Overview
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, chromium (Cr), nickel (Ni), cadmium (Cd), lead (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 uranium (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.
| Finding | Source-reported claim |
|---|---|
| Sample count | 22 commercial seaweed samples sold in Japan |
| Species | Wakame (Undaria pinnatifida), Kombu (Laminaria spp.), Hijiki (Hizikia fusiform), sea lettuce (Ulva rigida) |
| Elements measured | V, Se, Mn, Fe, Cu, Zn, Mo, Co, Cr, Ni, Cd, Pb, Th, U (fourteen) |
| Method | ETHOS Microwave Digestion + ICP-MS, Hokkaido University Open Facility |
| Sea lettuce ranking | Highest among the four species for V, Mn, Co, Ni, Zn, and Pb |
| Hijiki ranking | Highest for Th, Mo, Cu, and Fe |
| Wakame / Kombu ranking | Highest for Cr, Cd, Se, and U (distributed across the two brown algae) |
| Nemuro-source Kombu | Approximately 3× higher Cu, Zn, and Cd than Kombu from other Hokkaido sites |
| Chinese-source Wakame | Higher Ni, Co, Cr, and Cd than Japanese-source Wakame |
| Author’s overall framing | Japanese kombu and wakame samples showed lower metal concentrations than literature seaweed values from other countries |
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.
Update history
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