Paraquat—

Eisler, R. 1990. Paraquat hazards to fish, wildlife, and invertebrates a synoptic review. U.S. Fish Wildl. Serv. Biol. Rep. 85(1.22), 28 pp. 

Eisler, R. 2000. Paraquat. Pages 1159-1192 in Handbook of Chemical Risk Assessment Health Hamtds to Humans, Plants, and Animals. Volume 2, Organics. Lewis Publishers, Boca Raton, Florida. 

Paraquat is a broad-spectrum contact weed killer and herbage desiccant that is used widely in agriculture and horticulture. Paraquat was originally formulated in 1882, but its her-bicidal properties were not discovered until 1955. Since its introduction in the early 1960s, paraquat has been used extensively in about 130 countries, including the United Kingdom, Canada, and the United States, on a wide variety of agricultural crops. 

Stmctural formula of paraquat cation (upper) and of paraquat dichloride salt (lower). 

The recommended field application rates for terrestrial weed control usually range between 0.28 and 1.12kg paraquat cation/ha (0.25 and 1.0 pounds/acre), or 0.56 and 2.24 kg paraquat dichloride/ha (0.5 and 2.0 pounds/acre) - both applied as an aerosol - and 0.1 and 2.0mg/L for aquatic weed control, although sensitive aquatic plants may be affected between 0.019 and 0.372 mg/L. Paraquat is frequently used in combination with other herbicides. Water solutions of the dichloride salt, which usually contain 240.0 g/L, have been successfully mixed with 2,4-d, substituted ureas, dalapon, amitrol, and various triazines. 

Other toxic lung furans, such as the atmospheric contaminants 2-methylfuran and 3-methylfuran, may exert their toxicity through the formation of reactive metabolites, probably reactive aldehydes. 

Kulle TJ et al Pulmonary function adaptation to ozone in subjects with chronic bronchitis. Environ Res 34 55-63, 1984 

Hackney JD et al Adaptation to short-term respiratory effects of ozone in men exposed repeatedly. J Appl Physiol 43 82-85, 1977 

Stokinger HE, Scheel LD Ozone toxicity Immunochemical and tolerance-producing aspects. Arch Environ Health 4 327-334, 1962 

ACGIH Ozone. Documentation of the Threshold Limit Values and Biological Exposure Indices, 7th ed, pp 1-9. Cincinnati, OH, American Conference of Governmental Industrial Hygienists, 2001 

Synonyms 1, T-Dimethyl-4,4 -bipyridinium dichloride gramoxone methylviologen 

IUPAC name l,T-dimethyl-4,4 -bipyridinium Molecular formula C12H14N2 Toxicity class USEPA II WHO II 

Uses Paraquat is a colorless, odorless, white or pale yellow crystalline solid that is hygroscopic. Paraquat is a quaternary nitrogen herbicide that is widely used for broadleaf weed control. It is a quick-acting, nonselective compound that destroys green plant tissue on contact and by translocation within the plant. It has been employed for killing marijuana in the United States and Mexico. It also is used as a crop desiccant and defoliant, as well as an aquatic herbicide. Paraquat is highly persistent in the soil environment, with a reported field half-life of greater than 1,000 days.5-7,17 

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Paraquat, 1, r>dimethyM,4 >bipyridylium dimethylsulphate or dichloride Both salts are... 

A wide class of aiyl-based quaternary surfactants derives from heterocycles such as pyridine and quinoline. The Aralkyl pyridinium halides are easily synthesized from alkyl halides, and the paraquat family, based upon the 4, 4 -bipyridine species, provides many interesting surface active species widely studied in electron donor-acceptor processes. Cationic surfactants are not particularly useful as cleansing agents, but they play a widespread role as charge control (antistatic) agents in detergency and in many coating and thin film related products. 

Bipyridiniums. The bipyridinium herbicides (Table 2), paraquat and diquat, ate nonselective contact herbicides and crop desiccants. Diquat is also used as a general aquatic herbicide (2,296). Bipyridinium herbicides are organic cations and are retained ia the soil complex via cation exchange. They are strongly sorbed to most soils and are not readily desorbed (332). Both paraquat and diquat are not readily leached (293). 

Most of them are generally classified as poisons. Exceptions to this rule are known. A notable one is 4-dimethyl aminopyridine (DMAP) (24), which is widely used in industry as a superior acylation catalyst (27). Quaternary salts of pyridines are usually toxic, and in particular paraquat (20) exposure can have fatal consequences. Some chloropyridines, especially polychlorinated ones, should be handled with extra care because of their potential mutagenic effects. Vinylpyridines are corrosive to the skin, and can act as a sensitizer for some susceptible individuals. Niacin (27), niacinamide (26), and some pyridinecarbaldehydes can cause skin flushing. 

Quaternary Salts. Herbicides paraquat (20) and diquat (59) are the quaternary salts of 4,4 -bipyridine (19) and 2,2 -bipyridine with methyl chloride and 1,2-dibromoethane, respectively. Higher alkylpyridinium salts are used in the textile industry as dye ancillaries and spin bath additives. The higher alkylpyridinium salt, hexadecylpytidinium chloride [123-03-5] (67) (cetylpyridinium chloride) is a topical antiseptic. Amprolium (62), a quaternary salt of a-picohne (2), is a coccidiostat. Bisaryl salts of butylpyridinium bromide (or its lower 1-alkyl homologues) with aluminum chloride have been used as battery electrolytes (84), in aluminum electroplating baths (85), as Friedel-Crafts catalysts (86), and for the formylation of toluene by carbon monoxide (87) (see QuaternaryAA ONiUM compounds). 

Bipyridines. Siace the 1960s, the most important commercial agrochemical based on pyridine has been the herbicide paraquat (20) which is made from 4,4 -bipyridine (19). The isomeric herbicide diquat (59) is made by an analogous route, but utilising 2,2 -bipyridine [366-18-7] as a precursor. 

Paraffin wax fume Paraquat, respirable sizes Parathion... 

There are at least 22 chemical families of organic herbicides. Even a cursory treatment of the chemistry of these materials would be extensive. Herbicides of limited toxicity (Treflan, Atrazine) as well as extremely toxic ones (Paraquat. Dinoseb) are in use in many parts of the world. They range from water soluble to insoluble. The detailed chemistry of each should be determined prior to handling. 

Grain Processing Corporation, 230 GRAMOXONE , paraquat, 73 Grand Pacific Petroleum Corporation, 205 Grande Paroisse SA, 156-157 Graphit Kropfmuhl AG, 164 Graphite, 73... 

Union Carbide Corporation, 226, 251 Union Derivan SA (UNDESA), 203 Union Espanola de Explosivos SA, 203 Union Miniere N.V., 145 Uniqema, 210 Uniqema Eiternatiional, 196 UNIQUAT alklyl pyridines, 134 UNIQUAT , paraquat, 134 Uniroyal Chemical Co., 224, 251 Unisource India, 176 United Chemical Products Ltd., 198 United Chemical Technologies, 251... 

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