Yao et al. 2022 — Copper, lead, cadmium, chromium, and nickel in Tieguanyin tea (Fujian, China)

This study quantifies copper, lead, cadmium, chromium, and nickel in 91 Tieguanyin oolong tea samples from Fujian Province, China, characterises their transfer rates from dry leaf to brewed infusion in a fixed-protocol brewing experiment, and computes hazard quotients and lifetime carcinogenic risks for six demographic subpopulations (male/female, age 18–40/age ≥41, urban/rural) using subpopulation-specific tea consumption and body-weight inputs from the authors’ previous consumption survey. It is routeable for Cu, Pb, Cd, Cr, and Ni occurrence evidence on Camellia sinensis tea (oolong-class Tieguanyin) and on Tieguanyin tea infusions in a Chinese production-region market.

Key numbers

• Sample design: 91 Tieguanyin tea samples (500 g each) randomly collected from tea shops, supermarkets, and tea factories in Fujian Province, China. Each sample was crushed, homogenised, and sifted through a 60-mesh (0.25 mm pore size) polyethylene sieve, then stored dark and dry until analysis. All dry-leaf concentrations are reported on a dry-weight basis.
• Copper, dry tea (mg/kg, mean ± SD; range, Table 4): 8.18 ± 2.10; 2.65–11.61. The authors note Cu in Tieguanyin is below the level previously reported in Pu-erh tea but well above the green/oolong/black-tea levels reported by Shen and Chen (0.4/0.9/0.3 mg/kg respectively).
• Lead, dry tea (mg/kg, mean ± SD; range, Table 4): 0.84 ± 0.40; 0.21–2.00. Comparable to Pu-erh and green-tea ranges in the cited literature and much lower than black tea from Iran (8.2 mg/kg) reported by Falahi and Hedaiati.
• Chromium, dry tea (mg/kg, mean ± SD; range, Table 4): 0.51 ± 0.28; 0.08–1.38. Reported as total Cr; the paper does not run a Cr-VI extraction. The authors apply the USEPA Cr-VI oral slope factor (0.5 mg/kg/day) to the total-Cr exposure for the cancer-risk calculation, citing biological reduction of Cr-VI to Cr-III as justification.
• Cadmium, dry tea (mg/kg, mean ± SD; range, Table 4): 0.04 ± 0.02; below detection–0.11. Below-detection samples were assigned the corresponding LOQ value.
• Nickel, dry tea (mg/kg, mean ± SD; range, Table 4): 1.90 ± 0.70; 1.02–2.93. Lower than Pu-erh from southwest China (6.27 mg/kg), green tea from Jiangxi (7.71 mg/kg), and Turkish tea (23.3 mg/kg) reported in the cited literature.
• Mean infusion transfer rates (% of dry-leaf metal released into the brewed infusion under the 7 g leaf : 150 mL boiling water, 10 min steep protocol, Figure 1): Cu 10.2, Pb 31.5, Cr 42.3, Cd 53.6, Ni 70.4. Ni and Cd are the most readily extracted; Cu is the most strongly retained in the leaf.
• Reference doses (RfD, µg/kg bw/day, Table 4): Cu 40, Pb 3.57, Cr 3, Cd 1, Ni 20. The Pb RfD was adapted from Yao et al. 2015; the Cd slope factor (6.3 mg/kg/day) was adapted from Bamuwamye et al. 2015; the remaining RfDs and slope factors (Pb 0.0085, Cr 0.5) were adapted from USEPA IRIS.
• Non-carcinogenic hazard quotient (HQ, Table 5, dimensionless, expressed in %): for the six subpopulations and five analytes, every individual HQ is well below 1. Maximum HI by subpopulation is 6.1×10⁻² (age ≥41); minimum HI is 3.8×10⁻² (female). Pb consistently contributes the largest single-element HQ within the HI sum; Cd consistently contributes the smallest.
• Bioavailability-adjusted HQ (Table 5, “Adjusted HQ”): computed by multiplying HQ by analyte bioavailability (Cu 40%, Pb 60%, Cr 1%, Cd 50%, Ni 10%). Adjusted HI for the six subpopulations falls in the 1.1×10⁻² (female) to 1.6×10⁻² (age ≥41) range — roughly 20% lower than the unadjusted HI across subpopulations.
• Carcinogenic risk (TR, lifetime probability, dimensionless, Figure 2): computed for the three analytes with established oral slope factors (Pb, Cr, Cd). Individual TR values range from 1.62×10⁻⁷ (Cr in females) to 1.60×10⁻⁵ (Cd in age ≥41). None of the TR_total values for the six subpopulations exceeded the USEPA acceptable upper bound of 10⁻⁴. Cd contributes approximately 97% of the total cancer risk across subpopulations.

Methods

Ninety-one Tieguanyin tea samples (500 g each) were randomly collected from tea shops, supermarkets, and tea factories in Fujian Province, China; each sample was crushed, homogenised, and sifted through a 60-mesh (0.25 mm pore size) polyethylene sieve, then stored dark and dry until analysis. All glassware and polyethylene bottles were soaked in 10% HNO₃, rinsed with de-ionised water, and air-dried before use. For dry-leaf analysis, 0.3 g of sifted tea was digested overnight with 5 mL HNO₃ in a Teflon vessel, then microwave-digested on a TOPEX system (Preekem Instrument Technology, Shanghai) in a three-step program (120 °C / 5 min; 160 °C / 10 min; 180 °C / 10 min), evaporated to remove HNO₃, and reconstituted to volume with 0.2% HNO₃. For infusion analysis, 7 g of made tea was poured into 150 mL boiling de-ionised water and steeped for 10 minutes; the infusion was then filtered, cooled, and acidified to 0.2% HNO₃ before measurement. Copper, lead, chromium, cadmium, and nickel were measured by inductively coupled plasma mass spectrometry on a Thermo Fisher XSERIES 2 ICP-MS at 1.2 kW plasma power with 8.0 L/min plasma gas, monitoring isotopes ⁶⁵Cu, ²⁰⁸Pb, ⁵²Cr, ¹¹⁴Cd, and ⁶⁰Ni. Method accuracy was validated against the GBW10052 green-tea certified reference material (Institute of Geophysical and Geochemical Sciences, Beijing); spike recoveries were also computed at three concentrations (10, 50, 100 µg/L). Linearity R² ≥ 0.999 for all elements. Limits of detection (LOD, three SD of ten reagent blanks in 1% HNO₃) were 0.09, 0.01, 0.009, 0.003, and 0.02 µg/L for Cu, Pb, Cr, Cd, and Ni respectively; limits of quantification (LOQ, ten SD) were 0.3, 0.03, 0.03, 0.01, and 0.06 µg/L. All samples were measured in triplicate, and undetected samples were assigned the value of the corresponding LOQ. The transfer rate T (%) of each element from dry leaf to infusion was computed as T = (Cᵢ × Vᵢ) / (Cₜ × Mₜ) × 100% where Cᵢ and Cₜ are infusion and dry-leaf concentrations, Vᵢ is the infusion volume (150 mL), and Mₜ is the dry-leaf mass (7 g). The risk model used estimated daily intake EDI = (C × D × T) / Bw, hazard quotient HQ = EDI / RfD, and target carcinogenic risk TR = EDI × Sf, with D (tea consumption amount) and Bw (body weight) drawn from the authors’ previous consumption survey of male/female × age 18–40/age ≥41 × urban/rural subpopulations in Fujian (Yao et al. 2021, J. Food Sci.); bioavailability factors used in the adjusted-HQ calculation were Cu 40%, Pb 60%, Cr 1%, Cd 50%, Ni 10%, drawn from previously published bioavailability studies.

Implications

The source supports occurrence evidence for Cu, Pb, Cd, Cr, and Ni in Camellia sinensis dry leaf from a Chinese production-region market (Fujian Tieguanyin oolong), and for Cu, Pb, Cd, Cr, and Ni in the corresponding brewed infusion at a fixed 7 g/150 mL/10 min protocol. The internal infusion-exposure model returns unadjusted hazard indices of 3.8×10⁻² to 6.1×10⁻² across six demographic subpopulations and bioavailability-adjusted hazard indices of 1.1×10⁻² to 1.6×10⁻², in both cases well below the USEPA action threshold of 1. Cd contributes approximately 97% of the total carcinogenic risk across subpopulations even though Cd is the lowest single-analyte HQ contributor, because Cd’s oral slope factor (6.3 mg/kg/day) is more than ten times Cr’s (0.5) and more than 700 times Pb’s (0.0085). The paper applies the Cr-VI oral slope factor (0.5 mg/kg/day) to total-Cr exposure for the cancer-risk calculation on the grounds of biological reduction of Cr-VI to Cr-III; the paper does not run a Cr-VI extraction, so all Cr values are total Cr and the cancer-risk numbers are upper-bound estimates that assume the worst-case Cr-VI fraction. Cu is in the dry leaf at much higher mass concentrations than any of the other four analytes (8.18 mg/kg, roughly 4–200× the others) but has the lowest infusion transfer rate (10.2%) and a high oral RfD (40 µg/kg/day), so Cu’s HQ contribution stays small. The infusion-exposure ranking the paper highlights — Pb > Ni > Cd by adjusted-HQ contribution to HI, with Cu and Cr lowest — flips the dry-leaf ranking, which is driven by the dramatic differences in transfer rate between analytes. The paper’s HI and TR conclusions are conditioned on the 7 g/150 mL/10 min brewing protocol and on the Fujian-specific consumption survey; other brewing geometries (looser steep, multiple infusions, longer steep, smaller leaf:water ratio) would shift the infusion concentrations and the resulting risk numbers. The paper does not attach brand or grower names to any of the 91 sampled lots; all values reported here are sample-pool-level, consistent with the public-wiki brand firewall.

Wiki pages this source may touch

• camellia-sinensis
• tea
• tea
• tea-infusions
• true-tea-camellia-sinensis
• copper
• lead
• cadmium
• chromium
• nickel

Verification notes

The raw PDF is filed under raw/Manual Fetch Discovery/yao2022-matcha-heavy-metal.pdf and the raw_handle is preserved as MFD_yao2022-matcha-heavy-metal to keep the file-system pointer stable, but the file name is a misnomer: the paper studies Tieguanyin oolong tea (Camellia sinensis, semi-fermented), not matcha (Camellia sinensis, shade-grown green tea powder). Matcha is not within the scope of this source and the matcha product slug (matcha) is intentionally not in the products array. The cite-key yao2022-tieguanyin-tea-heavy-metals reflects what the paper actually reports.

Chromium values are total Cr; the paper does not speciate Cr-III vs Cr-VI and does not extract Cr-VI specifically, so the source does not route to metals/chromium-hexavalent. The paper’s application of the Cr-VI oral slope factor to total-Cr exposure for the cancer-risk calculation is reported in Key numbers and Implications as a paper-internal assumption, not adopted by the wiki as a synthesis claim. Below-detection Cd values were assigned the LOQ rather than half-LOQ per the paper’s own convention (§2.2 last sentence). The sampling year is not stated in the paper and sampling_year_range is left null. Method-section instrument and CRM identifiers (Thermo Fisher XSERIES 2 ICP-MS, TOPEX microwave digestion system, GBW10052 green-tea CRM) are preserved per the Part 12 scientific-reproducibility carve-out. No brand or grower names appear in the source’s findings, so the brand firewall is not engaged. The paper is open-access under CC BY 4.0 (MDPI Foods).

Page history

The five most recent substantive edits to this page. The full version history lives in git; when DOI minting comes online (see schema docs), each entry below will also link to a version-pinned DataCite DOI.