Is zeolite carcinogenic? What does science actually say?
You may have read somewhere that ‘zeolite powder is carcinogenic’. It’s a perfectly reasonable concern — and the answer lies in just one word: which zeolite. Because dozens of different minerals are grouped under the same name, each behaving completely differently within the body.
Where did the concern originate?
On Greek gardening websites and in readers’ comments, the claim that ‘zeolites for spraying are carcinogenic’ circulates from time to time. The claim is not entirely unfounded — it simply confuses two completely different minerals. There is indeed a type of zeolite that the World Health Organisation classifies as carcinogenic to humans. However, it is not the one you apply to plants or animals, or take for detoxification. Let’s sort them out one by one, based on official scientific data.
There is no ‘single’ zeolite — there are over 40
The word ‘zeolite’ does not describe a single material, but an entire family of clay-silicate minerals. In nature, there are over 40 different types of natural zeolite, the most common being clinoptilolite. The crucial point is that these minerals not only have different chemical compositions — they also have radically different crystal morphologies. Most natural zeolites are non-fibrous; but a few, such as erionite, can form fine fibres. And it is precisely this morphology — not the fact that it is a ‘zeolite’ — that determines whether a mineral is hazardous to the lungs.
Van Gosen et al., Frontiers in Chemistry
(2022) — ‘Global geological occurrence and character of the carcinogenic zeolite mineral, erionite’ (describes the family of natural zeolites).[1]
Erionite: the zeolite that is indeed carcinogenic
Erionite is a rare natural zeolite with a fibrous, asbestiform structure — that is, it forms long, thin fibres, similar to those of asbestos. When these fibres become airborne and are inhaled, they penetrate deep into the lungs, causing chronic inflammation and, in the long term, mesothelioma (an aggressive form of cancer of the pleura). The World Health Organisation’s International Agency for Research on Cancer (IARC) classifies it as Group 1 — carcinogenic to humans. Scientific reviews even consider it to be more potent than the six regulated types of asbestos.
The story behind this classification originates in Cappadocia, Turkey: in three villages built on erionite rock, herionite is believed to be responsible for over 50 per cent of deaths among the population, whilst in a neighbouring control village with no exposure, no such cases were recorded. This is precisely where the confusion arose: the equation ‘zeolite = cancer’ applies only to this specific, rare, fibrous mineral.
clinoptilolite: why it is a completely different case
The zeolite used in agriculture, livestock farming, aquariums, the home and as a medical detoxification product is almost always clinoptilolite — a non-fibrous mineral with platy, non-asbestiform crystals. It does not form the long, respirable fibres that make erionite dangerous, and therefore does not behave like asbestos in the lungs.
The IARC — the same organisation that classified erionite as Group 1 — assessed clinoptilolite and the other non-fibrous zeolites separately and classified them as Group 3: ‘not classifiable as to carcinogenicity to humans’. In experiments on rats exposed to clinoptilolite in respirable particle size, no significant increase in tumours was found. Put simply: the same organisation places the two minerals in two completely different categories.
Erionite → Group 1 (carcinogenic). Clinoptilolite
(the one you buy) → Group 3 (unclassifiable, insufficient evidence of carcinogenicity).
And what about ‘crystalline silica’? Why zeolites are not quartz
There is also a second, equally common misconception — this time not about fibres, but about chemistry: ‘zeolite is crystalline silica; it contains 75–80 per cent of it, so it causes silicosis and lung cancer’. Here, too, however, two completely different things are being confused.
clinoptilolite is an aluminosilicate mineral: the silicon is bound within a stable crystalline lattice of SiO₄ and AlO₄ tetrahedra, together with exchangeable ions (sodium, potassium, calcium). It is not pure, free silicon dioxide. Rather, ‘crystalline silica’ in the toxicological sense — which the IARC classifies as a Group 1 carcinogen and which causes silicosis — refers to the free crystalline forms of SiO₂: quartz, cristobalite and tridymite. zeolites are none of these.
And what about the ‘75–80 per cent’? It is, at best, a measurement of total silicon as oxide (SiO₂) in a chemical analysis — that is, it includes all the bound silicon in the lattice, not just any free quartz. Free quartz in natural clinoptilolite is merely an impurity; and the clinoptilolite authorised by the EFSA is explicitly defined as ‘free of fibres and quartz’. Silicosis is caused by the inhalation of free, respirable quartz — not by the bound silica in the zeolite lattice.
This is clearly evident in the product documentation itself: in the material data sheet (MDS) for Thracian zeolite, the XRF chemical analysis gives SiO₂ 71.6% — explicitly ‘as oxide, for reference purposes’. This refers to the total, bound silica in the framework, not to free quartz — and it is precisely the figure that is misleadingly presented as ‘75–80 per cent crystalline silicon’. Furthermore, in a repeated-dose study (product SDS, §11) the lungs showed no signs of fibrosis or connective tissue growth — that is, not even the onset of the silicosis mechanism.
Crystalline silica (quartz) = free
SiO₂, a Group 1 carcinogen. Clinoptilolite
= an aluminosilicate mineral with silicon bound
within the lattice — a different mineral, not quartz.
IARC Monographs Vol. 68 — zeolites are clay-silicate minerals, a separate category from crystalline silica;[5]
OSHA — ‘crystalline silica’ = quartz/christobalite/tridymite ·[13]
EFSA (2025) — ‘free of fibres and quartz’ ·[8]
MDS for Thracian zeolite — XRF SiO₂ 71.6% ‘as oxide’ ·[15]
SDS §11 — no fibrosis of the lungs.[14]
Institutional recognition of safety
Beyond the IARC classification, pure clinoptilolite has undergone safety assessments by leading regulatory authorities:
| Body | Assessment |
|---|---|
| EFSA (European Food Safety Authority) | clinoptilolite of sedimentary origin is an authorised feed additive for all animals and has been deemed safe for animals, consumers and the environment. |
| FDA (USA) | clinoptilolite, of sedimentary origin, is recognised as GRAS (Generally Recognised As Safe), specifically as an anti-caking agent in animal feed (up to ~1% of the ration) — this does not constitute general authorisation as a food additive for human consumption. |
| CE / Medical Devices | The detoxification zeolite (e.g. Zeolith MED®) is marketed as a certified medical device (CE 0477). |
| REACH — Product SDS | The Safety Data Sheet for Thracian zeolite (Regulation 1907/2006) explicitly classifies it as ‘not classified as hazardous’ — with no carcinogenicity or STOT labelling, and no requirement for a chemical safety assessment. |
It is worth noting a significant finding by the EFSA: there is no evidence that clinoptilolite breaks down as it passes through the digestive system — in other words, it acts as an inert mineral and is excreted, which explains why consumers are not exposed to it via animal products.
Why purity and origin matter so much
This is the most crucial — and often overlooked — point. Because erionite belongs to the same family of minerals, natural clinoptilolite may theoretically contain traces of erionite as a geological impurity, depending on the deposit. This is why certified provenance and purity testing are not merely a marketing gimmick, but a vital safety issue.
A reliable supplier knows their deposit and can document the product’s composition through analyses (e.g. X-ray diffraction / XRD and scanning electron microscopy / SEM), which would reveal any fibrous impurities. (Thracian zeolite, according to its technical data sheet, is identified petrographically and mineralogically using XRD.) In the context of animal feed, in fact, the EFSA itself defines approved clinoptilolite as a product that must be ‘free of fibres and quartz’ — free from fibres and quartz. In other words: the safety criterion is not ‘zeolite or not’, but ‘certified, non-fibrous, high-purity clinoptilolite or an unidentified mineral of unknown origin’.
Always look for a product with a stated clinoptilolite content (e.g. ≥85 per cent), a clear origin and available compositional analyses. Certified Thracian zeolite
is available with a high, documented purity of clinoptilolite.
The sensible precaution that applies to any fine dust
The fact that clinoptilolite is not carcinogenic does not mean that it is safe to inhale its dust — just as you would not want to inhale a cloud of flour, cement or any other fine-grained mineral dust.
The Safety Data Sheet (SDS) for Thracian zeolite is clear: the product is not classified as hazardous, it is not a skin sensitiser (Buehler / OECD 406 tests) and, in a repeated-dose study, it did not cause pulmonary fibrosis. Nevertheless, as it is a fine mineral powder, the SDS itself recommends — quite sensibly — a P2-filtered dust mask, safety goggles and basic hygiene measures when dust is generated. Some precautionary assessments (e.g. EFSA 2025, for a specific feed additive) go a step further and recommend respiratory protection, considering the dust to be a potential sensitiser. The practical conclusion is the same in both cases: with any fine-particle dust, wear a mask — this is common sense in occupational health and safety, not an indication of carcinogenicity.
When dusting in dry conditions (fields, stables, plant pots), wear a dust mask and avoid stirring up clouds of dust in enclosed spaces. For foliar application to plants, the correct choice is a ready-to-use paste formulation, specifically designed for foliar application (such as ZeTe
): it mixes with water without forming dust and forms a protective mineral film on the foliage (providing sun protection and mechanical repellency against insects). For edible use, the zeolite
is always taken dissolved in water, so the issue of inhalation does not arise.
See the guide ‘Which zeolite should you choose?
’ or use the Dosage Guides
.
Frequently Asked Questions
Is zeolitethe the same as asbestos?
No. Asbestos and zeolite are different minerals. Only one type of zeolite — the rare, fibrous erionite — has an asbestos-like structure and is carcinogenic. clinoptilolite, which is used in zeolite products, is non-fibrous and is classified by the IARC as Group 3.
Does zeolite contain ‘crystalline silica’? Does it cause silicosis?
No. clinoptilolite is an aluminosilicate mineral, in which the silica is bound within the crystal lattice — it is not free crystalline silica (quartz). Silicosis and the associated cancer risk stem from the inhalation of free, respirable quartz (quartz/cristobalite/tridymite), which the IARC classifies as Group 1 — not from zeolite. The ‘75–80 per cent’ often cited actually refers to the total SiO₂ content as an oxide in XRF analysis (e.g. 71.6 per cent in our technical data sheet) — bound, not free quartz. The EFSA-approved clinoptilolite is, in fact, explicitly defined as being free from fibres and quartz.
Can I safely spray zeolite onto my plants?
Yes. clinoptilolite is not carcinogenic. For foliar application, the best option is a specialised paste formulation (such as ZeTe): it mixes easily with water without leaving a powdery residue and forms a protective mineral film on the leaves, providing sun protection and mechanical repellency against insects. It remains good practice to apply a mask whenever there is dry dust.
Is edible detoxifying zeolite safe?
zeolite MED® for detoxification is a certified medical device (CE 0477) made from 100% natural clinoptilolite. It is taken dissolved in water. For dosage, contraindications and interactions with medicines, please refer to the detailed Instructions for Use of MED® Zeolite.
How do I know that the zeolite I am buying does not contain erionite?
Choose a product with a certified origin and a stated clinoptilolite content. clinoptilolite, as approved by the EFSA, is explicitly defined as free from fibres and quartz, and its composition is documented by analyses such as XRD and SEM.
Certified Greek clinoptilolite
High-purity natural Thracian zeolite, with clear provenance and documentation — for agriculture, livestock farming, the home and detoxification.
Related articles
📚 Scientific sources
- Van Gosen, B. et al. (2022). Global geological occurrence and character of the carcinogenic zeolite mineral, erionite: A review. Frontiers in Chemistry / PMC. pmc.ncbi.nlm.nih.gov/articles/PMC9715606
- IARC Monographs Vol. 100C — Erionite (Group 1 — carcinogenic to humans). NCBI Bookshelf. ncbi.nlm.nih.gov/books/NBK304368
- Annals of Work Exposures and Health (2025). Environmental and occupational exposure to erionite and related health risks. Oxford Academic. academic.oup.com/annweh/article/69/7/677
- U.S. National Toxicology Program. Erionite — 15th Report on Carcinogens (villages in Cappadocia & control village). NCBI Bookshelf. ncbi.nlm.nih.gov/books/NBK590941
- IARC Monographs Vol. 68 (1997). Zeolites other than Erionite (clinoptilolite… Group 3). inchem.org/documents/iarc/vol68/zeol.html
- IARC — List of Group 3 agents (Zeolites other than erionite). IARC Group 3 List
- EFSA FEEDAP Panel (2013). Scientific Opinion on the safety and efficacy of clinoptilolite of sedimentary origin for all animal species. EFSA Journal 11(1):3039. efsa.europa.eu/en/efsajournal/pub/3039
- EFSA FEEDAP Panel (2025). Renewal of authorisation of clinoptilolite of sedimentary origin (ZEOCEM, a.s.). EFSA Journal 23(4):e9364 — definition of ‘free of fibres and quartz’, classification as a sensitiser and recommendation of protective measures. doi.org/10.2903/j.efsa.2025.9364
- Zeolife.gr — What is zeolite? (origin and purity of Thracian clinoptilolite). Zeolife.gr/what-is-zeolite
- U.S. FDA — GRAS Notice Inventory. Sedimentary clinoptilolite is recognised as GRAS as an anti-caking agent in animal feed — not as a food additive for human consumption. fda.gov/grasnoticeinventory
- Zeolife.gr — CE Certification 0477 / medical devices. Zeolife.gr
- Cosmetic Ingredient Review (2022). Amended Safety Assessment of Zeolites as Used in Cosmetics — natural zeolites may contain erionite. cir-safety.org
- OSHA — Crystalline Silica (Quartz, Cristobalite, Tridymite). Occupational Safety and Health Administration — definition of ‘crystalline silica’. osha.gov/chemicaldata/278
- Safety Data Sheet (SDS) ‘Thracean Zeolite – Thracian Zeolite’, Avgi Ltd — in accordance with Regulation (EC) No 1907/2006 (REACH). §2.1 not classified as hazardous; §8 recommendation for a P2 mask; §11 toxicological properties (non-sensitiser, no fibrogenicity). thraceanzeolite.gr
- Material Data Sheet ‘Thracean Zeolite®’, Avgi Ltd — §3 chemical analysis by XRF (SiO₂ 71.6% as oxide), mineralogical identification by XRD. thraceanzeolite.gr
This article is for information purposes only and is based on published scientific and regulatory data, as well as the product’s official documents (SDS/MDS). It is not a substitute for medical or agricultural advice. For use in people with underlying health conditions or who are taking other medication, consult a doctor.