Q. Is paraquat poisonous to people? With which substances can paraquat be compared?

A. Like many readily available chemicals, paraquat is harmful and fatalities have occurred when the concentrated product has been swallowed in sufficient quantity, usually in an attempt to commit suicide. The label for products containing paraquat states that the product should always be kept in its original container and never stored in food, drink, or other containers. Products containing paraquat should also be locked away when not in use. According to the FAO specification paraquat technical material as well as SL and SG formulations must contain an effective emetic at minimum levels. These materials may also include colorants and olfactory alerting agents. Syngenta’s paraquat products comply with the FAO specification most recently updated in 2003 and 2008. Syngenta has added the three 'safening' agents into all of its SL (soluble concentrate) paraquat formulations to avoid accidental ingestion and to deter misuse: A blue dye to avoid confusion with beverages, an olfactory alerting agent (a strong and deterring odor), and an emetic to induce vomiting after ingestion. It is widely believed that these developments have contributed to a reduction in accidents. The WHO International Program for Chemical Safety classification system of pesticides classifies over 500 chemicals.
Class Number of AIs
“Extremely hazardous, class Ia”   29
“Highly hazardous, class Ib”   61
“Moderately hazardous, class II” 123
“Slightly hazardous, class III” 122
“Unlikely to present acute hazard” 246
Paraquat is classified as “moderately hazardous” (WHO class II) along with more than 100 other AIs. Information about the full classification system is available here.