Seaweed & kelp foods (nori, wakame, kombu, dulse): HMTc Standard

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 Seaweed & kelp foods (nori, wakame, kombu, dulse)’s own as-sold 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-sold basis. 10 of 11 analytes carry a firm ceiling; the remaining 1 are toxic species bounded by their parent totals (species ≤ total, measured on every lot), so every analyte carries an enforceable ceiling. A brand meeting every value on a like-for-like basis qualifies for the mark.

Tier 1 (Pb, iAs, Hg, MeHg, Cd) are zero-tolerance toxics with no established safe threshold. Tier 2 (tAs, Ni, Cr, Cr-VI, Sn, Al) carry a 150% transitional allowance under the program’s Status A–E framework. 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 Seaweed & kelp foods (nori, wakame, kombu, dulse). Each row lists every government maximum level in force worldwide, converted to the as-sold 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.

All values µg/kg (ppb), as-sold 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. &sup5; a toxic species governed by and bounded by its parent total (for example inorganic arsenic ≤ total arsenic): the species can never exceed the total, so the total ceiling is the species ceiling. The total metal is measured on every lot and the species is established at baseline; no separate species ceiling is published. On ongoing lots the species is speciated whenever the total exceeds its limit.

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.

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.

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. “Seaweed & kelp foods (nori, wakame, kombu, dulse).” In Heavy Metal Tested & Certified (HMTc) Seafood standard, version 1.0. Institute of Contaminant Standards (ICS), 2026. DOI: registration pending.

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.