Heavy metals in rice samples on the Torbat-Heidarieh market, Iran

Overview

This survey reports total concentrations of arsenic (HGAAS, treated here as total arsenic (tAs) absent any inorganic-species separation step), cadmium and lead in 210 packed long-grain (Indica) rice samples drawn from 10 imported rice types — three originating from India and seven from Pakistan — on the Torbat-Heidarieh retail market in 2015, plus a weekly-intake risk assessment under a 110 g/day per-capita rice-consumption assumption and a 60 kg adult-Iranian body-weight reference. Mean lead (Pb) concentrations across the 10-type panel exceeded the FAO/WHO Codex Alimentarius 0.2 mg/kg cereal limit in 9 of 10 types and exceeded the Iranian (ISIRI 12968) 0.15 mg/kg cereal limit in all 10 of 10 types; mean cadmium (Cd) exceeded the FAO/WHO 0.1 mg/kg cereal limit in 8 of 10 types; mean arsenic (As) exceeded the FAO/WHO 0.2 µg/g cereal limit in 4 of 10 types and exceeded the Iranian 0.15 µg/g limit in 5 of 10 types. The estimated weekly intake (EWI) of Pb computed from per-type means exceeded the JECFA Pb provisional tolerable weekly intake (PTWI, 25 µg/kg body weight per week) in 3 of 10 types; EWIs for Cd and As remained below their respective PTWI ceilings across the full panel.

Key numbers

Reference values cited by the paper for comparison:

PTWI reference values used for the risk assessment (µg/kg body weight per week, attributed by the paper to FAO/WHO Joint Expert Committee on Food Additives 2004 / FAO/WHO food standards programme):

Method validation parameters (Table 1, p. 2; values as printed in the paper, expressed in µg/g):

Per-type mean ± SD concentrations across the 10-type panel (Table 2, p. 3; µg/g on dry-weight basis):

Notes on the per-type SD structure: per-type SDs across the panel ranged from ±0.005 to ±0.017 for As (across the nine non-outlier types), ±0.008 to ±0.039 for Cd, and ±0.013 to ±0.223 for Pb. One Pakistan-origin type carries an As SD of ±0.20 in the published Table 2, a 10-fold outlier from the other nine As SDs and almost certainly a typographic error for ±0.020; see Verification notes.

Exceedance pattern (paper’s framing, Table 2 and prose, pp. 3-4):

• Mean Pb exceeded the FAO/WHO 0.2 mg/kg cereal ceiling in 9 of 10 types (3 of 3 Indian-origin and 6 of 7 Pakistani-origin; only one Pakistani-origin type at 0.199 mg/kg fell just below). Mean Pb exceeded the Iranian 0.15 mg/kg cereal ceiling in all 10 of 10 types. The three highest per-type Pb means (1.999, 1.961, 1.827 mg/kg) all fell in the same band and the prose identifies them by name as the top tier; under strict Part 12 reading the wiki page reports them as “the three highest-Pb types of the 10-type panel” without name attribution.
• Mean Cd exceeded the FAO/WHO 0.1 mg/kg cereal ceiling in 8 of 10 types; the two below-ceiling means (0.085 and 0.098 mg/kg) were both in the Pakistani-origin group. The three highest Cd means (0.385, 0.295, 0.242 mg/kg) span both origins. The paper does not cite an explicit Iranian Cd cereal ceiling for direct comparison.
• Mean As (HGAAS, treated as total) exceeded the FAO/WHO 0.2 µg/g cereal ceiling in 4 of 10 types (2 of 3 Indian-origin at 0.206 and 0.225 µg/g, and 2 of 7 Pakistani-origin at 0.243 and 0.314 µg/g). The panel mean of 0.161 µg/g fell below the FAO/WHO ceiling but above the Iranian 0.15 µg/g ceiling. Five of 10 types exceeded the Iranian 0.15 µg/g ceiling (3 Indian-origin and 2 Pakistani-origin).

Estimated weekly intake (EWI) across the 10-type panel (Table 3, p. 3; µg/kg body weight per week, computed as EWI = C_rice × (WI_rice / BW) with WI_rice = 770 g/week per capita (110 g/day × 7) and BW = 60 kg, per the Institute of Standards and Industrial Research of Iran 2010 assumption):

EWI exceedances vs PTWI:

• Pb EWI exceeded the 25 µg/kg bw/week PTWI in 3 of 10 types (1 Indian-origin at 25.66 and 2 Pakistani-origin at 25.54 and 25.17 µg/kg bw/week). An additional Indian-origin type fell at the PTWI ceiling itself (24 µg/kg bw/week, rounded as published in Table 3).
• Cd EWI was below the 7 µg/kg bw/week PTWI for all 10 types (panel maximum 4.60).
• As EWI was below the 15 µg/kg bw/week PTWI for all 10 types (panel maximum 4.03).

Methods (brief)

Sample collection. 210 packed long-grain (Indica) rice samples were drawn from 10 imported rice types available in retail stores in Torbat-Heidarieh city (Razavi Khorasan province, northeastern Iran) in 2015. Three types originated from India and seven from Pakistan; each retail pack weighed 15-20 kg. A 250 g aliquot was taken from each pack, sieved through 50 mesh (<0.30 mm), sealed in a plastic box, and stored at room temperature until analysis. The paper notes that production area was usually only vaguely described on the packaging (“India” or “Pakistan” without further geographic detail).

Sample preparation — arsenic. Rice samples were turned into ash with nitric acid and evaporated to dryness. The ash was then heated by a gradual temperature increase to 425 °C, re-dissolved in hydrochloric acid, and presented to the hydride generation atomic absorption spectrometer (HGAAS) for As determination at 193.7 nm absorption band, per CEN EN 14546:2005 (“Foodstuffs - Determination of trace elements - Determination of total arsenic by hydride generation atomic absorption spectrometry (HGAAS) after dry ashing”).

Sample preparation — cadmium and lead. Dry ashing per AOAC Official Method 999.11 (Jorhem 2000). Rice samples were dried at 105 °C for 48 h, then ashed at 450 °C with a gradual temperature ramp (≤50 °C/h). 6 M HCl (1+1) was added; the solution was evaporated to dryness; the residue was dissolved in 0.1 M HNO₃. The digested solution was analysed for Pb and Cd by flame and graphite furnace atomic absorption spectrometry on a Young Lin model 8020 (YL Instrument Co., Anyang, Republic of Korea). All samples were digested and analysed in triplicate. Concentrations were expressed as mg/kg on dry-weight basis (per Jorhem 2000).

Instrumentation and reagents. Chemicals and reagents from Merck (Darmstadt, Germany) at maximum purity; high-purity de-ionised water; certified reference material SRM 1568 (rice flour, National Institute of Standards and Technology, Gaithersburg, MD, USA). Quality control included reagent blanks, repeated samples, and the SRM 1568 CRM. Per Table 1 the As recovery was 93 % (certified 0.285 vs measured 0.251 µg/g); the Pb recovery was 95 % (certified 0.008 vs measured 0.0057 µg/g); the Cd recovery was 97 %, but the certified and measured values printed in Table 1 (118.4 and 111.55 µg/g) are inconsistent with the published NIST SRM 1568 / 1568a / 1568b rice-flour Cd certified values (which are on the order of 0.022 µg/g) — see Verification notes; this is a paper-internal anomaly, not a wiki-side transcription issue.

Speciation. Total As by HGAAS without arsenic-species separation; the wiki page uses tAs (total arsenic) rather than iAs. Total Cd and total Pb by AAS. No mercury panel, no As speciation, no chromium speciation.

Statistical analysis. SPSS version 23. Duncan method for comparison of means. Sample t-test for comparison of mean values against available standards. Significance level p < 0.05.

Risk assessment. EWI = C_rice × (WI_rice / BW), with C_rice as the per-type mean (mg/kg dry weight), WI_rice as the weekly intake of rice = 110 g/day × 7 = 770 g/week per the ISIRI 2010 per-capita assumption, and BW = 60 kg average Iranian adult body weight. EWI values are reported in Table 3 in µg per kg body weight per week. PTWI reference values (15, 7, 25 µg/kg bw/week for As, Cd, Pb respectively) were attributed by the paper to FAO/WHO Joint Expert Committee on Food Additives 2004 / FAO/WHO food standards programme.

Implications

This source contributes Iranian retail-market occurrence data for total As, total Cd, and total Pb in imported long-grain (Indica) rice on a single-city (Torbat-Heidarieh) panel of 10 rice types in 2015, plus a worked single-commodity weekly-intake risk assessment under a defined 770 g/week per-capita and 60 kg body-weight Iranian adult assumption. Principal contributions to the wiki evidence pool:

• A Pb signal in imported long-grain rice with per-type means spanning 0.199-1.999 mg/kg across the 10-type panel and 9 of 10 type-means exceeding the Codex Alimentarius 0.2 mg/kg cereal ceiling (all 10 of 10 exceed the Iranian 0.15 mg/kg ceiling). The 3 highest type-means (1.999, 1.961, 1.827 mg/kg) cluster nearly an order of magnitude above the Codex ceiling. The Pb-in-rice band falls broadly within the range reported by the parallel Iranian cereal-market work Essential and toxic heavy metals in cereals and agricultural products marketed in Kermanshah, Iran, and human health risk assessment (Kermanshah-market rice mean 1.35 mg/kg, 2014 sampling — Roya 2016 cites this paper as “Pirsaheb et al. 2016” per its print issue year), and the paper itself also cites prior Iranian work (Mirlohi et al. 2013; Naseri et al. 2015) in the same band.
• A Cd signal with per-type means spanning 0.085-0.385 mg/kg, 8 of 10 type-means exceeding the Codex 0.1 mg/kg cereal ceiling. The Cd mean range and exceedance frequency are higher than the Kermanshah-market rice Cd mean reported by the same parallel Iranian work (0.055 mg/kg, Essential and toxic heavy metals in cereals and agricultural products marketed in Kermanshah, Iran, and human health risk assessment), and notably higher than several non-Iranian retail-market datasets the paper cites (Taiwan, South Korea, Sweden, Brazil, Nigeria — per-paper means in the 0.003-0.035 mg/kg band).
• A total-As (HGAAS, no species separation) signal with per-type means spanning 0.048-0.314 µg/g and 4 of 10 type-means exceeding the Codex 0.2 µg/g cereal ceiling. The panel mean of 0.161 µg/g sits just above the Iranian 0.15 µg/g ceiling.
• An origin-stratified contrast: the 3-type Indian-origin subgroup carries higher per-type Pb (range 1.430-1.999) and higher per-type Cd (range 0.221-0.385) means than the 7-type Pakistani-origin subgroup (Pb 0.199-1.961, Cd 0.085-0.295), though the Pakistani-origin subgroup contains the panel maximum Pb-mean and Cd-mean values. The paper does not attempt to attribute the origin contrast to specific cultivation, water, soil, or post-harvest pathways and explicitly notes that production area was vaguely described on the packaging.
• A 3-of-10 Pb-EWI-above-PTWI signal under the single-commodity 770 g/week assumption, including one Indian-origin type at 25.66 and two Pakistani-origin types at 25.54 and 25.17 µg/kg bw/week. The single-commodity Pb-EWI range for this Torbat-Heidarieh-market panel (2.87-25.66 µg/kg bw/week) brackets the single-EWI value reported by the parallel Kermanshah-market rice work (17.32 µg/kg bw/week, Essential and toxic heavy metals in cereals and agricultural products marketed in Kermanshah, Iran, and human health risk assessment).
• A small-panel (n = 10 brands), single-city, single-year, single-cohort (adult 60 kg) sampling footprint with no As-species separation, no mercury (Hg) panel, no chromium (Cr) panel, and several paper-internal data-quality anomalies (see Verification notes). The B-tier classification reflects these limitations; the source should pool with other Iranian-market rice work for occurrence-distribution purposes rather than anchor any standalone characterisation.

Related evidence

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

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