Evaluation of carcinogenic risk of heavy metals due to consumption of rice in Southwestern Iran

Overview

This study measured lead (Pb), cadmium (Cd), Zn, and nickel (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 arsenic (As) or mercury (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 Risk assessment of heavy metals in north of Iran (Sari) rice and implications for human health result of widespread Iranian rice Pb exceedance.

Related evidence

• Rice
• Rice (white, brown, wild — bulk grain)
• Lead
• Cadmium
• Nickel
• Zinc

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