How limits are set
The standard for each analyte is the strictest maximum level set by any credible government regulator — among them the European Union, Codex Alimentarius, the US FDA, Australia/New Zealand, the Gulf states (GSO), and the national authorities of every jurisdiction that regulates the product — converted into Shellfish (crustaceans and bivalve molluscs)’s own as-consumed basis. It is a lookup of sovereign law, carrying at most one disclosed basis conversion where the law is written in another basis, and an explicit read-across where no government regulates the exact product. A certified product sits at or below every applicable sovereign limit at once.
Where no government regulates the exact product for an analyte, the standard does not go blank or invent a number: the limit is read across from the nearest government value for an analogous product, so a certified product still sits at or below a real sovereign limit. The ratchet tightens these after publication as surveillance warrants.
Master Limit Table
All values in ppb (µg/kg), as-consumed basis. Every analyte carries a firm ceiling. A brand meeting every value on a like-for-like basis qualifies for the mark.
| Analyte | HMTc limit | Binding basis |
|---|---|---|
| Lead (Pb) | 500 | strictest government ML (India) |
| Inorganic arsenic (iAs) | 100 | strictest government ML (EU) |
| Total arsenic (tAs) | 1000 | strictest government ML (Singapore) |
| Mercury, total (tHg) | 500 | strictest government ML (EU) |
| Methylmercury (MeHg) | 500 | government read-across (Mexico) |
| Cadmium (Cd) | 500 | strictest government ML (EU) |
| Nickel (Ni) | 2000 | government read-across (EU) |
| Total chromium (Cr) | 1000 | strictest government ML (Hong Kong) |
| Hexavalent chromium (Cr-VI) | 10 | government read-across (US-CA) |
| Tin (Sn) | 200000 | government read-across (EU) |
| Aluminium (Al) | 100000 | government read-across (China) |
Every claim analyte is equal at the gate. A product is certified only when every analyte is at or below 100% of its published government floor or disclosed read-across; above the limit, on any metal, it is not certified and carries no mark. Mercury is limited in both forms: total mercury (tHg) and methylmercury (MeHg) are separate ceilings that must both be met, set to the species-specific tier each government assigns (predatory fish carry the higher methylmercury ceiling, lower-trophic species the lower; where the total-mercury ceiling is stricter, methylmercury is bounded by it). Total arsenic (tAs) operates as a reflex screen to inorganic-arsenic (iAs) speciation, since most arsenic in seafood is non-toxic organic arsenobetaine. Every panel analyte carries a limit of record; where no government regulates the exact product (nickel, hexavalent chromium, aluminium, and non-canned tin), the ceiling is a disclosed read-across to the nearest applicable sovereign instrument named in the derivation, never an occurrence-derived number. Tin migrates from the can, so for non-canned seafood the read-across is a packaging-migration baseline that clean product clears.
Derivation
The full derivation for Shellfish (crustaceans and bivalve molluscs). Each row lists every government maximum level in force worldwide, converted to the as-consumed basis; the HMTc limit is the strictest of them, and the last column names which sovereign law binds. A blank cell means that government sets no limit for this analyte in this product.
| Analyte | EU | FDA | AU/NZ | GSO | India | Mercosur | Costa Rica | Fiji | Guyana | Israel | Morocco | Mexico | Panama | Philippines | Paraguay | Singapore | Thailand | Vietnam | Hong Kong | HMTc | Binds |
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| Lead (Pb) | 1500 | — | — | 500 | 500 | 500 | 500 | 500 | 500 | 500 | 500 | 500 | 500 | — | 500 | 2000 | — | 500 | 500 | 500 | India |
| Inorganic arsenic (iAs) | 100 | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 100 | EU |
| Total arsenic (tAs) | — | — | 2000 | — | 76000 | 1000 | — | — | — | — | — | 80000 | — | — | 1000 | 1000 | — | — | — | 1000 | Singapore |
| Mercury, total (tHg) | 500 | — | 500 | 1000 | 500 | 500 | 500 | — | 500 | — | 500 | — | 500 | — | 500 | — | — | 500 | — | 500 | EU |
| Methylmercury (MeHg) | — | 1000 | — | 1000 | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 500² | read-across |
| Cadmium (Cd) | 500 | — | — | 500 | 500 | 500 | 500 | 500 | 500 | 500 | 500 | — | 500 | 2000 | 500 | — | 2000 | 500 | 2000 | 500 | EU |
| Nickel (Ni) | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 2000² | read-across |
| Total chromium (Cr) | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 1000 | 1000 | Hong Kong |
| Hexavalent chromium (Cr-VI) | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 10² | read-across |
| Tin (Sn) | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 200000² | read-across |
| Aluminium (Al) | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | — | 100000² | read-across |
All values µg/kg (ppb), as-consumed basis. ² no government regulates this analyte for this exact product form: the value is a disclosed read-across from the nearest applicable government maximum, and the derivation names the instrument it comes from. It is never taken from occurrence data. After publication the standards ratchet may tighten it, using certified-lot results only. ³ not material in this matrix: measured but with no standalone number, controlled by packaging control or by the total-metal screen, not an invented value.
Occurrence and derivation rationale
For each analyte on the panel: what the peer-reviewed and survey literature measured in this category, cited one way to the Heavy Metal Index, and the Method v2.0 reasoning behind the certification limit — including, where no government sets a number, why the program sets one anyway. Occurrence figures are literature findings; the derivation is the certifier's.
13 studies in the certified-market pool measured lead in Shellfish across 903 certified-market samples. The pooled distribution centres on a median of 319 ppb and reaches 2.9 mg/kg at the 95th percentile, with a measured maximum of 3.2 mg/kg. Garofalo 2025, Valencia 2021, Shue 2012, Romero-Estevez 2020, Singhato 2025, Onyegeme-Okerenta 2023, Raju 2021, Helcom 2017 and 5 more.
HMTc sets 500 ppb (regulatory-alignment): the strictest applicable government maximum level for this product form, adopted under Method v2.0 as the default certification standard. The certified-market pool's P97 is 3.1 mg/kg, at or above the government ceiling of 500 ppb, so the government maximum binds. Why lead is limited →
3 studies in the certified-market pool measured inorganic arsenic in Shellfish across 137 certified-market samples. The pooled distribution centres on a median of 39 ppb and reaches 109 ppb at the 95th percentile, with a measured maximum of 160 ppb. Schoof 2007, Munoz 1999, FERA 2015.
HMTc sets 100 ppb (regulatory-alignment): the strictest applicable government maximum level for this product form, adopted under Method v2.0 as the default certification standard. The certified-market pool's P97 is 110 ppb, at or above the government ceiling of 100 ppb, so the government maximum binds. Why inorganic arsenic is limited →
4 studies in the certified-market pool measured total arsenic in Shellfish across 20 certified-market samples. The pooled distribution centres on a median of 2.1 mg/kg and reaches 15.9 mg/kg at the 95th percentile. Onyegeme-Okerenta 2023, Chou-Uthe 1993, Singhato 2025, FERA 2015.
HMTc sets 1 mg/kg (regulatory-alignment): the strictest applicable government maximum level for this product form, adopted under Method v2.0 as the default certification standard. The certified-market pool's P97 is 33 mg/kg, at or above the government ceiling of 1 mg/kg, so the government maximum binds. Why total arsenic is limited →
8 studies in the certified-market pool measured total mercury in Shellfish across 1260 certified-market samples. The pooled distribution centres on a median of 1.4 ppb and reaches 297 ppb at the 95th percentile, with a measured maximum of 520 ppb. Garofalo 2025, Bjerregaard 2023, Harding 2018, Singhato 2025, Chou-Uthe 1993, Pawlaczyk 2020, FERA 2015, Nielsen 1975.
HMTc sets 500 ppb (regulatory-alignment): the strictest applicable government maximum level for this product form, adopted under Method v2.0 as the default certification standard. The certified-market pool's P97 is 377 ppb, against a government ceiling of 500 ppb. Why total mercury is limited →
1 study in the corpus measured methylmercury in Shellfish (23 samples reported across those studies): Harding 2018. Reported concentrations range from 5.1 ppb to 7.1 ppb, with a typical value of 5.1 ppb.
HMTc sets 500 ppb by read-across: No mollusc/crustacean-specific methylmercury ML below the general-fishery value applies. Read-across to the general/other-fishery methylmercury ML (Mexico NOM-242 other fishery products, 500), stricter than the crustacean-specific 1000 and more protective for low-trophic shellfish. Held at or below the total-mercury ceiling. Why methylmercury is limited →
13 studies in the certified-market pool measured cadmium in Shellfish across 2227 certified-market samples. The pooled distribution centres on a median of 131 ppb and reaches 4.8 mg/kg at the 95th percentile, with a measured maximum of 5.6 mg/kg. Garofalo 2025, Valencia 2021, Shue 2012, Romero-Estevez 2020, De-Anda-Montanez 2023, Onyegeme-Okerenta 2023, Raju 2021, Helcom 2017 and 5 more.
HMTc sets 500 ppb (regulatory-alignment): the strictest applicable government maximum level for this product form, adopted under Method v2.0 as the default certification standard. Why cadmium is limited →
4 studies in the certified-market pool measured nickel in Shellfish across 123 certified-market samples. The pooled distribution centres on a median of 5.3 mg/kg and reaches 10.2 mg/kg at the 95th percentile. Shue 2012, Yap-Almutairi 2022, De-Anda-Montanez 2023, Onyegeme-Okerenta 2023.
HMTc sets 2 mg/kg by read-across: No government sets a nickel ML for animal seafood (EU 2024/1987 nickel covers plant foods and seaweed only). Read-across to the nearest whole-food nickel ceiling (EU 2024/1987 husked rice, 2000) that accommodates observed seafood nickel occurrence; clean product passes, grossly nickel-elevated product fails. Why nickel is limited →
13 studies in the corpus measured tin in Shellfish (7254 samples reported across those studies): Jiang 2026, Uc-Peraza 2022, Wickramaarachchige 2022, Chung 2020, Cfs 2019, Ho 2016, Lee 2016, FERA 2015 and 5 more.
HMTc sets 200 mg/kg by read-across: Tin is a can-migration analyte; no government sets a tin ML for non-canned seafood (every seafood tin ML is canned/tinplate-only). Read-across to the EU 2023/915 general canned-food inorganic-tin ML (200000) as a packaging-migration baseline; fresh/frozen shellfish has no tin source and passes. Canned shellfish is certified under the canned-seafood subcategory. Why tin is limited →
5 studies in the corpus measured aluminium in Shellfish (4910 samples reported across those studies): ANSES 2026, Simionov 2023, Wickramaarachchige 2022, FERA 2015, FSANZ 2011.
HMTc sets 100 mg/kg by read-across: No government sets an aluminium contaminant ML for food; dietary aluminium is managed by weekly intake against the EFSA/JECFA TWI. Read-across to the nearest food aluminium instrument (China GB 2760 baked-foods aluminium, 100000) as a monitor/baseline ceiling; shellfish aluminium sits below it, so clean product passes while gross contamination fails. Flagged monitor/baseline, not per-lot-critical. Why aluminium is limited →
Risk Flag
Where certification is demanding for this subcategory, and why. These carry a natural or process background that runs above the limit — the limit being the strictest government maximum for the product, never a percentile of market data (Method v2.0). A product is not disqualified by this — only its own tested result decides certification, and a well-sourced lot can sit well below the market.
Nickel
Legumes, nuts, cocoa, and oats are naturally high in nickel.
Multipliers are the ratio of the pooled occurrence median to the published limit; occurrence characterises the market only and carries no compliance weight. See the cross-category summary.
Cite this standard
Pendergrass, K. (2026). Shellfish (crustaceans and bivalve molluscs): HMTc standard (Standard No. 10.83138/hmtc.std.6.shellfish). Institute of Contaminant Standards. https://doi.org/10.83138/hmtc.std.6.shellfish
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The literature baseline for every analyte is maintained independently at the Heavy Metal Index. This certification standard applies those findings; the two are kept editorially separate by design.