Aluminium: High in the Leaf, Low in the Cup
Tea plants are exceptional aluminium accumulators — concentrations of 500–3,000 mg/kg dry leaf weight in mature leaves from acidic soils are reported. This looks alarming until the transfer rate to brewed tea is measured: multiple studies find only 2–6% of leaf aluminium enters the brew. For a typical 3g serving of leaf brewed in 200ml, this translates to 0.01–0.1 mg of aluminium per cup — compared to a PTWI (Provisional Tolerable Weekly Intake) of 7mg/kg body weight (WHO).
A 70kg individual could consume approximately 70mg of aluminium per week from all sources before reaching the PTWI. The contribution from brewed tea is therefore a small fraction of normal aluminium exposure from food (1–10mg/day from food in general). The exception is matcha, where the whole leaf is consumed — matcha could contribute substantially more aluminium if grown on high-aluminium soils.
| Metal | Leaf concentration (range) | Typical brew transfer | Per-cup exposure | PTWI (adult, 60kg) |
|---|---|---|---|---|
| Aluminium | 500–3,000 mg/kg | 2–6% | 0.05–0.5 mg | 2,500 mg/week |
| Lead | 0.1–5 mg/kg | 10–60% (surface contamination) | 0.001–0.05 mg | 0.025 mg/day (FAO/WHO) |
| Cadmium | 0.01–0.5 mg/kg | 5–20% | <0.001–0.02 mg | 0.4 mg/week |
| Arsenic (inorganic) | 0.01–1 mg/kg | 20–40% | <0.001–0.1 mg | 0.015 mg/day |
| Fluoride | 30–500 mg/kg | 40–80% | 0.3–4 mg | 10 mg/day (UL) |
🧠 Expert Tip: Matcha Sourcing
If you drink matcha regularly, source from producers who publish third-party heavy metal analysis. Reputable Japanese matcha producers (particularly from Uji, Nishio) routinely test for heavy metals and are subject to strict Japanese food safety regulations. Cheap matcha from unknown sources — particularly those grown on soils with industrial history — carries higher risk.
Lead: The Atmospheric Deposition Problem
Lead in tea arrives primarily as surface contamination from atmospheric deposition — lead aerosols from combustion, traffic, and industrial sources settle on tea leaves in the field. Unlike aluminium (which is absorbed internally by the plant), much of the lead load sits on the physical surface of leaves and can be substantially removed by rinsing. Studies show that a 5-second rinse of tea leaves removes 35–60% of surface lead before brewing begins.
Arsenic and Origin Matters
Inorganic arsenic — the toxic form — is elevated in tea grown on soils with legacy contamination from old pesticide use (lead arsenate was widely used before 1970) or mining activity. Most Darjeeling, Chinese, and Japanese teas from modern estates show very low arsenic. Higher arsenic levels have been documented in some Chinese teas from specific industrial mining regions. Origin transparency and third-party testing provide the necessary assurance.
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