Compost awareness week day three – is ink from printed cardboard toxic?

Filed in Blog by on May 6, 2009 18 Comments
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cardboard for compostI received the following question about compost: “If you compost all your cardboard-including stuff like cereal boxes with pictures and text, does the ink leach into the compost ?!

What a great question and one that many people worry about.

Lots of people use their shredded bank statements as fodder for the compost heap. It provides a great balance for some of the wetter ingredients like vegetable peelings and grass clippings and is the perfect way to prevent identity theft!

Newspapers are ok to shred and add to the compost, along with things like toilet roll inner and egg boxes.

Glossy paper, such as magazines are not recommended because they take too long to break down and can contain toxic inks. Other toxic inks come from metalicised or fluorescent products and it’s no good composting card that has a plastic coating on it as it won’t break down.

I think, unless we contact the manufacturers of cereal boxes and ask them direct about the toxicity of the inks, and then check out their answers with MSDS it’s a hard question to answer!

You might decide to go ahead and compost these products and use the compost around non-edible plants. If you’re a purist, however, and are worried about contaminating the ground, the best bet is to recycle such cardboard in your local recycling facility and use non-printed cardboard for your compost heap or wormery.

I’d love to hear everyone else’s thoughts on this as it’s quite a conundrum!

Yay or nay – should we compost cardboard with printed pictures and text such as cereal boxes?


About the Author ()

I am a long time supporter of the Green and Sustainable lifestyle. After being caught in the Boscastle floods in 2004, our family begun a journey to respect and promote the importance of Earth's fragile ecosystem, that focussed on reducing waste. Inspired by the beauty and resourcefulness of this wonderful planet, I have published numerous magazine articles on green issues and the author of four books.

Comments (18)

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  1. Compostwoman says:

    Paper and card is usually printed with fairly harmless inks now (in the UK at least) and I certainly don’t worry too much about that in my compost bins ( although I *do* have such a lot of compost that its all well diluted, anyway), as anything in there is well diluted and a lot of inks are ( I understand) vegetable based now, with the glossinesss being from clay particles. BUT I wouldn’t be composting very glossy magazines? They go to other people to read, first, and then in the recycling bin

    Am doing a series of posts on my blog at the moment about composting.

  2. Sarah says:

    I tend to use paper in the compost, loo rolls for planting and egg boxes are for eggs and only get composted when they finally fall apart after being passed round my friends with our hens eggs in!

    But the inks on stuff don;t bother me at all, the glossy finish on some card and paper does but only really because they’ll take forever to rot down as it doesn’t let the water in.

  3. Claire Brown says:

    I was asked this question at a compost special that I was an “expert” at a couple of years ago, – at the time I didn’t know the answer, so I found out from several printers and was assured that in the uk about 99% of inks used are water soluble and harmless, and the person I asked thought that the other 1% was probably on industrial packaging not anything to do with food, – I certainly compost as much cardboard as I can, and worms in my worm bin seem to love loo roll middles and cereal boxes

  4. John Costigane says:

    For composting, egg boxes, cardboard inner rolls and other similar cardboard are my main additions, Mrs Green. Other paper is occasionally used but most is recycled for pulping. Reduce aims to minimise this latter paper type.

  5. Graham says:

    I’ve read these comments. As a horticulturalist and retired science teacher, I think we are being complacent about some of the inks used for printing on cardboard, which individuals are recycling domestically.
    Manufacturers of some of the compost on sale in our garden centres, and local councils that are selling compost made from recycled cardboard, don’t seem to be aware that there is a possibility that this ‘green’ intention could be introducing carcinogenic components in the organic food that people like myself are trying to feed our familles with.
    i would avoid any recycled cardboard products, even unprinted cardboard is suspicious if you research the subject.

    • jackie says:

      Hi graham. Did you find any additional information regarding cardboard processing and its safety in the compost? I know its 2016 now so not sure if this thread will be active. Thanks

  6. Mrs Green says:

    @Graham: Graham, welcome to the site and thank you for taking the time to leave a comment.

    I’m very interested in your response and would like to know more.

    Do you have any links or information we could read up on? It’s interesting the the 5 comments all favour using printed cardboard, so I’m sure we would all love to gain more knowledge in order to make an informed choice.

  7. Environmental planner says:

    hello there,

    I have been doing some research into this composting thing particularly the composting of paper with ink. From everything that I have gathered from the internet it appears that we need to be careful with what we are composting because ink can have anything from heavy metals to petroleum based chemicals in them. I dont know about the UK but I am based in Barbados and we use postly HP porinter cartridges. I called HP and they referred me to their content page where they have all the various content of the ink, it is not looking good people check it out

    This story is bringing back memories of reading Rachael Carson’s book ‘Silent Spring’ you know the one that was published in the 1960’s and revealed to the US just how toxic our environment is. Well, this book was the impetus to the modern environmental revolution. I say let’s use the precautionary principle and recycle paper and cardboard from now on, we dont want to find out in a few years studies reveal that we were contaminating the environment and our own bodies with a seemingly environmentally friendly act.

    Hope this was helpful


  8. Poppy says:

    @Environmental planner:

    The very small amounts of printed matter that get into my compost bin, will not be a worry to me. Small receipts and the cocasional toilet roll tube, are unlikely to be causing any environmental disasters in my garden, but I guess if anyone is trying to bypass their council collections by putting everything into a compost bin that they then use for agricultural purposes, it could be something to be more aware of.

  9. Mrs Green says:

    @Environmental planner: Hi Lani, welcome to the site from Barbados! Great to see you and thank you for sharing that information – much of what I read is conflicting, but I guess HP would be a pretty reliable source.

  10. Michael says:

    I recycle all my cardboard. I caution putting most cardboard in a compost pile. any layered cardboard or tubes are held together with glues. The glues maybe toxic and can build up in the soil. At one time I would save my scrap wood in cardboard and burn the whole box in back yard fires in the fall. The cardboard make great kindling until I noticed the blues and greens coming from the cardboard as it burned. My educational guess is these colors came from the chemicals in the glue binding the cardboard. It’s not worth the risk. All my cardboard goes to the recycle bins now.

  11. Carl Smith says:

    Under European regulations, packaging can only be claimed as compostable and biodegradable when certified in accordance with the criteria of the European standard
    EN 134323
    In fact, the compostability of printed packaging largely depends on the properties of the substrate. Printing ink layers are very thin (1 to max. 5 µm) and account for only 0,5 to a maximum of 3% of the packaging by weight.
    Printed packaging may be certified as compostable under European standard EN 13432 when the following criteria are met:

    Each individual printed package must comply with the specified heavy metal (arsenic, lead, cadmium, chromium, copper, molybdenum, nickel, mercury, selenium, zinc) and fluorine limit values.

    However the specified values can be manipulated. It is calculated on % of the whole packaging weight.
    Where many manufactures are using thinner substrates to reduce cost and weight. It increases the substrate to ink ratio and thus can bring it in or out of specification for what is deemed compostable.

    Example: 50 g/m² biodegradable film, 1 g/m² ink grammage

    – solid print of 1 colour shade: the ink part is non compliant with EN 13432, as its share is approximately 2%;

    – 49 % ink coverage: the ink part is compliant with EN 13432, as its share remains < 1%

    – full-surface process print: the ink part is compliant with EN 13432, as the share of each colour is 0,5% and the sum of the four colours is 2%.

    The real solution is to replace many of the metal based pigments (based on copper and zinc for example) with less bright substitutes.

    My answer is based on white paper produced by Siegwerk.

  12. JimTumber says:

    I’m a career packaging buyer and for what it’s worth corrugated (the proper term for what some here are calling “cardboard”) is composed of wood pulp and corn starch. Corn starch is used as the glue. There are some glue additives that improve adhesion in moist conditions, and I don’t have the detail on what those additives are, but it’s not commonly used. As for inks, brown kraft corrugated is commonly fed to cows on farms, and so the brown box industry went over to vegetable-based (soy) inks decades ago. I should think that the rule of thumb here would be is the corrugated is brown and dull (not varnished to make it shiny), if it’s printed with just one or two colors, and if the product it was used to package wasn’t a damp product (like vegetables), it’s probably fine to compost or use as week control on your garden.

    • Mrs Green says:

      Hello Jim – thank you for sharing such a comprehensive response and adding value to the conversation 🙂

  13. Helen Butt says:

    Great to get the most up-to-date information from Jim and Carl.

    In 2010, I went to a recycling event run by Wakefield City Council. Their information clearly stated that it was fine to compost paper and cardboard – as far as I remember. That said, I don’t suppose these will have the same nutritive value as wood, so in terms of feeding your soil it is probably best to find other brown ingredients for the heap.

  14. Bo says:

    CONCLUSION: Painted cardboard/paper is fine in relative small amounts, but may take a while to breakdown, may contain “heavy metals” (many of which are trace minerals essential to life), and may contain some weird glues.

    Lesson 1: Don’t make your primary carbon source painted cardboard or paper (duh)… but adding SOME is likely fine.

    Also, if you compost “correctly” (center of pile ~140f), and you turn the compost frequently (like weekly) the hot temperature and hordes of bacteria should breakdown a ton of the unnatural molecules that may be carcinogenic.

    Nevermind that we eat the PLANTS, not the compost, and plants are selective in what they uptake vs leave in the soil… However, it IS possible for them to absorb certain “bad” heavy metals (eg some American grown rice has elevated arsenic from being grown in old tobacco fields).

    Also I’d expect the inks to be relatively safe and they’re painted very THIN, as mentioned above.

    “Arsenic, lead, cadmium, chromium, copper, molybdenum, nickel, mercury, selenium, zinc” …in paint? Half of those are ingredients in my synthetic fertilizers (good for plants)!

    The other half are nasty (lead, mercury) … I hope to God those are forbidden in painted consumer products in America by now. If they aren’t, it’s probably in trace amounts. Ever eaten seafood? Heavy metal city, baby.

    TLDR: IMO, painted cardboard/paper is totally fine in relative small amounts (but NOT as your primary carbon source).

    Thanks for the article and contributions in the comments to help me arrive at this answer.

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