The Mercury Concentration in Spice Plants

Overview

This Medical University of Silesia study measured total mercury (tHg) in 48 dried leafy-spice samples comprising four species — peppermint (Mentha piperita), common basil (Ocimum basilicum), lovage (Levisticum officinale), and parsley (Petroselinum crispum) — comparing commercially purchased Polish products (n=28; 24 non-organic and 4 producer-certified organic) with plants grown by consumers in home gardens at five locations in southern Poland (n=20). Detection was by cold-vapour AAS on an AMA 254 direct mercury analyzer. All samples were below the EU maximum level of 0.03 mg/kg (30 µg/kg) for mercury in deciduous spice plants. Self-cultivated plants had statistically significantly higher Hg concentrations than commercial products (p < 0.001), while producer-labelled organic vs. non-organic commercial products showed no significant difference. Among home-grown samples, location influenced Hg level, with plants from Płoki (Małopolskie voivodeship, near a coal-fired power plant and closed hard-coal mine) showing the highest concentrations across species.

Key numbers

All concentrations in µg/kg dry weight, total mercury.

All samples combined (n=48):

Range: 1.20–17.35 µg/kg
Mean ± SD: 6.95 ± 3.70 µg/kg
Median (Q1–Q3): 6.17 (4.58–8.83) µg/kg

By species (Table 2):

Peppermint (n=10): mean 9.39 ± 5.83 µg/kg; median 9.58 (Q1–Q3 2.40–14.18) µg/kg
Parsley (n=12): mean 6.72 ± 2.39 µg/kg; median 6.40 (Q1–Q3 5.83–7.64) µg/kg
Basil (n=15): mean 6.19 ± 2.08 µg/kg; median 5.52 (Q1–Q3 4.72–7.24) µg/kg
Lovage (n=11): mean 6.02 ± 3.67 µg/kg; median 5.27 (Q1–Q3 3.08–8.27) µg/kg
Species differences not statistically significant (Kruskal–Wallis p = 0.2968)

By product type (Table 2):

Commercial products (n=28): mean 5.15 ± 2.58 µg/kg; median 4.99 (Q1–Q3 3.23–6.54) µg/kg
Home-grown (n=20): mean 9.47 ± 3.58 µg/kg; median 8.70 (Q1–Q3 6.38–11.55) µg/kg
Difference statistically significant (Mann–Whitney U p < 0.001; reported p = 0.00003)

Commercial sub-comparison (Table 2):

Non-organic (n=24): mean 5.20 ± 2.64 µg/kg; median 4.99 (Q1–Q3 3.65–6.19) µg/kg
Producer-certified organic (n=4): mean 4.88 ± 2.56 µg/kg; median 4.91 (Q1–Q3 2.69–7.07) µg/kg
Difference not statistically significant (p = 0.97381)

Per-species means within each product type (text §3):

Commercial: parsley 6.03, basil 5.43, lovage 3.23, peppermint 2.40 µg/kg
Home-grown: peppermint 14.18, lovage 8.27, parsley 7.62, basil 6.00 µg/kg
Within-species commercial-vs-home-grown differences were statistically significant only for lovage and peppermint

By growing location, home-grown only (text §3 + Figure 3):

Highest median across species: Płoki (Małopolskie, near coal-fired power plant and closed hard-coal mine), median ≈ 12.90 µg/kg across all four species
Lowest median across species: Jemielnica (Opolskie, rural, no major industrial sources)
Rural Jastrząb (Śląskie) was comparable to urban Katowice/Mysłowice and lower than rural Płoki, indicating that rural-vs-urban location does not predict Hg burden on its own
Highest individual location-species values at Płoki: parsley 12.19 µg/kg (the maximum parsley value in the home-grown set, range 5.76–12.19 µg/kg)
Home-grown sample range overall: 4.98–17.35 µg/kg (text §4)

EU regulatory context:

Commission Regulation (EU) 2018/73 (amending Annexes II and III of Reg. (EC) 396/2005): maximum mercury residue level in leafy spice plants (deciduous herbs) = 0.03 mg/kg = 30 µg/kg
All 48 samples were below the limit (observed maximum 17.35 µg/kg in a home-grown peppermint sample)

Estimated daily intake (EDI), authors’ calculation (text §4):

Assumed consumption 0.7 g/day spices and herbs (Polish average; Kowalska 2021); adult body weight 70 kg
Home-grown: EDI = 9.47 µg/kg × 0.7 g/day ÷ 70 kg ≈ 9.47 × 10⁻⁵ mg Hg/kg bw/day
Commercial: EDI = 5.15 µg/kg × 0.7 g/day ÷ 70 kg ≈ 5.15 × 10⁻⁵ mg Hg/kg bw/day
Both values are below the JECFA PTWI for inorganic mercury (4 µg/kg bw/week, equivalent to ≈ 5.7 × 10⁻⁴ mg/kg bw/day); authors conclude Polish dietary spice consumption does not constitute a mercury risk

Methods (brief)

Direct mercury analyzer AMA 254 (Altec, Praha, Czech Republic): catalytic combustion thermal-decomposition cold-vapour atomic absorption at 253.65 nm with O₂ carrier gas (purity ≥ 99.5%, inlet 200–250 kPa; stage times 120, 140, 60 s). LOD 0.01 ngHg/g (i.e. 0.01 µg/kg). Method covers total Hg regardless of speciation. Each spice sample was prepared as three ~50 mg replicate weighings on a RADWAG analytical balance (Radom, Poland); final reported value is the arithmetic mean of three measurements. Home-grown plant material was air-dried at room temperature in a shaded room, then ground in a porcelain mortar; commercial products were ground identically. Method validation used the INCT-MPH-2 Mixed Polish Herbs reference material (Institute of Nuclear Chemistry and Technology, Warsaw): six replicate determinations gave 0.0166 ± 0.0001 mg/kg with 92.22% recovery against the certified value. Statistical analysis used Statistica 13.3 (StatSoft, Kraków): Shapiro–Wilk normality testing, Mann–Whitney U (two groups), Kruskal–Wallis (more than two groups), p < 0.05 two-tailed.

Study limitations: small group sizes (notably n=4 organic commercial samples; n=20 home-grown samples spread across five locations and four species, leaving only one replicate per species per location); restricted to four species and southern-Poland growing locations; commercial-product origin not characterised beyond “popular Polish-market producers”; no speciation (total Hg only); single-season harvest (June, mid-growing-season) so seasonal accumulation effects reported in cited prior work were not captured.

Implications

Certification: Contributes occurrence data for leafy culinary herbs (peppermint, basil, lovage, parsley) and for the commercial-vs-home-grown comparison, in a Polish/EU regulatory context. Across this dataset, total Hg in dried leafy herbs sat well below the EU 30 µg/kg residue limit, with the observed maximum (17.35 µg/kg, home-grown peppermint) at approximately 58% of the limit. The commercial-vs-home-grown gap (mean 5.15 vs 9.47 µg/kg) is the principal occurrence finding for supplier-context purposes; the producer-labelled “organic” vs. non-organic commercial subset showed no statistically significant Hg difference within this study’s small organic subsample (n=4).

Courses: Adds an example for course material on the relationship between certification labelling and contamination outcome: within this study’s commercial subset, the producer-labelled “organic” subsample (n=4) did not differ statistically significantly in Hg content from non-organic commercial products (n=24). Adds a worked EDI calculation (authors’ method) for spice intake at Polish per-capita consumption (0.7 g/day).

App: Provides total-Hg occurrence values for four leafy herb species in Polish/EU supply context. Cultivation-origin metadata (commercial vs. home-grown, near vs. far from coal-fired industrial point sources) is informative for app-side scoring of provenance categories where reported.

Verification notes

2026-05-29 merge-enhance pass (v2.0 skill): re-read PDF cover-to-cover including all tables.

Corrected broken regulation wikilink: [[regulations/eu-reg-2018-73-mercury-herbs]] → [[regulations/eu-reg-2018-73-mercury-compounds-mrls]] (the existing regulation page slug).
Corrected misattribution of the 12.90 µg/kg figure: prior page text “Płoki … e.g., peppermint up to 12.90 µg/kg” implied 12.90 was a peppermint-specific value. Per paper page 5, “Hg concentration was the highest for all plants (12.90 µg/kg)” — this is the location median across all four species at Płoki (visible in Figure 3), not a peppermint-specific value. The peppermint maximum at any location is captured by the home-grown peppermint mean of 14.18 µg/kg (text §3) and the overall range maximum of 17.35 µg/kg.
Removed fresh-herbs from matrices:: all 48 samples (both commercial and home-grown) were measured as dried plant material (home-grown samples were air-dried at room temperature before grinding and analysis, paper page 3). dried-herbs and spices better describe what was measured; fresh-herbs is retained as an ingredients: wikilink because the home-grown subset documents fresh-grown supply that was then dried for the analysis.
Added [[ingredients/parsley]] to ingredients:: parsley has a dedicated wiki ingredient page and this paper provides species-specific parsley data (n=12, mean 6.72 µg/kg overall and 12.19 µg/kg maximum at Płoki).
Populated sampling_locations: from Table 1 (Katowice, Mysłowice, Jastrząb in Śląskie voivodeship; Płoki in Małopolskie; Jemielnica in Opolskie).
Trimmed Part 2 wiki/HMTc-firewall slips in ## Implications: removed an HMTc operational directive (“brands sourcing fresh herbs from contract growers in industrially contaminated regions should include Hg testing in their QC protocols”); removed a synthesis claim (“a recurring theme in heavy-metals literature”); reframed consumer-risk wording as neutral occurrence-data contribution per Part 2.
Paper-internal labelling discrepancy noted, not flagged as a wiki error: paper page 8 reports “For the tested cultivated plants, the EDI value was 0.0000515 mg/kg/day, and in the group of commercial products it was 0.0000947 mg/kg/day” — but the underlying means (Table 2: cultivated 9.47 µg/kg, commercial 5.15 µg/kg) imply the reverse assignment, and EDI = concentration × intake / bw confirms cultivated → 0.0000947 and commercial → 0.0000515. The wiki page assigns EDI values to the group that matches each group’s reported mean; the paper text has the two labels switched.
Paper-internal location-naming discrepancy noted: Table 1 lists five collection points (Katowice, Mysłowice, Jastrząb, Płoki, Jemielnica), but Figure 3 plots a slightly different five-name set (Dąbrówka Mała, Mysłowice, Płoki, Poraj, Jemielnica). Treated as the paper’s own inconsistency; not amended on the wiki page.

Wiki pages updated on ingest

Update history

The five most recent substantive edits to this page, classified major (evidence or structure moved), correction (a published value or statement was wrong and has been fixed), or minor (narrative rewritten without changing the underlying evidence). Each description is derived from what the edit did to this page; the linked commit is the authoritative record, routine regeneration passes are excluded, and the full version history lives in git. When DOI minting comes online (see schema docs), each entry below will also link to a version-pinned DataCite DOI.

Commit	Date	Change	Description
e317189	2026-08-11	correction	7 sections added; narrative text revised