Ichikawa et al. 2006 - arsenic removal during hijiki cooking

Ichikawa and colleagues measured total arsenic and arsenic species in edible brown algae Hijikia fusiforme and tested arsenic removal by soaking and cooking. The source is directly relevant to hijiki/seaweed occurrence because it reports dry-weight total arsenic and measured As(V), As(III), DMAA, and arsenosugar fractions across samples from Japan, South Korea, and China. The mouse metabolism experiment is exposure context, not product occurrence.

Key numbers

All concentrations below are reported by the source in µgAs/g, dry weight; no unit conversion was performed.

Total arsenic in Table 2:

Arsenic speciation in Table 3:

The source states that inorganic arsenate was the main species in hijiki, and that the ratio of inorganic to organic arsenic was 55.4-88.1%. Minor components were inorganic arsenite (0-28.1%), dimethylarsinic acid (0.6-4.8%), and arsenosugar (0.9-3.1%).

Soaking/cooking removal from Table 4:

The abstract and results state that 28.2-58.8% (w/w) of total arsenic in hijiki was eluted with soaking water, 49.3-60.5% (w/w) of arsenic in the residue was dissolved by cooking, and 88.7-91.5% (w/w) of arsenic was removable by the full cooking process. The source also states that 75.0-81.4% of the eluted arsenic was arsenate.

Mouse metabolism context:

• After administration of soaking water, arsenate was metabolized to DMAA in urine.
• After cooked hijiki administration, arsenate and DMAA were excreted in urine.
• Administered arsenosugar was metabolized to DMAA with five unknown compounds in urine.

Methods (brief)

Hijiki sprout and long-portion samples came from Japan, South Korea, and China via the Hijiki Cooperative Society Japan. For total arsenic, uniform hijiki powder was digested with nitric acid, hydrogen peroxide, sulfuric acid, ammonium hydrogencitrate, hydrochloric acid, ascorbic acid, and potassium iodide, then measured by hydride-generation atomic absorption spectrometry. Arsenic speciation used HPLC/ICP-MS with an Inertsil AS column and standards for arsenate, arsenite, MMA, DMAA, arsenobetaine, TMAO, tetramethylarsonium, arsenocholine, and synthesized arsenosugar.

The preparation experiment soaked 5 g dried hijiki in 20 mL pure water for 30 min at room temperature, then boiled the soaked hijiki in 30 mL pure water for 20 min at 90 °C. Extracts were filtered through 0.2 µm filters before speciation analysis. The mouse experiment used an arsenic-free diet before administration and collected urine/feces for arsenic-species analysis; those biological matrices are not treated as product occurrence values here.

Implications

This source is a primary hijiki occurrence and preparation study. It reinforces that hijiki can carry high total arsenic with a large measured inorganic fraction, and it provides dry-weight source-region/speciation values useful for seaweed-kelp-food evidence routing. The soaking/cooking results are preparation-context values: they document source-measured arsenic removal into water and cooking liquid, but they should not be converted into a consumer-facing safety claim or an HMTc threshold.

Wiki pages this source may touch

• seaweed-kelp-foods
• seaweed
• arsenic-total
• arsenic-inorganic

Verification notes

• Identity checks before writing found no existing source page for DOI 10.1002/aoc.1102, raw handle MFK_ichikawa2006, title text, or cite key ichikawa2006-hijiki-cooking-arsenic.
• All Key numbers were rechecked against /tmp/hmi-seaweed-035.txt, extracted with pdftotext -layout. Tables 2, 3, and 4 are transcribed in source order, including N.D./ND censoring and parenthetical percentage values.
• Units and bases are preserved as µgAs/g, dry weight, %, w/w, mL, min, and °C; no unit conversion was performed.
• Speciation check: As(V) and As(III) are recorded as inorganic arsenic species; DMAA and arsenosugar are kept separate and are not collapsed into iAs or tAs.
• Brand firewall: no brand-linked values are reported. The Hijiki Cooperative Society Japan is a sample supplier, not a consumer brand comparison.
• Missing-slug check: no missing product or ingredient slug blockers. Exact hijiki/Hijikia fusiforme remains in source text while frontmatter uses broad seaweed/kelp food slugs.

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.