Concentration of heavy metals in Iranian market rice and associated population health risk

Overview

This Mashhad market-survey paper reports total concentrations of cadmium, lead and arsenic (the latter measured by hydride-generation AAS on the wet-ashed extract, treated here as total arsenic in the absence of any inorganic-species separation step) in 120 packed rice samples collected from local agricultural agencies and retail markets in Mashhad. Samples were split into four producer-origin groups of n=30 each: two domestic Iranian categories (Mazandaran and Gilan provinces — together accounting for >80% of Iranian rice cultivation per the paper) and two imported categories (Pakistani and Indian). Across the full panel the cadmium (Cd) concentrations ranged 0.001-0.156 mg/kg (mean 0.064 ± 0.001 mg/kg), the lead (Pb) concentrations ranged 0.108-0.234 mg/kg (mean 0.153 ± 0.001 mg/kg), and the arsenic (As) concentrations ranged 0.039-0.378 mg/kg (mean 0.129 ± 0.017 mg/kg). The paper reports significant differences between Iranian- and imported-origin rice for all three metals but no significant difference between Mazandaran and Gilan or between Pakistani and Indian (one-way ANOVA, Tukey post-test, p<0.05). Estimated daily intakes for the population-weighted “mean rice” via Equation 1 (EF 365 d/y, ED 70 y, FIR 100 g/person/day, WAB 70 kg) were 0.217 µg/kg bw/day for Pb, 0.183 µg/kg bw/day for As, and 0.090 µg/kg bw/day for Cd. Target hazard quotients (THQ = EDI × 7 / PTWI) were below 1 for every metal in every origin group; the hazard index HI summed across the three metals was 0.331 for the population-weighted mean. The paper concludes there is no aggregate health risk from rice-borne Pb, As and Cd at the modelled consumption rate, while noting that 96.66% of the 120 samples exceeded the Iranian national lead ceiling and 58.33% exceeded the Iranian arsenic ceiling (all four origin-group mean Cd concentrations also exceeded the Iranian Cd ceiling). The compliance contrast against FAO/WHO is much milder.

Key numbers

Panel-wide ranges and means (Results §3, p. 251-252; values in mg/kg):

Per-origin mean ± SD concentrations (Results §3, pp. 251-252; values in mg/kg). The Pb and As per-origin means for Gilan and Pakistani groups are reported only via Figures 2 and 3 (bar-chart axis labels, no in-text numeric values); the Mazandaran and Indian values are the in-text published per-origin extremes and are reproduced exactly. The Gilan and Pakistani Pb and As values are read from the bar charts and reported here as approximate (≈) with the per-group SD bars matching the in-text per-origin precision style:

Regulatory ceilings cited by the paper for direct mean-vs-ceiling comparison (Results §3, pp. 251-252; both authorities cited via INSO 2013 and FAO/WHO 2004):

Sample exceedance against the Iranian ceiling (Results §3, pp. 251-252):

• Cd: all four origin-group means (0.052, 0.043, 0.082, 0.081 mg/kg) exceeded the 0.04 mg/kg INSO Cd ceiling.
• Pb: 96.66% of the 120 samples (116 / 120) exceeded the 0.12 mg/kg INSO Pb ceiling, while the panel mean (0.153 mg/kg) was below the 0.20 mg/kg FAO/WHO Pb ceiling.
• total arsenic (tAs): 58.33% of the 120 samples (70 / 120) exceeded the 0.12 mg/kg INSO As ceiling and 15% (18 / 120) exceeded the 0.20 mg/kg FAO/WHO As ceiling.

Estimated daily intake (EDI, µg/kg bw/day) per origin group (Table 1, p. 253; computed with EF 365 d/y, ED 70 y, FIR 100 g/person/day, WAB 70 kg, TA 365 × 70):

Target hazard quotient (THQ, dimensionless; THQ = EDI × 7 / PTWI) per origin group (Table 2, p. 253; PTWIs: Cd 7 µg/kg bw/week, Pb 25 µg/kg bw/week, As 15 µg/kg bw/week per Bilandžić et al. 2011):

Hazard index (HI = ΣTHQ across Pb, Cd, As) for the population-weighted mean rice: 0.331 (Conclusions §4, p. 253). The published HI exceeds the simple arithmetic sum of the Table 2 mean-row THQs (0.060 + 0.091 + 0.084 = 0.235); the discrepancy is unexplained in the paper and is flagged in Verification notes.

Exposure-assessment parameters used in EDI / THQ / HI computation (paper §2.4, pp. 250-251):

Method validation parameters (paper §2.3, p. 250):

Calibration linearity (paper §2.3, p. 250): Cd R² = 0.998 (standards 5, 10, 15, 20 mg/kg); Pb R² = 0.995 (standards 5, 10, 15, 20 mg/kg); As R² = 0.998 (standards 1, 5, 15, 20 mg/kg). The paper does not publish recovery percentages, certified-reference-material results, or measurement-uncertainty values; a “standard plant sample” and reagent blanks are mentioned as quality-assurance controls but their results are not tabulated.

Methods (brief)

Sample collection. 120 packed rice samples were collected from local agricultural agencies and retail markets in Mashhad, the second-most-populous city of Iran. Samples were grouped by producer origin into four categories of n=30: Mazandaran-province domestic rice, Gilan-province domestic rice, Pakistani-origin imported rice, and Indian-origin imported rice. Manufacturer identities were coded and analytical work was conducted by an examiner blind to the producers.

Sample preparation. Dry-ashing for Cd and Pb: 5 g of each sample dried at 80 °C for 2 h, then 105 °C for 6 h; preliminary burning on a hotplate; ashing in oven at 550 °C for 10 h with an initial 200 °C ramp at 50 °C/h. Ash moisturised with distilled water, evaporated to dryness over a water bath, residue dissolved in 10 mL HNO₃ and made up to 100 mL with deionised water (per Morekian et al. 2013 protocol). Wet-ashing for As: 30 mL concentrated HNO₃ added, kept at room temperature for 24 h, heated on hotplate to boiling and simmered to a transparent 3 mL extract, filtered through Whatman filter paper and brought to 100 mL with deionised water (per Morekian et al. 2013 protocol).

Instrumentation. Atomic absorption spectrophotometry on a Varian model AA-1275 (Varian Medical Systems, Inc., Palo Alto, CA, USA). Pb and Cd determined by graphite-furnace AAS with auto-sampler at furnace temperatures of 1,800 °C (Pb) and 2,100 °C (Cd). As determined by hydride-generation AAS on the wet-ashed extracts using the same Varian AA-1275 platform fitted with a hydride generation system. Three replicates per sample. Reagent blanks and a “standard plant sample” run alongside; recovery and CRM values not published.

Speciation. Total As (hydride-generation AAS measures the total arsenic that can be reduced to AsH₃ under the digestion-and-hydride-formation conditions used; no As-species separation step is described). The wiki page accordingly uses tAs rather than iAs. No mercury (Hg) panel, no chromium (Cr) or hexavalent chromium (Cr-VI) panel, no nickel (Ni) panel.

Statistical analysis. SPSS v13.0 (SPSS Inc., Chicago, IL, USA). Mean ± SD by descriptive statistics. One-way ANOVA with Tukey post-test for per-province comparisons. Significance threshold p < 0.05.

Risk assessment. EDI (µg/kg bw/day) per Equation 1: EDI = (EF × ED × FIR × C) / (WAB × TA), with EF 365 d/y, ED 70 y, FIR 100 g/person/day, C = metal concentration in rice (µg/g, equivalent to mg/kg), WAB 70 kg, TA = 365 × ED days. THQ (dimensionless) per Equation 2: THQ = EDI × 7 / PTWI, with the JECFA PTWIs cited via Bilandžić et al. 2011 (Cd 7, Pb 25, As 15 µg/kg bw/week). HI per Equation 3: HI = ΣTHQ across the three metals. Per Lemly 1996, HI ≤ 1.0 indicates no significant health hazard; 1.1-10 moderate hazard; >10 high hazard.

Implications

This source contributes Iranian retail-market occurrence data for Cd, Pb and total As in 120 packed rice samples (30 each of Mazandaran-domestic, Gilan-domestic, Pakistani-imported, Indian-imported) on the Mashhad market in the mid-2010s, plus a deterministic THQ / HI risk assessment under a generic 70 kg / 100 g/day Iranian-population assumption. Principal contributions to the wiki evidence pool:

• A four-origin contrast within a single Iranian retail city: Mazandaran-domestic rice carries the lowest mean concentrations for Cd (0.052 mg/kg), Pb (0.134 mg/kg) and tAs (0.093 mg/kg); Indian-imported rice carries the highest mean concentrations for Pb (0.171 mg/kg) and tAs (0.188 mg/kg); Pakistani-imported rice carries the highest mean concentration for Cd (0.082 mg/kg) by a narrow margin over Indian (0.081 mg/kg). The Iranian-vs-imported contrast is statistically significant for all three metals (one-way ANOVA p<0.05); the within-country contrasts (Mazandaran vs Gilan, Pakistani vs Indian) are not significant.
• A 100%-origin-mean-exceedance signal for Cd against the Iranian ceiling: all four origin-group means (0.043-0.082 mg/kg) exceed the INSO 0.04 mg/kg Cd cereal ceiling, although none exceed the FAO/WHO 0.10 mg/kg Cd ceiling. This pattern (per-origin mean Cd above the Iranian standard but below the FAO/WHO standard) is consistent with the broader pattern in Iranian-market rice work (cf. Human health risk assessment for some toxic metals in widely consumed rice brands (domestic and imported) in Tehran, Iran: Uncertainty and sensitivity analysis on the Tehran market 2018, Heavy metals in rice samples on the Torbat-Heidarieh market, Iran on the Torbat-Heidarieh market 2015, Essential and toxic heavy metals in cereals and agricultural products marketed in Kermanshah, Iran, and human health risk assessment on the Kermanshah market 2014).
• A 96.66% sample-level Pb-exceedance signal against the Iranian ceiling: 116 of 120 samples exceeded the 0.12 mg/kg INSO Pb cereal ceiling, while the panel mean Pb concentration (0.153 mg/kg) was below the 0.20 mg/kg FAO/WHO ceiling. This is the same divergence pattern between the tighter Iranian ceiling and the looser FAO/WHO ceiling that the abovementioned Iranian-market rice papers report.
• A 58.33% sample-level As-exceedance against the Iranian ceiling and a 15% sample-level As-exceedance against the FAO/WHO ceiling: 70 of 120 samples exceeded the 0.12 mg/kg INSO As cereal ceiling, and 18 of 120 exceeded the 0.20 mg/kg FAO/WHO As ceiling. Indian-imported rice (mean 0.188 ± 0.032 mg/kg) carried the highest As contamination among the four origin groups.
• A deterministic HI / THQ risk-assessment outcome of “no aggregate non-carcinogenic risk” (population-weighted-mean HI 0.331, all individual-origin THQs below 1.0 for every metal), under the paper’s chosen 100 g/day rice ingestion rate, 70 kg adult body weight, and JECFA PTWIs (Cd 7, Pb 25, As 15 µg/kg bw/week). Notable assumption: the 100 g/day FIR is materially lower than the 165 g/day FIR used by Human health risk assessment for some toxic metals in widely consumed rice brands (domestic and imported) in Tehran, Iran: Uncertainty and sensitivity analysis for the Tehran population from ISIRI 12968; the present paper’s HI would scale roughly linearly with FIR and would push toward 0.5 under the Sharafi-style 165 g/day assumption.
• A paper-internal HI-vs-sum-of-THQs anomaly (published HI 0.331; sum of mean-row THQs in Table 2 is 0.235). The wiki Key numbers section reports both values and flags the discrepancy in Verification notes; it does not propagate the published HI as authoritative when the underlying per-metal THQ sum is auditable. No carcinogenic-risk (ILCR) computation is published; the paper restricts its risk framing to non-carcinogenic HI / THQ.
• A small-to-medium-panel (n = 30 samples per origin group, n = 120 total, triplicate measurements per sample), single-city, single-time-period (sampling year not stated; bounded to roughly 2014-2015 by the December-2015 receipt date), single-cohort (generic 70 kg adult / 100 g/day) sampling footprint with no As-species separation, no Hg panel, no Cr or Cr-VI panel, no Ni panel, no recovery / CRM / measurement-uncertainty validation data published, and the per-origin Pb and As values for the Gilan and Pakistani groups available only via Figures 2 and 3 (numeric values not given in the prose). The B-tier classification reflects these limitations; the source should pool with other Iranian-market rice work for occurrence-distribution purposes.

Related evidence

• Arsenic, Total
• Cadmium
• Lead
• Rice
• Rice (white, brown, wild — bulk grain)

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