Natural Sources:

1. Plants: There are various plants which are poisonous and deter herbivores from consuming them. Examples: Allium spp that contains thiosulphate is poisonous to cats, dogs if given in high dosage. Similarly, tall fescue has alkaloid which is generally toxic to animals.
2. Animals: Poisonous animals are numerous in the globe, it includes reptiles mainly. They produce poisons for their self protection which can be deadly for other animals. Examples: spiders, scorpions, toads, etc.
3. Microorganisms: This includes fungi, bacteria which produce toxic substances. The toxin produced by fungi is mycotoxin while that of bacteria is bacteriotoxin. Examples: aflatoxin produced by two species of Aspergillus, is commonest mycotoxin, can produce carcinogenic reactions in animals body when eaten. Microbial toxins like Botulinum neurotoxins promote infection and disease by directly damaging host tissues and by disabling the immune system.
4. Minerals: Minerals are the vial source of toxin. It’s toxicity is the concentration in the body of any mineralsnecessary for life is abnormally high, and has an adverse effect on health. There are minerals which are toxic in nature normally as well like; asbestos, silica, etc.