Pompa et al. 2021 — Six years of Cd, Pb, Hg monitoring in imported durum wheat (Italy, 2015–2020)
This six-year Italian official control study (2015–2020) measured cadmium, lead, and mercury in 346 whole durum wheat grain samples imported into Italy from six countries (Australia, Canada, Kazakhstan, Russia, Turkey, United States), analyzed by ICP-MS per EN 15763:2009. All samples were compliant with FAO/WHO and EU regulations. Overall means were Cd 0.0322 mg/kg and Pb 0.0162 mg/kg; all mercury concentrations were below the LOD (0.004 mg/kg). The study is notable for reporting statistically significant temporal (year-to-year) and geographic (origin country) variation in Cd, but no significant seasonal variation, with the United States being flagged for an anomalous cluster of high-Cd samples in November 2017 (five samples from the US, 0.099–0.125 mg/kg Cd).
Key numbers
- Total samples: n = 346 durum wheat grain, imported to Italy, 2015–2020; 50–92 samples per year (2020 reduced to 14 due to COVID-19)
- Origin countries: Australia, Canada, Kazakhstan, Russia, Turkey, United States
- Method: ICP-MS (PerkinElmer Elan DRC II to 2017; PerkinElmer NexION 2000 from 2018); CRM NIST SRM 1567b (wheat flour)
- LOQ: Pb 0.012 mg/kg; Cd 0.0040 mg/kg; Hg 0.012 mg/kg
- Cadmium: mean 0.0322 mg/kg (0.032 mg/kg); detected in 337/346 samples (97%); 9 samples <LOQ; no sample above EU ML (0.200 mg/kg for durum wheat grain). 17 samples (5%) showed values >0.100 mg/kg (half the wheat ML; twice the infant cereal-product ML)
- Lead: mean 0.0162 mg/kg; 103/346 samples (30%) had quantifiable Pb; 243 samples <LOQ; 2 samples exceeded ML 0.200 mg/kg but were compliant when accounting for measurement uncertainty per Commission Regulation 333/2007. 6 samples (2%) showed Pb >0.100 mg/kg
- Mercury: all 346 samples <LOD (0.004 mg/kg); compliant with EU Regulation 73/2018 MRL (0.010 mg/kg total Hg)
- Temporal variation in Cd: statistically significant year effect (ANOVA P = 0.0021); decreasing trend 2015–2020 except for anomalous 2017 spike. 2017 mean Cd 0.0352 mg/kg significantly higher than 2016 and 2018 due to 5 US samples (0.099–0.125 mg/kg) collected November 2017
- Geographic variation in Cd: statistically significant (ANOVA P reported); no further breakdown of country-level means provided in first 5 pages
- Seasonal variation: no significant seasonal effect for Cd (ANOVA P = 0.060); limited discriminatory power due to undefined stocking phase between harvest and importation
Methods (brief)
Microwave-assisted wet digestion in HNO₃/H₂O₂ per EN 13805:2014; ICP-MS per EN 15763:2009; two replicates per sample; internal standards Rh and Bi; isotopes monitored ¹¹¹Cd, ²⁰²Hg + ²⁰⁰Hg sum, ²⁰⁶Pb + ²⁰⁷Pb + ²⁰⁸Pb sum. Samples collected by Port, Airport, Border Health Offices and Border Inspection Posts per ISO 24333:2009. Values below LOQ imputed at LOQ/2 (middle bound approach). Statistical analysis: Kolmogorov-Smirnov normality test; one-way ANOVA; MetaboAnalyst 5.0.
Limitations
Samples are imported durum wheat; results may not represent domestic Italian durum wheat. Harvest date unknown — cannot cleanly separate seasonal from temporal effects. 2020 dataset reduced to 14 samples (COVID-19), limiting statistical power for that year. No speciation (total metals only for all three elements). Only three metals analyzed; other wheat contaminants (iAs, Ni) not included.
Implications
- Certification: Durum wheat Cd mean 0.0322 mg/kg is well within regulatory limits. The 5% of samples exceeding 0.100 mg/kg Cd (moderately elevated but not ML-exceeding) and the US November 2017 cluster (0.099–0.125 mg/kg) illustrate that geographic origin and temporal batch effects can drive meaningful variation within an otherwise compliant population. Relevant to HMT&C supplier-control language for wheat-based products.
- Courses: Strong illustrative case for seasonal-geographic-variance teaching: statistically significant year and country effects for Cd but no measurable seasonal effect, raising the question of whether apparent year effects reflect true temporal trends or anomalous batches from specific origins.
- App: Durum wheat Cd mean 0.0322 mg/kg (dry weight as grain) feeds into wheat ingredient contamination profile. This is an imported-grain dataset covering major global export origins and is more representative of supply-chain exposure than domestic European surveys.
- Microbiome: Not primary topic.