Paraquat

Paraquat is a toxic chemical that is widely used as an herbicide (plant killer), primarily for weed and grass control. Paraquat is one of the most widely used herbicides in the world. It has had a tarnished reputation because of its acute oral toxicity and ill-health associated with operators - particularly in the plantation sectors of many developing countries.

Paraquat is produced synthetically. There are no known natural sources. Paraquat is part of the bipyridinium derivative group. Two technical products are manufactured: 1,1'-dimethyl-4,4'-bipyridinium dichloride and 1,1'-dimethyl-4,4'-bipyridinium dimethyl sulphate. The product is synthesised from pyridine, by treatment with sodium in liquid ammonia, followed by oxidation to form 4,4'-bipyridine, and subsequent methylation.

Paraquat is used to control broad-leaved weeds and grasses, being less effective on deep rooted plants such as dandelions. It does not harm mature bark, and is thus widely used for weed control in fruit orchards and plantation crops, including coffee, cocoa, coconut, oil palms, rubber, bananas, vines, olives and tea, ornamental trees and shrubs and in forestry. Other uses include weed control in alfalfa, onion, leeks, sugar beet, asparagus. It is used for weed control on non-crop land and can be used as a defoliant for cotton and hops before harvesting. Paraquat is used as a desiccant for pineapples, sugar cane, soya beans and sunflower. In pineapples, for example, paraquat is applied after harvest to accelerate the drying out process and enabling plants to be burnt after 3-5 weeks, compared to 13 weeks after the alternative cutting and natural drying.

Paraquat is increasingly used to destroy weeds in preparing land for planting in combination with no-till agricultural practices which minimise ploughing and help prevent soil erosion. Although toxic to fish, it is used as an aquatic herbicide where it is absorbed by plant matter and silt.

Paraquat is a quartenary nitrogen herbicide widely used for broadleaf weed control. It is a quick acting, non-selective compound, that destroys green plant tissue on contact and by translocation within the plant. It has been employed for killing marijuana in the U.S. and in Mexico. It is also used as a crop desiccant and defoliant, and as an aquatic herbicide.

Paraquat is a non-selective herbicide, which kills green plant cells on contact. Paraquat is widely used for weed-control in fruit orchards, on non-agricultural cropland and on plantation crops including coffee, cocoa, coconut, oil palms, rubber, bananas and tea. It is also used as a drying agent in the production of pineapples, sugar cane, soybeans and sunflowers. While the USA is the largest single-country market for paraquat, the two regions with by far the greatest use are Asia and Latin America.

CAS No.: 1910-42-5; 4685-14-7 (Paraquat dichloride)
Chemical name: 1,1'-Dimethyl-(4,4'-bipyridinium) cation
Specifications: 42% TC, 20% SL