The concentration of heavy metals in noodle samples from Iran's market: probabilistic health risk assessment

Overview

This Tehran retail-market study reports total concentrations of lead, chromium, cadmium, and aluminium in commercial instant noodle samples drawn from three Iranian-produced brands (coded 1, 2, 3) and one imported brand (coded 4), collected in Spring 2017 and analysed by ICP-OES after acid digestion on samples dried at 85 °C for 24 h before grinding. The principal occurrence finding is that mean concentrations in every brand exceeded the WHO 0.025 mg/kg food-products ceiling for lead (Pb), the WHO 0.003 mg/kg ceiling for cadmium (Cd), the WHO 0.050 mg/kg ceiling for chromium (Cr), and the WHO 0.237 mg/kg ceiling for aluminum (Al). Significant brand-vs-brand differences (Kruskal-Wallis p < 0.05) were observed for all four metals, and significant Iranian-vs-imported differences (Mann-Whitney p < 0.05) were observed for all four metals: imported noodles carried higher Cr, Cd, and Al but slightly lower Pb than the pooled Iranian noodles. The principal risk-assessment finding is that the Monte-Carlo (10 000-iteration) 95th-percentile target hazard quotient for aluminium exceeded 1 in both adult (P95 THQ_Al 1.789) and child (P95 THQ_Al 6.167) consumer panels, indicating a considerable non-carcinogenic health risk for Al from instant-noodle ingestion at the Iranian per-capita rate of 0.0027 kg/person/day; THQ for Pb, Cr, and Cd was below 1 at P95 in both panels. Children carried roughly 3.5× the adult THQ across all four metals owing to the lower-body-weight denominator.

Key numbers

Pooled per-origin mean ± SD concentrations (Abstract, p. 1; Results §“Lead in instant noodle samples” through §“Aluminum in instant noodle samples”, pp. 4-6; values in mg/kg on a dried-product basis):

Per-brand mean ± SD concentrations (Results §3.1-§3.4 prose, pp. 4-6; not all four metal values are published in the prose for every brand — gaps below are paper-internal):

Single-sample maxima and minima across the four-brand panel (Results §3.1-§3.4 prose, pp. 4-6):

The Al maximum and minimum both falling within Brand 1 is consistent with the very wide intra-brand SD (Brand 1 Al 6.83 ± 4.13 mg/kg, the highest coefficient of variation in the Al panel) and reflects sample-to-sample heterogeneity within the same commercial brand.

Reference / regulatory limits cited by the paper for direct mean-vs-ceiling comparison (Introduction §“Heavy metals introduction” and Discussion, pp. 2-3 and pp. 4-6):

The Iranian National Standard is reported to set no specific Pb limit in noodles per the paper text (“Iranian National Standard Institute established the limit of 0.15 (mg/kg) for the Pb in wheat-based food products there is no recognized standard for Pb in noodle”); the Bangladesh BSTI 2 mg/kg noodle ceiling is cited as the nearest noodle-specific regulatory comparator. The paper cites the WHO 0.050 mg/kg cereal limit as hexavalent chromium (Cr-VI), not total Cr (Introduction p. 3: “The permissible limit set by WHO for chromium(VI) in cereals is 0.050 (mg/kg)”). See Verification notes for the speciation-vs-comparator mismatch this introduces.

Brand-level exceedance fractions versus WHO food-product ceilings (Conclusion p. 8):

Brand-level exceedance fractions versus Iranian National Standard / ISIRI cereal Cd ceiling (Conclusion p. 8): 40.74% of samples exceeded the ISIRI 0.03 mg/kg Cd ceiling for wheat-based food products. The Conclusion paragraph also states “Cd in 40.74% and Al in all instant noodle samples were higher than the recommended levels by Iranian Institute of Standard and Industrial Research (0.03 mg/kg) and WHO (0.237 mg/kg), for Cd and Al, respectively.” No explicit per-brand Pb-exceedance fraction against ISIRI is published (the paper notes ISIRI has no noodle-specific Pb ceiling).

Method-validation limits of detection and quantification (Results §3.1-§3.4 leading paragraphs, pp. 4-6):

ICP-OES instrumental operating conditions (Table 1, p. 3):

Exposure-assessment parameter set used in Monte-Carlo simulation (Table 2, p. 4):

Oral reference doses applied in the THQ computation (Materials and Methods §“Health risk assessment”, p. 4):

95th-percentile (P95) target hazard quotients from Monte-Carlo simulation (10 000 iterations, Oracle Crystal Ball v11.1.2.4; Results §“Health risk assessment” and Conclusion, pp. 6-8; Figs. 2-4):

The TTHQ row is wiki-computed as the sum of the four metal-specific THQ_P95 values; the paper publishes the four component THQs and Figure 4 plots a stacked bar of “TTHQ for adult and children consumers” showing TTHQ > 1 in both groups, dominated by Al. The Cr child:adult ratio of ~33 is anomalous relative to the ~3.5 ratio for the other three metals; the Cr values are at the limit of meaningful precision (Adult 7×10⁻⁶, Child 2.3×10⁻⁴) and likely reflect tail-distribution behaviour in the Monte-Carlo rather than a real ~10× elevation, but the paper does not comment on this directly. See Verification notes.

The risk-rank order in both adult and child panels was Al > Pb > Cd > Cr (Conclusion p. 7), driven by the combination of the high Al concentrations (≈ 9-16 mg/kg vs sub-mg/kg for the other three metals) and the low Al RfD (4 × 10⁻⁴ mg/kg/day vs 8.5 × 10⁻³ mg/kg/day for Pb, 5 × 10⁻⁴ mg/kg/day for Cd, and 1.5 mg/kg/day for Cr).

Methods (brief)

Sample collection. 27 Iranian-produced instant noodle samples drawn from three commercial brands (coded 1, 2, 3) and an unspecified number of imported instant noodle samples from one brand (coded 4) were collected from the Tehran retail market in Spring 2017 (Materials and methods §“Sample collection and preparation”, p. 3). The total panel size including the imported brand 4 is not explicitly published — the abstract reports “27 Iranian instant noodle samples from three commercial brands … and imported instant noodle in one brand,” and the per-brand replicate count would need to be assumed (likely 9 samples per Iranian brand × 3 brands = 27 Iranian + N imported). The wiki source metadata sample_n: 27 records the Iranian-only count published in the abstract; the imported-brand replicate count is not stated.

Sample preparation. Instant noodle samples were dried in a hot-box oven with fan (Gallenkamp OHF097.XX1., UK) at 85 °C for 24 h, then ground with a ceramic mortar and pestle for 10 min. To prevent contact with metal surfaces, a plastic spoon was used for weighing, mixing, and collecting the powder. Powders were stored in polyethylene bags until analysis (maximum 1 week). Acid digestion was performed by combining 1 g of weighed powder with 6.0 mL of 65% HNO₃ (Merck KGaA, Darmstadt, Germany) and 2.0 mL of 30% H₂O₂ (Merck KGaA) and heating in an oven at 130 °C for 1 h. Digests were diluted to 10 mL with double-distilled deionised water, filtered through Whatman No. 42 filter paper, and re-diluted to 10 mL with double-distilled deionised water. Blank samples (6.0 mL HNO₃ + 2.0 mL H₂O₂ without any noodle aliquot) were prepared in parallel.

Instrumentation. The digested extracts were analysed by inductively coupled plasma optical emission spectrometry (ICP-OES) on a Spectro Arcos system (SPECTRO Analytical Instruments, Germany) equipped with a Flared End EOP Torch (2.5 mm). Operating conditions are tabulated above. The method follows Fathabad et al. 2018.

Quality control. One package of Iranian instant noodle was dried, ground, and split into three glassware beakers; each was acid-digested (1 g) in parallel under the same procedure, with one beaker receiving 1 mL of standard solution A, the second receiving 2 mL of standard solution B, and the third receiving no spike (solution C). Quality-control samples were injected to ICP for each heavy metal. Solutions A and B carried higher heavy-metal content than C, with B approximately double the heavy-metal content of A. The difference between the measured-vs-true content for the multielement standard (Fluka Analytical reagent no. 51844, multielement standard solution 4 for ICP) was less than 5%.

Speciation. ICP-OES on acid-digested noodle samples measures total elemental content. The paper reports Pb, Cr, Cd, and Al as total concentrations with no species separation (no Cr-VI vs Cr-III speciation step, no Al-species fractionation). The Introduction discusses Cr toxicity primarily in terms of Cr(VI) as the human carcinogen and cites the WHO 0.050 mg/kg cereal limit specifically as a Cr-VI limit, but the analytical method measures total Cr. The wiki page accordingly tags Cr as total chromium in the metals source metadata (not Cr-VI) and flags the comparator-vs-measurand mismatch in the Verification notes.

Statistical analysis. SPSS v22.0 (SPSS Inc., USA). Differences between country origins (Iranian vs imported) were tested by Mann-Whitney U test. Differences between brands (1, 2, 3, 4 across the four-brand panel) were tested by Kruskal-Wallis H test. Significance threshold p < 0.05.

Risk assessment. Non-carcinogenic risk via the Target Hazard Quotient method (USEPA 2011):

• CDI = (C × IRi × EFi × EDi) / (BWi × ATn) — Equation 2
• THQ = CDI / RfD — Equation 1
• TTHQ = Σ THQi across metals — Equation 3

Adult and child consumer panels were modelled with the Iranian per-capita instant noodle ingestion rate of 0.0027 kg/person/day from WINA 2018. Probabilistic risk was computed by Monte-Carlo simulation (10 000 iterations) in Oracle Crystal Ball v11.1.2.4 with normal distributions assumed for C, IRi, EFi, EDi, BW, AT, and RfD. The 95th-percentile THQ was reported as the panel risk benchmark; THQ ≤ 1 indicates non-carcinogenic adverse effect is not likely, THQ > 1 indicates potentially adverse effect is likely (USEPA 2011).

Implications

This source contributes Iranian retail-market occurrence data for total Pb, Cr, Cd, and Al in commercial instant noodles drawn from three Iranian-produced brands and one imported brand on the Tehran market in Spring 2017, plus a probabilistic non-carcinogenic risk assessment under Iranian-adult (70 kg, 30 y) and Iranian-child (20 kg, 6 y) consumer assumptions. Principal contributions to the wiki evidence pool:

• A four-brand Tehran-market occurrence panel showing pooled-Iranian instant-noodle Pb 1.21 ± 0.81 mg/kg, Cr 0.08 ± 0.10 mg/kg, Cd 0.03 ± 0.06 mg/kg, and Al 9.15 ± 4.82 mg/kg; imported-brand instant-noodle Pb 1.00 ± 0.61 mg/kg, Cr 0.07 ± 0.07 mg/kg, Cd 0.04 ± 0.03 mg/kg, and Al 15.90 ± 0.93 mg/kg. All four metals separated significantly between Iranian and imported origins (Mann-Whitney p < 0.05) and across the four brands (Kruskal-Wallis p < 0.05).
• A 100%-exceedance signal against the WHO 0.025 mg/kg food-products Pb ceiling: every brand’s mean Pb concentration (1.004 to 1.57 mg/kg) exceeds this ceiling by 40× to 63×. The paper notes that no Iranian noodle-specific Pb ceiling exists (ISIRI publishes a 0.15 mg/kg ceiling for wheat-based food products generally, against which all four brand means also exceed by 7× to 10×).
• A 40.74% exceedance signal against the ISIRI 0.03 mg/kg Cd cereal ceiling, driven primarily by Brand 2 (Iranian) which carries the highest Cd panel mean of 0.14 ± 0.19 mg/kg and the panel-maximum single sample of 0.35 mg/kg.
• A 100%-exceedance signal against the WHO 0.237 mg/kg food-products Al ceiling: every brand’s mean Al concentration (6.83 to 15.91 mg/kg) exceeds this ceiling by 29× to 67×. The paper attributes the Al loading to Al-containing food additives used in instant-noodle production for decorative, stabilising, firming, and anti-caking purposes (metallic Al, Al sulphates, Al silicate).
• An imported-vs-domestic origin contrast: imported instant noodles carry significantly higher Cr, Cd, and Al but slightly lower Pb than Iranian instant noodles in this Tehran-market panel. The paper recommends additional control measures specifically targeting imported instant noodles for Cr, Cd, and Al quality.
• A worked probabilistic non-carcinogenic risk assessment showing P95 THQ_Al > 1 in both adult (1.789) and child (6.167) consumer panels, identifying Al as the only metal of the four whose Tehran-market instant-noodle exposure at the Iranian per-capita ingestion rate poses a considerable non-carcinogenic risk at the 95th-percentile threshold. P95 THQs for Pb, Cr, and Cd were all below 1 in both panels under the Iranian per-capita instant-noodle ingestion rate of 0.0027 kg/person/day, indicating that despite very high concentration-vs-WHO-ceiling exceedance ratios for Pb, Cr, and Cd, the low per-capita instant-noodle ingestion rate keeps the noodle-specific health-quotient contribution below the non-carcinogenic-risk threshold for those three metals in isolation. The TTHQ sum across the four metals exceeds 1 in both panels, driven almost entirely by Al.
• A child-vs-adult risk-ratio of ~3.5× across all four metals, consistent with the body-weight ratio (70 kg adult / 20 kg child = 3.5) given the same per-capita ingestion rate. The Cr child:adult ratio of ~33 in the published P95 THQs is anomalous; see Verification notes.
• A medium-panel (27 Iranian + N imported, N not published), single-city, single-season (Tehran Spring 2017), single-cohort (Iranian adult 30 y, Iranian child 6 y) sampling footprint with no Cr-species separation, no arsenic (As) panel, no mercury (Hg) panel, no nickel (Ni) panel, no recovery / CRM / measurement-uncertainty validation data published beyond the multielement-standard <5% accuracy statement, and no per-brand replicate count published for the imported brand. The B-tier classification reflects these limitations; the source should pool with other Iranian-market noodle and wheat-based-pasta work for occurrence-distribution purposes (e.g., the Iranian per-brand mean concentration tables sit naturally in any Iranian instant-noodle dataset built alongside Analysis of lead, arsenic, and cadmium concentrations in instant noodles within the Canadian market for cross-market comparison).

Related evidence

• Lead
• Chromium
• Cadmium
• Aluminum
• Noodles
• Wheat
• Pasta (wheat-based)

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