Arsenic in edible macroalgae: an integrated approach

Overview

Camurati and Salomone reviewed the literature to 2019 on arsenic in edible marine macroalgae, integrating arsenic speciation and toxicity, the behaviour of arsenic species during digestion and cooking, analytical/CRM challenges, and current legislation, with a view to informing future regulation as seaweed consumption grows (including in South America). This is a secondary source: it reports no primary measurements, and its quantitative statements are syntheses of cited primary studies. Its principal value for the index is the synthesized picture it confirms — that inorganic arsenic in seaweed is generally low but with species-specific high exceptions (hijiki and Laminaria digitata), that brown algae carry both higher total arsenic and a higher inorganic fraction than red or green algae, and that cooking and digestion can change arsenic bioaccessibility and speciation in ways current total-As/inorganic arsenic (iAs) limits do not capture.

Key numbers

This is a review; the figures below are the review’s syntheses of cited primary literature, not new measurements, and should be treated as leads/context rather than poolable occurrence data.

• Total arsenic in macroalgae spans roughly 0.1–250 mg/kg dw across species (review of Ma et al. 2018).
• Inorganic arsenic “rarely exceeds 1 mg/kg dw in seaweed” (citing Almela 2002, Díaz 2012, Morrison 2014, Pétursdóttir & Gunnlaugsdóttir 2019), with notable exceptions hijiki (Hizikia fusiforme) and Laminaria digitata (citing Ichikawa 2006, Mise 2019, Ronan 2017).
• Brown algae (Phaeophyta) contain higher total arsenic, and a higher proportion of inorganic arsenic relative to total, than red (Rhodophyta) or green (Chlorophyta) algae (citing Desideri 2017, Ma et al. 2018).
• Organic arsenic can reach ~89% of total in seaweed (citing Cubadda et al. 2017); all organic arsenic (As) species except arsenobetaine are considered potentially toxic.
• Seawater arsenic typically 0.5–2 µg As/L; total As in macroalgae 0.1–250 mg/kg dw; WHO estimate of total dietary As intake 20–300 µg/day.
• Digestion/cooking transformation (cited primary findings): ~85% of inorganic arsenic in hijiki is released into gastrointestinal juices and thus bioaccessible (Brandon 2014); in vitro bioaccessibility of total As from macroalgae ranged ~12–80% across studies; cooking can raise total-As availability (e.g., Porphyra 87→106%; H. fusiforme As(V) rising 8.65→41.7 µg/g, Almela 2005); 34–71% of As can be removed into cooking water (García-Sartal 2012).
• Exposure context: Japanese children and pregnant women may be exposed to high inorganic arsenic via daily hijiki consumption (Mise 2019); a 3% hijiki diet caused arsenic accumulation and poisoning signs in rats (Yokoi & Konomi 2012).

Legislation summary (as compiled by the review):

• Australia & New Zealand: maximum inorganic As in seaweed 1 mg/kg dw (ANZ Food Standards Code).
• France and USA: maximum inorganic As 3 mg/kg dw in algae-based products.
• Argentina (Argentine Food Code): no specific maximum for As in macroalgae; only a general 1 mg/kg total-As for solid foods, and 0.3 mg/kg inorganic As for leafy vegetables / 1 mg/kg for fish/shellfish/bivalves — which the authors argue is inappropriate for seaweed.
• General (the review does not name the EU or Commission Regulations): existing food and drinking-water limits refer only to total or inorganic arsenic; regulation of maximum As levels in edible seaweed is limited and principally refers to inorganic forms; the review argues species-specific regulation based on individual As compounds is needed for edible seaweed.

Analytical/CRM note: certified reference materials for arsenic species in seaweed are scarce — SRM 3232 Kelp Powder (Thallus laminariae, Yu et al. 2018, first to certify arsenosugar species), Ulva lactuca BCR-279 (total As), NMIJ CRM 7405-a hijiki (t-As + As(V)), and NIES CRM 09 Sargassum fulvellum (t-As) are the commonly used materials.

Methods (brief)

Narrative critical review. The authors searched SCOPUS using keywords (marine algae, seaweed, macroalgae combined with arsenic, inorganic arsenic, and other arsenical compounds), covering literature published up to 2019. They organised the synthesis around arsenic speciation and toxicity, arsenic in macroalgae, transformation during digestion and cooking, extraction and analytical techniques (HPLC-ICP-MS, HPLC-HG-AAS/AFS) and CRM availability, and current legislation. No primary sampling or measurement was performed; all concentrations and percentages are attributed to the cited primary studies.

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.