Heavy metals, iodine, and residues in Spirulina: What is proven, and what is not

The essentials in brief

Iodine warnings for algae products concern marine algae such as kombu or nori, not the freshwater alga Spirulina.

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

However, the greatest proven risk is microcystins from foreign cyanobacteria that can enter open cultivation tanks.

Home cultivation significantly changes this risk profile, but does not reduce it to zero.

When you Google "Spirulina," you end up at the consumer advice center, and that’s a good thing

The consumer advice center (Verbraucherzentrale) has not rated Spirulina very favorably. We think that is correct.

Any provider who ignores or explains away this criticism makes themselves untrustworthy. So we will go through it, point by point, because that is the only way to provide you with an honest assessment. This article doesn’t sugarcoat anything. It separates three things that are constantly being mixed up 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 concern the same products, the same causes, or the same people.

No health promises, no efficacy claims. This is solely about residues, quality, and what you really need to know as a beginner.

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

Spirulina is not a sea vegetable. It is a cyanobacterium, colloquially a blue-green alga, that grows in highly alkaline freshwater. This one sentence is more important than it sounds because it is the source of half the confusion surrounding iodine.

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

Iodine warnings concern marine algae

Consumer protection agencies have been warning about excessive iodine levels in dried marine algae for years. The Hamburg Consumer Advice Center detailed this in their article Eating algae? Pay attention to iodine content. These warnings are justified. Kombu can reach iodine levels that exceed the recommended daily maximum by many times over with regular consumption. The Federal Office of Consumer Protection and Food Safety also published information in 2024 regarding elements and iodine in algae products.

Spirulina is not the focus here. It grows in freshwater and is not considered a relevant source of iodine. Anyone who applies iodine warnings for algae products across the board to Spirulina has overlooked the difference between two biologically completely different organisms. This is not a marketing statement, but simply biology. It is easy to remember: the question of iodine belongs to marine algae, not the freshwater alga Spirulina.

Heavy metals and PAHs in dried imported goods

This is where it gets serious, and we will say it directly: heavy metals in Spirulina are a real issue with dried imported goods.

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

The cause does not lie in the alga itself. Spirulina absorbs what is in the water. In open facilities, often in regions with less stringent water quality control, the alga can absorb heavy metals from the cultivation medium. Added to this are the invisible steps between harvest and shelf: drying, transport, storage, and filling. All points where contamination can be introduced.

PAHs, or polycyclic aromatic hydrocarbons, are a second issue. They are formed when organic material comes into direct contact with smoke or exhaust gases during drying, and several compounds are considered mutagenic and carcinogenic. They have been repeatedly detected in dietary supplements made from algae. Maximum limits now apply in the EU.

That does not mean that every Spirulina powder on the shelf is contaminated. Origin and production method are the deciding factors, and precisely those are what you don't know with cheap imported goods lacking transparency.

The risk that almost every provider hides: microcystins

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

We say this openly, even though we sell Spirulina, because it is the most honest reason to think about origin in the first place. 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 tanks, 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 reason 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	Marine algae such as kombu, nori, wakame	Accumulation from seawater	Does not affect Spirulina anyway
Heavy metals	Dried imported goods	Contaminated cultivation water, long supply chain	Water and nutrient salt are known and controllable
PAHs	Dried goods	Drying with direct contact to smoke or exhaust	It is not dried at all
Microcystins	Open cultivation tanks	Introduction of foreign cyanobacteria	Closed glass and tested culture lower the risk, but do not rule it out

What home cultivation changes about this, and what it does not

Some things. But not everything, and anyone claiming otherwise is selling you a fairy tale.

A closed glass with a lab-tested culture, filled with tap water and a defined amount of nutrient salt, has a different risk profile than an open tank somewhere in the world. Heavy metal uptake depends directly on the cultivation medium. Anyone who knows what water and nutrient salt are in the glass does not have an unknown supply chain in between. Our culture and nutrient salt are created in Germany and go to the lab before reaching you. The nutrients that fresh Spirulina naturally contains can be found on the Ingredients page.

A home farm is still not sterile. Foreign organisms can be introduced through air, hands, or equipment. That is why there are two concrete rules we recommend to everyone. Perform the smell test with every harvest: Fresh Spirulina smells slightly earthy, never rotten or musty. The Harvesting Spirulina correctly page explains exactly what this test means. And start a fresh, tested culture every three months. The Care Subscription is designed for exactly this; a regular change of culture significantly lowers the risk of creeping contamination.

We have written out the direct comparison between fresh home harvest and dried imported goods regarding the supply chain in detail in the article Fresh Spirulina vs. Powder. Anyone who wants to start their own journey will find everything necessary for the first batch in the MySpirulina Starter Kit.

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 cases of PKU.

Anyone suffering from an autoimmune disease should seek medical advice first. The professional literature discusses whether Spirulina influences immune reactions, and this can be undesirable in this situation. Pregnant and breastfeeding women should also clarify with 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 that interactions are possible.

This article does not replace medical advice. When in doubt, ask 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 read. However, it is the legally correct classification.

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

Recognizing Spirulina quality: what matters

Anyone wanting to buy Spirulina, whether as powder or as a home farm, should be able to ask a few questions.

Is the place of cultivation known, and is it a closed or open system? Are there laboratory tests for heavy metals, PAHs, and microcystins that are accessible? How long is the supply chain between harvest and use? With fresh home harvest, this question is irrelevant; with imported powder, it is central. And is the culture regularly renewed, or has the same colony been growing uncontrollably for months?

These are not questions intended to disparage a specific provider. 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 marine algae such as kombu, nori, or wakame, which accumulate iodine from seawater.

Are heavy metals in Spirulina a real problem? For dried imported goods, yes. Authorities and consumer protection organizations have repeatedly found elevated cadmium and lead levels in algae products. The alga absorbs what 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 along with it.

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

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

Conclusion

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

Anyone who keeps these three things separate can make an informed decision, regardless of whether they are buying, growing, or both.