Heavy metals in food databaseSeaweedChecked 2026.10.03
Wakame: arsenic
Total arsenic in dried wakame averages 33 mg/kg, but in a MAFF survey (fiscal 2006–07), inorganic arsenic was below the limit of quantification (0.5 mg/kg) in all 100 samples tested. Unlike hijiki, it is a seaweed in which inorganic arsenic does not stand out. However, nothing finer than “below 0.5” is known.
Levels measured in Japanese government surveys and studies
| Metal | Form / state | Mean | Range / max | Samples | Survey |
|---|---|---|---|---|---|
| Arsenic | Total arsenic, dried | 33 (median 33) | 15–52 | 100 samples | MAFF, fiscal 2006–07 |
| 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 average inorganic arsenic of 0.15 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 wakame was found |
| Codex (international standards) | No Codex standard for wakame | — |
| EU (Regulation 2023/915) | No wakame-specific limit confirmed | — |
| 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 is organic arsenic, and inorganic arsenic was below 0.5 mg/kg in all 100 dried samples tested. The situation differs from hijiki (average inorganic arsenic 67 mg/kg), even though both are “seaweed.”
- In an older one-off study (Shinagawa et al. 1983, dry weight), wakame had 0.6 inorganic arsenic (about 7%) out of 8.3 mg/kg total arsenic. The difference from MAFF’s total arsenic of 33 is probably due to differences in samples and years.
- 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.”
- For Japanese intake, the “other vegetables and seaweeds” group, which includes wakame (total diet study, 2024), contributed 80.4 μg/day of total arsenic (about 37% of the overall 219) and 2.01 μg/day of inorganic arsenic (about one tenth of the overall 21.2). The main source of inorganic arsenic is rice.
- MAFF’s survey covers dried wakame. No public survey values were found for salted wakame, fresh wakame, wakame after soaking in water, or cooked dishes such as miso soup.
- No public survey values were found for cadmium in Japanese wakame. 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. Wakame is a brown alga).
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”
- 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.