This study measured total mercury in 48 dairy products from 6 regional cooperatives (OSM A–F) located in south and south-east Poland, representing areas of varying industrialization. Products included milk, kefir, yogurt, cream, cream cheese, cottage cheese, butter, and milk powder, analyzed after lyophilization using a dedicated mercury analyzer (AMA 254) with non-flame atomic absorption spectrometry. All products met the Polish legal limit for Hg in foodstuffs (0.01 mg/kg for milk; 0.01 mg/kg for general foods). The lowest tHg was found in kefir (0.01 mg/kg) and the highest in butter (maximum 0.79 mg/kg — note this is in the lyophilized form; concentration in base product was 0.79 mg/kg for one butter sample, which exceeds the 0.01 mg/kg limit for general foodstuffs). The study documents a consistent pattern across producers: kefir has lowest tHg, butter has highest, with yogurt, cream, and cream cheese in between.
Key numbers
All values in mg/kg (product basis, converted from lyophilizate measurements). n = 48 samples from 6 cooperative producers. Method: AMA 254 mercury analyzer (non-flame AAS); LOD = 10⁻⁵ mg/g; each sample analyzed in triplicate.
tHg by product category across producers:
- Milk: 0.03–0.06 mg/kg (OSM A and F: ~0.06; OSM B: ~0.03 mg/kg)
- Kefir (all producers): 0.01–0.04 mg/kg (lowest values overall)
- Yogurt: 0.01–0.09 mg/kg
- Cream: 0.01–0.09 mg/kg
- Cream cheese: 0.01–0.14 mg/kg
- Cottage cheese: ~0.01–0.10 mg/kg
- Butter: 0.47–0.79 mg/kg (highest values overall; OSM A: 0.79; OSM C: 0.58; OSM F: 0.47)
- Milk powder (OSM A): ~0.30 mg/kg (in lyophilizate; base product value not specified in extracted text)
All values below the Polish permissible level of 10 mg/kg for dairy (general foodstuffs); all milk samples below the 0.01 mg/kg limit specific to milk. The butter values are unusually high relative to other dairy; the authors do not explain the mechanism but suggest fat concentration may drive Hg accumulation in butter.
Note: The legal limit invoked (10 mg/kg general foodstuffs) is the pre-2012 Polish regulation. The current EU Regulation 2023/915 does not set a specific Hg limit for dairy products (only fish), though Regulation 396/2005 sets MRL for Hg compounds at 0.01 mg/kg as a general food MRL.
Methods (brief)
Non-flame atomic spectrometry absorption technique using AMA 254 mercury analyzer (Altec, Czech Republic). Samples lyophilized (Labconco Model 64132) prior to analysis. Dry combustion in oxygen (99.999%), decomposition products trapped on amalgamator, released at 120°C, measured in double cuvette. Dynamic range: 0.05–600 ng Hg per measurement. LOD: 10⁻⁵ mg/g. Calibration: NIST-traceable Hg standard solutions (AccuStandard). Each sample analyzed in triplicate; values are mean ± SD.
Implications
Certification: Total mercury monitoring across the dairy product spectrum from south-east Poland shows that kefir accumulates least Hg and butter accumulates most, consistent with fat-phase concentration of lipophilic mercury species. Butter values (0.47–0.79 mg/kg) are orders of magnitude above milk values, which is relevant to certifying dairy products that include butter as an ingredient.
Courses: Illustrates how processing concentration (lyophilization to butter) dramatically increases Hg concentration in the product even when raw milk Hg is well within limits. The kefir-to-butter gradient is a teaching point for dairy supply chains.
App: Contributes tHg data for milk, yogurt, cheese, and butter in a European context.