Seaweed, kelp and sea moss comparison: heavy metals, iodine and price per day (UK + EU)
In short: Of the six seaweed products we list, three kelp iodine capsules are lab verified (VitaMoment, naturalie and edubily, all from German shops, all within EU heavy-metal limits). The lowest measured lead and cadmium are in VitaMoment Jod. The only sea moss we list, Mighton’s gel (UK), has a partial report. For seaweed, iodine dose matters as much as metals: four of the five kelp products declare 150 µg or more per day, above BfR’s 100 µg advice.
6 seaweed products with a recent independent lab report; 3 are lab verified with numeric heavy-metal results for a named batch, re-opened by us on 26 Oct 2026.
The other 3 are labelled “Partial report”: two certificates state that the batch passed without giving values, and one sea moss gel report has values but no batch number.
Five are kelp iodine capsules from EU sellers in Germany and Spain (Sunday Natural also has a UK shop); one is a fresh sea moss gel from a UK seller.
Prices were checked on 26 Oct 2026 and price per day is calculated at the label dose; € and £ are never mixed or converted. Iodine dose matters as much as metals with seaweed: see the iodine table below.
Iodine measured at 218 µg per capsule, 45% above the 150 µg on the label and more than twice the 100 µg per daily dose Germany’s BfR recommends for supplements.
Total arsenic 7.6 mg/kg (inorganic arsenic, the more toxic form, 0.44 mg/kg).
The sample was sent in by the brand: check the batch number on your pack.
Iodine per capsule is above the 100 µg per daily dose that Germany’s BfR recommends as the maximum for supplements (150 µg in pregnancy and breastfeeding); ask a doctor or pharmacist first if you have a thyroid condition.
Total arsenic 36 mg/kg, the highest in this list (inorganic arsenic only 0.090 mg/kg).
Report dated 31 Jul 2025 (about 15 months old) and iodine was not measured.
The sample was sent in by the brand: check the batch number on your pack.
pack: £9.99 / 300 ml (500 ml £14.99), plus £4.99 chilled postage (seen 26 Oct 2026). No daily serving is stated, so we can’t calculate a daily cost. UK seller; no EU seller found.
No batch number on the certificate, and all four metal tests are marked as subcontracted outside the lab’s UKAS accreditation (the brand’s page describes the testing as accredited).
Cadmium 0.72 mg/kg and total arsenic 5.78 mg/kg; arsenic was not split into inorganic and organic forms, so the brand’s statement that it is mostly harmless organic arsenic is not shown by this report.
No iodine result and no daily serving on the label page.
Pass/fail certificate only: it states compliance with EU limits but gives no measured values, so we list it as a partial report.
Iodine per capsule is above the 100 µg per daily dose that Germany’s BfR recommends as the maximum for supplements (150 µg in pregnancy and breastfeeding); ask a doctor or pharmacist first if you have a thyroid condition.
The sample was sent in by the brand: check the batch number on your pack.
Heavy-metal colours:0.01 Well under the EU limit (below half) or below detection▲1.6 Near the EU limit (half the limit up to the limit)■3.2 Over the EU limit0.30 Grey: no EU limit (arsenic), not tested, or the lab’s reporting limit is above the EU limitEU 2023/915 limits for food supplements: lead (Pb) 3.0, cadmium (Cd) 1.0, mercury (Hg) 0.10 mg/kg. Values in mg/kg. NT = not tested; c = calculated by us from µg per serving.
Pb = lead, Cd = cadmium, Hg = mercury, As = arsenic, all in mg/kg. “<” means below the lab’s detection limit. Pass* = certificate states compliance without a figure. — = no data. Label match = the lab measured the active content against the label. The lab name, full notes and per-serving details are on each product page.
Pb0.074 (well under the EU limit or below detection)Cd0.12 (well under the EU limit or below detection)Hg<0.010 (well under the EU limit or below detection)As7.6 (no EU limit)
Label match
Yes
Fillers
None
Form & serving
Capsules
1 capsule a day = 150 µg iodine declared (100% NRV)
Price per daily dose
€0.17/day(EU)
calculated: €19.97 ÷ 120 · 1 capsule a day · price incl. VAT, excl. shipping
Iodine measured at 218 µg per capsule, 45% above the 150 µg on the label and more than twice the 100 µg per daily dose Germany’s BfR recommends for supplements.
Total arsenic 7.6 mg/kg (inorganic arsenic, the more toxic form, 0.44 mg/kg).
The sample was sent in by the brand: check the batch number on your pack.
Pb0.11 (well under the EU limit or below detection)Cd0.29 (well under the EU limit or below detection)Hg0.014 (well under the EU limit or below detection)As36 (no EU limit)
Label match
Unknown
Fillers
—
Form & serving
Capsules (screw-top glass jar)
1 capsule a day = 200 µg iodine declared
Price per daily dose
€0.13/day(EU)
calculated: €22.99 ÷ 180 · 1 capsule a day · price incl. VAT, excl. shipping
Iodine per capsule is above the 100 µg per daily dose that Germany’s BfR recommends as the maximum for supplements (150 µg in pregnancy and breastfeeding); ask a doctor or pharmacist first if you have a thyroid condition.
Total arsenic 36 mg/kg, the highest in this list (inorganic arsenic only 0.090 mg/kg).
Report dated 31 Jul 2025 (about 15 months old) and iodine was not measured.
The sample was sent in by the brand: check the batch number on your pack.
Pb0.07 (well under the EU limit or below detection)Cd▲0.72 (near the EU limit)Hg0.01 (well under the EU limit or below detection)As5.78 (no EU limit)
Label match
Unknown
Fillers
None
Form & serving
Gel (fresh, refrigerated jar)
Price per daily dose
—
pack: £9.99 / 300 ml (500 ml £14.99), plus £4.99 chilled postage (seen 26 Oct 2026). No daily serving is stated, so we can’t calculate a daily cost. UK seller; no EU seller found.
No batch number on the certificate, and all four metal tests are marked as subcontracted outside the lab’s UKAS accreditation (the brand’s page describes the testing as accredited).
Cadmium 0.72 mg/kg and total arsenic 5.78 mg/kg; arsenic was not split into inorganic and organic forms, so the brand’s statement that it is mostly harmless organic arsenic is not shown by this report.
No iodine result and no daily serving on the label page.
PbPass* (certificate states compliance, no figure)CdPass* (certificate states compliance, no figure)HgPass* (certificate states compliance, no figure)AsPass* (certificate states compliance, no figure)
Label match
Unknown
Fillers
Yes (see product page)
Form & serving
Capsules
1 capsule a day = 150 µg iodine declared
Price per daily dose
€0.066/day(EU)
calculated: €23.99 ÷ 365 · 1 capsule a day · price incl. VAT, excl. shipping
PbPass* (certificate states compliance, no figure)CdPass* (certificate states compliance, no figure)HgPass* (certificate states compliance, no figure)AsTested† (tested, but the certificate gives no figure or verdict)
Label match
Unknown
Fillers
None
Form & serving
Capsules
1 capsule a day = 250 µg iodine declared (167% NRV)
Price per daily dose
€0.11/day(EU)
calculated: €12.90 ÷ 120 · 1 capsule a day · price incl. VAT, excl. shipping
Pass/fail certificate only: it states compliance with EU limits but gives no measured values, so we list it as a partial report.
Iodine per capsule is above the 100 µg per daily dose that Germany’s BfR recommends as the maximum for supplements (150 µg in pregnancy and breastfeeding); ask a doctor or pharmacist first if you have a thyroid condition.
The sample was sent in by the brand: check the batch number on your pack.
Heavy-metal colours:0.01 Well under the EU limit (below half) or below detection▲1.6 Near the EU limit (half the limit up to the limit)■3.2 Over the EU limit0.30 Grey: no EU limit (arsenic), not tested, or the lab’s reporting limit is above the EU limitEU 2023/915 limits for food supplements: lead (Pb) 3.0, cadmium (Cd) 1.0, mercury (Hg) 0.10 mg/kg. Values in mg/kg. NT = not tested; c = calculated by us from µg per serving.
EU 2023/915 limits for food supplements: lead 3.0, cadmium 1.0, mercury 0.10 mg/kg; for supplements made of at least 80% dried seaweed the cadmium limit is 3.0 mg/kg, which is the limit some labs applied here. There is no EU limit for arsenic in supplements. Seaweed often has high total arsenic, mostly in organic forms; inorganic arsenic is the more toxic form, so we show it where the report measured it. “Pass (no value)” means the certificate states compliance without a figure; “Tested†” means the certificate lists the test but gives no figure or verdict. We make no health claims for seaweed or sea moss. Prices can change.
Iodine per daily dose
Iodine is the main reason to take kelp, and also the main risk. The EU reference intake (NRV) is 150 µg a day. Germany’s Federal Institute for Risk Assessment (BfR) recommends no more than 100 µg per daily dose in supplements (150 µg in pregnancy and breastfeeding), and the EU tolerable upper intake for adults is 600 µg a day from all sources. Declared values are from the label; measured values only where the batch report measured iodine.
Not measured; no iodine or daily serving on the label page
Not medical advice. Testing status can’t be bought; seller links may be affiliate links (see disclosure). Disclosure
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About Seaweed
What it is
Brown seaweeds such as kelp (Laminaria species) and knotted wrack (Ascophyllum nodosum, often sold as “Norwegian kelp”), dried and sold in capsules mainly as a natural source of iodine; and sea moss (Irish moss or gold sea moss, red seaweeds), usually sold as a gel.
Common forms
Capsules of dried seaweed powder standardised to an iodine dose, or fresh sea moss gel in a refrigerated jar.
Typical label doses
Kelp capsules in our directory declare 100–250 µg iodine per daily capsule. The sea moss gel we list states no daily serving.
Note
Seaweed concentrates iodine and can take up cadmium, lead and arsenic from seawater. Iodine varies hugely between seaweeds and batches, so a measured iodine value matters as much as the metals. Germany’s BfR recommends no more than 100 µg iodine per daily dose in supplements (150 µg in pregnancy and breastfeeding). If you have a thyroid condition, are pregnant or take thyroid medicine, ask a doctor or pharmacist before taking iodine supplements.
Seaweed and sea moss have no authorised EU or GB health claims of their own. Iodine has authorised claims, but they only apply to products that provide at least 15% of the iodine reference intake per daily portion, so we don’t repeat them on these comparison pages and we make no benefit claims for sea moss.
Information only, not medical advice. Food supplements are not intended to diagnose, treat, cure or prevent any disease. Speak to a healthcare professional before use, especially if pregnant or on medication.
FAQ
Do kelp supplements contain heavy metals?
Yes, in small amounts: seaweed takes up lead, cadmium, mercury and arsenic from seawater. In the three lab-verified kelp capsules we list, measured lead was 0.074–0.14 mg/kg and cadmium 0.12–0.79 mg/kg, all within the EU 2023/915 supplement limits (lead 3.0, cadmium 1.0, or 3.0 for supplements of at least 80% dried seaweed, mercury 0.10 mg/kg).
Is there a lab-tested sea moss in the UK?
Only one in our directory: Mighton’s Plain Sea Moss Gel (UK), with measured lead, cadmium, mercury and total arsenic (Aug 2026). It is a “Partial report”: no batch number, metal tests subcontracted outside the lab’s UKAS scope, and no iodine result.
Which seaweed supplement has the least iodine?
edubily Iod Kapseln declares 100 µg per capsule, the only one within BfR’s 100 µg advice. Others declare 150–250 µg. Only VitaMoment’s report measured iodine: 218 µg against 150 µg declared.
Where are spirulina and chlorella?
They are microalgae, not seaweed, and are compared on the spirulina and chlorella (greens) page.
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