Anonymous asks: "Would like to know if you can get sulphuric acid poisoning from rotting onions? Had a bag of onions in my cupboard for months and they had rotted now all I can smell is onions. Really strong at times. "
A few bits to this:
Firstly, sulphuric acid is not volatile, so you cannot smell it. Heat it sufficiently and you will get sulphur trioxide fumes which you can definitely smell but I am talking 400degC, somewhat warmer that the average cupboard.
Secondly, it is corrosive rather than toxic.
But on to the onions. When things rot, all manner of compounds are formed and released. What compound and what level will be dependent on onion type and the organisms associated with the rotting. Onions contain a lot of sulphur so the breakdown products will be smelly. Unpleasant but not necessarily harmful.
Chuck them out and air the cupboard. There is not much else you can do.
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