Chlorophenoxy compounds

Linscott, D.L. and Hagin, R.D. Additions to the aliphatic moiety of chlorophenoxy compounds. Weed Sci, 18 197-198,1970. 

Chlorophenoxy compounds are absorbed across the gut wall, skin and lungs. Excretion times are relatively short (hours to days) primarily via the urine. They are not appreciably stored in body fat. When fed in large doses to experimental animals, 2,4-D caused vomiting, diarrhea, ulcerations of mouth and pharynx, anorexia, loss of weight, and injury to the kidneys, liver and CNS. Some species developed myotonia of the hind extremities, attributed to the demyelination observed in the dorsal column of the cord. EEQ changes indicating disturbance of brain function were also observed at high dose. 

Figure 16.6 Herbicidal chlorophenoxy compounds and TCDD manufacturing by-product.

Herbicides are chemicals used to destroy unwanted plants (terrestrial or aquatic) called weeds. Herbicides fall into two broad categories inorganic (e.g., copper sulfate, sodium chlorate, and sodium arsenite) and organic (e.g., chlorophenoxy compounds, dinitrophenols, bipyridyl compounds, carbamates, and amide herbicides). Historically, inorganic compounds were the first available and the first used. There has been over a long period a continuous effort to develop herbicide compounds that are more selective—that affect weeds, as opposed to desirable plants. 

The chlorophenoxy compounds 2,4-dichlorophenoxyacetic acid (2,4-D) and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) may be the most familiar herbicides. They have been used in agriculture (to eradicate broadleaf weeds) and to control woody plants in ditches and along highways. They act as growth hormones in many plants, and can evoke active plant growth in areas in which abnormal, twisted, or curtailed growth occurs. Massive doses... 

Methomyl Chlorophenoxy compounds Chronic toxicity, mutagenicity... 

Aldicarb, Benomyl, Carbaryl, Chlorpropham, Fenvalerate, Methomyl, Chlorophenoxy compounds 2,4-D, 2,4,5-T... 

Substituted phenols Chlorophenoxy compounds Substituted acetic and propionic acids Amides and thioamides Substituted ureas Carbamates and dithiocarbamates Symmetrical triazines Benzoic acid derivatives Miscellaneous herbicides... 

The chlorophenoxy groups of herbicides includes 2,4-D, 2,4,5-T, and many other chemically related compounds. The chlorophenoxy compounds are primarily selective herbicides and comprise approximately half the total domestic herbicide market. Although 2,4-D is essentially insoluble in water, its esters are slightly water-soluble, and salts of 2,4-D are completely water-soluble. Several of these compounds are used not only for application to plant foliage and soil but also as aquatic herbicides (8). Each year hundreds of tons of these compounds are applied directly to lakes, rivers, and other surface waters for weed control. Approximately 100,000 pounds of 2,4-D granules are applied annually to the lakes in the TVA system alone (7). The herbicide 2,4-D may persist for several months in lake water whereas the esters of 2,4-D are usually broken down in a few days (I). When applied to watershed areas, the phenoxy herbicides are not likely to constitute a major water pollution hazard since the rate of bacterial degradation is sufficiently rapid to destroy them within a few days (26). However, a few of these compounds can remain in the environment for a year or more. 

The benzoic acid derivatives, such as 2,3,6-trichlorobenzoic acid, behave like the chlorophenoxy compounds. In general, they are slightly soluble in water but tend to leach readily into the soil. In areas of light rainfall some of these compounds may persist for five or more seasons others are lost in one season. There is evidence that some of the loss may be caused by volatilization. 

Chlorophenoxy compounds are sometimes mixed into commercial fertilizers to control growth of broadleaf weeds. 

The chlorophenoxy compounds are absorbed across the gut wall, lung, and skin. They are not significantly fat-storable. Excretion occurs almost entirely by way of the urine. Apart from some conjugation of the acids, there is limited biotransformation in the body. Figure 5.9 pictures a retail package containing 2,4-D (Weed-B-Gon ). 

Tab. 3. Chlorine percentage measured in original humic adds (HA) and their products of interaction with chlorophenoxy compounds...

Data shown in Table 3 indicate a definite increase of chlorine content in the products of interaction between HAs and chlorophenoxy compounds, thus suggesting the occurred incorporation of xenobiotic chlorinated units into the humic polymer. 

ESR parameters Humic acid Chlorophenoxy compounds Free radical concentration (spins 10 ) Line width (gauss) Spectroscopic splitting factor (g — values) ... 

Chlorophenoxy compounds are moderately irritating to skin. In case of dermal or eye exposure, the contaminated area should be bathed or flushed with copious amounts of water for 15 min and if irritation persists a physician should be contacted. Ingestion of substantial amounts of these chemicals results in spontaneous emesis. If the patient is fully alert and there are no apparent signs of emesis, emesis is induced with syrup of ipecac (adults, 30 ml children <12 years, 15 ml), followed by one to two glasses of water. In order to limit the absorption of the herbicide in the gut, 30-50 g of activated charcoal is administered in 6-8 ounces of water. Severe intoxication with chlorophenoxy compounds may result in renal failure. To avoid... 

These herbicides can be measured in plasma and urine by high-performance liquid chromatography. Chlorophenoxy compounds do not affect blood cholinesterase activities. 

Organic herbicides Substituted phenols Chlorophenoxy compounds... 

Chlorophenoxy compounds have been widely used as herbicides. Agent Orange was a mixture of the chlorophenoxy herbicides 2,4-D (dichlorophenoxyacetic acid) and 2,4,5-T (trichlorophenoxyacetic acid) that also contained small amounts of the highly toxic contaminant TCDD (2,3,7,8-tetrachlorodibenzo-p-dioxin see p 184) derived from the process of manufacturing 2,4,5-T. Manufacture ot 2,4-D by chlorination of phenol does not produce TCDD. Populations involved in manufacture or handling of 2,4,5-T may show elevated levels of TCDD on serum testing and overall increased rates of cancer compared to the general population. 

---