Paraquat and Diquat are compounds of the bipyridinium group that serve as strong contact herbicides. Their effect sets in after just a very short time, since they are absorbed by the surface of the plants very quickly. The mode of action inhibits photosynthesis in the effected plants. Their cell membrane becomes porous and it loses water, leading the plant to dry up in sunny conditions within just a few hours. Whereas diquat has proven to be particularly effective in killing potato haulm before the harvest, paraquat is mainly used in warm, humid climates as an herbicide against broad-leaved plants and grasses. Since paraquat does not penetrate the bark of trees or the shells of nuts, it is used to combat weeds in orchards and vineyards, as well as on coffee, tea, cocoa, oil palm, nut, and banana plantations.
Both substances are extremely poisonous and improper usage can lead to death. For example, paraquat has led to several lethal cases of poisoning, because it used to come on the market as a reddish-brown, odorless solution, which could be confused for cola beverages or red wine. Nowadays it is mixed with a substance that releases a pungent odor as well as a fast-acting emetic agent. The United States EPA has even classified paraquat as being potentially carcinogenic. Due to their adverse health effects, the use of paraquat as a pesticide was banned in the European Union starting in 2007, followed by diquat in 2019. The maximum residue levels for both substances are listed in the Regulation (EC) No 396/2005.
The GBA Group routinely carries out the analysis of paraquat and diquat in various food matrices (e.g. fruit, vegetables, chia seeds, and more) using LC-MS/MS technology. If you have any questions we are gladly available to answer them.