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I was reading about the dangers of introducing pathogens in a compost pile. As you know, some moulds can be toxic. So I am curious if the normal household mould that appears in the kitchen or the refridgerator is something I should be concerned about.

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Moulds help break down organic matter. They are part of a good compost heap and there is no reason why food with moulds cannot be placed on your heap. However, your heap can become too mouldy but that is usually the result of the heap being too wet and/or containing to much nitrogen. It is true that moulds can be toxic, so you should not let your pets eat any compost heap material.

Once the decomposition process is done, the moulds will be gone and the risk of pathogens is very small. This is due to a number of things:

  • during the composting process the temperature in the heap rises, killing most of the pathogens
  • other micro-organisms will kill and eat pathogens
  • in time the pathogens will die by natural causes

To reduce the risk of pathogens even further you can:

  • make sure you have the correct C:N balance, the correct moisture balance and enough air in your heap. This is all to ensure the heap reaches a good temperature.
  • turn and mix your heap regularly so stuff on the edges of the heap (where it is less warm) are also heated.
  • don't throw cat and dog feces on the heap (see also this answer)
  • What are the “natural causes” of which pathogens die? It is sort of ambiguous, because one can consider “other micro-organisms” as a natural cause. – theUg Mar 1 '13 at 15:31
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    Extremes of temperature (especially by pasteurization), availability of water, untenable environmental PH, and just plain waiting to long for a new host to sustain the reproductive cycle. – OCDtech Mar 1 '13 at 17:16
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    @THelper: The problem are not only pathogens (as infectious living microorganisms) but also toxins - particularly mycotoxins. It seems that some mycotoxins can be difficult to decompose. By quick itnernet search I have found this abstract of an article Stability of mycotoxins during food processing. – pabouk Aug 26 '13 at 16:38
  • @pabouk Mycotoxins are toxins produced by fungi and fungi are also pathogens. I'm not sure how the article you are referring to is relevant here. The mycotoxins in processed food most likely come from fungi on the ingredients and the article describes that not all mycotoxins are destroyed during food processing. This doesn't seem to have any direct link to fungi in compost. – THelper Aug 27 '13 at 11:04
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    @THelper: The article is relevant to the problem I am referring to: stability of mycotoxins. Since I have found only texts related to food I linked at least the abstract above which reminds us that because not all mycotoxins are destroyed during food processing it is also highly probable that not all mycotoxins are destroyed in compost. – pabouk Aug 27 '13 at 13:16
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The concern about adding pathogens to a compost pile mostly overstated. The normal biological action of composting reduces but does not eliminate pathogens in the compost, and the fact is that a lot of things which we compost are potentially hazardous foods. I suppose if you want to be particularly paranoid you could avoid throwing things like cooked veggies into the compost heap. Aside from very high pathogen sources (like manure), composting is believed to cause great reduction in pathogen concentration, to safe levels.

See Pathogens and Public Health Concerns with Composting by Chris Cronin (PDF, via Vermont Waste Management Division).

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    Not all manure is high is pathogens – user141 Feb 15 '13 at 14:46

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