Hajmoradi & Moghadami 2024 — Pb and Zn in Verbascum speciosum near the Zehabad-e-Qazvin mine, Iran
This study measured lead and zinc in soil, roots, and aerial tissue of wild-harvested Verbascum speciosum Schrad. (Common Mullein, locally “Gole Mahur”), a medicinal plant collected by local people for traditional respiratory and gastrointestinal remedies, growing on and around the Zehabad-e-Qazvin Pb/Zn mine tailings area in Qazvin province, Iran. The authors paired the metal-uptake measurements with a cytogenetic assay on pollen mother cells (PMCs) to test whether the metal load translated into meiotic abnormalities. The principal source findings are that (i) soil, root, and aerial-part Pb and Zn concentrations all exceeded the source-cited regulatory comparators at every mining-area locality, (ii) the transfer factor exceeded 1 for both metals at every locality, indicating preferential translocation into aerial tissue, and (iii) the frequency of meiotic abnormalities (sticky chromosomes, bridges, laggards, cytomixis, micronuclei, tri-/penta-polar tetrads) tracked the metal gradient and the meiotic index fell from 98.5% in the control to 62.5% at the mine-adjacent locality.
Key numbers
Analytical method: flame atomic absorption spectroscopy (AAS) for both soil and plant tissue. Soil digestion: ~5 g + HNO3 (65%) / HCl (70%) / H2O2 (30%) at 6:4:1, heated to 200 °C for 3 h, filtered through Whatman No. 24, diluted to 50 mL with distilled water. Plant digestion: ~0.5 g of plant tissue dried at 105 °C to constant weight, digested with HNO3 / HCl / H2O2 at 6:3:1, heated to 80 °C for 3 h, filtered through Whatman No. 42, diluted to 50 mL.
Reporting basis: mg/kg dry weight for both soil and plant tissue (soil dried at 80 °C for 24 h, plant tissue dried at 105 °C to constant weight). Values reported as mean ± SE of three replicates per locality.
Soil Pb and Zn (mg/kg dry weight): Polluted-area Pb 1046 ± 0.23 to 6182 ± 0.04; polluted-area Zn 593 ± 0.13 to 2870 ± 0.07. Control soil Pb 43 ± 0.31, Zn 162 ± 0.19. The five-locality mean is 3527.4 ± 0.7 mg/kg Pb and 1671.4 ± 0.5 mg/kg Zn; this exceeds the source-cited 50 mg/kg permissible Pb floor (USEPA Supplemental Guidance for Developing Soil Screening Levels for Superfund Sites) by approximately 70x and the 200 mg/kg Zn floor by approximately 8x. The locality closest to the mine (area “a”) is not the highest-Pb soil; locality “e,” the most distant from the village but topographically downgradient of an upper mineral vein, recorded the highest soil Pb at 6182 mg/kg.
Plant Pb and Zn (mg/kg dry weight) — roots: area a 204 ± 0.05 Pb, 570 ± 0.16 Zn; area b 173 ± 0.14 Pb, 417 ± 0.3 Zn; area c 83 ± 0.2 Pb, 324 ± 0.08 Zn; area d 49 ± 0.07 Pb, 193 ± 0.15 Zn; area e 15 ± 0.16 Pb, 95 ± 0.07 Zn. Control roots 0.8 ± 0.23 Pb, 37 ± 0.15 Zn.
Plant Pb and Zn (mg/kg dry weight) — aerial parts: area a 312 ± 0.12 Pb, 638 ± 0.06 Zn; area b 216 ± 0.07 Pb, 519 ± 0.17 Zn; area c 114 ± 0.17 Pb, 460 ± 0.08 Zn; area d 83 ± 0.03 Pb, 317 ± 0.14 Zn; area e 37 ± 0.4 Pb, 172 ± 0.09 Zn. Control aerial 1.7 ± 0.12 Pb, 57 ± 0.01 Zn. The source-cited plant-tissue comparator standards (attributed to USEPA 2002 in the same reference as the soil floor) are 2 mg/kg Pb and 60 mg/kg Zn; every mining-area locality (including aerial parts of the most distant locality “e”) exceeds both.
Transfer factor (aerial / root): Pb 1.24 (area b) to 2.46 (area e); Zn 1.11 (area a) to 1.81 (area e); control TF Pb 2.12, Zn 1.54. TF exceeds 1 at every locality, indicating preferential aboveground accumulation rather than root retention.
Distance gradient: soil and plant concentrations of both metals decline monotonically with distance from the mine for localities a → b → c → d → e (with the locality-e soil Pb exception noted above). The control locality, 12 km upgradient at higher elevation, is approximately two to four orders of magnitude below the mining-area localities.
Cytogenetic / meiotic abnormalities (% of PMCs scored): chromosome stickiness, cytomixis, chromosomal bridges, laggards, non-synchronous segregation, micronuclei, and tri-/penta-polar tetrads were all dose-dependent on the soil and plant metal gradient. Examples at locality “a” vs control: sticky chromosome (D/MI) 35.2 ± 0.2% vs 3.3 ± 0.2%; cytomixis (D/MI) 17.6 ± 0.6% vs 0.9 ± 0.04%; bridge (AI/TI) 10.3 ± 0.7% vs 1.4 ± 0.1%; micronucleus (AII/TII) 8.3 ± 0.6% vs 0% (none observed in control). Tripolar tetrads appear only at localities a and b; pentapolar tetrads appear at all polluted localities (28.5% at a, 1.5% at control).
Meiotic index (MI, % normal tetrads): locality a 62.5; b 70; c 77.5; d 83; e 92; control 98.5.
PMC totals scored: 1969 cells at diakinesis / metaphase I; 1239 at anaphase I / telophase I; 690 at metaphase II; 1679 at anaphase II / telophase II.
Methods (brief)
The Zehabad-e-Qazvin lead-zinc mine sits at 36° 28’ 13” N, 49° 25’ 02” E, on the southern flank of the central Alborz range, ~85 km from the Qazvin-Rasht road. Mine tailings and processing wastewater are routed to a tailings dam ~1 km from the mine head; partial recirculation of wastewater into the process is described.
Five mining-area sampling localities (a closest to the mine head, e most distant within the impact area) and one upgradient control locality ~12 km away at higher elevation were established (Figure 1). At each locality, soil was sampled from the surface to 60 cm depth with a stainless-steel shovel, in triplicate. Soil was dried at 80 °C for 24 h, sieved at 2 mm, and digested for AAS. Aboveground plant material and roots from Verbascum speciosum at each locality were washed with distilled water, dried at room temperature and then at 105 °C to constant weight, ground, and digested separately.
For cytogenetics, flower buds were fixed in Carnoy’s solution (ethanol/chloroform/propionic acid, 6:3:2), rinsed, preserved in 70% ethanol at 4 °C, then squashed and stained with 2% acetocarmine. PMCs were scored on an Olympus light microscope. The meiotic index is reported as (normal tetrads / total tetrads) × 100. The base chromosome number for V. speciosum is given as 2n = 30.
Key limitations: small replicate count (three replicates per locality, n = 18 plant samples and n = 18 soil samples total); single-mine, single-region geography; AAS rather than ICP-MS (higher detection limits than current best practice; no isotope discrimination, though both Pb and Zn are typically reported as elemental totals regardless); no Pb-isotope or Zn-isotope source apportionment; no soil pH, organic-matter, or particle-size data reported in the main text; no quantitative QC such as recovery percentages, blanks, or certified reference material reported in the methods narrative; the paper draws on its own reference 19 (USEPA 2002 Supplemental Guidance) for both the soil and plant comparator floors, but USEPA 2002 itself addresses soil screening levels for Superfund sites and does not establish the 2 mg/kg Pb / 60 mg/kg Zn plant-tissue floor; the plant-tissue comparator origin is therefore opaque on the cited reference.
Speciation and methods caveats
- Lead is reported as total elemental Pb by AAS; no speciation.
- Zinc is reported as total elemental Zn by AAS; no speciation.
- Detection limits and recoveries are not stated in the methods narrative; only the digestion protocol and final dilution are reported.
- The “permissible threshold” of 50 mg/kg Pb in soil cited in Table 1 and the 200 mg/kg Zn soil floor are attributed to USEPA 2002 (the same reference 19) but USEPA 2002 is a US Superfund soil-screening guidance document, not an Iranian or international consumer-protection standard. The comparator origin should be treated as approximate.
- The abstract reports area-a aerial-part Zn as 519 ± 0.17 mg/kg; Table 2 reports area-a aerial-part Zn as 638 ± 0.06 mg/kg, with 519 ± 0.17 being the area-b aerial-part Zn value. Table 2 is the authoritative locality-by-locality table; this page uses 638 for area a aerial Zn. The abstract appears to have swapped one cell.
- Mining-area soil Pb in Table 1 is non-monotonic with distance: locality e (most distant from the mine head along the village transect) has the highest soil Pb (6182 mg/kg). The paper attributes this in the body text to the overall distance-from-mine trend but does not reconcile the e-locality soil-Pb anomaly explicitly. Plant Pb and Zn at locality e are nevertheless the lowest of the polluted localities, so the soil-Pb anomaly does not propagate into the plant-uptake series.
- Throughout the paper, the word “Pb” is occasionally substituted for “lead to” / “lead” in narrative sentences (e.g., “may Pb to the formation of micronuclei”), an apparent global find-and-replace artifact. The numerical results are not affected.
Implications
Standards work: this source provides Iranian environmental-baseline context for Pb and Zn uptake by a wild-harvested medicinal plant in a Pb/Zn-mining setting, with TF > 1 across both metals at every locality. The values are well above what would be expected in cultivated herbal-botanical supply chains and are most directly useful as a soil-to-plant uptake reference for mining-impacted geographies rather than as a baseline for commercial herbal-botanical or supplement contamination.
Courses: useful for teaching the soil-to-aerial-tissue translocation concept (TF), the methodology of paired soil and plant sampling along a distance gradient, and the link between heavy-metal exposure and genotoxic endpoints in plant cytogenetics (meiotic index, micronucleus, chromosomal bridges).
App: limited direct app utility. The source documents that wild-harvested medicinal plants growing on mining-impacted soils can carry Pb and Zn loads orders of magnitude above background, which is a category-level risk signal for the wild-harvested-supplements supply chain but not a per-product occurrence value.
Wiki pages this source may touch
Verification notes
- Discovery context: this PDF was auto-fetched by the
discoverskill against the seasonal-geographic-variance gap on a keyword match for “squash + Pb + ingredient.” The match is a false positive on the term: the paper uses the squash technique (a cytogenetic chromosome-preparation method) on Verbascum speciosum, not the squash food ingredient. The paper is nevertheless on-topic for HMI as Pb/Zn environmental-uptake context for the herbal-botanicals supply chain. - Brand-firewall check: no consumer brands named. Scientific-method names retained per Part 12 scientific-method exception: Olympus light microscope, Whatman filter papers No. 24 and No. 42.
- Wiki/HMTc-firewall check: no HMT&C-threshold comparisons or harmonization. Source-cited comparator floors (50 mg/kg soil Pb, 200 mg/kg soil Zn, 2 mg/kg plant Pb, 60 mg/kg plant Zn) are reported as the source reports them with the USEPA 2002 attribution caveat noted above.
- Taxonomy: routed to the existing
ingredients/herbal-botanicalsumbrella because Verbascum speciosum / Common Mullein is a botanical entering the herbal-medicinal / dietary-supplement supply chain in Iran and elsewhere. No species-level ingredient slug exists, and the 5-paper threshold for a stand-alonemulleinorverbascum-speciosumingredient page is not met. - Matrices set to
medicinal-plantsandbulk-soil; no product-shaped slug is appropriate because the source measures wild-harvested plant tissue and soil at mining-impacted localities, not a finished consumer product. - Paper-internal abstract/Table 2 swap on area-a aerial Zn (519 vs 638) documented in Speciation and methods caveats; Table 2 used as authoritative.
Page history
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