Analytical Methodologies for the Determination of Organoarsenicals in Edible Marine Species: A Review

Overview

Luvonga and colleagues (US National Institute of Standards and Technology) reviewed the analytical methodologies for determining organoarsenicals in edible marine species (seafood and seaweed): sample handling, extraction, cleanup, chromatographic separation, element-specific detection, and molecular characterization. This is a methods review with no primary occurrence measurements; its relevance to the Category 6 seaweed-kelp-foods row is methodological and toxicological framing rather than concentration data. Its load-bearing point for the row is that total arsenic is an inadequate dietary-risk indicator for seaweed: organoarsenicals (predominantly arsenosugars) make up >85% of total arsenic in most seafood, several organoarsenicals (arsenic-containing hydrocarbons and fatty acids) have toxicity approaching inorganic arsenic, and seaweed arsenic is especially difficult to extract and speciate reliably — so speciated inorganic-arsenic measurement (with quality standards and CRMs) is essential for credible risk assessment and regulation.

Key numbers

This is a methods review; the few quantitative statements are framing values cited from the primary literature, not new measurements and not poolable.

• Organoarsenicals constitute >85% of total arsenic in most seafood (notably fish); focusing only on inorganic arsenic can therefore misrepresent the picture, but for seaweed specifically, arsenosugars of unknown toxicity predominate and total arsenic overstates the directly-toxic fraction — both directions argue for speciation.
• Arsenosugars occur at high concentrations (~10–40 µg/g dry weight) in marine organisms used as human food.
• Toxicity framing (cited): three arsenic-containing hydrocarbons (AsHC 332, AsHC 360, AsHC 444) showed in vitro toxicity comparable to arsenite in human bladder (UROtsa) and liver (HepG2) cells; two arsenic-containing fatty acids (AsFA 362, AsFA 388) were less toxic than arsenite but active at micromolar levels; dimethylarsinic acid (DMA), which the review describes as a known tumour promoter and a metabolite of inorganic arsenic (iAs), is also an arsenosugar metabolite, with elevated urinary DMA after consumption of arsenosugar-rich seafood.
• Regulatory framing (cited): current arsenic regulations focus mainly on inorganic arsenic (which the review calls a “well-characterized Class A carcinogen” — the US EPA category — and treats as 100% bioavailable from drinking water); the review endorses a risk-based framework (after Feldmann, with an IARC-classification basis) categorising arsenic into (1) toxic inorganic arsenic, (2) non-toxic arsenobetaine, and (3) “leftover” arsenicals of potential/unknown toxicity.

Seaweed-specific analytical caveats (relevant to interpreting all seaweed arsenic data):

• Recoveries of arsenicals from seaweed are often low even with repeated (3–4) extractions; the non-extractable (“protein-bound”/“lipid-bound”) fraction is considerable, so quantitative extraction and species integrity are persistent challenges.
• Macroalgae must be cleaned of epiphytes/symbionts before analysis (which can carry their own arsenic species and bias speciation), and seaweed should not be frozen-and-thawed before freeze-drying because that can lose organoarsenicals.
• Acidic extraction improves arsenosugar recovery but can hydrolyse arsenosugars into degradation products; basic (TMAH) extraction can also degrade arsenosugars; there is no single universal extraction protocol, and species interconversion is a constant risk.
• Certified reference materials for organoarsenicals are scarce; this gap limits cross-study comparability.

Methods (brief)

Narrative review (received 2019, published 2020). The authors survey the arsenic-speciation analytical pipeline for marine species: sample pretreatment (cleaning, freeze-drying, cryogenic homogenisation; particle size affects extraction efficiency); extraction (solvent/water/methanol–water, supercritical fluid, accelerated solvent, microwave-assisted, ultrasound probe sonication, solid-phase microextraction, matrix solid-phase dispersion, enzymatic hydrolysis), with a comparison table of technique advantages/disadvantages; cleanup (silica-gel, solid-phase extraction, size-exclusion); separation (capillary zone electrophoresis, gas chromatography, liquid chromatography — ion-exchange, reversed-phase, ion-pair, micellar, multidimensional); element-specific detection (ICP-MS, ICP-AES, HG-AFS, CT-HG-AAS); and molecular characterization (XANES, EXAFS, Q-ToF-MS, Orbitrap-MS, FT-ICR-MS). The review focuses on hydrophilic organoarsenicals (methylated arsenicals, arsenoribosides) and lipophilic arsenolipids (AsHCs, AsFAs, arsenosugar-phospholipids); thioarsenicals are excluded as covered elsewhere. No primary sampling or measurement was performed.

Update history

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