>>/37287/
> I'm not talking about the effects of the toxins themselves
I am talking about the effects of the toxins themselves. 
> so even if humans feel that they're not getting poisoned
So 0,0000000000000000000000000000000000000000000001 g is exactly as harmful as 1 g of lead? Lead poisoning is not a "feeling", it is objective, observable damage. So is the damage plants suffer from disease. If it isn't exactly as harmful, then the same applies to the toxic fumes.