Determination of Inorganic Arsenic in Seaweed and Seafood by LC-ICP-MS: Method Validation

Overview

Matsumoto-Tanibuchi and colleagues validated an LC-ICP-MS method for inorganic arsenic in seaweed, seafood, and seafood products purchased from a local market in Japan. The occurrence-relevant data are Table 4 product concentrations and Table 5 tissue-part concentrations, which report inorganic arsenic, total arsenic, total arsenic in extracts, and extraction rates. The page keeps inorganic arsenic and total arsenic separate throughout.

Key numbers

All concentration values are reported by the source as mg/kg. No unit conversion was performed. Dried seaweed products are recorded on their dry/as-sold product basis; fish, shellfish, and sauces are recorded as analyzed/as-purchased because the paper does not report a moisture conversion.

Table 4 product concentrations:

Table 5 tissue-part concentrations:

Method-validation figures from Tables 1-3:

• HPLC-ICP-MS used a CAPCELL PAK C18 MG column (4.6 mm id × 250 mm, 5 μm particles), sodium 1-butanesulfonate 10 mmol/L, malonic acid 4 mmol/L, tetramethylammonium hydroxide 4 mmol/L, methanol 0.05%, flow 0.75 mL/min, injection volume 20 μL, and column temperature 20–30 °C.
• ICP-MS monitoring ion was m/z 75, with RF power 1.6 kW on the 7500ce and 1.55 kW on the 8800.
• LOD/LOQ, repeatability, and intermediate precision were: dried nori LOD 0.013 mg/kg, LOQ 0.042 mg/kg, RSDr 4.4%, RSDi 4.4%; Japanese oyster soft tissue LOD 0.0031 mg/kg, LOQ 0.011 mg/kg, RSDr 3.0%, RSDi 5.6%; oyster sauce LOD 0.0024 mg/kg, LOQ 0.0078 mg/kg, RSDr 7.4%, RSDi 7.4%.
• Recovery rates for spiked samples were: dried nori As(III) 94.8% (SD 0.8%) and As(V) 100.0% (SD 0.6%); Japanese oyster soft tissue As(III) 100.5% (SD 1.9%) and As(V) 99.2% (SD 2.7%); oyster sauce As(III) 105.0% (SD 1.9%) and As(V) 91.9% (SD 0.0%); NRCC DORM-4 As(III) 92.2% (SD 2.4%) and As(V) 93.2% (SD 2.8%). Spike level was 1 ng/g with n = 3.
• The abstract summarizes the method range as LOD 0.0023–0.012 mg/kg, LOQ 0.0077–0.042 mg/kg, repeatability 3.0–7.4%, intermediate precision 4.4–7.4%, and recoveries 94–107%.

The source text states that inorganic arsenic was detected in almost all evaluated dried seaweed products and only marginally in seafood. It specifically identifies akamoku, hijiki, and mozuku as the dried brown algae with significant inorganic arsenic. It also states that internal organs contained more inorganic arsenic than muscles in Japanese oyster, Japanese sardine, and Yezo giant scallop.

Methods (brief)

Dried seaweed products, seafood tissues, and seafood products were purchased from a local market in Japan. Dried seaweeds included kelp (Saccharina angustata), nori (Pyropia yezoensis), wakame (Undaria pinnatifida), sea lettuce (Ulva pertusa), green laver (uranium (U). prolifera), mozuku (Nemacystis decipiens), akamoku (Sargassum horneri), and hijiki (S. fusiforme). Seafood included albacore, rainbow trout, red-eye round herring, Japanese sardine, northern shrimp, Japanese common squid, Yezo giant scallop, Japanese oyster, nam pla, and oyster sauce.

For arsenic speciation, the authors weighed 0.1 g seaweed, 0.2 g seafood, or 0.5 g seafood product; extracted with 2 mL of 0.3 mol/L nitric acid at 100 °C for 2 h; diluted and filtered to 20 mL; then quantified arsenic species by LC-ICP-MS. Total arsenic used microwave digestion with 5 mL nitric acid and ICP-MS. The paper defines inorganic arsenic as the sum of As(III) + As(V), because interconversion can occur during extraction. Organic species including MMA, DMA, AB, AC, TMAO, and TeMA were chromatographic context, not HMI metals source metadata.

Implications

This source provides direct Japanese-market occurrence evidence for inorganic arsenic in dried seaweed products, fish/shellfish products, seafood sauces, and seafood tissue parts. It reinforces that total arsenic and inorganic arsenic are not interchangeable: several fish and shellfish muscle samples had measurable total arsenic while inorganic arsenic (iAs) was below LOQ, whereas hijiki, akamoku, and mozuku had much higher measured iAs. Seafood organ measurements should remain part-specific context and should not be pooled with ordinary edible-muscle rows without preserving the tissue distinction.

Related evidence

• Seaweed/kelp foods (nori, wakame, kombu, dulse — as food products)
• Seafood
• Fresh Fish
• Fish — marine, predatory (tuna, swordfish, shark, king mackerel)
• Fish — marine, non-predatory (sardines, anchovies, salmon, cod)
• Fish — freshwater (tilapia, catfish, trout)
• Shellfish (shrimp, crab, lobster, clams, oysters, mussels)
• Condiments (hot sauce, soy sauce, mustard, ketchup, mayonnaise, salsa)
• Seaweed
• Seafood
• Fish
• Shellfish
• Arsenic, Total
• Arsenic, Inorganic

Update history

The five most recent substantive edits to this page, classified major (evidence or structure moved), correction (a published value or statement was wrong and has been fixed), or minor (narrative rewritten without changing the underlying evidence). Each description is derived from what the edit did to this page; the linked commit is the authoritative record, routine regeneration passes are excluded, and the full version history lives in git.