Contaminant (noun)

1. A substance that makes something impure or unclean.
2. A substance that pollutes the environment.

Origin:

Mid 17th century: from latin contaminant- "polluting", from the verb contaminare, from con- "together with" + taminare "pollute".

Examples:

1. The water was found to contain high levels of contaminants.
2. The soil was contaminated with hazardous waste.
3. The air was filled with contaminants that can cause health problems.
4. The factory was emitting contaminants into the atmosphere.
5. The product was recalled due to the presence of contaminants.