Concentration of Some Heavy Metals in Rice Types Available in Shiraz Market and Human Health Risk Assessment

Overview

This Iranian market-basket survey quantifies total cadmium (Cd), lead (Pb), chromium (Cr), nickel (Ni), and Co in polished rice purchased from retail stores in Shiraz (Fars Province) in 2013. The corpus comprises 10 market labels (3 domestic Iranian short-grain japonica from Fars-region cultivars/origins; 7 imported long-grain indica from India n=6 and Thailand n=1), with five ~250 g sub-samples per label drawn from 210 retail packs (15–20 kg each), giving n=50 analytical sub-samples. Samples were dry-ashed at 450 °C per AOAC official method 999.11 (Jorhem 2000) and quantified by flame and graphite-furnace atomic absorption spectrometry (Shimadzu AA-680 and Shimadzu MUV-IA). Accuracy was anchored against NIST SRM 1568b rice flour (observed recoveries: Pb 87.5 %, Cd 90 %, Co 107 %; Cr and Ni were not validated against the CRM because SRM 1568b lacks certified values for these analytes per Table 2). Each sample was digested in triplicate; each digest analysed three times. All concentrations are reported on a dry-weight basis. Domestic-rice ranges (n=3 labels, 15 sub-samples): Cd 0.27–0.41 mg/kg, Pb 0.71–1.28, Cr 0.33–0.44, Ni 0.72–0.79, Co 0.13–0.41 mg/kg dry weight. Imported-rice ranges (n=7 labels, 35 sub-samples): Cd 0.29–0.48, Pb 0.76–2.00, Cr 0.36–0.55, Ni 0.65–0.90, Co 0.11–0.44 mg/kg dry weight. Both domestic and imported rice mean Cd and Pb values were above the FAO/WHO 2004 and Iranian national 2010 maximum limits cited by the authors (Cd 0.1 µg/g FAO/WHO, 0.06 µg/g Iran; Pb 0.2 µg/g FAO/WHO, 0.15 µg/g Iran). Estimated weekly intake (EWI) for an adult Iranian (60 kg body weight, 770 g/week rice consumption) was below the JECFA PTWI for Cd (7 µg/kg bw), Cr (23.3), and Ni (35) across all 10 labels but exceeded the JECFA PTWI for Pb (25 µg/kg bw) in two imported labels (Pb EWI 25.769 µg/kg bw/week, both labels). The paper concludes that approximately 65.9 % of the Iranian-adult daily Cd intake derives from rice given typical consumption, and recommends ongoing regulatory monitoring of both domestic and imported rice on the Shiraz market.

Key numbers

Table 1 — Rice categories included in the survey (page 19)

Each label was sampled at n=5 sub-samples of ~250 g; total n=50 analytical sub-samples from 210 retail packs.

Table 2 — SRM 1568b (NIST rice flour) recovery (page 19)

Each element analysed three times; means reported in observed column. The text §“Quality control procedures” (p. 7) summarises method accuracy as “within the 87.5 % confidence intervals of the stated reference values” — a phrasing that refers to the lowest recovery (Pb 87.5 %) rather than to a statistical confidence interval; see Verification notes. SRM 1568b does not carry certified values for Cr or Ni, so those two analytes were not CRM-anchored.

Table 3 — Rice heavy-metal contents by category aggregation (mg/kg dry weight; page 20)

Per Part 12 brand-firewall (strict reading 2026-05-17), per-label rows naming the 10 commercial market labels are not reproduced in the wiki page body. The label-resolved data is in the published paper (Table 3, p. 20). The category-level aggregation below preserves the contamination signal without naming labels:

All values mg/kg dry weight; ranges across label means (each label mean ± SD on n=5 sub-samples). Reported analytical precision: ±0.01–0.45 mg/kg SD across labels and analytes (see paper Table 3). Significant-difference groupings (Duncan post-hoc, p < 0.05) are reported in the paper but omitted from this wiki page since they require label-resolved disclosure.

Author-reported category and pooled means (text §3.1–§3.2, pp. 8–13)

• Domestic Cd: 0.27–0.47 mg/kg (text §3.1 reports 0.47 as the highest domestic mean; the corresponding Table 3 row rounds to 0.41 ± 0.02 — see Verification note on the text-vs-table 0.47/0.41 discrepancy). The highest-mean domestic label was a Fars-Province Iranian cultivar at 0.47 (text) / 0.41 (Table 3).
• Domestic Pb: 0.71–1.28 mg/kg, no significant difference between domestic labels.
• Domestic Cr: 0.33–0.44 mg/kg; all means above the European Union 2006 average-diet intake estimate (2.5 µg/kg bw/day from 150 µg/day total diet).
• Domestic Ni: 0.72–0.79 mg/kg, no significant difference between domestic labels; all means much higher than EU 2006 average-diet estimate (1.25 µg/kg bw/day from 75 µg/day).
• Domestic Co: 0.13–0.41 mg/kg, with a single domestic label at the 0.13 mg/kg low end and the other two domestic labels not significantly different from each other.
• Imported Cd: 0.29–0.48 mg/kg, mean of imported labels much higher than FAO/WHO and Iranian limits.
• Imported Pb: 0.76–2.00 mg/kg, with the highest mean at 2.00 mg/kg (an Indian-origin label). Far exceeds the FAO/WHO 0.2 µg/g and Iranian 0.15 µg/g limits.
• Imported Cr: 0.36–0.55 mg/kg, all means above the EU 2006 average-diet estimate.
• Imported Ni: 0.65–0.90 mg/kg, much higher than EU 2006 average-diet estimate; the text states 6 imported labels had higher Ni than the Thai-origin and one Indian-origin label.
• Imported Co: 0.11–0.44 mg/kg, no significant difference between most imported labels.

Table 4 — Estimated weekly intake (EWI, µg/kg body weight/week; page 21)

EWI for an Iranian-adult 60 kg body weight, 770 g rice consumption per week (110 g/day × 7).

N* = JECFA has not established a Co PTWI; the paper cites an MTDI of 100 µg/kg bw/day (= 700 µg/kg bw/week) for Co.

PTWI exceedances: Pb EWI exceeded the JECFA 25 µg/kg bw PTWI in two imported labels (both at 25.769 µg/kg bw/week, both Indian-origin). No exceedances of the JECFA PTWI for Cd, Cr, Ni, or Co at the reported consumption rate.

Regulatory comparator values cited

• FAO/WHO 2004 maximum levels (cited from §2.4 and Figures 1–2): Cd 0.1 µg/g (= 0.1 mg/kg); Pb 0.2 µg/g (= 0.2 mg/kg) in rice.
• Iranian national standard (ISIRI 12968:2010, Food and feed — maximum limit of heavy metals): Cd 0.06 µg/g; Pb 0.15 µg/g.
• EU 2006 average-diet Ni and Cr intake estimates (Commission Regulation EC No 1881/2006 context): Ni 75 µg/day ≈ 1.25 µg/kg bw/day; Cr 150 µg/day ≈ 2.5 µg/kg bw/day for a 60 kg adult.
• JECFA PTWI: Cd 7 µg/kg bw/week; Pb 25; Cr 23.3; Ni 35; Co — no PTWI (MTDI 100 µg/kg bw/day = 700 µg/kg bw/week cited in Table 4 footnote).

Cd-from-rice exposure burden (text §“Conclusion”, p. 16)

Per the paper: “approximately 65.9 % of the daily intake of cadmium comes from rice” for Iranian adults at the reported consumption rate. This is reported in the source text as a derived percentage; the underlying total-diet Cd intake reference value is not explicitly cited in the paper.

Methods (brief)

Study design. Single-year (2013) market-basket survey at retail stores in Shiraz, Fars Province, Iran. Ten market labels of polished rice (3 domestic Iranian short-grain japonica; 7 imported long-grain indica from India and Thailand); 210 retail packs (15–20 kg each) screened; five ~250 g sub-samples per label drawn for analysis (n=50 sub-samples total).

Sample preparation. Rice passed through a 50-mesh sieve (<0.30 mm), sealed in plastic boxes, stored at room temperature. Dry ashing per AOAC official method 999.11 (Jorhem 2000): drying at 105 °C for 48 h; ashing at 450 °C with gradual temperature increase (≤50 °C/h); addition of 6 M HCl (1+1); evaporation to dryness; residue dissolved in 0.1 M HNO₃.

Instrumentation. Flame atomic absorption spectrometry (Shimadzu AA-680, Kyoto, Japan) and graphite-furnace atomic absorption spectrometry (Shimadzu MUV-IA, Kyoto, Japan). Concentrations expressed in mg/kg dry weight.

Replication. Each sample digested in triplicate; each digest analysed three times.

Quality control. Reagent blanks; replicate samples; certified reference material NIST SRM 1568b (rice flour, National Institute of Standards and Technology, Gaithersburg, USA). Observed recoveries: Pb 87.5 %, Cd 90 %, Co 107 % (Cr and Ni not certified on SRM 1568b). All chemicals and reagents from Merck (Germany); de-ionised water from Agricultural Biotechnology Research Center, Shiraz University. Operations in Class II laminar-flow hood; plastic bottles cleaned in 8 % (v/v) HNO₃ for 48 h, rinsed three times with de-ionised water. Mean blank value deducted from readings; batch blanks used to validate batch acceptability per EN 13804.

Speciation. Total Cd, total Pb, total Cr, total Ni, total Co. No inorganic arsenic (iAs) or total arsenic (tAs) (arsenic not on the panel); no methylmercury (MeHg) or total mercury (tHg) (mercury not on the panel); no hexavalent chromium (Cr-VI) / Cr-III fractionation.

Exposure assessment. EWI = C_rice × wc_rice / body weight, where C_rice = mean rice concentration (mg/kg dry weight), wc_rice = weekly rice consumption per capita = 110 g/day × 7 = 770 g/week (Institute of Standards and Industrial Research of Iran 2010), body weight = 60 kg adult. Values expressed in µg/kg body weight/week. The paper applies the EWI formula directly to dry-weight rice concentrations without an explicit moisture correction; this somewhat overstates the as-consumed exposure if cooked-rice moisture (~65–70 %) is the operational basis.

Statistics. SPSS version 21 (Stanford, California, USA). One-way ANOVA across labels per metal; Duncan post-hoc means comparison at p < 0.05. One-sample t-test comparing each metal mean against the corresponding regulatory limit at p < 0.05.

Geographic / temporal context. Shiraz, Fars Province, southern Iran. Sampling year 2013. The paper notes the Rice Research Institute of Iran estimate of 40.15 kg per-capita per-year rice consumption (0.110 kg/day) and Iran’s import dependence following sanctions, with India, Pakistan, and Thailand identified as principal source countries for imports (the surveyed corpus drew only India and Thailand origins).

Implications

This source contributes Iranian market-rice occurrence data for five total metals (Cd, Pb, Cr, Ni, Co) with adult EWI/PTWI comparison. Principal contributions to the wiki evidence pool:

• Polished-rice Cd occurrence in an Iranian retail-market context (2013, Shiraz, n=50 sub-samples across 10 labels): category-pooled mean rice Cd 0.27–0.48 mg/kg dry weight. All 10 label means exceed the FAO/WHO 2004 maximum level of 0.1 mg/kg by 2.7× to 4.8× and the Iranian national 2010 limit of 0.06 mg/kg by 4.5× to 8.0×. Adds to the upper-tail Cd evidence for rice on the Rice contamination_profile.
• Polished-rice Pb occurrence: category-pooled mean 0.71–2.00 mg/kg dry weight. All 10 label means exceed the FAO/WHO 2004 maximum level of 0.2 mg/kg (= 3.6× to 10× the limit) and the Iranian 0.15 mg/kg limit (= 4.7× to 13× the limit). Two imported labels deliver EWI Pb of 25.77 µg/kg bw/week, ≈ 1.03× the JECFA PTWI of 25 µg/kg bw/week. The highest single label Pb mean (2.00 mg/kg dry weight) is among the highest rice Pb values in the corpus.
• Polished-rice Cr occurrence: category-pooled mean 0.33–0.55 mg/kg dry weight. EWI Cr 4.325–6.891 µg/kg bw/week, all below the JECFA PTWI of 23.3 cited by the paper. Speciation absent; total Cr only (no Cr-VI / Cr-III fractionation).
• Polished-rice Ni occurrence: category-pooled mean 0.65–0.90 mg/kg dry weight. EWI Ni 9.32–11.62 µg/kg bw/week, all below the JECFA PTWI of 35; but all means exceed the EU 2006 average-diet Ni intake reference (≈ 1.25 µg/kg bw/day → 8.75 µg/kg bw/week) from rice alone, indicating rice as a non-trivial Ni dietary contributor in this corpus.
• Polished-rice Co occurrence: category-pooled mean 0.11–0.44 mg/kg dry weight. EWI Co 1.49–5.69 µg/kg bw/week, all well below the JECFA-cited MTDI-equivalent 700 µg/kg bw/week.
• Imported-vs-domestic gradient: Both categories show overlapping ranges for Cd, Cr, Ni, Co; imported Pb means trend higher (range 0.76–2.00) than domestic Pb means (range 0.71–1.28), driven by 3 of 7 imported labels with Pb means above 1.6 mg/kg. The two PTWI-exceeding labels were both Indian-origin imports.
• Iranian-adult Cd exposure attribution: the paper’s text §Conclusion derives 65.9 % of total-diet Cd intake as attributable to rice for Iranian adults at the reported 110 g/day consumption rate, which is a notable Cd-from-rice burden estimate for southern-Iran market-basket exposure modelling.
• Brand-and-cultivar firewall consideration: the original paper labels its 10 market entries with a mix of cultivar/region descriptors (3 domestic Iranian short-grain japonica from Fars Province) and commercial brand names (7 imported long-grain indica, 6 from India and 1 from Thailand). The paper itself uses the term “brands” for all 10 entries. Per Part 12 strict reading (2026-05-17), the wiki body does not reproduce per-label rows or per-label Pb/Cd PTWI exceedance attributions; the published paper retains the label-level disclosure.
• Methodological reference point: AOAC 999.11 dry-ashing + flame/GF-AAS with NIST SRM 1568b accuracy anchoring (Pb 87.5 %, Cd 90 %, Co 107 % recoveries; Cr/Ni unanchored on SRM 1568b). Triplicate digestion × triplicate analysis. Reagents from Merck. Adequate Tier B methodology for a small market-basket survey; lack of CRM accuracy validation for Cr and Ni, single-year sampling window, single-province scope, and adult-only single-cohort 60-kg exposure modelling limit standalone authority. Pools well with other Iranian market-rice surveys.

Downstream double-counting flag. This paper is one of the constituent primary studies in Jafari 2018 (jafari2018-iran-rice-meta in the wiki), which pools 10 Iranian rice studies (2010–2016) into a single occurrence summary. When this source feeds an Rice contamination_profile synthesis, downstream pooling must treat Naseri 2015 and Jafari 2018 as overlapping evidence — not as two independent occurrence rows — or it will double-count this paper’s contribution.

Related evidence

• Cadmium
• Lead
• Chromium
• Nickel
• Cobalt
• Rice (white, brown, wild — bulk grain)
• Codex Alimentarius — Maximum Levels for Cadmium in Food
• JECFA — Provisional Tolerable Monthly Intake for Cadmium, 25 µg/kg b.w./month
• JECFA — Lead Provisional Tolerable Weekly Intake (Withdrawn 2010)

Update history

No substantive edit history is available in this build. The full commit record is available in git.