Zergui et al. 2023 — Trace metals in coffee by origin, form, and packaging (Algeria)
This cross-sectional study measured 10 trace elements (Ni, Cr, Pb, Zn, Cu, Co, Cd, As, Mn, Al) by ICP-MS in 44 coffee samples purchased from Chlef markets in Algeria, covering instant coffee (n=20) from 8 country origins (France, Italy, Sweden, Switzerland, UK, Poland, USA, Algeria), local-brand instant coffee (n=12), and roasted coffee sold in bulk (n=12). The study reports statistically significant differences (P < 0.0001) between coffee forms (ground, instant, beans) and packaging types (capsules, cartons, glass bottles, bulk) for most elements. Aluminum and manganese dominated by concentration; cadmium and arsenic were detectable but at low levels. Chronic daily intake (CDI) exceeded the reference dose (RfD) for Cd and Al in different forms. Evidence tier is B: single-location marketplace sampling in Algeria, small n, and no origin-confirmed trace of the 44 samples through supply chain.
Key numbers
- n = 44 samples: 20 instant (8 countries of origin), 12 local instant, 12 roasted bulk
- Dominant elements (mean mg/kg in coffee samples): Al 59.88 ± 54.86; Mn 16.26 ± 24.59; Cu 11.60 ± 11.55; Cd 9.92 ± 10.32; Ni 0.82 ± 0.81; As 0.25 ± 0.19; Pb 1.14 ± 1.99; Cr 2.71 ± 2.52
- Cd mean 9.92 mg/kg is anomalously high — substantially above other published coffee Cd values (typically 0.01–0.05 mg/kg in coffee beverages); this likely reflects dry-weight matrix in the coffee digest. Units are mg/kg in dry coffee not beverage; the authors apply EDI calculations using a 5 g/serving dose.
- LOD (mg/kg): Ni 0.008, Cr 0.02, Pb 0.02, Zn 0.03, Cu 0.001, Co 0.001, Cd 0.02, As 0.01, Mn 0.002, Al 0.06
- LOQ (mg/kg): Ni 0.025, Cr 0.06, Pb 0.06, Zn 0.1, Cu 0.06, Co 0.005, Cd 0.06, As 0.03, Mn 0.006, Al 0.18
- Highest TE levels found in ground coffee; lowest in coffee beans
- Capsule-packaged coffee: high Cu, Co, Zn, Mn, Al; carton-packaged: high As, Pb, Cr, Cd
- Maximum permissible levels referenced: Ni 0.10, Cr 0.10, Pb 1.0, Cd 0.1, As 1.4 mg/kg (per Omeje et al. and Pigozzi et al. references, not regulatory agency primary sources)
- Highest EDI: Al 0.0109 mg/kg BW/day (ground coffee, capsules); CDI for Cd and Al exceeded reference doses in different coffee forms
- THQ > 1.0 for Cd and Al (chronic non-carcinogenic risk flag); HI > 1.0 for different coffee forms
- PCA: first two axes explained 78.69% of variance; Al, Ni, Cu, Co, Zn correlated on axis 1; As and Pb on axis 2 (negatively correlated with Mn and Al)
Methods (brief)
Samples collected September 2022, Chlef region markets, Algeria. Digestion: 3 g coffee + 5 mL HNO₃ (65%) + 1 mL KOH (5%) in ceramic capsules; microwave (MPS 320, 200°C, 3-step). Filtered (0.45 µm), diluted to 25 mL. ICP-MS: ELAN DRC II (PerkinElmer). LOD and LOQ: 3× and 10× SD of 10 blank measurements. CRM: INC-TEL-1 Black Tea Leaves (INCT, Poland). Recovery: 97–102%. RSD < 5% required. Analysis in triplicate. Health risk: EDI, CDI, THQ per USEPA equations (RfDs from USEPA); HI = ΣTHQ.
Limitations
Evidence tier B: small n (44), single-marketplace sampling in Algeria. Country-of-origin on packaging reflects country of manufacture or import, not necessarily origin of coffee beans (especially for instant and packaged products). The Cd mean (9.92 mg/kg) is an order of magnitude higher than published literature for coffee Cd; this warrants scrutiny — the study does not explain this discrepancy and the CRM used (black tea leaves) is not the standard CRM for coffee. As mean (0.25 mg/kg) is also at the high end of reported coffee As values. The study reports on ground coffee and instant but not espresso as prepared beverage; dry-weight coffee values require dilution factor adjustment to estimate beverage exposure.
Implications
- Certification: Not directly relevant to HMT&C certification given the anomalous Cd values and methodology concerns. The geographic origin × metal form finding (carton-packaged ground coffee from Algeria contains elevated As, Pb, Cr, Cd) is an interesting origin-packaging interaction signal but not robustly established at n=44.
- Courses: Useful as a teaching example of how packaging type and coffee form affect extractable metals concentration, but the Cd anomaly should be discussed critically. The EDI/THQ/HI risk framework is well-illustrated here.
- App: As a single-market, small-n study with methodological questions around Cd values, this source should not drive the coffee ingredient contamination profile. Use as supplementary context only; weight lower than A-tier occurrence surveys.
- Microbiome: Not primary topic.