What does toxicity mean?

Toxicity refers to the degree of damage that a toxic substance can do to an organism as a whole or to a particular part of the organism.

Every substance has a certain toxicity, even seemingly innocuous substances such as water and oxygen. However, the toxicity of each substance is not constant between species. The toxicity of any one substance varies significantly from one species to another. This is because every species reacts to different toxins differently. For example, sulfur is beneficial to certain organisms living at the bottom of the ocean bed but is hazardous and even fatal to human beings. 

When damage occurs in an organism through a single exposure or short-term exposure, it is known as acute toxicity. Chronic toxicity occurs due to repeated or continuous exposure over an extended period of time.