Environmental and occupational exposure to cadmium in Iran: a systematic review

Overview

This narrative systematic review aggregates 18 Iranian biomonitoring studies (of 25 retrieved) reporting cadmium concentrations in human matrices — blood, urine, breast milk, hair, saliva, amniotic fluid, umbilical cord blood, and deciduous teeth — across general, occupational, and clinical populations in Iran, with sampling years spanning roughly 2003 through 2015. The authors report no formal meta-analysis because of population heterogeneity; the review’s value is corpus-level: it surfaces the Iranian biomonitoring evidence base for cadmium (Cd), in one place, with consistent attribution. Three headline patterns emerge from the assembled corpus: (1) Cd concentrations are systematically higher in industrial workers than in general-population referents (Yazd electroplating glazers post-shift urine 10.85 ± 12.88 µg/g creatinine vs office-worker referents 3.07 ± 7.24 µg/g; Borujen natural-gas-pipeline back welders 1.72 ± 0.65 µg/g creatinine vs unexposed controls 0.04 ± 0.07 µg/g); (2) Cd concentrations are higher in smokers than non-smokers in general-population samples (Farzin et al. blood Cd in male smokers 2.18 ± 0.89 µg/L vs male non-smokers 1.74 ± 0.66 µg/L; Ebrahim et al. amniotic-fluid Cd in pregnant smokers vs non-smokers, with a smoking-thiocyanate correlation r=0.882); and (3) Cd concentrations are elevated in residents of industrial regions relative to non-industrial regional referents (Tadayon et al. hair Cd Tehran 1.76 ± 1.09 µg/g vs Tekab 0.35 ± 0.56 µg/g; Norouzi et al. breast-milk Cd Lenjan/Mobarakeh-steel-region 2.31 µg/L vs Konjedjan rural-referent 0.772 µg/L). The review does not aggregate food-matrix Cd data and does not propose Iranian exposure or dietary-intake thresholds; the JECFA/FAO 25 µg/kg body weight per month provisional tolerable monthly intake is cited but not compared to per-study figures.

Key numbers

Search and inclusion (review prose, p. 458):

Iranian biomonitoring corpus aggregated by the review (Table 1, pp. 459-460; all values transcribed as published by the review, which transcribes them from the constituent studies):

Reference values cited by the review (Introduction, p. 457):

Comparative international Cd-in-hair values cited from constituent study #6 (Savabieasfahani 2010, p. 461):

Occupational signal magnitudes drawn from Discussion (pp. 461-462):

Two pregnancy-outcome correlations the review highlights:

• Ebrahim & Ashtarinejad 2015 (ref 17): amniotic-fluid Cd correlation with maternal smoking biomarker (plasma thiocyanate) r = 0.882; pre-eclampsia prevalence in smokers 26% vs non-smokers 10.5% (p < 0.05).
• Nejadchehrazin & Moghadam Banaem (ref 25): maternal-blood Cd correlation with umbilical-cord-blood Cd r = 0.734 (the review highlights this as evidence of transplacental transfer).

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; analytical methodology is reported in each constituent study and not re-described in detail by the review.

Database search. The authors searched both Iranian databases (Scientific Information Database (SID), Magiran, IranMedex) and international databases (PubMed, Web of Knowledge, Google Scholar, Science Direct). Search terms included “cadmium poisoning,” “cadmium toxicity,” “cadmium measuring,” “cadmium exposure,” “occupational exposure to cadmium,” “environmental exposure to cadmium,” and “heavy metals” in English and Persian translations. The search included all studies conducted in Iran and indexed in the named databases through March 15, 2016.

Inclusion criteria. Original studies investigating occupational or environmental exposure to Cd in Iran that measured Cd levels in human tissues (blood, hair, saliva, milk, urine) were eligible. Studies done outside Iran and studies on non-human samples were excluded. The review does not state inclusion/exclusion at the level of study-design type (cohort, cross-sectional, case-control); both general-population descriptive surveys and case-control clinical studies are included.

Data extraction. The authors state that all articles were reviewed by two people separately and that first author, year of data collection, population, sample size, mean and standard deviation of Cd levels, and location were extracted from each article.

Statistical analysis. The authors decided not to merge data in a meta-analysis because of population heterogeneity (industrial workers, pregnant women, children, clinical patient groups, general-population volunteers; biological matrices ranging from amniotic fluid to deciduous teeth). The review reports per-study summary statistics as published; no pooled estimates, no random-effects models, no heterogeneity (I²) calculations, no risk-of-bias scoring, and no formal PRISMA-style flow diagram are presented.

Constituent-study analytical methods (not re-described by the review). The 18 constituent studies span multiple analytical platforms: atomic absorption spectrometry (graphite furnace and flame variants), electrothermal AAS, and ICP-OES. Sample preparation, LOD/LOQ, and quality-control details are reported in the constituent papers and not aggregated by this review.

Implications

This source is a narrative systematic review aggregating Iranian human biomonitoring evidence on cadmium. It contributes a corpus-level characterisation of Iranian Cd exposure across general, occupational, and clinical populations; it does not contribute original measurement data, dietary-intake estimates, or food-matrix concentration values.

• Corpus pointer for Iranian Cd biomonitoring literature 2003-2015. The 18 constituent studies span Tehran, Isfahan, Yazd, Hamadan, Birjand (South Khorasan), Varamin, Borujen, Lenjan, Konjedjan, Zarrin Shahr, and Tekab (West Azarbaijan). They cover blood, urine, breast milk, hair, saliva, amniotic fluid, umbilical cord blood, and deciduous teeth. Downstream wiki synthesis on Iranian Cd biomonitoring should treat this paper as a pointer to the constituent studies rather than as a standalone quantitative source — the review’s per-study figures should be cross-checked against the original papers when those papers are ingested individually.
• Occupational-vs-environmental signal in Iranian biomonitoring. Urinary Cd in industrial cohorts (Yazd electroplating glazers, Borujen natural-gas-pipeline welders) runs roughly 3-40× higher than in unexposed referents drawn from the same studies. This is consistent with the broader occupational-Cd biomonitoring literature, but provides Iran-specific occupancy quantitatively for any HMTc work that needs Iranian-population referent ranges. The Yazd glazer post-shift figure (10.85 µg/g creatinine) sits in the same magnitude band as the ICdA-cited 2-50 ng/m³ “acceptable” occupational-air range when converted assuming standard pulmonary-uptake and creatinine-excretion kinetics.
• Smoking and Cd in Iranian populations. Three constituent studies (Farzin et al. blood Cd by smoking status; Ebrahim et al. amniotic-fluid Cd by smoking biomarker; the review’s secondary references to Hallen et al., Grasmick et al., Elinder et al., Ellis et al., Zenzes et al., and Mannino et al.) corroborate the smoker-vs-non-smoker Cd gap. Magnitudes are modest in blood (~1.25-1.3× for male smokers in Farzin’s Tehran cohort) but the smoking-thiocyanate correlation r = 0.882 in amniotic-fluid Cd (Ebrahim) is a strong gestational-exposure signal worth tagging for the Cadmium page’s smoking/pregnancy section.
• Regional industrial-area signal (Lenjan, Mobarakeh-steel region). Norouzi et al.’s Lenjan-vs-Konjedjan breast-milk Cd comparison (2.31 vs 0.772 µg/L, ≈3× elevated in the Mobarakeh-steel-region cohort) provides Iran-specific environmental-exposure quantification near a known industrial source. This is one of the few breast-milk Cd values in the corpus that includes a within-study geographic referent.
• Headroom-only-on-average breast-milk Cd values. Three breast-milk Cd values in the corpus (Nazarpour 5 ± 6.9 µg/mL, Goudarzi 1.92 ± 1.04 µg/mL, Norouzi-Lenjan 2.31 µg/L, Rahimi 2.44 µg/L) — see anomaly catalogue below for unit-label concerns on Nazarpour and Goudarzi — sit at or above the WHO breast-milk-Cd recommendation tier of approximately 1 µg/L. The review notes only that the Varamin figure “was even higher than the international standard” without naming the standard. Downstream synthesis on Breastmilk (cadmium sub-block) should treat these Iranian per-study values as candidate-pool contributors with the unit-attribution caveats below.
• Transplacental-transfer signal. Across the three studies in the corpus that paired maternal-blood Cd with umbilical-cord-blood Cd (Dahaghin maternal 2.3 vs umbilical 0.34 µg/L; Nejadchehrazi maternal 0.31 vs umbilical 0.29 µg/dL with r = 0.734; Vigeh maternal 0.50-0.54 µg/L), the cord/maternal ratio varies from ~0.15 (Dahaghin) to ~0.94 (Nejadchehrazi). The review treats Nejadchehrazi’s high correlation as evidence of placental Cd transfer; Dahaghin’s near-zero cord Cd in the presence of elevated maternal Cd is treated as evidence of placental barrier function. Both readings are present in the review without resolution.
• What this paper does not provide. This review reports human-biomarker concentrations; it does not report Iranian dietary-intake estimates, food-matrix Cd concentrations, or estimated weekly intake (EWI) figures for Iranian foods. It does not propose HMTc threshold values, does not compare biomarker concentrations to international biomarker reference values (e.g., German HBM-I/HBM-II, US CDC NHANES geometric means), and does not perform meta-analytic pooling. For Iranian food-matrix Cd values, see the parallel rice-specific review A review of heavy metals in rice (Oryza sativa) of Iran.
• Review-level limitations for downstream pooling. No formal risk-of-bias assessment. No PRISMA flow diagram. No I² heterogeneity statistics. Population mixing across vastly different exposure regimes (industrial workers, general-population volunteers, clinical patient groups, pregnant women) precludes pooled estimation; the authors explicitly state this is why no meta-analysis was attempted. The narrative-review category limits this paper to corpus-pointer status for the wiki’s purposes; per-study values should be re-verified against the constituent papers when those are independently ingested.

Related evidence

• JECFA — Provisional Tolerable Monthly Intake for Cadmium, 25 µg/kg b.w./month

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