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I'm new to indoor farming and I was wondering:

Is it safe to use Perlite in the soil or should I stick to more natural organic materials like pumice or gritty gravel?

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    I guess you don't have a cat? – Johannes_B Feb 10 at 10:45
  • No I dont need a cat for indoor farming – techpuffin Feb 10 at 11:30
  • Kitty litter is often just perlite. I wouldn't recommend to get a deep breath, but it is safe. Use some common sense though. – Johannes_B Feb 10 at 15:21
  • Kitty litter is never perlite. It is some times diatomaceous earth or calcined clay like Turface, but never perlite. It would never work. It's too lightweight it would be all over the cats feet and all over the house. It not absorbent enough. – GardenGems Feb 11 at 7:00
  • what would be wrong with it being on the cats feet? – techpuffin Feb 11 at 11:50
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I am a manufacturer of perlite and vermiculite. Perlite is very safe to use. Little known facts. Perlite is used to replace microbeads in lotions and soaps because it's a natural product and will not harm the environment like plastic beads. It's also used as a mild abrasive in toothpaste and safe to ingest. Yes, perlite is used as kitty litter and is highly adsorbent. Also it's Food Chemical codex approved as an absorbent is food packaging plants. Perlite is also used for water and air filtration on an industrial level. As with any dust avoid inhaling it and wear a dust mask.

https://www.perlite.org/wp-content/uploads/2018/03/health-effects-perlite.pdf

https://www.perlite.org/wp-content/uploads/2018/03/perlite-wheel.pdf

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Perlite is fine to use in soil at home - all it is is expanded volcanic 'glass'. It's been mined like other natural organic materials, then expanded by heat for horticultural use, see here https://sciencing.com/perlite-5402928.html. It would be sensible to wear a dust mask if you're taking it out of the bag indoors (in its dry state, in other words), but only because there's usually a fair amount of dust in the bag, not because the dust from it is particularly noxious when compared with other dusts, such as an excessive amount of household dust, or dust from fresh cat litter.

The only reason you might choose not to use it is because you don't want a substance that retains moisture in the soil for particular plants. or you need a gritty soil, in which case, horticultural grit would be a better choice.

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As with almost any substance used in industry, the manufacturer will provide a 'material safety data sheet' or MSDS. One such sheet found via search engine 'perlite MSDS' is available at http://www.schundler.com/Perlite%20SDS%202015%20Final.pdf which lists the following possible issues:

Inhalation: Pre-existing upper respiratory and lung disease may be aggravated. Acute inhalation can cause dryness of the nasal passage and lung congestion, coughing and general throat irritation. Chronic inhalation of dust should be avoided.

Eye: May cause irritation (tear formation and redness) if dust gets in eyes.

Skin: Not absorbed by the skin. But may cause dryness if prolonged exposure.

Ingestion: Ingestion of small to moderate quantities is not considered harmful, but may cause irritation of the mouth, throat and stomach.

Whether you consider a product with these characteristics safe or not is a value judgement on your part and not something that a stranger on the internet can answer for you, but personally I fill my pots outdoors as the dust is a nuisance and I do not consider it a hazard when left alone. I'm not breathing in the dust every day (or at all if I can help it), so there is no chronic exposure to the dust.

According to that sheet, perlite has <1% crystalline silicates and inhaling crystalline silicates can cause silicosis, but there is no evidence of a link between perlite itself and silicosis. Another manufactures' MSDS (https://edibleculture.co.uk/wp-content/uploads/2019/08/Expanded-Perlite-MSDS.pdf) has similar characteristics.

4.2 Most important symptoms and effects, both acute and delayed

Non-toxic. No evidence of causing pneumoconiosis or silicosis. Can cause irritation of throat if contact is prolonged. In some operations, may cause skin dryness or abrasion.

Comparing with a similar sheet for pumice (http://www.praannaturals.com/downloads/msds/MSDS_Pumice_Powder.pdf) which states it has <0.1% crystalline silica as opposed to the <1% in the perlite hazard sheet, you then have to work out how much dust each creates with your processing and how 'chronic' i.e. long term your exposure to dust in the air will be, and whether having less of a substance that can cause cancer in chronic dose but has not been shown to in these materials is something you're bothered about.

Also note that MSDS cover everything the manufacturer is aware of, hence they mention silicosis despite there being no evidence of it, and you also get sections like

It has been shown that prolonged contact with acids particularly at elevated temperatures does affect expanded Perlite, also direct contact with Ammonium Bifluoride and Hydrofluoric acids must be avoided

So don't use it to clean up your pet alien's blood.

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  • Very informative. MSDS/SDS are important document to learn about what you are using on a daily basis. They are made for employers to share with their employees handling that product. There is no obligation to create Safety Sheets nuisance or irritant products. That is something some companies voluntarily contribute to public. – GardenGems Feb 10 at 21:17
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It's impossible to work with perlite without making clouds of fine dust. I use it indoors but I try to be very careful how I pour it out of the bag. Once it's mixed with soil or wet the dust isn't an issue but particulate matter like that can cause lung issues maybe even cancer.

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  • It's best to keep a sensible perspective - the dust from perlite is no more likely to cause cancer than the dust you may be exposed to when emptying out your vacuum cleaner. Sensible precautions should be taken when carrying out both these procedures... and bear in mind, there is always risk in life - opening and using a bag of potting soil in a small, enclosed space may expose you to Legionnaire's disease, for instance - its possible, but not highly likely. – Bamboo Feb 10 at 12:37
  • I have seen a lot of people asking about the dust from perlite other places online so I thought that's what they meant by safe to use indoors. The dust is really really fine and makes a cloud when it's removed dry from the container. That's the only unsafe thing I could think of. – Youthful_Will Feb 10 at 12:59
  • I know how dusty it can be, I've used it myself many times - but I always wear a dust mask and rubber gloves, just like I do when emptying the vacuum or taking potting soil from the bag in my enclosed garage... there's nothing specially risky about perlite dust is what I'm saying. – Bamboo Feb 10 at 13:27
  • If you want to completely eliminate the dust, wet it down before you use it. Poke a few holes in the bottom of the bag and one the side. Pour water through the top (over the sink or outdoors). The water will wash away lots of the small dust and the rest causes no problem when wet. – GardenGems Feb 10 at 21:10

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