Heavy Metals, Iodine, and Residues in Spirulina: What is Proven and What is Not

Key points in brief

Iodine warnings for algae products concern sea algae like Kombu or Nori, not the freshwater algae Spirulina.

Heavy metals and polycyclic aromatic hydrocarbons are a real, officially documented issue for dried imported goods.

However, the biggest documented risk is microcystins from foreign cyanobacteria that can enter open cultivation ponds.

Home cultivation significantly alters this risk profile, but does not eliminate it.

If you google "Spirulina," you'll end up at the consumer advice center, and that's a good thing

The consumer advice center did not rate Spirulina particularly favorably. We think that's right.

Any provider who ignores or tries to explain away this criticism becomes unbelievable. So, we'll go through it point by point, because that's the only way to give you an honest assessment. This article doesn't sugarcoat anything for you. It separates three things that are constantly confused online: iodine warnings, heavy metals and PAHs in dried imported goods, and the risk of contamination by foreign cyanobacteria. All three are real. However, they do not affect the same products, the same causes, or the same people.

No healing promises, no efficacy claims. It's solely about residues, quality, and what you, as a beginner, really need to know.

What Spirulina actually is, and why that is crucial for the risk question

Spirulina is not sea vegetable. It is a cyanobacterium, colloquially blue-green algae, that grows in strongly alkaline fresh water. This single sentence is more important than it sounds, because half the confusion about iodine hangs on it.

"Algae" is a biological collective term for very different organisms. Nori, Kombu, and Wakame are sea algae. They grow in saltwater and accumulate iodine from the seawater. Spirulina grows in freshwater, has little in common biologically with sea algae, and risks cannot simply be transferred from one group to another.

Iodine warnings concern sea algae

Consumer protection agencies have been warning for years about excessive iodine levels in dried sea algae. The Hamburg consumer advice center has comprehensively presented this in their article Eating algae? Pay attention to the iodine content . These warnings are justified. Kombu can reach iodine levels that, with regular consumption, far exceed the recommended maximum daily amount. The Federal Office for Consumer Protection and Food Safety also published information on elements and iodine in algae products in 2024.

Spirulina is not at the center of this. It grows in freshwater and is not considered a relevant source of iodine. Anyone who generally applies iodine warnings for algae products to Spirulina has overlooked the difference between two biologically completely different organisms. This is not a marketing statement, but simply biology. It's easy to remember: the iodine question belongs to sea algae, not the freshwater algae Spirulina.

Heavy metals and PAHs in dried imported goods

Here it gets serious, and we'll say it directly: heavy metals in spirulina are a real issue with dried imported goods.

Official food surveillance and consumer protection organizations have repeatedly found elevated cadmium and lead levels in algae products from the market during market checks. The consumer advice center has compiled the findings on environmental toxins in natural food supplements . These findings are real.

The cause is not in the algae itself. Spirulina absorbs what is in the water. In open facilities, often in regions with less stringent water quality control, the algae can absorb heavy metals from the cultivation medium. In addition, there are the invisible steps between harvesting and the shelf: drying, transport, storage, bottling. All points where contamination can be introduced.

PAHs, or polycyclic aromatic hydrocarbons, are a second issue. They arise when organic material comes into direct contact with smoke or exhaust gases during drying, and several of their compounds are considered mutagenic and carcinogenic. They have been repeatedly detected in algae-based food supplements. Maximum levels now apply in the EU.

This does not mean that every spirulina powder on the shelf is contaminated. Origin and production method are decisive, and precisely these are unknown for cheap imported goods without transparency.

The risk almost every provider conceals: Microcystins

The biggest documented risk with Spirulina is not heavy metals. It is microcystins.

We state this openly, even though we sell Spirulina, because it is the most honest reason to even think about origin. Microcystins are liver toxins produced by certain cyanobacteria such as Microcystis aeruginosa . Spirulina itself does not produce microcystins. The problem arises when foreign cyanobacteria are introduced into the culture and grow there unnoticed.

In open production ponds, this can never be completely ruled out. Wind, water, insects—anything can introduce foreign organisms. Consumer protection organizations regularly point out this risk of contamination for blue-green algae products.

This is no cause for panic. It is the reason why culture quality and cultivation conditions matter at all.

The four risks at a glance

Risk	Primarily affects	Cause	What home cultivation changes
Iodine	Sea algae like Kombu, Nori, Wakame	Accumulation from seawater	Doesn't affect Spirulina anyway
Heavy metals	Dried imported goods	Contaminated cultivation water, long supply chain	Water and nutrient salt are known and controllable
PAH	Dried goods	Drying with direct smoke or exhaust gas contact	It is not dried at all
Microcystins	Open cultivation ponds	Introduction of foreign cyanobacteria	Closed glass and tested culture reduce the risk, but do not eliminate it

What home cultivation changes, and what it doesn't

Quite a lot. But not everything, and anyone who claims otherwise is selling you a fairy tale.

A closed glass with a laboratory-tested culture, filled with tap water and a defined amount of nutrient salt, has a different risk profile than an open pond somewhere in the world. Heavy metal absorption depends directly on the cultivation medium. If you know what water and what nutrient salt are in the glass, there is no unknown supply chain in between. Our culture and nutrient salt are produced in Germany and go to the lab before they go to you. The nutrients naturally contained in fresh spirulina can be found on the Ingredients page.

Nevertheless, a home farm is not sterile. Foreign organisms can be introduced through air, hands, or equipment. Therefore, there are two concrete rules that we recommend to everyone. Perform a smell test with every harvest: Fresh spirulina smells slightly earthy, never rotten or moldy. The page Harvesting Spirulina correctly explains exactly what this test means. And set up a fresh, tested culture every three months. The Care subscription is designed precisely for this; a regular culture change significantly reduces the risk of creeping contamination.

We have extensively described the direct comparison between fresh home-grown and dried imported goods regarding the supply chain in the article Fresh Spirulina vs. Powder . If you want to go the DIY route, the MySpirulina Starter Kit contains everything needed for the first attempt.

Who Spirulina is not suitable for

People with phenylketonuria (PKU) should avoid spirulina. It contains phenylalanine, an amino acid that cannot be broken down in PKU.

Anyone suffering from an autoimmune disease should seek medical advice beforehand. The specialist literature discusses whether spirulina affects immune responses, and this can be undesirable in this situation. Pregnant and breastfeeding women should also consult a doctor if in doubt. Anyone taking medication that affects blood clotting, such as phenprocoumon or warfarin, should be aware that spirulina contains vitamin K and interactions are possible.

This article does not replace medical advice. When in doubt, consult a doctor.

Why our nutrient salt is declared as fertilizer

The nutrient salt is declared as NPK fertilizer in Germany. This sounds unpleasant at first glance. However, it is the legally correct classification.

The nutrient salt feeds the culture. It is not the food itself. The spirulina is harvested and eaten, not the salt. Nutrient salts for algae fall under fertilizer law because they provide nutrients to plant organisms, just like a plant fertilizer in the garden. We prefer to explain this openly rather than hope no one looks at the packaging. All information can be found on the Nutrient Salt page.

Recognizing Spirulina quality: what matters

Anyone looking to buy spirulina, whether as powder or for a home farm, should be able to ask a few questions.

Is the cultivation site known, and is it a closed or open system? Are laboratory tests for heavy metals, PAHs, and microcystins available and accessible? How long is the supply chain between harvest and use? For fresh home-grown produce, this question is irrelevant, but for imported powder, it is central. And is the culture regularly renewed, or has the same colony been growing uncontrolled for months?

These are not questions meant to disparage a particular supplier. These are the criteria by which quality can be measured.

Frequently asked questions

Is Spirulina contaminated with iodine? No, Spirulina is not considered a relevant source of iodine. The known iodine warnings concern dried sea algae such as Kombu, Nori, or Wakame, which accumulate iodine from seawater.

Are heavy metals in Spirulina a real problem? Yes, for dried imported goods. Authorities and consumer protection organizations have repeatedly found elevated cadmium and lead levels in algae products. The algae absorbs whatever is in the cultivation water.

What are microcystins? Liver toxins produced by certain cyanobacteria. Spirulina itself does not produce them. They become a problem when foreign cyanobacteria enter an open culture and grow there.

Is home-grown Spirulina free of contaminants? "Free of contaminants" is too strong a statement. A closed system with known water, known nutrient salt, and a tested starter culture significantly reduces the risk, but does not replace the smell test with every harvest.

Who should not eat Spirulina? People with phenylketonuria. For autoimmune diseases, during pregnancy and breastfeeding, and when taking anticoagulants, the question should be discussed with a doctor beforehand.

Conclusion

The criticism of Spirulina is justified, but it doesn't apply equally to everything. The iodine question belongs to sea algae. Heavy metals and PAHs are an issue of the long, invisible supply chain. Microcystins are an issue of open ponds.

By separating these three things, one can make an informed decision, whether buying, cultivating, or both.