A toxicant is any toxic substance. In popular usage, the term is often used to denote substances made by humans or introduced into the environment by human activity, in contrast to toxins, which are toxicants produced naturally by a living organism. Toxicants are poisonous.
There are numerous types of toxicant.
Biocides include many toxicants specifically developed to fight pests.
Toxins are naturally produced toxicants, often as part of a metabolic process or similar.