Includes the chemical elements and chemical compounds.

Persistent Bioaccumulative Toxic (PBT) Chemicals
Chemicals that are toxic, linger in the environment, and bioaccumulate in living organisms.

PCBs and dioxins are just two examples.

Active ingredient
The meaning varies depending on how a chemical is used and which agency is regulating it.

FDA — An ingredient in a drug or cosmetic that causes the intended pharmacological effect.

EPA — An ingredient in a pesticide that prevents, destroys, repels, mitigates, desiccates, defoliates, or regulates the growth of a target organism as defined in FIFRA 7USC136(a).

Household hard surface cleaners also fall under the pesticide category.

"Other" ingredient
Any ingredient not already defined as "active" for the product's particular use. Not to be confused with the common definition of "inert" (chemically inactive) or "harmless".

EPA defines inert as "any ingredient in the product that is not pesticidally active".

FDA defines inert as "any ingredient in the product that is not pharmacologically active".

Under EPA and FDA jargon, something "inert" can still be quite active and even hazardous.

Food additive
Any substance that is intentionally added to food.

Substances whose use meets the definition of a pesticide, a dietary ingredient of a dietary supplement, a color additive, a new animal drug, or a substance approved for such use prior to September 6, 1958, are excluded from the definition of food additive.

Synergistic toxicity
Two or more toxics acting together in such a way that the total effect is greater than if each one acted alone.