Summary
This is the selenium speciation companion to Dobrzynska et al. 2025 (elemental composition, cite key: dobrzynska2025-milk-formulae-elemental-composition). The 2026 paper adds Se speciation by HPLC-ICP-MS to the same 148 Polish market formula corpus, identifying the chemical forms of selenium. Total Se was measured by ICP-MS; speciation (selenite Se(IV), selenate Se(VI), selenomethionine SeMet, methylselenocysteine MeSeCys) was performed by HPLC-ICP(iCRC)MS. The dominant Se species in infant formulae were inorganic (selenite and selenate), consistent with manufacturer declarations. Trace organic Se species (SeMet and MeSeCys) were detected. Six of 148 formulae had Se estimated daily intakes exceeding the tolerable upper intake level for 6-month-old infants (45 µg/day).
Key numbers
Total Se concentrations (Table 2, µg/100 kcal; median, 1st-3rd quartile, min-max):
Infant formulae (n=37):
- Median 4.9 µg/100 kcal
- Range 0-15.6 µg/100 kcal
- 78.4% of all 148 formulae were within EU recommended range (3.0-8.6 µg/100 kcal)
- 9 formulae were below detection limit
- 18 formulae had Se detected but below the minimum of 3.0 µg/100 kcal
- 6 formulae had EDI exceeding the tolerable upper intake level (45 µg/day) for a 6-month-old
Validation (Table 1):
- LOD for total Se: 28 µg/kg (by ICP-MS)
- LOQ for total Se: 93 µg/kg
- LOD for Se species (HPLC-ICP-MS): Se(IV) 1.5, Se(VI) 4.9, SeMet 2.4, MeSeCys 1.8 µg/kg
- Median speciation mass balance: 77% (1st 51%, 3rd 92%) — substantial variation indicating incomplete extraction efficiency for some samples
Se species distribution: Dominant species were sodium selenite (Se(IV)) and sodium selenate (Se(VI)), consistent with the two inorganic Se forms permitted in infant formula under EU regulations (Commission Directive 2016/127, Regulation (EU) 609/2013). SeMet and MeSeCys were detected as trace organic species. The presence of organic Se species may reflect contamination from raw materials (e.g., milk proteins containing selenomethionine from animal feed) or incomplete processing.
EDI at 6 months: EDI for Se at 6 months exceeded the tolerable upper intake level (45 µg/day) in 6 of 148 formulae. The tolerable upper intake level for infants 6-11 months is 55 µg/day according to EFSA; the EU law value used in this study is 45 µg/day.
Methods (brief)
Same 148 Polish market formula corpus as Dobrzynska et al. 2025. Total Se by ICP-MS with integrated collision reaction cell (ICP-iCRC-MS Plasma Quant MS Q, Analytik Jena, Jena, Germany). Se speciation by HPLC (anion-exchange column PRP-X100, 50 mm x 4.1 mm, 5 µm) coupled to ICP(iCRC)MS; enzymatic extraction with protease (Streptomyces griseus type XIV) followed by HPLC-ICP-MS. Validation with ERM-BD150 (skimmed milk powder) and wheat flour BC210a. Recovery 80-120% for total Se. The CRMs used confirmed acceptable recovery (90% for ERM-BD150, 106% for BC210a). Firth penalized logistic regression and generalized linear model with Gamma distribution used for statistical modeling of organic Se species detection probability and concentration.
Limitations
Corpus is powdered formulae only; ready-to-feed and concentrated liquid formulae were not analyzed. Polish market 2019-2023 scope may not be representative of global market or of US-brand RTF formula. Speciation mass balance averaged 77%, indicating incomplete Se extraction in some samples; total organic Se content may be underestimated. The paper does not report lead (Pb), cadmium (Cd), arsenic (As), mercury (Hg), nickel (Ni), or aluminum (Al), which are covered by the companion Dobrzynska 2025 paper.
Implications
- Certification: Se speciation data are relevant for HMTc formula monitoring programs that track Se adequacy (not just toxicity). The finding that inorganic Se dominates is reassuring for formula formulation practices. The 6 formulae exceeding the tolerable upper intake level identify an upper-concentration concern.
- Courses: Useful for teaching Se speciation in infant formula, the distinction between Se adequacy (too low) and Se toxicity (too high), and the analytical challenge of incomplete extraction efficiency for organic Se species.
- App: Adds Se concentration data for Polish-market infant formula powder (median 4.9 µg/100 kcal). Note that Se is not a certified analyte in the HMTc 10-analyte panel, so this data is context only for the certification workflow.
- Microbiome: No direct microbiome endpoint.
Provenance notes
Open-access CC BY article. PDF retrieved from PMC (PMC13564777). SHA256 verified against MANIFEST.csv for HMI-PROD-ready-to-feed-formula-1. This is a separate publication from the companion Dobrzynska 2025 paper (doi: 10.1007/s12011-025-04687-x; cite key: dobrzynska2025-milk-formulae-elemental-composition) which covers Cd, Hg, As, Ni, tin (Sn), chromium (Cr), Co in the same 148-formula corpus.
Update history
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