What is the classification criterion for toxic substances?

The classification criterion for toxic substances primarily hinges on their ability to cause harm to humans or the environment through exposure. This includes any potential adverse effects that can arise from contact, inhalation, or ingestion of these substances. The definition encompasses a wide range of chemicals and materials, recognizing not only those that are acutely toxic but also those that may be harmful over longer periods or at lower concentrations.

Although regulatory bodies like the Environmental Protection Agency (EPA) do oversee many toxic substances, not all toxins are listed under specific regulations, and some may not be under EPA control yet remain harmful. The ability to detect toxicity through strong odors can be misleading, as many toxic substances have no smell at all, and their danger cannot be determined solely by olfactory signals. Additionally, toxicity is not exclusively dependent on the quantity of a substance; even small amounts can be hazardous depending on the substance and the type of exposure. Thus, recognizing the ability of a substance to pose harm is fundamental in classifying it as toxic.