Overview
Assuncao and colleagues conducted a PRISMA-aligned systematic scoping review of the safety of fermented foods for human consumption, registered on the Open Science Framework (https://osf.io/hsakz/). The review searched PubMed, Scopus, and Cochrane Library for studies published between 1970 and 2024. The scope covered dairy, meat and fish, fruits and vegetables, beverages (excluding alcoholic beverages above 1.25% ABV), legumes, cereals, and grains. Fermented beverages explicitly named in the product scope include kombucha and kefir.
The chemical hazards section addresses heavy metals, polycyclic aromatic hydrocarbons (PAHs), and acrylamide. The heavy metals subsection (Section 3.3.2, Table 4) summarizes concentrations and risk metrics for the fermented products for which primary data were identified in the literature. The products for which heavy metal data were reported are limited to cereal-based fermented foods (bread), fermented dairy (sour cream, cheese, cheese curd, sheep cheese, fermented milk including the Armenian traditional Matsun, and yogurt), and coffee and chocolate. No measured heavy metal concentrations for kombucha, kefir, water kefir, kvass, tepache, or other fermented beverages appear in Table 4 or in the supporting narrative.
The absence of kombucha and similar fermented beverage entries from Table 4 reflects a primary literature gap: the systematic search of three databases covering 54 years of publications did not identify published studies reporting measured heavy metal concentrations in these beverage products that met the review’s eligibility criteria.
Key numbers from Table 4
Cereal-based fermented foods (bread):
Multi-grain, wholemeal, rye, and white breads (multiple studies). Manganese 19,084 to 28,151 µg/kg; copper 3,139 to 4,377 µg/kg; nickel 260 to 710 µg/kg; lead 20.1 to 56.3 µg/kg; arsenic 13.4 to 22.0 µg/kg; chromium 49.0 to 127 µg/kg; cobalt 7.20 to 25.3 µg/kg; cadmium 11.0 to 23.6 µg/kg; mercury 0.13 to 0.41 µg/kg. Mean estimated daily intakes (µg/kg body weight per day): Mn 44.0, Cu 6.62, nickel (Ni) 0.69, lead (Pb) 0.15, arsenic (As) 0.06, chromium (Cr) 0.04, Co 0.03, cadmium (Cd) 0.03, mercury (Hg) less than 0.00. Individual THQs less than 1; cumulative Hazard Index (HI) 1.37 to 1.71.
Bread (second dataset, Pb and Ni): Pb 13.64 µg/kg, Ni 194 µg/kg; estimated daily intakes Pb 0.0267 µg/kg/day, Ni 0.3802 µg/kg/day; Margin of Exposure (MOE) 18.7 for lead and nickel combined.
Bread (third dataset, range values, As/Cd/Cr/Ni/Pb): As 0.11 to 1.31 mg/kg, Cd 0.13 to 0.2 mg/kg, Cr 0.056 to 1.44 mg/kg, Ni 0.61 to 1.2 mg/kg, Pb 0.054 to 0.36 mg/kg. Hazard Index less than 1 for adults and children.
Fermented dairy:
Processed dairy products: titanium (Ti) 0.12 plus or minus 0.17 mg/kg; risk characterization not reported.
Sour cream: Pb 1.98 µg/kg, Ni 48 µg/kg; Pb intake 0.0004 µg/kg/day, Ni intake 0.0109 µg/kg/day; MOE 1,111.6 (low concern per authors).
Cheese: Pb 52.24 µg/kg, Ni 48 µg/kg; Pb intake 0.0087 µg/kg/day, Ni intake 0.0214 µg/kg/day; MOE 57.4.
Cheese curd: Pb 183.28 µg/kg, Ni 135 µg/kg; Pb intake 0.2327 µg/kg/day, Ni intake 0.1714 µg/kg/day; MOE 2.15 (narrowest margin among dairy products cited).
Sheep cheese (mean values in mg/kg): Sb 0.22 plus or minus 0.15; As 0.73 plus or minus 0.29; Ba 1.26 plus or minus 0.58; Cr 0.04 plus or minus 0.01; Cu 0.26 plus or minus 0.08; Fe 6.57 plus or minus 0.84; Pb 0.13 plus or minus 0.09; Li 0.07 plus or minus 0.03; Mo 0.06 plus or minus 0.05; Ni 0.70 plus or minus 0.52; Sr 4.96 plus or minus 0.74. THQ for arsenic: 11.06 for preschool children, 3.48 for adults. THQ for antimony: 2.5 for preschool children, 0.79 for adults. All other elements THQ less than 1.
Fermented milk (range, all matrices within fermented milk category): Hg 0 to 26 µg/kg, Pb 0 to 35.01 µg/kg, Cd 0 to 305 µg/kg, Cr 0 to 433 µg/kg, As 0 to 17 µg/kg, Zn 2,893 to 28,980 µg/kg, Cu 31.09 to 1,133 µg/kg, Fe 341.83 to 8,320 µg/kg, Mn 22.67 to 793 µg/kg, Ni 0 to 81.9 µg/kg. All THQ less than 1; HI less than 1.
Matsun (traditional Armenian fermented milk): Pb 0.84 µg/kg, Ni 19 µg/kg; Pb intake 0.0003 µg/kg/day, Ni intake 0.0075 µg/kg/day; MOE 1,513.8 (low concern per authors).
Yogurt: Ti 0.47 plus or minus 0.46 mg/kg; risk characterization not reported.
Coffee (first dataset): Pb 192.56 µg/kg, Ni 142 µg/kg; Pb intake 0.1398 µg/kg/day, Ni intake 0.1031 µg/kg/day; MOE 3.6 for lead.
Coffee (survey range, multiple datasets): Cd 0.002 to 0.100 mg/kg, Cu 0.507 to 10.527 mg/kg, Pb 0.033 to 0.695 mg/kg, Ni 0.952 to 1.511 mg/kg, Zn 4.472 to 26.109 mg/kg. Individual THQ less than 1 for the survey dataset.
Chocolate: arsenic identified as a concern in individual case reports; direct concentration not tabulated (arsenic poisoning via chocolate noted in footnote to Table 4).
Methods (brief)
Systematic scoping review following PIMENTO COST Action CA20128 Working Group 3 protocol, aligned with PRISMA guidance (Muka et al., 2016) and registered at OSF. Searches of PubMed, Scopus, and Cochrane Library from January 1, 1970 to December 31, 2024. PECO framework: Population = general population including vulnerable groups; Exposure = ingestion of any fermented food across dairy, meat and fish, fruits and vegetables, beverages (excluding greater than 1.25% ABV alcoholic beverages), legumes, cereals and grains; Comparison = not applicable (scoping review); Outcome = occurrence, exposure, risk, and foodborne outbreaks. LOD/LOQ, CRM, and recovery data are not reported by this review (it aggregates primary study data without re-extracting method QA).
Evidence fitness
The review is a high-quality systematic scoping review using PRISMA methodology and pre-registered protocol; it is an A-tier source for the finding that primary heavy metal measurement data for kombucha and fermented beverages were not identified in a comprehensive search of three databases covering 54 years. It is not a source of primary measurement data for fermented beverages. For fermented dairy and bread, the review synthesizes primary studies but does not report individual study sample counts, geographic detail, or analytical methods at the level needed for contamination-profile cell entry. The dairy and bread values are reproduced here as tabulated context from Table 4, not as cell-ready occurrence data for those product pages.
Related evidence
- Kombucha and other fermented beverages
- Kombucha (Tea-Based)
- Fermented Beverages, Non-Tea-Based
- Lead
- Arsenic
- Cadmium
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