Brum et al. 2025 — Essential elements and PTEs in organic vs conventional flaxseeds
This study quantified 20 chemical elements (11 essential, 9 PTEs) in 52 commercially available European flaxseed samples using ICP-OES, comparing organic (n=15) and conventional (n=37) seeds. The headline finding is that organic flaxseeds had statistically significantly higher Pb concentrations than conventional samples, while conventional samples had higher Al and Ni. Cadmium concentrations in both groups remained well below the EU regulatory limit of 0.50 mg/kg for linseeds. Hazard Index modelling showed that Al and Pb — not Cd — pose the more pressing health risk at typical consumption levels of 15–30 g/day, with Pb HI values of 612–1,578 depending on seed type and intake scenario.
Key numbers
Concentrations in Table 2 (mg/kg dry weight, mean ± SD or range):
Organic flaxseeds (n=15):
- Al: mean 2,040.609 µg/kg (2.04 mg/kg); range not fully resolved in text extraction
- Cd: mean 0.116 mg/kg (116 µg/kg); below EU ML of 0.50 mg/kg
- Pb: mean 0.652 mg/kg (652 µg/kg); statistically higher than conventional (p < 0.05)
- Ni: mean 0.368 mg/kg (368 µg/kg)
- Cr: mean 0.113 mg/kg (113 µg/kg)
Conventional flaxseeds (n=37):
- Al: mean 3,890.695 µg/kg (3.89 mg/kg); higher than organic (p < 0.05)
- Cd: mean 0.127 mg/kg (127 µg/kg); below EU ML
- Pb: mean 0.249 mg/kg (249 µg/kg)
- Ni: mean 0.638 mg/kg (638 µg/kg); higher than organic (p < 0.05)
- Cr: mean 0.048 mg/kg (48 µg/kg)
Hazard Index (HI) at 15 g/day intake:
- Al: HI = 3.22 (organic), 4.79 (conventional) — both > 1
- Pb: HI = 789.15 (organic), 612.01 (conventional) — both >> 1
Hazard Index at 30 g/day intake:
- Al: HI = 6.45 (organic), 9.58 (conventional)
- Pb: HI = 1,578.3 (organic), 1,224.02 (conventional)
Note: The extreme Pb HI values reflect the very low USEPA reference dose for Pb (no safe level assumption underlying RfD-based calculation); these values should be interpreted in the context of the EFSA BMDL approach rather than taken as standalone risk verdicts.
EU regulatory context: Only Cd has a defined maximum limit for flaxseeds (linseeds) in EU Regulation (EC) 1881/2006 as amended: 0.50 mg/kg. No EU ML exists for Pb, Al, or Ni in flaxseeds as of the study date.
LOD/LOQ: Determined per ICP-OES instrument response from 15 blanks under reproducibility conditions; values tabulated in Supplementary Table S2 (not fully extracted here).
Sample_n notes: 52 total; 15 organic, 37 conventional. Samples were commercially sourced across the EU and other European countries.
Methods (brief)
ICP-OES (Thermo Scientific iCAP PRO). Samples (5 g) were dried at 80°C for 24 h, then ashed in a muffle furnace at 450°C for 72 h, dissolved in 65% HNO3, and diluted to 25 mL in 1.5% HNO3. Certified reference materials used for quality control. No arsenic or mercury speciation was performed; As and Hg were not listed among the 20 quantified elements in this study.
Implications
Certification: Flaxseeds are a relevant case for the HMT&C multi-analyte panel. Pb values in organic flaxseeds (mean 652 µg/kg) are notably elevated — comparable to or higher than peanut Pb levels — and there is no EU ML to anchor pass/fail determinations, making HMT&C threshold-setting dependent on the wiki’s literature-derived distribution. Al concentrations are in the mg/kg range and exceed reference dose-based thresholds at typical consumption; this is consistent with Al being a concern in flaxseed-inclusive formulations. Ni in conventional seeds (mean 638 µg/kg) warrants attention in products targeting Ni-sensitive consumers.
Courses: The organic/conventional comparison is an instructive counterexample to the common assumption that organic labelling uniformly reduces heavy metal exposure. Soil history, geographical origin, and agronomy of the specific growing region appear to dominate over organic certification status for Pb, Al, and Ni in this dataset.
App: Provides mean Cd, Pb, Al, Ni, and Cr concentrations per seed type for dietary exposure modelling in flaxseed-containing products. Use as dry-weight basis.