Heavy metals in food databaseSeaweedChecked 2026.10.03
Nori: arsenic
Total arsenic in dried nori averages 25 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. Among seaweeds, hijiki is the one exception with high inorganic arsenic.
Levels measured in Japanese government surveys and studies
| Metal | Form / state | Mean | Range / max | Samples | Survey |
|---|---|---|---|---|---|
| Arsenic | Total arsenic, dried | 25 (median 23) | 13–51 | 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 0.16 in MAFF’s material is a value calculated by substituting for the results below the limit of quantification and is not a measured average. The material does not say whether processed forms such as roasted nori and seasoned nori were distinguished.
Limits (Japan, international, EU)
| Set by | Limit | Note |
|---|---|---|
| Japan (Food Sanitation Act) | No standard | No limit for inorganic or total arsenic in nori was found |
| Codex (international standards) | No Codex standard for nori | — |
| EU (Regulation 2023/915) | No nori-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. However, because the limit of quantification is high, nothing finer than “below 0.5” is known.
- 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.” MHLW’s Q&A (2004) says that “other seaweeds also exist as organic arsenic of low toxicity.”
- For Japanese intake, the “other vegetables and seaweeds” group, which includes nori (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, not nori.
- No public survey values were found for cadmium in Japanese nori. 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. Nori is a red alga).
- MAFF’s survey covers dried nori. No public survey values were found for processed products such as seasoned nori 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)”
- MHLW, “On arsenic in hijiki,” Q&A (July 30, 2004)
- 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.