Yaqub et al. 2018 — Monitoring heavy metals and pesticides in Pakistani tea samples (Mansehra gardens and market brands)
This study assessed heavy metals and pesticides in tea samples from two sources: 52 samples from Mansehra tea gardens (Pakistan) and 25 commercial brand tea samples from local markets. Heavy metals measured were Zn, Fe, Cr, Cu, Mn, and Co by AAS; pesticides (Bifenthrin, Lambda-Chalothrin, Dichlorovas, Glyphosate, Imidacloprid, Difenaconazole, Emamectin) by HPLC. The paper is B-tier due to limited sample characterisation, AAS rather than ICP-MS, and primary focus on pesticide detection rather than metals risk for human health. Key metals findings: Co in source tea exceeded the EU allowed limit (0.01 ppm); Mn exceeded EU standards in both sample types; other metals (Zn, Fe, Cu, Cr) were within limits.
Key numbers
Tea samples from source (Mansehra gardens, n=52) — mean concentrations (ppm = mg/kg):
- Zinc: 1.3 ± 0.5; Iron: 45 ± 56; Copper: 1.5 ± 0.6; Manganese: 4 ± 3; Chromium: 2 ± 0.7; Cobalt: 1 ± 0.7
Tea brand samples (n=25):
- Zinc: 0.1 ± 0.2; Iron: ND; Copper: 0.02 ± 0.02; Manganese: 0.2 ± 0.2; Chromium: 0.002 ± 0.004; Cobalt: 0.006 ± 0.001
EU Maximum Residue Limits (MRLs) reference values:
- Zinc: 100; Iron: 500; Copper: 0.01; Manganese: 0.16; Chromium: 2.3; Cobalt: 0.01 (ppm)
Notable: Cobalt in garden source tea (mean 1 ppm) exceeded EU MRL of 0.01 ppm in all samples; Manganese in source tea (mean 4 ppm) exceeded EU MRL of 0.16 ppm. Note: Pb, Cd, As, Ni not measured — significant omission for HMT&C relevance.
Pesticides in brand tea: Imidacloprid at mean 379 ± 329 ppm (well above MRL of 0.01 ppm) in several commercial brand samples — a major pesticide contamination signal, though not a metal.
Methods (brief)
AAS (Buck Scientific 210 VGP) for metals; HPLC (Agilent 1260, ODS 18 Column) for pesticides. Microwave digestion for metals: 30 mL H₂O₂ + 50 mL HNO₃. LOD calculated as 3:1 signal:noise; LOQ as 10:1.
Limitations
Pb, Cd, As, and Ni not measured — the four highest-priority HMT&C analytes are absent. AAS limits sensitivity compared to ICP-MS for trace elements. Small commercial brand sample set (n=25). No speciation for Cr (total only). Pakistan-specific gardens; limited geographic generalisability.
Implications
- Certification: Low direct value for HMT&C threshold-setting because Pb, Cd, and As not measured. Useful only as a background reference for Mn and Co in Pakistani tea.
- Courses: Useful for pesticide-metal co-contamination module; Imidacloprid result is striking. Not a primary metal reference.
- App: Do not use for contamination_profile updates — key analytes not measured.