Kazeminia et al. 2023 — Systematic review: heavy metals in tea herb, health effects, and mitigation strategies
Kazeminia et al. present a systematic review of 157 articles (screened from 961, published 2000–2022) examining heavy metal contamination in tea herb (Camellia sinensis), associated health effects, and strategies to reduce exposure. Metals covered include As, Cd, Cr, Pb, Hg, Al, Fe, Ba, Ni, and Co. The review synthesises tolerable daily intake (PTDI) and tolerable weekly intake (PTWI) data for multiple metals in black tea and tea infusion, and documents that HM levels in tea vary substantially by region, proximity to pollution sources, genetic cultivar differences, brewing method, and steeping time. Key mitigation strategies reviewed include cleaner irrigation water, avoiding acidifying fertilizers, liming soil, restricting cultivation near pollution sources, shorter brewing times, and phytoremediation.
Key numbers
- 157 articles included after systematic screening
- Maximum HM concentrations for black tea raw herb (from Table 2): Ni PTDI 0.51 mg/kg·d, PTWI 3.60; Co 0.39/2.73; Cr 0.18/1.30; Cd 0.018/0.13; Pb 0.16/1.12; As 0.006/0.042 (all mg/kg·d or mg/kg·w at 65 kg body weight)
- Black tea infusion values (Table 3) approximately 6–10× lower than dry herb values, reflecting brewing extraction efficiency
- Geographic drivers: China, India, Sri Lanka, Turkey, Kenya cited as highest-metal origins in certain metals depending on regional soil and air quality
- Brewing time effect: longer steeping increases HM extraction into infusion; 3 min vs. 10 min can increase extracted Pb by 2–3×
Methods (brief)
Systematic review; PRISMA-style screening; 2000–2022 literature; Science Direct, Google Scholar, PubMed; 157 articles included; Iranian-led authorship; B-tier (secondary synthesis, not primary data).
Implications
Certification: Provides the systematic evidence base for tea herb as a multi-metal contamination matrix. Brewing method (steeping time, water temperature) modulates exposure substantially. Courses: Good overview reference for tea HM landscape; particularly useful for the brewing-method exposure discussion. App: Tea herb matrix carries Pb, Cd, Al, Ni, Cr signals; brewing parameters affect as-consumed concentrations and should be considered in exposure modeling.