Fischer and Brodziak-Dopierała 2022 — Mercury in Polish spice plants: commercial vs. home-grown
This study from the Medical University of Silesia measured total mercury (tHg) in 48 samples of four leafy spice species — peppermint (Mentha piperita), common basil (Ocimum basilicum), lovage (Levisticum officinale), and parsley (Petroselinum crispum) — comparing commercially purchased products (n=28, including organic and non-organic) with plants grown independently by consumers in home gardens at five locations in southern Poland (n=20). All values were below the EU maximum level of 0.03 mg/kg (30 µg/kg) for deciduous spice plants. Self-cultivated plants had statistically significantly higher Hg concentrations than commercial products, while organic vs. non-organic commercial products showed no significant difference. Growing location influenced Hg level, with plants from Płoki (Małopolskie voivodeship, near a coal-fired power plant) showing the highest concentrations.
Key numbers
All concentrations in µg/kg (ppb), total Hg:
All samples combined (n=48):
- Range: 1.20–17.35 µg/kg
- Mean: 6.95 µg/kg; median: 6.17 µg/kg; IQR: 4.58–8.83 µg/kg
By species:
- Peppermint (n=10): mean 9.39 ± 5.83 µg/kg; median 9.58 µg/kg; range highest standard deviation, indicating high variability
- Parsley (n=12): mean 6.72 ± 2.39 µg/kg; median 6.40 µg/kg
- Basil (n=15): mean 6.19 ± 2.08 µg/kg; median 5.52 µg/kg
- Lovage (n=11): mean 6.02 ± 3.67 µg/kg; median 5.27 µg/kg
- Species differences were not statistically significant (p=0.2968)
By product type:
- Commercial products (n=28): mean 5.15 ± 2.58 µg/kg; median 4.99 µg/kg
- Home-grown (n=20): mean 9.47 ± 3.58 µg/kg; median 8.70 µg/kg
- Difference statistically significant (p=0.00003)
Commercial sub-comparison:
- Non-organic (n=24): mean 5.20 µg/kg
- Organic (n=4): mean 4.88 µg/kg; not significantly different (p=0.97381)
By growing location (home-grown only):
- Płoki (Małopolskie, near coal power plant): highest across all species, e.g., peppermint up to 12.90 µg/kg
- Jemielnica (Opolskie, rural): lowest home-grown values
- Urban areas (Katowice, Mysłowice) similar to or lower than rural Płoki
EU regulatory context:
- Commission Regulation (EU) 2018/73: maximum level for mercury in deciduous spice plants (herbs) = 0.03 mg/kg (30 µg/kg)
- All tested samples were below this limit (maximum observed 17.35 µg/kg vs. limit 30 µg/kg)
Estimated daily intake (EDI) at 0.7 g/day consumption, 70 kg adult:
- Home-grown: EDI = 9.47 µg/kg × 0.7 g/day / 70 kg = 0.0000947 mg Hg/kg bw/day (vs. reference value)
- Commercial: EDI = 5.15 µg/kg × 0.7 g/day / 70 kg = 0.0000515 mg Hg/kg bw/day
- Both below the WHO PTWI; per Kowalska (2021) the level is not considered dangerous at Polish consumption rates
Methods (brief)
Mercury analyzer AMA 254 (Altec, Czech Republic), AAS-based cold vapor technique, wavelength 253.65 nm, O₂ carrier gas. LOD 0.01 ngHg/g (0.01 µg/kg). Validated against INCT-MPH-2 reference material: found 0.0166 ± 0.0001 mg/kg, recovery 92.22%. Detection method covers total Hg regardless of speciation. Each sample measured three times; final result is arithmetic mean. Statistical analysis: Shapiro-Wilk normality test, Mann-Whitney U (two groups), Kruskal-Wallis (multiple groups), p<0.05 two-tailed.
Limitation: Small sample sizes (n=4 organic, n=20 home-grown total), limited to four species and five growing locations in southern Poland; not representative of all commercial spice origins.
Implications
Certification: Total Hg in leafy herbs and spices is well below EU regulatory limits even at the highest values observed. However, the source of cultivation matters: home-grown herbs near industrial point sources (coal-fired power plants, steel mills) can have Hg levels approximately twice those of commercial products. HMT&C does not certify home-grown product, but this finding informs supplier verification requirements: brands sourcing fresh herbs from contract growers in industrially contaminated regions should include Hg testing in their QC protocols even though field values are below EU limits, because the gap between observed maximums and the limit is smaller than it appears when expressed as a single-point mean.
Courses: The organic vs. non-organic finding (no significant difference) is a recurring theme in heavy-metals literature and is worth featuring as a case study: the “organic” label does not guarantee lower heavy-metal content because contamination is driven by soil and atmospheric deposition conditions, not by fertilizer and pesticide choices.
App: tHg in herbs and spices is not a meaningfully elevated risk at typical dietary consumption rates. App risk scoring for herb/spice categories should treat tHg as low priority relative to Pb and Cd, consistent with the EDI values in this study.