Improving the Efficiency of Organoarsenic Extraction from Seaweeds

Overview

Hata and colleagues developed an enzymatic plus methanol extraction method for organoarsenic species in wakame. The occurrence-relevant material is a single commercial dry wakame product from Japan; the rest of the paper tests extraction efficiency and speciation preservation. The source reports total arsenic in the dry wakame and method-dependent extractable arsenic peaks, but it does not report measured inorganic arsenic.

Key numbers

All product concentrations are reported by the source on a dry-wakame basis.

Enzymatic pre-treatment elution rates from Table 2:

Extraction rates from Table 3:

Arsenic species/peak contents in wakame extracts from Table 4, reported as mg/kg dry wakame:

The authors identified AsSug 328 and AsSug 482 in the wakame extracts. Peak a was estimated to correspond to arsenic-hydrocarbon 388 (C21H46OAs in the results text) and arsenic-phospholipid 1012 (C49H95O14PAs in the results text); peak c was not identified. Neither AsSug 254 nor DMA was detected in this study, which the authors used as evidence that the enzymatic method did not alter the arsenic-compound composition.

Methods (brief)

A commercial dry wakame product, harvested from the Sanriku Coast and purchased from a retail market in Choshi City, was ground to powder before analysis. Total arsenic was measured by ICP-MS after microwave acid digestion of 100 mg powdered sample with 2.5 mL of HNO3:H2O2 = 5:2 and dilution to 30 mL with 5% HNO3. The total-As method was validated with NMIJ CRM 7405-a Hijiki: certified 35.8 ± 0.9 mg/kg, measured 35.5 ± 0.4 mg/kg (mean ± SD, n = 3).

For extraction testing, 100 mg dry wakame was incubated for 6 hours at 37 °C with alginate lyase, cellulase, both enzymes, or no enzyme in 0.1 M phosphate buffer (pH 6.0). Methanol extraction was then tested at 0, 50, and 100% MeOH. Arsenic species/peaks were separated by cation- and anion-exchange HPLC-ICP-MS and identified or tentatively assigned with HPLC-ESI-Q-TOF-MS.

Implications

This source should be treated as a narrow method-plus-occurrence record for dry wakame. It supports the seaweed/kelp food row by adding a Japanese retail dry-wakame total-arsenic value and showing that extraction conditions strongly affect the recovered organoarsenic profile. Because inorganic arsenic was not reported, this page should not be used as an inorganic-arsenic occurrence value.

Related evidence

• Seaweed/kelp foods (nori, wakame, kombu, dulse — as food products)
• Seaweed
• Arsenic, Total

Update history

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