Heavy metals in food databaseSeaweedChecked 2026.10.03
Kombu: arsenic
Total arsenic in dried kombu averages a fairly high 53 mg/kg, but most of it is organic arsenic. In a MAFF survey (fiscal 2006–07), inorganic arsenic was below the limit of quantification (0.5 mg/kg) in all 100 samples tested. Because the limit of quantification is high, however, all that can be said is “below 0.5.”
Levels measured in Japanese government surveys and studies
| Metal | Form / state | Mean | Range / max | Samples | Survey |
|---|---|---|---|---|---|
| Arsenic | Total arsenic, dried | 53 (median 51) | 25–110 | 200 samples | MAFF, fiscal 2006–08 |
| Arsenic | Inorganic arsenic, dried | <0.5 (all 100 samples below the limit of quantification) | — | 100 samples | MAFF, fiscal 2006–07 |
Units are mg/kg (= ppm), dry weight. The limit of quantification for inorganic arsenic is 0.5 mg/kg. The average of 0.19 in MAFF’s material is “a value calculated by substituting for the results below the limit of quantification” and is not a measured average.
Limits (Japan, international, EU)
| Set by | Limit | Note |
|---|---|---|
| Japan (Food Sanitation Act) | No standard | No limit for inorganic or total arsenic in kombu was found |
| Codex (international standards) | No Codex standard for kombu | — |
| EU (Regulation 2023/915) | No kombu-specific limit confirmed | For cadmium, food supplements made from 80% or more dried seaweed or bivalves have a limit of 3.0 mg/kg |
| Australia/New Zealand (FSANZ) | Inorganic arsenic in seaweed: maximum 1 mg/kg | A standard for seaweed as a whole, including hijiki |
| China | Aquatic products (excluding fish) 0.5 mg/kg | As organized on MAFF’s “standards in other countries” page (a value for inorganic arsenic) |
Good to know
- Most of the total arsenic in kombu is organic arsenic (arsenosugars and others), and inorganic arsenic was below 0.5 mg/kg in all 100 dried samples tested. Even among seaweeds, hijiki is an order of magnitude different, with inorganic arsenic averaging 67 mg/kg.
- Because the limit of quantification for inorganic arsenic is high, nothing finer than “below 0.5” can be said. In an older one-off study (Shinagawa et al. 1983, dry weight), ma-kombu had 0.8 inorganic arsenic (about 3%) out of 25.4 mg/kg total arsenic.
- No official document states flatly that “organic arsenic is harmless.” MAFF writes both that “the degree of adverse effects is generally said to be small” and that “the effects in the human body are not well understood at present.” In 2025 JECFA set separate health-based guidance values for two organic arsenic forms, DMA(V) and MMA(V) (6 and 5 μg/kg body weight/day).
- For Japanese intake, the “other vegetables and seaweeds” group, which includes kombu, wakame, and hijiki (total diet study, 2024), contributed 80.4 μg/day of total arsenic, about 37% of the overall figure (219 μg/day), and 2.01 μg/day of inorganic arsenic (about one tenth of the overall 21.2).
- No Japanese public survey values were found for cadmium in kombu. France’s ANSES found that 26% of about 250 samples of edible seaweed exceeded 0.5 mg/kg (dry matter) and proposed a limit of 0.35 (levels tend to be higher in brown and red algae).
- MAFF’s survey covers dried kombu. No public survey values were found for inorganic arsenic in the broth from simmering dashi kombu or in processed products such as kombu rolls and tsukudani (food simmered in soy sauce and sugar).
Related explainers
Pages for each metal
Sources
- MAFF, “Survey of arsenic contained in food” (updated December 2025)
- MAFF, “Basic information on arsenic (Q&A)”
- FSCJ, “Food health impact assessment: arsenic” (December 2013)
- MHLW research grant, Total Diet Study, fiscal 2024, sub-study report
- MAFF, “International and other countries’ standards for arsenic”
- FSANZ, “Hijiki seaweed and inorganic arsenic”
- ANSES, “Recommendations to limit cadmium exposure from edible seaweed”
Last checked 2026.10.03 (against the original government documents and papers, collected and cross-checked in Gemini Notebook).
Heavy metals occur naturally in soil and the sea, and every food contains small amounts. This page lists facts from government surveys, limits and assessments and from published papers; it does not judge any food as good or bad. Where there is official advice — such as on eating fish during pregnancy — follow it.