Mosusu 2023 — Heavy metals in edible Japanese seaweeds

A 2023 master’s thesis abstract from Hokkaido University’s Graduate School of Environmental Science reports ICP-MS analysis of fourteen elements (V, Se, Mn, Fe, Cu, Zn, Mo, Co, Cr, Ni, Cd, Pb, Th, U) in 22 commercial seaweed samples sold in Japan, covering four species: Wakame (Undaria pinnatifida), Kombu (Laminaria spp.), Hijiki (Hizikia fusiform), and sea lettuce (Ulva rigida). Of the fourteen elements measured, five fall within the Heavy Metal Index analyte vocabulary: Cr, Ni, Cd, Pb, and U. The abstract reports inter-species ranking patterns and a geographic signal — Chinese-sourced Wakame and Hokkaido-sourced Kombu from off Nemuro — but does not include numerical concentration tables; only the full thesis would contain those.

Key numbers

The submitted document is a one-page Japanese master’s thesis abstract (令和4年度 環境科学院 修士論文内容の要旨) and does not report numerical concentrations. The only quantitative-comparative claims in the abstract are described below as ranking statements, not absolute values.

Per-sample µg/g or µg/kg values are not in the abstract; downstream synthesis requiring concentration figures must defer to the full thesis (Hokkaido University library) or to other peer-reviewed Japan-seaweed sources.

Methods (brief)

Twenty-two commercial seaweed samples were sourced from Japanese retail and labeled by packaging-declared origin (Japan, China, Korea). Samples were dried overnight, ground, and digested using an ETHOS Microwave Digestion System. Quantification used Inductively Coupled Plasma Mass Spectrometry (ICP-MS) at the Hokkaido University Open Facility. Arsenic was not measured (not in the fourteen-element panel); chromium reported without speciation; arsenic speciation not applicable. The abstract does not name reference materials, digestion blank counts, or limits of detection.

Implications

The source provides geographic-origin signal for Kombu and Wakame consumed in Japan, with Nemuro (Hokkaido) Kombu showing an approximately threefold elevation in Cu/Zn/Cd over Kombu from other Hokkaido sites, and Chinese-source Wakame showing elevated Ni/Co/Cr/Cd relative to Japanese-source Wakame. The author interprets the variation as a signal of underlying seawater and sediment contamination at production sites. Without per-sample numerical values, the abstract supports qualitative inter-species and inter-region rankings only; it does not support computing percentile thresholds for any HMTc category.

Verification notes

• Source-document scope: only the one-page Japanese-format master’s thesis abstract was provided in the manual-fetch folder. The full thesis is not in the corpus.
• No DOI; access_url left null. Source type is thesis (master’s level); evidence tier C reflects abstract-only access and absence of peer review.
• Metals frontmatter lists only HMI analyte-vocabulary intersect (Cr, Ni, Cd, Pb, U). Non-tracked elements measured in the underlying study (V, Se, Mn, Fe, Cu, Zn, Mo, Co, Th) are documented in the Key numbers body table but not lifted to frontmatter.
• Jurisdictions include JP (sale and analysis), CN, and KR (packaging-declared origin countries for sample subset).
• Matrices include kelp because the species set includes Laminaria spp. (Kombu) which is a brown kelp; macroalgae and edible-seaweed cover the full species panel.
• No brand names were present in the abstract. Brand firewall: not engaged.
• Speciation: arsenic not measured; chromium reported as total Cr (Cr-VI not distinguished).
• Numerical values: none in the abstract; the Key numbers table records only the qualitative ranking statements the source actually makes.
• Audit subagent (2026-06-04) flagged matrices: [edible-seaweed, macroalgae, kelp, dry-weight] for vocabulary verification (⚠️). Verified against existing corpus: all four slugs are in active use across wiki/sources/*.md — dry-weight appears alongside red-seaweed in aziz2021-gracilaria-seaweed-bangladesh.md; edible-seaweed, macroalgae, and kelp each appear across multiple source pages. The basis-vs-matrix critique on dry-weight is structurally valid but reflects established Heavy Metal Index convention rather than a defect of this page. No correction applied; finding logged as false positive against current corpus convention.
• Audit subagent (2026-06-04) recommended adding ## Wiki pages this source may touch section. Declined: the v2.0 ingest skill (line 92, docs/ingest-workflows) explicitly treats ## Wiki pages updated on ingest as a legacy heading; the routing layer (Part 5b of CLAUDE.md) is now the system’s responsibility, not the source page’s. Recommendation logged as false positive against current architecture.

Page history

The five most recent substantive edits to this page. The full version history lives in git; when DOI minting comes online (see schema docs), each entry below will also link to a version-pinned DataCite DOI.