Overview
This study measured total mercury in 48 dairy products from six regional milk cooperatives across south and south-east Poland (Lublin, Podkarpackie, Silesia, and adjacent regions) using non-flame atomic absorption (AMA-254 direct mercury analyzer). Mercury levels ranged from 0.01 µg/kg on a wet-product basis (reached by natural kefir from two cooperatives, cream, buttermilk, and strawberry flavoured yogurt) up to 0.79 µg/kg (butter extra), all well below the Polish national maximum permissible level of 10 µg/kg for milk. Butter and whole milk powder consistently showed the highest concentrations across producers; kefir consistently showed the lowest. Speciation was not measured (total Hg only).
Key numbers
Mercury content in product (mean ± SD, µg/kg wet product basis, Table 1). Producer letter codes A–F as in the paper, in lieu of producer identification.
Producer A (n=10): Milk 0.06 ± 0.01; Kefir 0.02 ± 0.01; Natural yogurt 0.03 ± 0.00; Natural yogurt (second product line) 0.05 ± 0.01; Cream 0.06 ± 0.02; Cream cheese (vanilla) 0.12 ± 0.00; Half-fat cottage cheese 0.23 ± 0.01; Whole milk powder 0.30 ± 0.01; Buttermilk 0.09 ± 0.03; Butter extra 0.79 ± 0.79.
Producer B (n=8): Milk 0.03 ± 0.01; Cream cheese (vanilla) 0.05 ± 0.02; Cream cheese (natural) 0.05 ± 0.01; Cream 0.04 ± 0.01; Cream cheese with horseradish 0.09 ± 0.04; Cream cheese with caraway 0.06 ± 0.02; Natural buttermilk 0.06 ± 0.01; Half-fat cottage cheese 0.10 ± 0.01.
Producer C (n=10): Natural yogurt 0.07 ± 0.02; Cream cheese (vanilla) 0.14 ± 0.01; Cream cheese (natural) 0.05 ± 0.01; Natural yogurt (second product line) 0.03 ± 0.00; Buttermilk 0.01 ± 0.01; Kefir 0.01 ± 0.01; Cream 0.03 ± 0.02; Milk 0.03 ± 0.02; Half-fat cottage cheese 0.04 ± 0.01; Butter extra 0.58 ± 0.26.
Producer D (n=8): Cream cheese (vanilla) 0.04 ± 0.02; Yogurt (probiotic-marketed) 0.06 ± 0.04; Strawberry flavoured yogurt 0.01 ± 0.01; Tzatziki (cucumber and garlic) 0.02 ± 0.01; Cream 0.01 ± 0.01; Natural yogurt 0.04 ± 0.02; Natural kefir 0.01 ± 0.00; Cream cheese (vanilla, second product line) 0.11 ± 0.05.
Producer E (n=6): Cream 0.05 ± 0.04; Natural cottage cheese 0.12 ± 0.02; Natural cottage cheese (second product line) 0.08 ± 0.02; Cream cheese with spring onion 0.16 ± 0.04; Kefir 0.04 ± 0.02; Half-fat cottage cheese 0.13 ± 0.07.
Producer F (n=6): Cream 0.03 ± 0.01; Kefir 0.02 ± 0.01; Granular cottage cheese 0.08 ± 0.03; Half-fat cottage cheese 0.05 ± 0.03; Butter extra 0.47 ± 0.16; Milk 0.06 ± 0.02.
Range minima and maxima by category (µg/kg product, wet basis): kefir 0.01–0.04; milk 0.03–0.06; natural yogurt 0.01–0.07; buttermilk 0.01–0.09; cream 0.01–0.06; cream cheese 0.04–0.16; cottage cheese 0.04–0.23; butter extra 0.47–0.79; whole milk powder 0.30 (single sample). Across all 48 samples mercury concentration in product ranged 0.01–0.79 µg/kg. Detection limit of the AMA-254 instrument was 10⁻⁵ µg/g (0.01 ng/g, equivalent to 0.01 µg/kg on a mass basis).
Comparative cited values for milk and dairy mercury from the literature (Pankiewicz Discussion, with cite-key references retained from the paper): Korea (Roh 1975) 3–10 ppb; North Dakota (Sell 1975, Sell and Davison 1975) <1–2 ppb; Poland Wrocław (Dobrzański 2009) 0.24 and 0.27 ppb; Silesia late 1980s 0.3–6.7 ppb; Zgorzelec/Bogatynia region ~2 ppb; Spain Canary Islands 0.09–0.61 ppb; China 1.0–3.9 ppb; Italy Rome surroundings 0.9–38 ppb; Egypt 86–556 ppb. National maximum mercury content for foodstuffs cited as 1 mg/kg in Sweden and Japan, 1.5 mg/kg in Norway, 0.5 mg/kg in Poland (general foodstuffs); Polish maximum for mercury in milk specifically established at 10 µg/kg (10 ppb).
Regulatory limits cited by the paper: EU Commission Regulation (EC) No. 1881/2006 of 19 December 2006 sets maximum mercury concentration explicitly only for fish and seafood (0.5 mg/kg wet weight, or 1.0 mg/kg for selected species) and not for dairy. Polish national permissible Hg in milk = 10 µg/kg (10 ppb). JECFA provisional tolerable weekly intake (PTWI) for mercury from all sources = 5 µg/kg body weight/week, including 1.6 µg/kg body weight/week for organic mercury compounds (the JECFA PTWI for methylmercury has since been revised downward; this paper cites the 2009-era values).
Methods (brief)
Forty-eight dairy products purchased from local markets in regions of varying industrialization across south and south-east Poland. Water content of products determined separately on a Radwag WPS50SW moisture analyzer by drying at 100 °C in triplicate. Samples lyophilized in a Labconco Model 64132 freeze dryer (Kansas City, MO, USA) and lyophilizates stored in an exsiccator. Total mercury determined on lyophilized samples by non-flame atomic absorption spectrometry with thermal decomposition and gold-amalgam trapping (AMA-254 mercury analyzer, Altec, Czech Republic): samples pre-dried in the internal oven, burned in oxygen (99.999% purity), decomposition products carried to amalgamator for selective Hg trap, amalgamator stabilised at 120 °C, mercury released by short heat-up and quantified in a double measuring cuvette at two sensitivities. Dynamic range 0.05–600 ng Hg per measurement; instrumental detection limit 10⁻⁵ µg/g. Calibration controlled with NIST-traceable Hg standard solutions (AccuStandard, New Haven, CT, USA). Each sample analyzed in triplicate; reported values are mean ± SD. Hg in lyophilizate converted to Hg in base product using the measured water content of each product. Speciation not measured — total Hg only; no MeHg or inorganic-Hg fractionation.
Implications
- Certification (HMTc): Polish regional cooperative dairy products contribute to the dairy total-Hg occurrence baseline. All 48 samples fall well below the 10 µg/kg Polish national permissible limit for milk and orders of magnitude below the EU 0.5 mg/kg limit for fish. Within-category gradient is consistent across producers: butter (0.47–0.79 µg/kg) > whole milk powder (0.30 µg/kg) > cottage and cream cheese (0.04–0.23 µg/kg) > fluid milk (0.03–0.06 µg/kg) ≈ cream and buttermilk ≈ yogurt > kefir (0.01–0.04 µg/kg). The gradient is consistent with concentration of Hg into the lipid and lyophilised fractions during processing rather than with fermentation reducing Hg load. Useful sub-format granularity for the dairy occurrence baseline.
- Courses: Demonstrates the value of AMA-254 direct-mercury analysis at sub-ppb detection limits for dairy QC and illustrates how product moisture content drives apparent concentration differences across dairy formats (butter > milk powder > cheese > fluid milk > fermented). Also serves as a regional reference for Polish dairy supply chains drawing from south-east Poland (Lublin, Podkarpackie).
- App: Contributes Hg occurrence data to the milk-and-dairy ingredient page and the butter-and-ghee product page in a European context, with sub-category structure for butter, milk powder, cottage cheese, cream cheese, yogurt, kefir, and buttermilk. Values sit in the lower tail of the dairy total-Hg distribution and contribute occurrence weight rather than threshold-setting weight.
Related evidence
- Mercury, Total
- Milk and Dairy
- Whole milk
- Butter
- Yogurt
- Butter and ghee
- EFSA — Inorganic Mercury Tolerable Weekly Intake (4 µg/kg b.w./week)
- Cheddar cheese
- Half and half
Update history
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