Mohammadi et al. 2024 — Carcinogenic risk of heavy metals in Champa rice, southwestern Iran

This study measured Pb, Cd, Zn, and Ni in 16 samples of locally grown Champa rice purchased from farmers in Lordegan (Chaharmahal and Bakhtiari Province) and Ahvaz (Khuzestan Province), southwestern Iran, and computed carcinogenic risk (CR) and non-carcinogenic hazard quotients (HQ) for children and adults. Mean Pb in Champa rice from both cities exceeded the Iranian national rice limit (0.15 mg/kg) by roughly seven-fold in Lordegan and nine-fold in Ahvaz; mean Cd and Ni were within Iranian and Codex limits in both cities. CR values for Pb, Cd, and Ni were within the USEPA-defined acceptable range (1×10⁻⁶ to 1×10⁻⁴) and HQs were all below 1, leading the authors to characterize cancer and non-cancer risk as within the safe range despite the Pb exceedance.

Key numbers

Mean concentrations in Champa rice by city (mg/kg dry weight, n = 16 total split between cities; Table 1):

Mann–Whitney test for between-city differences (Table 1): Zn and Ni differed significantly between cities (both P < 0.001, test statistic −3.361); Cd (P = 0.066) and Pb (P = 0.195) did not.

Regulatory comparisons stated by the paper:

• Iranian National Standard No. 12968 for rice: Cd max 0.06 mg/kg; Pb max 0.15 mg/kg.
• Both city means for Cd (0.0165 and 0.0295 mg/kg) are below the Iranian and Codex Cd limits.
• Both city means for Pb (1.1265 and 1.3496 mg/kg) exceed the 0.15 mg/kg Iranian limit — described as “7 times” higher in Lordegan and “9 times” higher in Ahvaz.
• Codex cereal Ni limit: 10 mg/kg; both city means (0.0196 and 0.1876 mg/kg) are well below.
• Zn: no rice/cereal limit defined in the cited national or Codex standards.

EDI parameters used by the paper (Section 2.4):

• EFr = 365 days/year; ED = 15 years (children) and 70 years (adults).
• IR (rice consumption) = 25 mg/day (children); 82 mg/day (adults).
• BW = 32.7 kg (children); 70 kg (adults).
• AT = 2,190 days (children); 10,950 days (adults; the paper writes “10,950 kg” — units typo for days).
• Cancer slope factors (mg/kg/day)⁻¹: Pb 0.0085; Cd 0.380; Ni 1.7.
• Reference doses (mg/kg/day): Cd 0.0005; Pb 0.0035; Ni 0.02; Zn 0.3.

Estimated carcinogenic risk (CR) and non-carcinogenic hazard quotient (HQ) values as reported in Table 2:

All reported CR values fall below 1×10⁻⁶ (the USEPA “inconsequential” threshold cited by the paper); all reported HQ values are well below 1. The paper interprets both findings as “in the safe range” despite the order-of-magnitude Pb exceedance over the Iranian rice limit.

Methods (brief)

Sampling: 16 Champa rice samples collected after harvesting and husking from farmers in Lordegan and Ahvaz, purchased in 2021. Per-city allocation is not stated. Lordegan sits at ~1,700 m elevation in the Zagros mountains (Chaharmahal and Bakhtiari Province); Ahvaz is at 12 m elevation in Khuzestan Province and hosts petrochemical, metallurgy, and oil industries served by the Karun River.

Sample preparation: rice rinsed with double-distilled water, oven-dried at 110–120 °C, ashed at 151 °C to obtain white carbon-free ash. 1 g sub-samples were powdered in an electric mill and acid-digested in 4 M HNO₃ at 95 °C. Digestates were filtered through Whatman 42 paper, brought to a working standard concentration of 100 µg/L, and read.

Determination: Varian 710-ES inductively coupled plasma atomic emission spectrometer (ICP-AES), three replicates per sample, results expressed as µg per dry gram (equivalent to mg/kg dry weight). The paper does not report method detection limits, instrument calibration ranges, or use of certified reference materials.

Speciation: no speciation. Pb, Cd, Ni, and Zn are reported as total elemental concentrations. No As or Hg measurement.

Statistics: SPSS 22. Kolmogorov–Smirnov used to test normality; Mann–Whitney U used for between-city comparison of metal concentrations.

Risk assessment: CR = EDI × CSF (Section 2.4); HQ = ADI / RfD (Section 2.5). CR thresholds quoted from USEPA: <1×10⁻⁶ inconsequential; >1×10⁻⁴ likely hazardous; in between, acceptable.

Implications

The paper contributes Iranian (southwestern) occurrence data for Pb, Cd, Zn, and Ni in locally grown Champa rice, with both city means for Pb several-fold above the Iranian national rice limit (0.15 mg/kg). For rice ingredient profiling, the Pb values (means 1.13 and 1.35 mg/kg = 1,127 and 1,350 µg/kg) sit at the upper end of the global rice Pb literature and align with prior Iranian and Asian reports the authors cite (Ziarati 2017; Shokrzadeh 2013; Morekian 2013; Zazouli 2008; Malakootian 2013). The Ahvaz Cd mean (0.0295 mg/kg = 29.5 µg/kg) is well below Codex and Iranian limits but is roughly double the Lordegan mean, consistent with the paper’s framing of Ahvaz as a city with petrochemical, metallurgy, oil-industry, and Karun-River wastewater pressure on agricultural soils.

The carcinogenic-risk calculation produces CRs in the 10⁻¹⁰ to 10⁻⁸ range across all city/age/metal combinations — values that hinge on the rice-consumption inputs the paper uses (25 mg/day for children, 82 mg/day for adults). These intake values are roughly three orders of magnitude smaller than the Iran-typical per-capita rice consumption reported elsewhere in the same paper’s Introduction (per-capita rice consumption in Asia 85 kg/year ≈ 233 g/day) and from typical Iranian dietary surveys (commonly cited 100–150 g/day cooked rice). The resulting CRs are therefore best read as a conservative-toward-zero arithmetic product rather than as a real-world risk estimate; downstream synthesis should rely on the underlying concentration values, not on the CR/HQ outputs.

Source contributes:

• Occurrence data for ingredients/rice (Pb, Cd, Zn, Ni) in southwestern Iran.
• Geographic-breakdown evidence (Lordegan vs. Ahvaz) for the rice ingredient page’s geographic_breakdown field for Pb, Cd, Ni.
• An A-tier data point on Iranian rice Pb that joins the existing zafarzadeh2025-heavy-metals-rice-sari-iran result of widespread Iranian rice Pb exceedance.

Wiki pages this source may touch

• rice
• rice-bulk-grain
• lead
• cadmium
• nickel
• zinc

Verification notes

• Identity checks: DOI grep for 10.1016/j.toxrep.2024.05.005 returned no prior page; raw_handle grep for MFK_evaluation-of-carcinogenic returned no prior page; cite-key glob for mohammadi2024* returned only an unrelated mohammadian-hafshejani2024-cadmium-prostate-cancer-meta.md. This is a fresh NEW-path ingest.
• License: paper carries a CC BY-NC license per the masthead (“This is an open access article under the CC BY-NC license”).
• Speciation: paper measures total Pb, Cd, Ni, Zn by ICP-AES with no speciation. metals: frontmatter uses Pb, Cd, Ni, Zn accordingly. No As or Hg in the analyte panel; not claimed.
• Paper-internal data anomaly 1: Table 1 reports Pb Lordegan Min 0.0200 mg/kg and Max 0.2100 mg/kg, but the Mean (1.1265 mg/kg) and SD (0.0634) cannot be reconciled with that Min/Max range. The Mean is consistent with the paper’s text claim that Lordegan Pb is “7 times” the 0.15 mg/kg Iranian limit (1.1265/0.15 ≈ 7.5). The reported Min/Max for Pb Lordegan appear to be a typesetting error in the source table; preserved as printed and flagged here, not silently corrected.
• Paper-internal data anomaly 2: Table 1 reports Ahvaz means higher than Lordegan means for all four metals (consistent with the paper’s framing of Ahvaz as the more industrially impacted city), but Table 2’s “Lordegan” CR/HQ values are systematically higher than the “Ahvaz” CR/HQ values across Pb, Cd, and Ni. EDI scales linearly with concentration, so given the Table 1 means, Ahvaz CRs should be higher, not lower. The most likely explanation is that the city labels in Table 2 (and the matching Section 3.2 prose) are swapped. The values are preserved as the paper prints them and the inconsistency is flagged here rather than corrected; downstream synthesis should treat the CR/HQ outputs as advisory and rely on the Table 1 concentration values.
• Paper-internal data anomaly 3: the paper writes the children EDI averaging time as “2190 for children and 10,950 kg for adults” — the “kg” is a units typo; AT is in days (2,190 days = 6 years × 365 days × … actually 6 years; 10,950 days = 30 years). The Section 2.4 sentence is preserved verbatim in Key numbers; no correction was applied to the values.
• Per-city sample allocation: the paper says “a total of 16 samples of Champa rice … were collected from farmers in Lordegan and Ahvaz cities,” but does not state how many came from each city. sample_n: 16 is the aggregate; per-city n is not in the source.
• Brand firewall (Part 12): the paper names no commercial brands. “Champa” is the rice cultivar/landrace, not a brand. Instrument vendor (Varian 710-ES atomic emission spectrometer) and statistical software (SPSS 22) appear in Methods only and fall under the scientific-method vendor exception locked 2026-05-17.
• HMTc firewall (Part 2): the paper does propose threshold-level rhetoric (“more studies are needed,” “regular monitoring is recommended”), which is preserved as paper content but not converted to wiki-side threshold claims; Implications notes the CR computation’s sensitivity to the unusually low rice-intake values the paper used, without proposing any HMTc threshold.
• products/rice-bulk-grain is the closest current product taxonomy slug for raw post-husking rice purchased from farmers; the paper measures the cultivated grain (post-harvest, post-husking) before commercial milling/packing, so the bulk-grain product slug is the routing destination. products/rice-noodles, products/rice-snacks-crackers, and products/rice-bran-oil are not relevant.
• Codex cereal Ni limit of 10 mg/kg cited by the paper does not have a current regulation slug in the snapshot; not linked.
• Iranian National Standard No. 12968 (rice contaminants) does not have a current regulation slug in the snapshot; not linked.

Page history

The five most recent substantive edits to this page. 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.