Overview
This review article aggregates 28 prior studies (25 full-text plus 3 abstracts) published 2005-2016 on heavy metal contamination of rice (Oryza sativa) cultivated in or imported into Iran, drawn from Iranian and international databases (Magiran, Iran Medex, Irandoc, SID, Google Scholar, Scopus, ISI Web of Knowledge, Cochrane CDSR, PubMed). The authors tabulate province-level means and ranges for cadmium, arsenic, lead, chromium, cobalt, nickel, and mercury reported across the assembled corpus (Table 1) and compute a single Iran-wide estimated weekly intake (EWI) per metal for a 60 kg adult under a 165 g/day average per-capita rice consumption assumption (Table 2). The headline finding: averaged across the assembled corpus, weekly intakes of cadmium (Cd), arsenic (As), lead (Pb), chromium (Cr), Co, and nickel (Ni) from rice fall below their respective WHO/FAO provisional tolerable weekly intake ceilings, but the average weekly intake of mercury (9.68 µg/kg body weight per week) exceeds the 4 µg/kg bw/week PTWI by approximately 2.4×. The review also reports that in 14 of 23 Cd-reporting studies and 16 of 22 Pb-reporting studies, province-level mean concentrations exceeded the Iranian national standards (ISIRI 12968: 0.06 µg/g Cd, 0.15 µg/g Pb, 0.15 µg/g As).
Key numbers
Search and inclusion (Figure 1, p. 2):
| Stage | Count |
|---|---|
| Distinct references identified | 342 |
| References excluded at first screening (title/abstract, non-original, non-Iran) | 314 |
| Distinct references in rice (included in review) | 28 |
| Full-text papers sought | 25 |
| Abstracts only | 3 |
Iranian national reference standards cited by the review (attributed to ISIRI 12968, 1st ed., 2010):
| Metal | Iranian standard for rice |
|---|---|
| cadmium (Cd) | 0.06 µg/g |
| arsenic (As) | 0.15 µg/g |
| lead (Pb) | 0.15 µg/g |
| chromium (Cr) | not defined (WHO standard for rice 1 µg/g cited; Iranian water standard 0.05 mg/L) |
| Co | not defined |
| nickel (Ni) | not defined (Iranian water standard 0.02 mg/L) |
| mercury (Hg) | not defined (Iranian water standard 0.001 mg/L) |
WHO/FAO provisional tolerable weekly intake (PTWI) reference values used by the review for the risk assessment (µg/kg body weight per week):
| Metal | PTWI |
|---|---|
| cadmium (Cd) | 7 |
| arsenic (As) | 15 |
| lead (Pb) | 25 |
| Co | (MTDI 100 µg/kg bw/day = 700 µg/kg bw/week used in lieu of PTWI) |
| nickel (Ni) | 35 |
| chromium (Cr) | 23.30 |
| mercury (Hg) | 4 (total Hg) |
Province-level minimum-maximum concentrations across the 28-study corpus (Table 1, p. 3; µg/g on dry-weight basis where reported; “not detected” preserved as published; ranges represent the spread of per-study mean values across the assembled corpus, not within-study variability):
| Metal | Min per-study mean | Max per-study mean | Province extremes (paper’s framing) |
|---|---|---|---|
| cadmium (Cd) | 0.008 µg/g | 0.3802 µg/g | min Kermanshah (0.008 ± 0.000); max Gillan (0.3802 ± 0.0508) per the prose; Table 1 also reports 0.40 ± 0.16 in Mazandaran |
| arsenic (As) | 0.005 µg/g | 3 µg/g | min Ghaemshahr (0.005-0.135 µg/g range); max Gillan (3 µg/g) per Farsani et al. 2014 |
| lead (Pb) | 0.01 µg/g | 35 µg/g | min Gillan (0.01-0.31 µg/g range); max Mazandaran (35 µg/g per Farsani et al. 2014); Zahedan reaches 11.5 ± 6.4 µg/g |
| chromium (Cr) | 0.098 µg/g | 6.416 µg/g | min Mazandaran province (0.098 ± 0.000 µg/g); max Gillan (6.416 µg/g per Farsani et al. 2014); Feridonkenar reaches 5.916 µg/g |
| Co | 0.13 µg/g | 0.41 µg/g | reported in Shiraz only (Table 1); 0.13-0.41 range |
| nickel (Ni) | 0.72 µg/g | 2.411 µg/g | min Shiraz (0.72 µg/g); max Gillan (2.411 µg/g per Farsani et al. 2014); Feridonkenar 1.901, Isfahan 1.173 µg/g |
| mercury (Hg) | 0.00 µg/g | 1.267 µg/g | min Tarom (0.00 µg/g); max Feridonkenar (1.267 µg/g per Farsani et al. 2014); Gillan 3.007 µg/g per the prose (Table 1 reports a Ghaemshahr Mazandaran-province value of 0.044 ± 0.003 µg/g) |
Exceedance counts versus Iranian national standards (review prose, pp. 2-4):
| Metal | Studies reviewed | Studies/cases exceeding Iranian standard |
|---|---|---|
| cadmium (Cd) (vs ISIRI 0.06 µg/g) | 23 studies | 14 studies above standard |
| lead (Pb) (vs ISIRI 0.15 µg/g) | 22 studies | 16 cases above standard |
| arsenic (As) (vs ISIRI 0.15 µg/g) | not tabulated separately | review prose notes Gillan (3 µg/g), Khuzestan (1.97 µg/g), Feridonkenar (0.545 µg/g) all exceeded the standard |
Iran-wide estimated weekly intake (EWI) for a 60 kg adult, computed from per-capita rice consumption (Table 2, p. 4; µg/kg body weight per week; consumption range 158-178 g/day with 165 g/day average per ISIRI 2010):
| Metal | Mean rice content range (µg/g) | Average mean rice content (µg/g) | Weekly intake range (µg/kg bw/week) | Weekly intake at average (µg/kg bw/week) | PTWI ceiling (µg/kg bw/week) | Status |
|---|---|---|---|---|---|---|
| cadmium (Cd) | 0.008 - 0.40 | 0.172 | 0.147 - 8.306 | 3.311 | 7 | below PTWI on average; per-study max exceeds |
| arsenic (As) | 0.005 - 0.94 | 0.151 | 0.092 - 19.52 | 2.91 | 15 | below PTWI on average; per-study max exceeds |
| mercury (Hg) | 0.044 - 0.963 | 0.503 | 0.81 - 20.00 | 9.68 | 4 | above PTWI on average and per-study max |
| lead (Pb) | 0.01 - 11.5 | 1.158 | 0.18 - 238.81 | 22.29 (table) / 22.9 (prose) | 25 | below PTWI on average; per-study max exceeds substantially |
| Co | 0.13 - 0.41 | 0.247 | 2.40 - 8.51 | 4.75 | (MTDI 100 µg/kg bw/day used) | below reference |
| nickel (Ni) | 0.78 - 0.963 | 0.829 | 14.38 - 20.00 | 15.96 | 35 | below PTWI |
| chromium (Cr) | 0.098 - 2.39 | 0.55 | 1.81 - 49.63 | 10.59 | 23.30 | below PTWI on average; per-study max exceeds |
mercury (Hg) PTWI exceedance is the review’s headline finding: the Iran-wide average weekly intake of mercury from rice (9.68 µg/kg bw/week) is approximately 2.4× the WHO/FAO total-mercury PTWI of 4 µg/kg bw/week.
Methods (brief)
This is a systematic review of the published literature rather than an original measurement study. The methods section describes only the search-and-inclusion procedure; per-study analytical methodology is reported in each constituent study and not re-described here.
Database search. The authors searched both local Iranian databases (Magiran, Iran Medex, Irandoc, SID) and international databases (Google Scholar, Scopus, ISI Web of Knowledge, Cochrane Database of Systematic Reviews, PubMed). Search terms included “Iran,” “heavy metals,” “pollutant,” “toxic element,” “arsenic,” “cadmium,” “mercury,” “lead,” “cobalt,” “nickel,” “chromium,” and “rice.” The search was limited to manuscripts published between 2005 and 2016.
Inclusion criteria. Manuscripts were selected from the studies aimed to cover the presence and levels of heavy metals in rice, screening on title and/or abstract. Of 342 distinct references identified, 314 were excluded at first screening for (a) inappropriate title/abstract, (b) non-original data, or (c) non-Iran geographic scope. The remaining 28 were retained: 25 sought as full-text and 3 retained as abstracts only.
Aggregated analytical methods (from the constituent studies, as the review describes). The 28 constituent studies collectively used atomic absorption spectrometer, mercury analyzer, and inductively coupled plasma optical emission spectrometer (ICP-OES) instruments for quantitation, with acid digestion for sample preparation. Per-study analytical method, sample preparation, and quality control details are reported in the constituent papers (Table 1 references) and not re-aggregated by the review.
Estimated weekly intake (EWI) calculation. The review applies a single EWI formula across the corpus:
EWI = C × FIR_w / BW
where C is heavy metal concentration in rice (µg/g), FIR_w is the average weekly intake rate of rice (g/person/week), and BW is the average body weight (set to 60 kg for an Iranian adult). The FIR_w value is derived from per-capita daily rice consumption in Iran ranging 158-178 g/person/day with an average of 165 g/person/day, per ISIRI 2010 — yielding FIR_w ≈ 1,155 g/person/week at the average. The review compares the computed EWI values against the WHO/FAO PTWI references.
Implications
This source is a systematic literature review that aggregates province-level Iranian rice contamination data from 28 prior studies spanning 2005-2016. It does not contribute original measurements to the wiki evidence pool; it contributes a meta-level characterisation of the Iranian rice contamination corpus and a single Iran-wide EWI estimate per metal. Principal contributions:
- Mercury PTWI exceedance signal. The review’s central numerical finding is that the Iran-wide average weekly intake of mercury from rice (9.68 µg/kg bw/week, computed from an average rice Hg content of 0.503 µg/g across the corpus and 165 g/day per-capita rice consumption) exceeds the WHO/FAO total-mercury PTWI of 4 µg/kg bw/week by approximately 2.4×. This is the only PTWI exceedance reported in the aggregated EWI table; all other metals’ average-rice-content-based EWI values fall below their respective PTWI ceilings. The Hg signal is driven by high-mercury rice samples from northern Iranian provinces (Gillan, Mazandaran/Feridonkenar) per Farsani et al. 2014 and Rezaitabar et al. 2015 (review references).
- Pb headroom-only-on-average signal. Iran-wide average rice Pb content (1.158 µg/g) yields an EWI of 22.9 µg/kg bw/week, just under the 25 µg/kg bw/week PTWI ceiling. The per-study maximum rice Pb content reported in the corpus (11.5 µg/g, Zahedan, Mobaraki & Safarzai 2013 per review reference; with one citation of 35 µg/g in Mazandaran per Farsani et al. 2014) yields an upper-bound EWI of 238.81 µg/kg bw/week — nearly 10× the PTWI. The mean is below PTWI; the tail substantially exceeds it.
- Cd corpus-wide exceedance of Iranian standard. 14 of 23 Cd-reporting studies in the corpus reported province-level mean concentrations above the Iranian standard of 0.06 µg/g, though the Iran-wide average-rice-content EWI (3.311 µg/kg bw/week) remained below the WHO/FAO Cd PTWI of 7 µg/kg bw/week.
- As corpus-wide pattern. The Iran-wide average-rice-content EWI (2.91 µg/kg bw/week) sits well below the WHO/FAO As PTWI of 15 µg/kg bw/week, but specific provincial samples (Gillan 3 µg/g, Khuzestan 1.97 µg/g, Feridonkenar 0.545 µg/g per the review prose) exceeded the Iranian 0.15 µg/g standard substantially. The review does not separate inorganic from organic arsenic; treatment of As in the constituent studies is generally total As by AAS or ICP-OES.
- Trace metals (Cr, Co, Ni) below references. Iran-wide average-rice-content EWI values for Cr (10.59 µg/kg bw/week, vs PTWI 23.30), Co (4.75 µg/kg bw/week, vs MTDI 700 µg/kg bw/week), and Ni (15.96 µg/kg bw/week, vs PTWI 35) all fell below their respective WHO/FAO reference ceilings. These metals are present in Iranian rice but the per-capita consumption-based dietary burden does not exceed established intake ceilings on average.
- Geographic pattern across Iranian provinces. Table 1 reports per-province per-study values from at least 17 Iranian sampling locations (Kashan, Tehran, Shiraz, West Azarbaijan, Khuzestan, Ghaemshahr/Mazandaran, Tabriz, Gillan, Kermanshah, Khuzestan province, Golestan, East Azarbaijan, Shahrekord, Yazd, South Caspian, Isfahan/Brojerd, Zahedan, Babol, Lorestan, Mobarakeh, Ghaemshahr-Mazandaran). The northern Caspian-region provinces (Gillan, Mazandaran, Feridonkenar, Golestan) and central agricultural regions (Khuzestan, Ghaemshahr) carry the highest per-study mean values across multiple metals.
- Review-level limitations for downstream pooling. The review aggregates per-study means without re-pooling raw measurements or estimating between-study heterogeneity, and assumes a single 60 kg / 165 g-per-day per-capita scenario for the EWI calculation. The “average rice content” figures in Table 2 are simple summaries across the heterogeneous corpus rather than weighted pooled means. Downstream wiki synthesis should treat this paper as a corpus pointer (it identifies the 28 constituent studies) rather than as an authoritative single-source quantitative estimate; per-study values pulled from Table 1 should be cross-checked against the constituent paper when ingested.
Related evidence
- Cadmium
- Arsenic, Total
- Lead
- Mercury, Total
- Chromium
- Cobalt
- Nickel
- Rice
- Rice (white, brown, wild — bulk grain)
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