Metal concentrations in traditional and herbal teas and their potential risks to human health

Overview

de Oliveira and colleagues measured aluminum, total arsenic, cadmium, total chromium, and lead in 47 traditional and herbal tea products collected in the US market, and then measured the same metals in 5-minute boiling-water infusions. The sample set covered herbal, black, green, and oolong teas with declared origins across 13 countries. The source reports both dry tea-leaf concentrations in mg kg-1 and infusion concentrations in mg L-1 for aluminum or µg L-1 for arsenic, cadmium, chromium, and lead.

Key numbers

• Sample frame: 47 total tea products, including 16 herbal teas, 16 black teas, 11 green teas, and 4 oolong teas collected in the US market.
• Total aluminum in tea leaves: herbal teas ranged 47 to 1745 mg kg-1; traditional teas ranged 50.3 to 2517 mg kg-1. Table 2 reports mean aluminum (Al) 548 ± 111 mg kg-1 for herbal teas, 1655 ± 147 mg kg-1 for black teas, 885 ± 253 mg kg-1 for green teas, 1089 ± 356 mg kg-1 for oolong teas, 1309 ± 135 mg kg-1 for traditional teas overall, and 1050 ± 192 mg kg-1 for all teas.
• Aluminum in 5-minute infusions: herbal tea infusions ranged 0.09 to 3.95 mg L-1; traditional tea infusions ranged 0.02 to 7.51 mg L-1. Table 2 reports mean infusion Al 0.42 ± 0.25 mg L-1 for herbal teas, 4.59 ± 0.47 mg L-1 for black teas, 1.56 ± 0.67 mg L-1 for green teas, 2.58 ± 0.99 mg L-1 for oolong teas, 3.3 ± 0.43 mg L-1 for traditional teas overall, and 2.29 ± 0.62 mg L-1 for all teas.
• Percent aluminum infused after 5 minutes ranged from 0.9 to 49%; Table 2 reports means 6.29 ± 1.84% for herbal teas, 28.2 ± 2.06% for black teas, 14.8 ± 2.75% for green teas, and 19.8 ± 5.72% for oolong teas.
• Total arsenic in leaves: herbal teas had mean 0.26 ± 0.07 mg kg-1; black teas 0.22 ± 0.02 mg kg-1; green teas 0.18 ± 0.07 mg kg-1; oolong teas 0.09 ± 0.01 mg kg-1; all teas 0.21 ± 0.03 mg kg-1. The Results text reports one herbal tea at 1.10 mg kg-1 arsenic (As), exceeding the WHO 1 mg kg-1 medicinal-plant limit cited by the authors.
• Arsenic in infusions: As was detected above the 0.18 µg L-1 detection limit in 54% of tea infusions and ranged 0.19 to 1.33 µg L-1, below the drinking-water MCL of 10 µg L-1 cited by the authors.
• Cadmium in leaves: Table 3 reports mean cadmium (Cd) 0.19 ± 0.06 mg kg-1 for herbal teas, 0.05 ± 0.01 mg kg-1 for black teas, 0.04 ± 0.01 mg kg-1 for green teas, 0.05 ± 0.01 mg kg-1 for oolong teas, and 0.09 ± 0.15 mg kg-1 for all teas. The Results text reports all tea Cd values from 0.01 to 0.82 mg kg-1, averaging 0.09 mg kg-1, and states that 11% of teas exceeded the 0.3 mg kg-1 WHO herb limit cited by the authors.
• Cadmium in infusions: the Results text reports Cd infusion values 0.13 to 0.61 µg L-1, with 5 to 21% soluble, and below the drinking-water MCL of 5 µg L-1 cited by the authors.
• Total chromium in leaves: Table 3 reports mean chromium (Cr) 2.32 ± 0.36 mg kg-1 for herbal teas, 7.37 ± 2.04 mg kg-1 for black teas, 1.55 ± 0.42 mg kg-1 for green teas, 0.97 ± 0.29 mg kg-1 for oolong teas, and 3.86 ± 0.83 mg kg-1 for all teas. The abstract reports Cr in 47% of herbal teas and 73% of traditional teas exceeded the Canadian 2 mg kg-1 limit cited by the authors.
• Lead in leaves: Table 3 reports mean lead (Pb) 2.37 ± 1.78 mg kg-1 for herbal teas, 0.64 ± 0.11 mg kg-1 for black teas, 0.76 ± 0.12 mg kg-1 for green teas, 0.63 ± 0.21 mg kg-1 for oolong teas, and 1.24 ± 0.56 mg kg-1 for all teas. The abstract reports one herbal tea with 26.4 mg kg-1 Pb, above the WHO 10 mg kg-1 medicinal-plant limit cited by the authors.
• Lead in infusions: the Results text reports soluble Pb from 0.21 to 19.9 µg L-1 after excluding two teas, corresponding to 1.9 to 80% total Pb; the high infusion value was from the same herbal-tea sample that contained 26.4 mg kg-1 Pb in leaves.
• Aluminum intake estimates from tea drinking were reported as 0.001-0.39 mg kg-1 for children and 0.003-0.56 mg kg-1 for adults, below the provisional tolerable weekly intake for Al of 1.0 mg kg-1 cited by the authors.

Methods (brief)

Tea samples were dried at 65 °C to constant weight, ground, and digested as approximately 0.5 g portions with HNO3/H2O2 using USEPA Method 3050B on a hot block. Infusions were prepared by adding 50 mL boiling double-DI water to 0.5 g tea leaves, mixing, covering, boiling for 5 min, filtering through Whatman No. 40 filter paper, cooling, and diluting to 50 mL. Al, As, Cd, Cr, and Pb were analyzed by ICP-MS. NIST Tomato Leaves SRM1573a was analyzed with each batch; reported CRM results were Al 560 ± 11, As 0.110 ± 0.003, Cd 1.59 ± 0.005, and Cr 1.86 ± 0.110 µg g-1, compared with certified values Al 598 ± 12, As 0.112 ± 0.004, Cd 1.52 ± 0.04, and Cr 1.99 ± 0.06 µg g-1. The paper reports total As and total Cr only; it does not speciate inorganic arsenic or hexavalent chromium.

Related evidence

• Aluminum
• Arsenic, Total
• Cadmium
• Chromium
• Lead
• Tea
• Camellia sinensis
• Herbal botanicals
• True Tea (Camellia Sinensis)
• Herbal/Botanical Infusions
• Tea
• Tea Infusions

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