Chlorophenoxy herbicides

Abstract

Chlorophenoxy herbicides are derivatives of phenoxyacetic acid, to which at least one chlorine atom has been attached to the phenyl ring. These agents are structurally similar to and share many of the growth regulatory characteristics of, the natural auxin, indoleacetic acid (IAA). The most frequently used member of this class of herbicides is 2,4-dichlorophenoxyacetic acid (2,4-D). 2,4-D is one of the earliest of this class of herbicides to have been developed (1944), and also one of the best known, because of its use as one of the two herbicides in the manufacture of the military defoliating agent, Agent Orange; the other being 2,4,5-trichlorophenoxyacetic acid (2,4,5-T). As herbicides, this class of agents stimulates uncontrollable growth in susceptible plants, leading ultimately to their death. The chlorophenoxy herbicides are one of the most commonly used groups of herbicides because of their low cost, effectiveness and good water solubility. They have been produced extensively since the 1950s and are used both agriculturally and recreationally for post-emergence control of annual and perennial broad leaved weeds in cereals, herbage seed crops, flax, rice, vines, peas, potatoes, asparagus, grassland, turf, orchards, roadsides, forestry, and aquatic areas. Exposure to chlorophenoxy herbicides can occur through inhalation of contaminated air, consumption of foods containing herbicide residues, dermal contact during their application, or by entering areas where the compounds have been recently applied. Signs and symptoms of exposure to chlorophenoxy herbicides typically include vomiting, diarrhea headache, confusion, bizarre or aggressive behavior, peculiar odor on breath, muscle weakness, peripheral neuropathy, and loss of reflexes. The mechanism of toxicity is unclear but may involve mitochondrial injury, cell membrane damage, uncoupling of oxidative phosphorylation, and disruption of acetyl coenzyme A metabolism. Widespread muscle damage occurs, and the cause of death is usually ventricular fibrillation.