Spirulina and microcystins.

What microcystins are

Microcystins are a family of hepatotoxic cyclic peptides produced by certain cyanobacteria — primarily Microcystis aeruginosa, Anabaena, and related species. These organisms are not spirulina (Arthrospira platensis), but they can grow alongside spirulina in open-pond production conditions, contaminating the batch.

When consumed, microcystins are absorbed from the gut and concentrate in the liver, where they inhibit protein phosphatases (PP1 and PP2A) — enzymes critical for normal cell function. Acute exposure causes hepatocellular damage and, at high doses, liver failure. Chronic low-dose exposure is associated with increased liver cancer risk (classified as a Group 2B possible carcinogen by IARC).

Microcystins are heat-stable — cooking does not destroy them. They are also not destroyed by stomach acid alone. Once ingested, they act.

Why open-pond spirulina is the primary risk

Spirulina for human consumption is produced in two primary systems:

• Open raceway ponds: Large, shallow outdoor ponds exposed to the environment. High-volume, lower cost. Vulnerable to contamination by wind-borne cyanobacteria spores and other organisms. This is where microcystin-producing species can establish and compete with spirulina.
• Closed photobioreactors: Enclosed systems with controlled environments. Much lower contamination risk. Higher cost and lower volume. Most premium European producers use closed or semi-closed systems.

Open-pond spirulina is not inherently unsafe — many open-pond operations maintain rigorous monitoring. But the risk is production-system dependent, and open-pond products from producers without regular microcystin testing should be viewed with caution.

Regulatory limits for microcystins in spirulina

Regulatory limits vary by country:

• EU: No specific EU-wide limit for microcystins in spirulina supplements as of 2024. Some member states apply general EFSA guidance.
• USA: No specific FDA limit for dried spirulina products. The WHO drinking water guideline of 1 µg/L for microcystin-LR is used as a reference point.
• Industry standard:Most quality producers target not detectable or <1 µg/g total microcystins in dried product. High-quality products test at <0.1 µg/g or below detection limits.

How to verify your product

The same CoA approach that applies to heavy metals applies to microcystins:

1. Batch-specific CoA from an accredited laboratory— not a general product certificate
2. The CoA should specify “total microcystins” or individual microcystin variants (MC-LR, MC-RR, MC-YR) — all variants should be tested, not just MC-LR
3. Results should show “not detected” or values below 1 µg/g at the instrument’s detection limit
4. The testing method should be ELISA or HPLC-MS/MS — both are established methods for microcystin detection in algae products

If a producer’s CoA does not include microcystin testing, ask for it specifically. A reputable producer should have this data.

Real-world contamination: what the literature shows

Several analyses of commercial spirulina products have found microcystin contamination:

• A 2014 study analysed 13 spirulina products sold in health food stores in several countries — 4 out of 13 contained detectable microcystins above 1 µg/g (Gallo et al.). The contaminated products were from producers without published testing data.
• Multiple survey studies have found that contamination rates are significantly higher in low-cost bulk spirulina products from producers with no published CoA data.
• Products from producers with established quality programs consistently test at not detected levels.

The conclusion: microcystin contamination is a real quality-tier issue, not a theoretical one. It is the primary reason that “all spirulina is the same” is incorrect and potentially harmful as a purchasing philosophy.

Closed systems and microcystin risk

Spirulina produced in fully enclosed photobioreactors or indoor controlled facilities has essentially zero microcystin risk — contaminating organisms cannot enter. Most premium European and Japanese producers use such systems. For buyers primarily concerned about this risk, choosing products from closed-system producers is the most reliable mitigation.

For the full overview of production systems, see open pond vs closed system spirulina.