8 Regulatory Traps for Mercury
that block exports and pull supplement batches from the market

The European Union and the United States base their mercury risk assessments on different reference values and different sensitive population groups. Regulation (EU) 2023/915, as amended, sets maximum limits in the EU, while the FDA and ATSDR publish guidelines that are binding on the US market. A manufacturer operating solely in the domestic market may be unaware of this difference — until their product reaches a customs line or undergoes laboratory testing by a foreign business partner.

1. EFSA and ATSDR Use Different Reference Doses — and That Is the Source of All the Confusion

In its 2012 scientific opinion (EFSA Journal 2012;10(12):2985), EFSA established a Tolerable Weekly Intake (TWI) for methylmercury of 1.3 µg/kg body weight/week. The ATSDR (Agency for Toxic Substances and Disease Registry) applies a Minimum Risk Level (MRL) for chronic oral exposure of 0.1 µg/kg/day, which converts to 0.7 µg/kg/week. The difference is nearly twofold. What does this mean for a manufacturer? A calculation model based on the EFSA dose permits a higher mercury concentration per daily serving without exceeding the TWI than the ATSDR model allows. A food supplement manufacturer formulating a fish oil product to the EFSA value may fail to meet US market requirements — particularly when positioning the supplement for pregnant women or children, where the FDA applies additional 2024 guidelines on fish consumption.

• EFSA TWI for methylmercury: 1.3 µg/kg body weight/week (EFSA Journal 2012;10(12):2985)
• ATSDR MRL for chronic oral exposure: 0.1 µg/kg/day ≈ 0.7 µg/kg/week
• Difference: approximately 85% in favour of the EFSA standard — higher permissible exposure level
• Practical consequence: the same product may be legally compliant in the EU yet challenged by a US distributor

2. Regulation (EU) 2023/915 Does Not Cover All Forms of Mercury — and Inspectors Are Well Aware of This Gap

Regulation (EU) 2023/915, as amended by Commission Regulation (EU) No 2023/915, establishes Maximum Levels (MLs) for mercury in the following categories: fish and fishery products, food supplements, and foods for special purposes. For most fish species the limit is 0.5 mg/kg wet weight; for predatory species such as swordfish, shark, and Atlantic bluefin tuna it is 1.0 mg/kg. The problem is that Regulation (EU) 2023/915 does not explicitly specify whether the limit refers to total mercury or exclusively to methylmercury — even though methylmercury is the toxicologically relevant form. ATSDR and the FDA in the US consistently refer to methylmercury as the reference fraction. In EU laboratory practice, total mercury is measured as a proxy, which may overstate the result if the product contains inorganic mercury compounds from natural sources (e.g. marine algae). Manufacturers of food supplements containing chlorella or spirulina should commission laboratory speciation of mercury forms before the product undergoes customs analysis in the US.

3. Supplements Containing Marine Algae Are a Separate Risk Category — and the Polish Chief Sanitary Inspectorate (GIS) Is Already Aware

Inspection practice at the Polish Chief Sanitary Inspectorate (GIS) shows that food supplements containing spirulina, chlorella, wakame, and other marine algae are disproportionately often selected for heavy metal testing, including mercury. This stems from the EFSA scientific opinion of 2021 on novel food from algae (EFSA Journal 2021;19(1):6290), in which the CONTAM Panel identified elevated mercury background levels in algal biomass sourced from certain Pacific regions. In the EU, food supplements do not have a separate ML for mercury under Regulation (EU) 2023/915 — the general 'food supplements' category applies, with a limit of 0.1 mg/kg for total mercury. The FDA, by contrast, has not established a federal ML for mercury in food supplements, meaning that assessment is conducted on the basis of a 'reasonable expectation of safety' — leaving the burden of proof with the importer.

• ML for mercury in food supplements in the EU: 0.1 mg/kg (Regulation (EU) 2023/915, as amended)
• FDA has no federal ML for mercury in food supplements — assessment is case-by-case; burden of proof lies with the importer
• Pacific-sourced algae: elevated risk according to EFSA CONTAM scientific opinion 2021
• Recommendation: Certificate of Analysis (CoA) distinguishing total mercury from methylmercury as the export standard

4. The RASFF System Reveals That Poland Is an Exporter with Notifications — Not Only a Recipient

The RASFF (Rapid Alert System for Food and Feed) database contains notifications concerning Polish fish products and food supplements with exceeded mercury levels. RASFF notifications in the 'contaminants' category for mercury in fish and supplements from Poland appeared during the period 2019–2023, with some classified as border rejections rather than market withdrawals — meaning the goods never entered circulation, but the exporter incurred logistical and reputational costs. Every RASFF notification is publicly accessible to foreign business partners, which in practice means that a single alert can block further orders from a given buyer for 12 to 18 months. What does this mean for an exporter? It is essential to maintain an internal database of laboratory testing history and to be able to demonstrate a compliance trend — this is a key argument in negotiations with an importer who has checked the RASFF history before placing an order.

5. The 1.0 mg/kg Limit for Tuna in the EU — but Only for Specific Species, and This Is Where Classification Problems Begin

Regulation (EU) No 2023/915 (consolidating amendments to Regulation (EU) 2023/915) provides for a limit of 1.0 mg/kg mercury for tuna — but exclusively for the species listed in the annex: Thunnus thynnus (Atlantic bluefin tuna), Thunnus obesus (bigeye tuna), and Xiphias gladius (swordfish). Species such as Katsuwonus pelamis (bonito/skipjack), which accounts for the majority of canned tuna, are subject to the 0.5 mg/kg limit. Classification problems arise with 'tuna blend' products and canned mixtures where the label does not always specify the species. Customs laboratories in Japan or South Korea — destinations for part of Poland's processed fish exports — apply their own national limits: Japan has set 0.4 mg/kg for fish generally, with no exemptions for predatory species. An exporter that meets the EU standard of 1.0 mg/kg for swordfish may have goods detained at the Japanese border.

6. Pregnant Women as the Reference Population — EFSA and ATSDR Define This Group Differently, Which Changes the Calculations for Prenatal Supplements

When establishing the TWI for methylmercury, EFSA adopted pregnant women and the foetus as the reference population — the most sensitive group — and on that basis derived the value of 1.3 µg/kg/week. ATSDR applies an MRL of 0.1 µg/kg/day as a protective value for the general population, without a separate value for pregnant women. However, the FDA, in its updated guidance for pregnant women and children (2024), recommended avoiding fish with high mercury content and limiting consumption to 2–3 servings per week from the 'best choices' list. A manufacturer of prenatal food supplements containing DHA from fish oil who places a health claim on the label relating to foetal brain development (authorised under Regulation (EC) No 432/2012 for DHA) must ensure that the actual mercury content per capsule falls below the ATSDR threshold — because it is that threshold which will be applied by the US distributor when assessing the safety of a product intended for pregnant women.

• Health claim for DHA and foetal brain development: authorised under Regulation (EC) No 432/2012
• A manufacturer using this health claim automatically positions the product within the high mercury-exposure risk group
• Practical requirement: the product safety assessment should include a mercury exposure calculation at the maximum dosage stated in the product leaflet

graph LR
  A["Mercury in product"] --> B["EU Market\nReg. (EU) 2023/915"]
  A --> C["US Market\nFDA / ATSDR"]
  A --> D["Codex Alimentarius\nCXS 193-1995"]
  B --> B1["Fish generally:\n0.5 mg/kg"]
  B --> B2["Predatory species\n(tuna, swordfish):\n1.0 mg/kg"]
  B --> B3["Food supplements:\n0.1 mg/kg"]
  C --> C1["Fish: FDA guidelines\nno federal ML"]
  C --> C2["Supplements: no\nfederal ML\nATSDR MRL: 0.1 µg/kg/day"]
  D --> D1["Fish: 0.5 mg/kg\nno exemptions\nfor predatory species"]
  style B fill:#003399,color:#fff
  style C fill:#cc0000,color:#fff
  style D fill:#006633,color:#fff

7. The Analytical Method Matters: CV-AAS vs ICP-MS — and Polish Laboratories Do Not Always Use the Method Accepted by the FDA

Commission Regulation (EC) No 333/2007 (as amended by Regulation (EU) 2021/1756) specifies the sampling and analytical methods for heavy metals in food applicable in the EU. For mercury, both cold vapour atomic absorption spectrometry (CV-AAS) and inductively coupled plasma mass spectrometry (ICP-MS) are permitted. The FDA, in its guidance for importers, favours ICP-MS as the method offering greater sensitivity and selectivity, particularly at low concentrations (<0.05 mg/kg). A Certificate of Analysis issued by a Polish laboratory accredited under the PCA system using the CV-AAS method may be challenged by a US importer as insufficiently sensitive — not because the result is incorrect, but because the method does not meet the buyer's internal procurement standards. The solution: for exports to the US and Japan, commission analyses using ICP-MS with a Limit of Quantification (LOQ) of ≤0.01 mg/kg.

8. The Absence of Global Harmonisation Means That the Same Compliance Certificate Is Not Sufficient for Three Markets Simultaneously

An exporter of fish or food supplements operating simultaneously in the EU, the US, and, for example, Singapore (which applies Codex Alimentarius Standard CXS 193-1995 with a limit of 0.5 mg/kg for mercury in fish generally) must maintain three parallel compliance documentation sets. Codex Alimentarius does not distinguish predatory species with a higher limit as the EU does — meaning that swordfish compliant with the EU limit (1.0 mg/kg) does not meet the Codex limit (0.5 mg/kg). In commercial practice, a certificate of compliance with EU standards is not automatically accepted by the Singapore Food Agency (SFA) or by Australia's FSANZ. A food supplement manufacturer exporting simultaneously to the EU and Australia must take into account that Food Standards Australia New Zealand Standard 1.4.1 sets a limit of 0.5 mg/kg total mercury for food supplements without exceptions — while the EU applies the same limit for supplements but with different rules for calculating daily exposure. The systemic solution: a regulatory compliance matrix updated with every change in product composition or every new target market, with specific standards and analytical methods assigned to each market.

• EU (Regulation (EU) 2023/915, as amended): 0.5 mg/kg fish generally, 1.0 mg/kg predatory species, 0.1 mg/kg food supplements
• USA (FDA): no federal ML for food supplements; fish guidelines based on ATSDR MRL
• Codex Alimentarius CXS 193-1995: 0.5 mg/kg for fish — no exemptions for predatory species
• Australia/NZ (FSANZ Standard 1.4.1): 0.5 mg/kg for food supplements and fish — uniformly applied
• Singapore (SFA): uses Codex as the basis with its own implementing guidelines
• Practical conclusion: a single CoA does not cover all markets simultaneously