Overview
This Tajan-river-basin survey reports total concentrations of lead, cadmium, chromium, zinc, iron and copper in 33 cultivated rice samples drawn from 11 paddy locations along the 140-km Tajan river course (Mazandaran province, northern Iran) in the summer of 2018, alongside 33 paired paddy-soil samples and 75 winter + 33 summer surface-water samples. The paper computes soil-to-plant transfer factors (TF), USEPA target hazard quotients (THQ) and a summed hazard index (HI) for adult human consumption of the cultivated rice. The reported per-metal mean concentrations in rice (Pb 9.02 ± 0.2 mg/kg, cadmium (Cd) 0.7 mg/kg per Tables 2–3, chromium (Cr) 7.7 ± 0.39 mg/kg, Zn 10.7 ± 0.67 mg/kg, Cu 10.4 ± 0.32 mg/kg, Fe 2526 ± 77.13 mg/kg) and the resulting THQ values (Pb 13.80, Fe 7.73, Cr 5.51 per the abstract / 0.08 per Table 3 — the Table 3 row transposition is flagged in Verification notes, Cd 1.50, Zn 5.51 per Table 3 / not stated in the abstract, Cu 0.56) push the summed Hazard Index for adult rice consumers in the basin to 29.18 — i.e., roughly 29× the USEPA non-carcinogenic threshold. TF ranges for the two most toxicologically relevant elements (Pb 4.89–23.65, Cd 3.67–12.42) sit one to two orders of magnitude above the WHO permissible-crop ceiling. The basin’s lead (Pb)/Zn mineral processing operations, road dust along the highway-adjacent paddies, and phosphate-fertiliser use are advanced by the authors as the likely anthropogenic sources, supported by a principal-components analysis that loads Cr, Fe, Cd and Pb on PC1 (79.7% of variance in rice) and Zn + Cu on PC2 (14.4%).
Key numbers
Rice — per-metal panel mean ± SD across the 11-location, summer-2018 panel (Results §3.1.1, p. 8; Table 2, p. 17; values in mg/kg dry weight). The Cd row uses the Table 2 / Table 3 mean of 0.7 mg/kg rather than the contradicting body-text figure of 0.11 ± 0.02 mg/kg (the body-text value matches the per-paddy mean soil Cd, not rice Cd — see Verification notes for the swap analysis):
| Metal | Panel mean ± SD (mg/kg dw) | Per-location range (mg/kg dw) |
|---|---|---|
| lead (Pb) | 9.02 ± 0.20 | 2.66 – 18.18 |
| cadmium (Cd) | 0.7 (panel mean from Table 2; body text reports 0.11 ± 0.02, contradicting Table 2/Table 3; see Verification notes) | 0.38 – 1.48 |
| chromium (Cr) | 7.7 ± 0.39 | 2.09 – 20.24 |
| Zn | 10.7 ± 0.67 | 1.62 – 17.42 |
| Cu | 10.4 ± 0.32 | 2.35 – 23.18 |
| Fe | 2526 ± 77.13 | 522 – 8065 |
Paddy soil — per-metal panel mean across the 11 paired soil samples (Table 2, p. 17; values in mg/kg dry weight; body text “highest for … Cd (0.7 ± 0.003 mg/kg)” is inconsistent with Table 2 data and is treated here as a body-text transcription error — see Verification notes):
| Metal | Soil mean (mg/kg dw, computed from Table 2) | Per-location range (mg/kg dw) |
|---|---|---|
| lead (Pb) | 0.591 | 0.501 – 0.778 |
| cadmium (Cd) | 0.108 | 0.089 – 0.129 |
| chromium (Cr) | 0.180 | 0.084 – 0.424 |
| Zn | 52.32 | 35.3 – 68.7 |
| Cu | 25.42 | 16.7 – 30.4 |
| Fe | 71.89 | 14.3 – 215.4 (note: one outlier SS12 = 215.4; without SS12 the range is 14.3–182.3) |
Surface water — per-metal summer-mean and per-sample range (Table 1, p. 16; mg/kg, which for water of unit density is equivalent to mg/L; the body text “highest recorded concentrations” appear to refer to the summer-mean values rather than per-sample maxima, see Verification notes):
| Metal | Summer mean (mg/L) | Per-sample range across summer + winter (mg/L) |
|---|---|---|
| lead (Pb) | 0.631 ± 0.029 (body text) | 0.022 – 1.386 |
| cadmium (Cd) | 0.035 (computed) ≈ 0.03 ± 0.001 (body text) | 0.000 – 0.082 |
| chromium (Cr) | 0.180 (computed) ≈ 0.2 ± 0.011 (body text) | 0.030 – 1.092 |
| Zn | 0.493 (computed) ≈ 0.5 ± 0.068 (body text) | 0.040 – 2.364 |
| Cu | 0.243 (computed) ≈ 0.24 ± 0.034 (body text) | 0.040 – 1.146 |
| Fe | 71.89 (computed) ≈ 71.9 ± 3.35 (body text) | 0.865 – 215.4 |
Soil-to-plant transfer factors (TF = MC_plant / MC_soil; Results §3.1.3, p. 11; abstract; trend Pb > Cd > Cu > Zn > Fe > Cr):
| Metal | TF range | Notes |
|---|---|---|
| lead (Pb) | 4.89 – 23.65 | Far exceeds the WHO permissible-limit threshold for crops (abstract); ranked highest among the six metals |
| cadmium (Cd) | 3.67 – 12.42 | Also exceeds the WHO permissible-limit threshold; ranked second |
| Cu | 0.03 – 0.53 | Below 1; typical for an essential metal |
| Zn | 0.03 – 0.45 | Below 1; typical for an essential metal |
| Fe | 0.03 – 0.42 | Below 1 |
| chromium (Cr) | 0.08 – 0.76 | Below 1 |
USEPA target hazard quotients and hazard index for adult rice consumers (Results §3.1.4, p. 12; Table 3, p. 18; abstract). Per-metal THQ values transcribed from Table 3 with both the in-paper figure and the abstract-consistent figure where the two disagree (the Cr/Zn row transposition in Table 3 is flagged in Verification notes):
| Element | Concentration in rice (mg/kg dw) | RfD (mg/kg·day) | THQ — Table 3 row label | THQ — abstract / Cr-Zn-corrected reading |
|---|---|---|---|---|
| lead (Pb) | 9.02 | 1.40 × 10⁻³ | 13.80 | 13.80 |
| cadmium (Cd) | 0.70 | 1.00 × 10⁻³ | 1.50 | 1.50 |
| chromium (Cr) | 10.7 (Table 3 row, transposed with Zn) / 7.71 (Cr-Zn-corrected reading) | 3.00 × 10⁻³ | 0.08 (Table 3 row label) | 5.51 (abstract Cr THQ = 5.5) |
| Zn | 7.71 (Table 3 row, transposed with Cr) / 10.7 (Cr-Zn-corrected reading) | 3.00 × 10⁻¹ | 5.51 (Table 3 row label) | 0.08 (Cr-Zn-corrected) |
| Fe | 2.53 × 10³ | 7.00 × 10⁻¹ | 7.73 | 7.73 |
| Cu | 10.4 | 4.00 × 10⁻² | 0.56 | 0.56 |
| HI | 29.18 | 29.18 (sum is invariant under the Cr↔Zn row swap) |
Principal-component-analysis loadings (Results §3.1.2, pp. 9–11):
| Compartment | PC1 % var | PC2 % var | PC1 dominant loadings | PC2 dominant loadings |
|---|---|---|---|---|
| Rice | 79.7 | 14.4 | Cr, Fe, Cd, Pb | Zn, Cu |
| Soil | (PC1+PC2 = 87.41%, individual splits not published) | — | Zn, Cr, Cu | Cd, Pb |
| Water (winter) | 58.8 | 30.3 | Fe, Cr, Cd, Pb | Cu (0.85), Zn (0.74); Pb loaded ≈0.5 on PC2 |
Exposure-assessment parameters used in THQ / HI computation (Methods §2.6.1, p. 7):
| Parameter | Value | Source |
|---|---|---|
| Exposure frequency EF | 365 days/year | paper |
| Exposure duration ED | 70 years | paper |
| Ingestion rate IR | not reported numerically in the body text; back-calculated from the published THQs at Pb conc 9.02 mg/kg and RfD 1.4 × 10⁻³ to be approximately 150 g/day | derived |
| Body weight BW | not reported numerically in the body text; back-calculated value consistent with ≈70 kg adult | derived |
| Averaging time AT_n | 365 days/year × 70 years | paper |
| Oral reference doses RfD (mg/kg·day) | Pb 1.4 × 10⁻³, Cd 1.0 × 10⁻³, Cr 3.0 × 10⁻³, Zn 3.0 × 10⁻¹, Fe 7.0 × 10⁻¹, Cu 4.0 × 10⁻² | Table 3, USEPA (2011) |
WHO/FAO/FDA/EU permissible-limit ceilings cited by the paper (Results §3.1.1 in-text references to EUROPEAN UNION 1998, FAO/WHO 1988, WHO 2004, FDA 2010, WHO 2016): the paper does not publish the specific ceiling values in a separate table; references the ceilings qualitatively to characterise each compartment’s exceedance pattern.
Methods (brief)
Study area and sampling. The Tajan River is a 140-km permanent river draining a 4147-km² watershed in Mazandaran province, northern Iran, between N 36°00′–36°22′ and E 51°27′–53°27′; the river passes Sari city and surrounding villages before reaching the Caspian Sea, and its watershed encompasses the most abundant rice-cultivation lands in the region. Mean annual water discharge is 19.4 m³ s⁻¹. The total study comprised 174 samples: 75 winter water samples from 25 monitoring locations (sampled in 2018 winter) plus 99 summer samples (33 water, 33 soil, 33 rice) drawn in 2018 from 11 paddy locations selected from the 25 winter sites. All sample locations were georeferenced with a hand-held GPS device.
Sample preparation. Water: 100 mL into sterile PVC bottles with 5 mL of ultra-pure HNO₃ for digestion on a hot plate, made up to 100 mL with double-distilled water. Soil: 0.5 g into oven for 6 h at 90 °C with 8 mL concentrated 3:1 v/v HCl:HNO₃ + 3 mL concentrated HClO₄ (“wet digestion”); cooled, filtered through Whatman N.42 paper, diluted to 25 mL with deionised water. Each soil sample digested in three replicates. Rice plants: oven-dried at 70 °C to constant weight, acid-digested per the AOAC International method with HNO₃ + HClO₄ (25:10 mL), each sample in three replicates. All reagents analytical grade (Sigma Aldrich); water for solution preparation was MilliQ ultra-pure (Millipore).
Instrumentation. Atomic absorption spectrometry on an Analytik Jena AG (Jena, Germany) contrAA 700 high-resolution continuum-source AAS, equipped with both flame and graphite-furnace atomisers in two separate sample compartments and a high-intensity xenon short-arc lamp in hot-spot mode. Double monochromator (prism and echelle grating) with a 588-pixel linear CCD array detector. WinAAS v4.5.0 software. Pb and Cd determined by GFAAS; Zn, Cr, Cu and Fe determined by FAAS in air/acetylene and N₂O/acetylene flames. All analyses performed in triplicate; mean values used for downstream analysis. Manufacturer-specified operating parameters; concentrations reported in mg/kg of dry matter (ppm). Acetylene, argon and N₂O of 99.99% purity. Standard calibration curves constructed by plotting absorbance against concentration in a metal-specific range; linearity confirmed.
Speciation. Total Cr (no hexavalent chromium (Cr-VI) / Cr-III separation step described). Cd, Pb, Zn, Cu, Fe by total-element measurement. No arsenic (As) panel, no mercury (Hg) panel, no nickel (Ni) panel, no inorganic-vs-total speciation work.
Statistical analysis. IBM SPSS v25 and XLSTAT 2016. Descriptive statistics (mean ± SD) for the metal levels per compartment; one-way Pearson correlation analysis for cross-metal relationships within compartments; principal-component analysis (PCA) for source apportionment and distribution-pattern visualisation. Significance threshold not explicitly stated.
Transfer factor. PCF = MC_plant / MC_soil (per Jolly et al. 2013); both terms on a dry-weight basis.
Health risk assessment. USEPA (2011) THQ for non-carcinogenic risk:
THQ = (EF × ED × IR × 10⁻³ × MC) / (RfD × BW × AT_n)
with EF 365 d/y, ED 70 y, MC = metal concentration (mg/kg), RfD = oral reference dose (mg/kg·day), BW = body weight (kg), AT_n = 365 × ED for non-carcinogens. THQ ≥ 1 interpreted as high health risk per the paper’s citation of Harmanescu et al. 2011. Hazard index HI = ΣTHQ across the six analysed metals (per USEPA 2011).
Implications
This source contributes a high-contamination, single-basin Iranian rice-cultivation-region survey (n = 11 paddy locations, n = 33 rice samples in summer 2018, with paired paddy soils and winter+summer surface-water sampling), plus a deterministic THQ / HI risk assessment under USEPA (2011) assumptions, to the Iranian-cultivation-region rice evidence pool. Principal contributions to the wiki:
- Per-metal mean rice concentrations one to two orders of magnitude above the Iranian-market-rice mean concentrations reported in Concentration of heavy metals in Iranian market rice and associated population health risk (Cd 0.064, Pb 0.153, total arsenic (tAs) 0.129 mg/kg on 120 packed-rice samples in Mashhad 2014–2015) and in Human health risk assessment for some toxic metals in widely consumed rice brands (domestic and imported) in Tehran, Iran: Uncertainty and sensitivity analysis, Heavy metals in rice samples on the Torbat-Heidarieh market, Iran, Concentration of Some Heavy Metals in Rice Types Available in Shiraz Market and Human Health Risk Assessment for the Iranian retail-market rice subsegment. The Tajan-basin values (Pb 9.02, Cd 0.7, Cr 7.7, Zn 10.7, Cu 10.4, Fe 2526 mg/kg dw in rice) place the basin in a “highly contaminated cultivation region” tier rather than in the typical-Iranian-retail-market tier. The Pb mean alone (9.02 mg/kg) is roughly 45× the FAO/WHO Codex Pb cereal ceiling of 0.2 mg/kg, and the Cd mean (0.7 mg/kg) is 7× the Codex Cd cereal ceiling of 0.1 mg/kg.
- A near-1 transfer-factor signal for the two most toxicologically relevant metals (Pb TF 4.89–23.65, Cd TF 3.67–12.42) — both far above 1.0, indicating substantial bioaccumulation from soil to grain — versus essential-metal TFs below 1.0 (Cu 0.03–0.53, Zn 0.03–0.45, Fe 0.03–0.42) and Cr 0.08–0.76. The Pb and Cd TF ranges sit one to two orders of magnitude above the WHO permissible-crop-TF threshold of approximately 1.0 cited in the paper.
- A summed hazard index of 29.18 for adult rice consumers, driven principally by Pb (THQ 13.80) and Fe (THQ 7.73), with a non-trivial Cr contribution (THQ 5.5 per the abstract / 0.08 per Table 3 row label, with the row-label value treated here as a Cr↔Zn transposition error — see Verification notes) and a moderate Cd contribution (THQ 1.50). HI = 29.18 sits well above the USEPA THQ ≥ 1 non-carcinogenic-risk threshold cited by the paper via Harmanescu et al. 2011.
- An anthropogenic-source pattern identification via PCA: in the rice samples, Cd, Pb, Cr and Fe co-load on PC1 (79.7% of variance), Zn and Cu on PC2 (14.4%); together the two components account for 94.10% of total variance. The paper attributes the PC1 cluster to nearby Pb/Zn mineral processing operations, road-dust deposition from the highway adjacent to the paddies, and industrial activities (textile, paint, battery and milling).
- A basin-wide environmental-compartment portrait — water, soil, and rice — that allows soil-to-plant transfer factor computation rather than requiring it to be inferred from the broader literature. The paper publishes per-location values for each compartment in Tables 1 and 2.
- A small-panel (n = 33 rice samples from 11 paddy locations × 3 replicates), single-basin, single-season (summer 2018), single-jurisdiction (Iran) Iranian-cultivation-region contamination footprint with no As panel, no Hg panel, no Ni panel, no Cr speciation (Cr-VI / Cr-III) work, no published recovery / CRM / measurement-uncertainty validation values, no published LOD / LOQ values, and no published numerical IR / BW values for the THQ computation (back-calculation suggests IR ≈ 150 g/day at BW ≈ 70 kg, but the paper does not state these explicitly). The B-tier classification reflects these limitations together with the data-integrity issues flagged in Verification notes (body-text Cd swap, Table 3 Cr↔Zn row transposition, ambiguous “rice plants (containing grains)” matrix description).
Related evidence
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