Toxicity in compost

I was asked by some workers in Myanmar the following question. “Is there any material we should NOT compost due to toxicity”? And I replied cautiously that as long as the pile is allowed to reach adequate temperatures that is not a significant concern. Obviously, the fecal matter of carnivores like us humans is a concern for healthy composting and I suppose one would like to limit the inputs of walnut leaves or juglone containing species. For the community: Is there any all encompassing answer that you might give to such a query especially in the tropics. Thanks much.

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Jeff, regarding the human waste dimension, we use a composting toilet on our campus. The solids and the liquid do not mix. The urine goes into buckets and is used each few days in making bokashi…which I recently described that process in another thread on Organic Fertilizer. After 30 days, the bokashi is spread on the fields.

The solids go into a closed dry chamber with saw dust. It takes about 6 months for the chamber to fill. Once the chamber is full, we use a different chamber for the toilet and allow the full chamber to compost for approximately 6 months before it is spread onto the fields. At the end of the 6 months, the contents have the appearance of compost without any sign of feces or toilet paper or saw dust remaining. During the 6 month composting time, we keep it moist and add some of the same micro-oganisms I described in the bokashi thread. We have been doing this now for about 15 yrs w/o a problem.

So, in this respect, we are using human waste in compost.

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Normally I use a compost pit for my composting. All biodegradable material, green or dry is dumped into this pit without any order.
However, there are rules that I observe;

  1. Pit is under shade
  2. Always ensure material is moist
  3. During hot season cover the pit
  4. During rainy season cover the pit
  5. Turn once a month

The idea is to mimick the forest environment as much as possible.
I saw it working for my mother and it is working for me.
"If it works, why change it?

AFHGlen and Harun_Ndagwe, thank you.
I understand about the bacteria in carnivore feces and about the composting toilet. Also, seeds from pernicious weeds may be composted so long as the temperature rises to 75 Celsius or so. The question I was asked is about other toxins which might be in vegetable matter such as we consider in cassava or walnut… Is there any plant material that is not advisable to compost - which does not break down in the microbial heat environment? I had never thought of this question, so thank you again.


Hi Jeff,

Questions of toxicity in compost are really interesting considerations! As you mentioned, you want to be cautious about including human or some animals’ fecal matter for various reasons.

Secondary metabolites are different from species to species and some varieties can even have less or more (eg. sweet vs. bitter cassava vary in concentration of cyanogenic glycosides). Most secondary metabolites are for pest defense (cyanogenic glycosides in chaya and cassava) and are not readily taken up by other plants from the soil. So you don’t have to worry about using cassava or chaya in compost.

Some plant materials (e.g. walnut roots and leaves) form secondary metabolites that are allelopathic compounds that will go into your compost and take time to dissipate. Allelopathic compounds suppress plant growth in one or more modes of action such as inhibited germination or stunted growth. The rate of dissipation depends on the chemical/compound as well as your environmental factors (how much water goes into the compost pile, temperature, etc.). Some recommendations have come out of research for common cover crops that are known to have allelopathic compounds such as sunn hemp (Crotalaria juncea), but these trials are in-field situations, not in compost.

With the aging process that goes into the creation of hot or cold compost, most allelopathic compounds are likely to dissipate within that time frame (3 weeks - 6 months). Things that are more stable and take longer to break down are antibiotics, fats and grease, or bones. Another thing I would be wary of is using residues from any sort of bioremediation whether intentionally done or not.

I’d be happy to research specific crops if there are ones you are concerned specifically about.


Stacey- I am OK with a simple answer to share with those new to composting such as, vegetable matter of most types will likely break down to a healthy level by the end of a normal composting batch time. Unless there is some reason to fret about the majority of compostable material, “go for it”. Variations in amounts and species should keep any issues at a minimum, is what I take from your good reply. So far I have not gotten any further input from the Myanmar practitioners so lets call it good for now. I appreciate your reply!

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