Knowledge update on macroalgae food and feed safety

Overview

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 inorganic arsenic (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 cadmium (Cd), mercury (Hg), lead (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 total mercury (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.

Related evidence

• Seaweed/kelp foods (nori, wakame, kombu, dulse — as food products)
• Ingredient class — algae/seaweed-based
• Seaweed
• Arsenic, Inorganic
• Cadmium
• Lead
• Mercury, Total
• Selenium
• Iron
• Zinc

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.