Cardboard - The Good, The Bad, and the Permie.

I saw in another thread a discussion about cardboard usage as mulch and it being a potential vector for toxic gick.

I decided to create a thread to start compiling my own thoughts, knowledge, 'research', as well as other peoples input. I however decided to put it into the Cider Press because I want the freedom to dive into all things nasty and icky. I have experience in the paper manufacturing world in many roles but I do not wish to misrepresent myself as an expert in the field. I feel that I have an understanding of the processes and nuances that might confuse people outside of the industry.

What inspired me was this article - https://gardenprofessors.com/cardboard-does-not-belong-on-your-soil-period/ (Shoutout to Mary Lotito for posting it!)

The study that is referenced in the article. - https://www.sciencedirect.com/science/article/pii/S0048969723030620?via%3Dihub

My first question was WHAT constituted 'cardboard' in this study. The opening sentence states "Some types of poultry bedding made from recycled materials have been reported to contain environmental contaminants"

Farther in the article, it discusses the process of making animal bedding from " “clean” solid softwood and hardwood, packaging waste, scrap pallets, packing cases etc. and is expected to use untreated wood." It is mentioned however that to decided this, the common practice is a visual inspection. This means this could be a vector for contaminants to enter. They then go into talking about shredded corrugated board having properties that could be advantageous to poultry bedding (Low dust, high absorbency).

One worry however with this recycled corrugated poultry bedding is, as mentioned before, the source material. "Recycled paper and card materials can contain flame retardants and perfluorinated alkyl substances (PFAS) that were originally part of the printing and labelling material or a grease-repellent coating." We take recycling to be a good thing, but what we are recycling into bedding/mulch is critical to pay attention to.

Cardboard is one of the highest recycled materials in the USA with an alleged rate of 93% in 2022. - https://www.afandpa.org/news/2023/us-paper-and-cardboard-recycling-rates-continue-hold-strong-2022

Lets look now towards one of the most common sources of cardboard for the modern person.

Amazon



This video shows how amazon boxes are made utilizing two different weight kraft board from Georgia Pacific. They are nice big spools that get placed together to make the boxes but it doesn't state what it is made of. I mean it is cardboard right! Lets dive a little deeper.

Lets go right to the source.



This is a corporate piece, so keep that in mind but the key here is they utilize a mixture of virgin pulp and recycled pulps. This means that if the paper that goes into the vats is contaminated, a significant amount of 'contaminated' cardboard can be produced and sent who knows where.

All of this put together shows me there is a risk of unintended contamination utilizing cardboard that has higher rates of recycled material put back into it compared to a 'virgin' pulp made board. Unfortunately, utilizing virgin pulp 100% is not profitable and probably near impossible to find.

I have sheet mulched... I probably still will sheet mulch in specific circumstances but it brings to mind that sometimes following the bandwagon could bite people in the rear is due diligence isn't done.

Potential Alternatives

You say "But Tim, I really want a smother layer that cardboard provided but I don't want all the extra gick. What could I use?"



The product that I now utilize is uncoated natural (unbleached) virgin kraft paper. Not recycled kraft paper. It is available in numerous widths on rolls of various yardages.

By going with unbleached kraft, you are avoiding Chlorine, Chlorine Dioxide, and other bleaching agents that could persist.

The tricky thing is A. sourcing and B. affordability.

I'm a lucky duck and I can get my hands on it for a low price/free locally but that might not be the case for everyone.

I keep some big cardboard boxes dry and flat in storage and occasionally use them in my garden.

One is for late freeze protection. In my climate, the spring is short and erratic, it may stay balmy for a month and suddenly get hit by late snow. At that time, if my strawberries are blooming or potatoes are already emerged, I would tried to protect them. Otherwise, the plant will waste energy and time to regrow and the hot summer is coming quickly. Although I can use wool or fleece blanket, cardboard sheets provide insulation over a large area without worrying about them getting dirty.

Another way I use cardboard is for slug control. I mulch my garden beds with plant debris in the winter and slugs lay eggs in insides. They will munch my spring crops down if let unattended. I cover the whole bed with cardboard at night and the slugs will crawl onto the underside due to condensation of water vapor. The lightweight of cardboard makes it possible to go on top of a plant without damaging it.

In either case, the cardboard is not in contact with soil and only be used briefly. I think it's benefits outweigh the possible harm in these cases.

My first question is what is considered to be contamination?   ….and at what levels?   I recently heard a person freak out about lead in her water.   The problem is that the levels of lead in the report she received were actually lower than what is naturally occurring.   Should we be careful? Of course.  But we need to weed out deliberately alarming statements designed to get hits.  As a news executive once told me … all news is entertainment.

Thank you for starting this topic Timothy.
As John points out sometimes the poison is in the dose, but in the case of PFAs, as far as I can tell, these do not break down and are not naturally occurring, so there is no base line level to reference against. Once introduced they may be in your soil forever. I'm not quite sure about this however, because in at least one online reference I found (UK HSE they talked about 'half lives', but in the timescale of 8 years or so (and that means half of it still remains...) From that reference "some PFAS are detectable in most groundwater, surface water bodies and biota in England" (and in many other parts of the world). There was lots of scary stuff in that report and it did make me think a bit.
Although in most countries PFAs are unlikely to be in virgin paper products they remain in the recycling stream, albeit (hopefully) in ever decreasing concentrations. So unless your cardboard has been made from virgin materials, in a country that has succeeded in eliminating addition of PFAs in paper products, then I think there is a risk that you could be adding this in small amounts to your soil.
It's mainly the worry of it accumulating over time that has made me rethink whether to use cardboard in the garden or not. A one off application of a sheet mulch is one thing, but routinely adding it to my compost heap is now something I prefer not to do.
The nice thing about sheet cardboard is that it is a good light excluding mulch, and is pretty good at knocking back easy weeds in one season. However persistent perennials like dock and creeping thistle will still punch their way through and weed seeds also will then have a bare soil to germinate in. Either a much thicker organic mulch like woodchip, spoilt hay or compost is required, or what I've taken to is digging and inverting the soil for a new bed. In my case my soil is very compacted, so I believe digging is actually beneficial for me as a one off remedial exercise.
I've been given some nice sawdust/wood shavings by a local joiner to add the carbon rich 'browns' for my compost, and our used paper/cardboard now goes back into the recycling stream wherever possible.
We do use some card and newspapers for fire starting, and I'd like to reduce this use also to a minimum, so as to be more comfortable with spreading the fire ash onto my growing beds. Unfortunately my husband is rather fond of this 'free fuel' and will actually burn quite a bit in our other stove.....how to break him of the habit?
Toilet paper is also a concern for me. We have our own septic system, so I feel quite strongly that what I put in our system will leach out into our local environment, river and sea loch. Toilet paper was also found to be a source of PFAs (Guardian article). I was unable to read the original paper they referred to online, but did find the supporting information here. I'm hoping to make my own toilet cloths soon, which will almost eliminate my toilet paper use; saves a bit of money too!

Nancy Reading wrote:We do use some card and newspapers for fire starting, and I'd like to reduce this use also to a minimum, so as to be more comfortable with spreading the fire ash onto my growing beds. Unfortunately my husband is rather fond of this 'free fuel' and will actually burn quite a bit in our other stove.....how to break him of the habit?

Is it clearly established that PFAS remains in the ash of an object after it is burned? Is any of it released with the escaping gases?

Coydon Wallham wrote:Is it clearly established that PFAS remains in the ash of an object after it is burned? Is any of it released with the escaping gases?

To be honest I can't quite remember now. I have a feeling that I read that burning spread the contamination (that the pfas were not destroyed in a normal fire) but more research is still going on on ways to reduce the pfa content of contaminated materials. My suspicion is that burning it will probably just spread it wider in the environment :(

Intense heat is required to break down PFAS 'completely', partial burning will break down PFAS into other contaminates that persist in the ash. (Related study) I question how long and how hot it would take because some PFAS are found in firefighting foams utilized for a variety of uncontrolled fires which are meant to NOT break down.

I recently read about PFAS (and other similar compound) soil contamination being in higher concentrations around refuse incinerators which operate at high temperatures so I assume we are still grappling with our own knowledge of how to handle it still.

Good discussion!  Just wanted to plug using leaves instead of cardboard.  Right now I have all I can use and my transfer station has a mountain of them.  

Timothy Norton wrote:Intense heat is required to break down PFAS 'completely', partial burning will break down PFAS into other contaminates that persist in the ash. (Related study) I question how long and how hot it would take because some PFAS are found in firefighting foams utilized for a variety of uncontrolled fires which are meant to NOT break down.

I recently read about PFAS (and other similar compound) soil contamination being in higher concentrations around refuse incinerators which operate at high temperatures so I assume we are still grappling with our own knowledge of how to handle it still.

Ack, that linked paper reminded me of the report I'd recently read on how the Chem Corporations lobbied to have natural wool regulated out of the firefighting industry back in the 70s, along with similar actions across the board. Served as a good reminder to look at my immediate environment and think about the smartphone I've been using too much lately. Wonder if that magical fingerprint free screen has anything to do with PFAS? I'm thinking something like that might make cardboard levels look like trace amounts by comparison for a selective tech abuser like myself (not to diminish the impact on someone who has otherwise been able to steer clear of such gick)...

Timothy Norton wrote:Intense heat is required to break down PFAS 'completely', partial burning will break down PFAS into other contaminates that persist in the ash. (Related study) I question how long and how hot it would take because some PFAS are found in firefighting foams utilized for a variety of uncontrolled fires which are meant to NOT break down.

I recently read about PFAS (and other similar compound) soil contamination being in higher concentrations around refuse incinerators which operate at high temperatures so I assume we are still grappling with our own knowledge of how to handle it still.

I posted this in another thread on PFAS around here, but at a recent event with a speaker from the DNR specializing in PFAS contamination in groundwater, he responded to my question about burning PFAS to claim that they are completely broken down in a fire that exceeds 1200*F.

I would think a house or forest fire might not exceed that temperature, at least not throughout the blaze. I would think that an incinerator is exceeding it though.

I also was told that thankfully PFAS is not supposed to be a concern with crossing the skin barrier, so cell phone screens would seem to be a minor concern (although fingernail cuticles present an unusual situation). Ingestion and inhalation would appear to be the primary areas to focus on.