This study measured total (acid-digested) and water-extractable boron in 36 tea-bag products sold in Poland, comparing black teas with fruit-flavored black teas and fruit brews made mostly of dried fruit and hibiscus. Fruit brews carried more total boron and released a much larger share of it into water than black teas. The authors also estimated boron per cup and compared it with published intake guidance.
Key numbers
- Total boron, black teas (24 samples): 8.31 mg/kg (lowest, sample 13) to 18.4 mg/kg (highest, sample 20); average 13.5 mg/kg (Results 3.1, p. 5; Figure 1).
- Total boron, black teas with fruit flavor (3 samples): 12.9 to 15.1 mg/kg; average 13.9 mg/kg (Results 3.1, p. 5).
- Total boron, fruit brews (9 samples): 12.1 to 22.8 mg/kg; average 17.4 mg/kg (Results 3.1, p. 5).
- Water-extractable boron in black teas: 0.72 mg/kg (sample 5) to 4.49 mg/kg (sample 15); highest in fruit brews 14.48 mg/kg (Results 3.2, p. 5).
- Share of total boron extracted by water: 8% to 27% in black teas and 17% to 69% in fruit teas (Abstract; Results, p. 6).
- Reference material NIST SRM 1515 (apple leaves, certified 27 ± 2 mg/kg): 27.68 ± 1.18 mg/kg after acid digestion (102.5% recovery); 15.19 ± 0.494 mg/kg in the water extract (Section 2.3, p. 2).
- Source-reported boron per 200 mL cup: 0.29 to 1.45 mg for black tea, 0.73 to 1.19 mg for fruit-flavored black tea and 2.52 to 7.24 mg for fruit brews (Section 3.3, p. 6; Table 1). These per-cup figures cannot be reconciled with the 1.3 to 3.0 g bag masses and mg/kg concentrations printed in the same paper, so they are recorded as reported and not used for exposure.
Methods (brief)
Tea-bag contents were digested by a modified EPA 3051 microwave method for total boron, and separately extracted with water (10 g in 100 mL, 1 hour at 80 °C) for the water-soluble fraction. Boron was measured by ICP-AES (iCAP 6500 duo) at three emission lines in triplicate, with relative standard deviation below 5%. Infusion pH was also recorded.
Evidence fitness
Supports dry-tea boron concentrations and the contrast in extractability between black teas and fruit brews. It does not support population intake estimates: the per-cup amounts are internally inconsistent with the reported bag masses, and the comparison with intake guidance relies on a secondary table of values from other bodies.
Limitations
Individual black-tea totals are shown only in a figure; the text gives ranges and group averages. Sample origins are often not stated. The water extraction (10 g in 100 mL for 1 hour) does not mimic home brewing of a single bag. The conflict-of-interest statement declares none.
Related evidence
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