Brzezicha-Cirocka et al. 2016 — Monitoring heavy metals in green tea from China, India, and Japan
This study measured Cd, Pb, and 11 other elements (Ca, K, Mg, Na, P, Mn, Fe, Zn, Cu, Co, Cr, Ni) in dry leaves and infusions of 41 green teas purchased in Poland representing China (17 original + 10 marketed), India (2 original), Japan (7 original), and mixed/unspecified origins (5 marketed). Both dry tea and prepared infusions were analysed to assess leaching percentages and PTWI exceedance risk. Indian teas had the highest Cd leaching (43.8%) while Chinese teas had the lowest (9.41%). Chemometric analysis (factor and cluster analysis) successfully differentiated samples by geographic origin using K, P, Mn, Fe, Cu, Co, and Cd as key discriminating elements.
Key numbers
Toxic metal concentrations in dry tea leaves (mg/100g, Table 3):
China original (n = 8×3):
- Cd: 0.01 ± 0.004 mg/100g, leaching 46.3 ± 21.6%
- Pb: 0.73 ± 0.36 mg/100g, leaching 16.9 ± 14.3%
India original (n = 2×3):
- Cd: 0.003 ± 0.0005 mg/100g, leaching 43.8 ± 8.3% (highest leaching)
- Pb: 0.1 ± 0.07 mg/100g (lowest Pb among origins)
Japan original (n = 7×3):
- Cd: 0.006 ± 0.001 mg/100g, leaching 17.6 ± 9.3%
- Pb: 0.84 ± 0.32 mg/100g
Marketed tea (n = 24×3):
- Cd: 0.004 ± 0.001 mg/100g; Pb: 0.45 ± 0.38 mg/100g
Average infusion Pb and Cd (from 200 mL beverage):
- Pb: 0.002 mg/200mL; Cd: 0.003 mg/200mL
Note: Units above are mg/100g dry leaf = 10,000 µg/kg. Converting: China Pb ~7,300 µg/kg dry leaf, India Pb ~1,000 µg/kg dry leaf. These are dry leaf concentrations — not as-consumed infusion values, which are substantially lower due to incomplete leaching.
PTWI exceedance: Cd PTWI could be approached with high daily tea consumption; study flags as concern primarily for Indian teas due to high leaching %.
Methods (brief)
AAS (Thermo Scientific i3000, flame air-acetylene) for Ca, K, Mg, Na, P, Mn, Fe, Zn, Cu, Co, Cd, Cr, Ni, Pb. Dry ashing at 540°C. Tea infusions prepared with 2.00g tea in 200mL water, 5 min infusion, then processed through same ashing procedure. LODs: Cd 0.003 mg/100g, Pb 0.004 mg/100g. NCS ZC73014 certified tea reference material used; recoveries satisfactory. Statistical analysis: Spearman rank correlation, Kruskal-Wallis, factor analysis, cluster analysis (Ward’s Euclidean distance).
Limitations
Small sample sizes per origin (2 India samples is notably thin). Samples purchased from a Polish retail market — all labelled origins are trust-dependent. No As or Hg measured. Pb levels are unusually high in dry tea leaf (mg/100g range); this is a known dry-leaf characteristic that overstates as-consumed exposure, which the leaching data addresses but the frontmatter cannot fully capture. Mn concentrations are very high in tea generally (Mn > Al > Ba… as found in Hangzhou study) but not emphasised here.
Implications
- Certification: Pb in dry tea leaf (particularly Chinese and Japanese origin) is high in absolute terms but leaching is low (17%); as-consumed Pb exposure from tea infusion is substantially lower. Cd leaching from Indian tea is higher (44%) — worth flagging for infusion-based risk assessment.
- Courses: Key geographic differentiation paper for green tea. Demonstrates that origin fingerprinting via mineral composition is analytically feasible (K, P, Mn, Fe, Cu, Co, Cd as origin markers).
- App: Dry-leaf Pb/Cd values are not directly usable for contamination_profile without conversion to as-consumed infusion basis. Flag for synthesis pass with other tea papers.