Duinker et al. 2020 - macroalgae food and feed safety

This Institute of Marine Research report updates Norwegian macroalgae food and feed safety evidence using data generated from 2014 to 2019. It reports species-level dry-weight concentrations for inorganic arsenic, cadmium, lead, total mercury, iodine, selenium, iron, and zinc across Norwegian macroalgae and selected Asian-origin imported products. The arsenic occurrence table is explicitly inorganic arsenic; mercury is reported as total mercury with most results below LOQ and without a methylmercury concentration table.

Key numbers

The report states that both fresh and dried macroalgae were sampled, but all concentrations in the occurrence review were converted to dry-weight basis for comparison. In one basis example, 141 fresh sugar-kelp samples had median iodine 410 mg/kg wet weight, while 16 dried sugar-kelp products had median iodine 3650 mg/kg dry weight.

Table 2 reports inorganic arsenic in mg/kg dry weight; selected high-signal and commercial species were:

The report highlights a distinct separation between the higher-iAs species and the rest: species with high iAs had median concentrations from 22 to 59 mg/kg dry weight, followed by other species with medians 0.23 and below. Oar weed had 50% of samples above 24 mg/kg dry weight, and its three highest samples were between 63 and 79 mg/kg dry weight. Four Laminaria hyperborea samples were low at 0.03-0.04 mg/kg dry weight.

Table 3 reports cadmium in mg/kg dry weight; selected species were:

Table 5 reports lead in mg/kg dry weight; selected species were:

Table 6 reports total mercury in mg/kg dry weight. Most values were below LOQ: only 100 of 406 samples were above LOQ, and only five species had more than 50% of samples above LOQ. The highest maximum concentrations were in sugar kelp, oar weed, and wrack siphon weed at 0.08, 0.07, and 0.07 mg/kg dry weight, respectively. Selected table rows include Laminaria digitata with 17/33 samples above LOQ, mean 0.03, median 0.024, and min-max <0.0059-0.067; Saccharina latissima with 17/148 samples above LOQ, median <0.047, and min-max <0.0098-0.081; and Alaria esculenta with 6/38 samples above LOQ, median <0.044, and min-max <0.0043-0.054.

Table 4 reports iodine in mg/kg dry weight and is not a heavy-metal table, but it is important matrix context. Laminaria and Saccharina kelps had the highest values, with typical concentrations between 3000 and 4000 mg/kg dry weight and maximum concentrations around 10000 mg/kg dry weight. Selected medians were oar weed 5000, tangle 4200, sugar kelp 3500, kombu 2600, winged kelp 740, hijiki 490, wakame 160, sea lettuce 100, and nori 37 mg/kg dry weight.

The nutrient table reports Se, Fe, and Zn medians with 25% percentile ranges. Selected non-ambiguous entries include wrack siphon weed Se 0.83 (0.69-1.2) mg/kg dry weight, hijiki Fe 820 mg/kg dry weight, green nori Fe 480 mg/kg dry weight, wrack siphon weed Zn 95 (18-100) mg/kg dry weight, tangle Zn 76 mg/kg dry weight, sugar kelp Se 0.095 (0.074-0.12) mg/kg dry weight, and sugar kelp Fe 44 (31-65) mg/kg dry weight. The extracted sugar-kelp Zn percentile text appears column-wrapped, so it is not transcribed as a verified value here.

For farmed sugar kelp, the report states that cadmium increased from south to north in a standardized Norwegian growth trial. Northern samples at 68-70N were above 1.0 mg/kg dry weight and more than four times higher than southern samples at 58-60N; inorganic arsenic and iodine did not show a similar geographic trend.

Methods (brief)

Samples were retrieved by IMR field work, kelp growers, and wild harvesters during 2014-2019, with arame, kombu, hijiki, wakame, and nori imported from Asian production. Samples were freeze-dried and homogenized before analysis. Metals including Cd, Hg, Pb, Fe, Zn, and Se were measured by ICP-MS after microwave decomposition using IMR method 197, which is accredited for Cd, Hg, Pb, Zn, and Se. Inorganic arsenic was measured by HPLC-ICP-MS using IMR method 261: samples were extracted with 10 ml 0.07 mol/l HNO3 in 3% H2O2 in a microwave oven for 20 minutes at 90°C, filtered, separated by anion-exchange HPLC, and determined as As5+ by ICP-MS. Iodine was extracted with TMAH and measured by ICP-MS. The report states the analyses were ISO accredited for most elements and otherwise run in accredited labs.

Implications

This source is high-value macroalgae occurrence evidence because it separates inorganic arsenic from total arsenic context and reports dry-weight species-level distributions for iAs, Cd, Pb, and tHg across Norwegian and imported seaweed materials. Oar weed, wireweed, sea oak, and hijiki should be treated as high-iAs species-specific context, while sugar kelp and winged kelp are the main cultivated Norwegian commercial species. The dry-weight basis should not be pooled with fresh or wet-weight seaweed rows without explicit basis conversion.

Wiki pages this source may touch

• seaweed-kelp-foods
• supplements-algae-seaweed-based
• seaweed
• arsenic-inorganic
• cadmium
• lead
• mercury-total
• selenium
• iron
• zinc

Verification notes

• Identity checks before writing found no existing source page for raw handle MFK_knowledgeupdateonmacroalgaefoodandfeedsafety2020, title text, or cite key duinker2020-macroalgae-food-feed-safety. The report has no DOI in the extracted text or PDF metadata; the publisher report page is recorded as the DOI fallback access URL.
• All Key numbers were rechecked against /tmp/hmi-seaweed-021.txt, extracted with pdftotext -layout. Tables 2-6 and the appendix were extractable; Table 7 was partially extractable but had some column wrapping, so only non-ambiguous Se/Fe/Zn entries are transcribed.
• Units and basis are preserved as mg/kg dry weight unless explicitly stated otherwise; the sugar-kelp basis example preserves both 410 mg/kg wet weight and 3650 mg/kg dry weight as printed.
• Speciation check: Table 2 is inorganic arsenic and is recorded as iAs. Mercury is reported as Hg/mercury only and is recorded as tHg; the report says methylmercury proportion seems low but does not provide a methylmercury concentration table, so no MeHg values are recorded.
• The report contains both primary IMR data and literature/project summaries. The concentration rows in Tables 2-8 and the sugar-kelp standardized trial summary are treated as the source’s own occurrence data; referenced literature and project background remain context.
• Brand firewall: the report describes species, production origin, and Norwegian/Asian source categories; no consumer brands are attached to contamination values.
• Missing-slug note: the taxonomy snapshot has no animal-feed or aquafeed seaweed row. Frontmatter routes the source to seaweed food and algae/seaweed supplement rows, while fish-feed and insect-larvae feed-chain context remains in prose only.

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.