Zhang et al. 2018 — Heavy metal accumulation in tea leaves, Puan County, Guizhou Province
This study measured Al, Mn, Pb, Cd, Hg, As, Cr, Ni, Cu, and Zn in 13 young tea leaf samples, 13 mature tea leaf samples, and 13 corresponding soil samples (0–30 cm) from the Puan tea-growing area of Guizhou Province, China, using ICP-MS and ICP-AES, and assessed potential health risks from consuming infusions brewed from young and mature tea leaves. Young tea leaf concentrations were well below China’s national safety limits for Pb, Cu, As, Hg, Cd, and Cr. Mature tea leaf concentrations for these same elements were also below safety limits. However, for mature tea infusions, 38.46% of samples had hazard index (HI) values above 1, with the risk primarily driven by Mn and Al. The soil was moderately polluted by Cu.
Key numbers
Tea leaf concentration ranges (mg/kg dry weight):
| Element | Young leaves (range) | Mature leaves (range) | China safety limit |
|---|---|---|---|
| Al | 250–660 | 4300–10,400 | N/A |
| Mn | 194–1130 | 536–4610 | N/A |
| Pb | 0.107–0.400 | 0.560–1.265 | 5.0 mg/kg |
| Cd | 0.012–0.092 | 0.040–0.087 | 0.3 mg/kg |
| Hg | 0.014–0.085 | 0.043–0.089 | 0.3 mg/kg |
| As | 0.073–0.456 | 0.189–0.453 | 1.0 mg/kg |
| Cr | 0.33–1.26 | 0.69–2.91 | 5.0 mg/kg |
| Ni | 6.33–14.90 | 3.43–14.20 | N/A |
| Cu | 14.90–26.10 | 6.17–16.25 | 30 mg/kg |
| Zn | 35.8–50.3 | 9.1–20.0 | N/A |
All Pb, As, Hg, Cd, and Cr values in both young and mature leaves were below China’s national standards (GB 2762-2017; NY/T 288-2012).
Soil heavy metal background: Al ~106×10³, Mn ~214, Pb ~20.9, Cd ~0.09, Hg ~0.12, As ~17.5, Cr ~121, Ni ~27.8, Cu ~131.2, Zn ~64 mg/kg. Soil pollution ranking: Cu > Cr > Hg > As > Ni > Zn > Pb > Mn > Cd.
Mature tea BCF for Mn: average 12.5 (strongest bioconcentration factor among all elements). Al BCF in mature leaves also elevated relative to young leaves.
Health risk (HI): Average HI for adults via young tea infusion = 0.272 (all below 1, no significant risk). For mature tea infusions, 38.46% of samples had HI > 1; risk dominated by Mn and Al contributions.
LOD values (tea samples): Al 10, Mn 0.1, Pb 0.005, Cd 0.001, Hg 0.001, As 0.005, Cr 0.05, Ni 0.02, Cu 0.01, Zn 0.1 µg/g. Mean recoveries 90–113% in two standard reference materials.
Methods (brief)
ICP-MS (Agilent 7700x) and ICP-AES (Vista-MPX, Agilent) at ALS Minerals-ALS Chemec laboratory (Guangzhou, China). Tea samples: 1.0 g digested in 5 mL concentrated HNO₃ in Teflon vessel (8 h room temperature, then 3 h graphite furnace); diluted to 25 mL with 2% HCl. Soil samples: HClO₄-HNO₃-HF-HCl digestion. Sampling April 2016: 13 soil samples, 13 young tea leaf and 13 mature tea leaf pairs. Health risk: THQ and HI per US EPA framework. Adult body weight 60 kg, exposure frequency 365 days/year, 70-year lifetime. Tea consumption assumed: 1250 mL/person/day (equivalent to 8 g dry tea leaves/day) for infusion; daily consumption of dry tea leaves not assessed.
Limitations
Single county (Puan), 13 sampling sites — geographically narrow. Puan County has specific geological characteristics (terrestrial siliceous clastic rocks, acidic sandy yellow soil) that may not represent broader Guizhou or Chinese tea production. Study does not speciate As (total As only). The Mn and Al health risk interpretation requires caution: Mn and Al health risk framework for oral exposure from tea is less established than for canonical heavy metals. BCF calculation based on soil total metal content, not bioavailable fraction.
Implications
- Certification: Mature tea leaves show substantially higher Al (up to 10,400 mg/kg) and Mn (up to 4,610 mg/kg) than young leaves — relevant if HMT&C were to consider tea products. Pb, Cd, As, Hg, and Cr all below Chinese national limits in both leaf types.
- Courses: Demonstrates the importance of leaf age and maturity in tea heavy metal accumulation — young vs mature leaves have dramatically different profiles. The Al accumulator characteristic of tea is well illustrated.
- App: Note only — contamination_profile for tea. This source reports Chinese tea; Puan County is a specific high-altitude, acidic-soil production area. Geographic specificity limits generalizability to globally traded tea.
- Microbiome: Not applicable.