalt (0.11–1.97 μg/mL), lead (0.02–1.22 μg/mL), chromium (0.10–1.01 μg/mL), selenium (0.04–0.47 μg/mL), arsenic (0.01–0.23 μg/mL), and cadmium (0.001–0.03 μg/mL). Average aluminium concentrations in tea infusions exceeded the Chinese maximum allowance level (MAL) established for drinking water (20 μg/mL). In pairwise comparisons of trace element levels in eight sequential infusions, greater concentrations were found in the 2nd infusion than the last six infusions (p < 0.05). Notably, the analysis showed considerable health risks associated with trace element exposure from drinking all of the first eight infusions of Tieguanyin tea, Hazard Index (HI) = 1.08, and Rock tea (HI=0.94). In addition, potential increases in cancer risks (2.5×10-5) associated with total arsenic intake were found among Tieguanyin or Rock tea consumers. Based on these findings, a tea brewing method is recommended which involves multiple successive infusions of 10 s each, discarding the first and second infusions. To the best of our knowledge, this is the first scientific verification of a traditional tea-making method to reduce trace element exposure.