This webpage is maintained by the Centers for Disease Control and Prevention (CDC). The webpage provides information and resources on Paraquat. "Paraquat is a toxic chemical that is widely used as an herbicide (plant killer), primarily for weed and grass control. [...] In the United States, paraquat is available primarily as a liquid in various strengths. It is classified as 'restricted use,' which means that it can be used only by people who are licensed applicators. [...] Because paraquat is highly poisonous, the form of it that is marketed in the United States has a blue dye to keep it from being confused with beverages such as coffee, a sharp odor to serve as a warning, and an added agent to cause vomiting if someone drinks it. Paraquat from outside the United States may not have these safeguards added."
Centers for Disease Control and Prevention: http://www.cdc.gov/