Dghaim et al. 2015 — Heavy metals in traditional herbs consumed in the UAE
This peer-reviewed primary study from Zayed University (Dubai) measured cadmium, lead, copper, iron, and zinc in 81 samples of seven traditional herbs purchased from Dubai markets. All concentrations are expressed as dry weight. Microwave-assisted digestion (US-EPA Method 3052) was applied, and metals were determined by AAS. The headline finding is that 64% of all samples exceeded the WHO/FAO permissible limit for lead in medicinal herbs (10 mg/kg dry weight), and 29% exceeded the WHO/FAO permissible limit for cadmium (0.3 mg/kg). The lead contamination was particularly high in sage (100% of samples above PL), oregano (90%), thyme (91%), and basil (90%), all with maximum values of 16–23 mg/kg. Cadmium exceedances were most prevalent in basil (80%) and sage (66%).
Key numbers
Cadmium (Cd) — concentration range (mg/kg dry weight):
- All herbs combined: < 0.1 to 1.11 mg/kg
- Mint: ND (0/13 samples above PL)
- Parsley: up to 0.21 mg/kg (0% above PL of 0.3)
- Chamomile: up to 0.82 mg/kg (55% above PL)
- Basil: 0.13–1.11 mg/kg (80% above PL)
- Sage: up to 0.88 mg/kg (66% above PL)
- Oregano: up to 0.35 mg/kg (9% above PL)
- Thyme: up to 0.63 mg/kg (27% above PL)
- Overall: 29% of all samples above WHO/FAO PL of 0.3 mg/kg
Lead (Pb) — concentration range (mg/kg dry weight):
- All herbs combined: < 1.0 to 23.52 mg/kg
- Mint: 1.44–9.24 mg/kg (0% above PL of 10)
- Parsley: up to 12.83 mg/kg (46% above PL)
- Chamomile: 5.37–11.40 mg/kg (44% above PL)
- Basil: 9.01–16.15 mg/kg (90% above PL)
- Sage: 12.66–21.76 mg/kg (100% above PL)
- Oregano: 9.39–18.06 mg/kg (90% above PL)
- Thyme: 9.07–23.52 mg/kg (91% above PL)
- Overall: 64% of all samples above WHO/FAO PL of 10 mg/kg
Note: The WHO/FAO permissible limit of 10 mg/kg for Pb in medicinal herbs is far above current EU limits (3 mg/kg for dried herbs, EU 1881/2006, later tightened to lower values). The high exceedance rates should be interpreted with this regulatory context.
Copper (Cu): 1.44–156.24 mg/kg; 12% above Chinese PL of 20 mg/kg. Zinc (Zn): 12.65–146.67 mg/kg; 19% above WHO PL of 50 mg/kg. Iron (Fe): 81.25–1,101.22 mg/kg; no WHO PL established.
Methods (brief)
Microwave-assisted digestion (US-EPA Method 3052) using HNO3/HCl/H2O2 in MARS CEM microwave system. AAS (Varian AA240FS). Method quantification limits: 0.1 mg/kg (Cd), 1 mg/kg (Pb). Calibration curve with r=0.995. Samples purchased from 13 sources in Dubai markets (supermarkets and specialist herb shops). Fresh samples air-dried at room temperature, then powdered and sieved. Results expressed as dry weight. Three subsamples per source averaged. Analytical QC included calibration checks and replicate analysis.
Limitations: Small n per herb type (9–13 samples); only total metals measured, no speciation; single city (Dubai), mix of local and imported product with origin not separately reported; no separate analysis of fresh vs dried within each herb type; 2015 data and UAE market conditions may differ from European retail.
Implications
Certification: UAE market herbs show high Pb contamination: 64% of samples exceed WHO PL of 10 mg/kg. However, EU limits are stricter (3 mg/kg for dried herbs under EU 1881/2006), making the EU-market contamination burden different from UAE retail. High-risk herbs for Pb in this dataset: sage, oregano, basil, thyme. For Cd: basil and chamomile are notably elevated.
Courses: Good illustrative case for geographic sourcing effects on herb contamination. The pattern of high Pb in sage, oregano, and thyme (Mediterranean herbs with a high proportion of Middle East–origin supply chains) is instructive for sourcing module content.
App: Pb in UAE-market dried herbs: typical range approximately 9–23 mg/kg for high-risk species (sage, oregano, thyme, basil), far above typical EU-sourced product levels. Cd in UAE herbs: up to 1.11 mg/kg in basil, 0.88 mg/kg in sage. These values represent an upper-end geographic bound; the app should flag herb origin region as a key risk modifier for lead and cadmium.