2,4-D toxicity

Omalizumab Humanized IgE antibody reduces circulating IgE Reduces frequency of asthma exacerbations Severe asthma inadequately controlled by above agents Parenteral duration 2-4 d Toxicity Injection site reactions (anaphylaxis extremely rare)... 

The fundamental chemistry, especially of the newer economic poisons, is of primary importance. The mechanism of action of the various types of economic poisons and the relation of structure to toxicity of insects are of fundamental interest. Chemical versus biological methods of evaluation should be presented. Performance methods of evaluation of these chemicals have been given careful consideration by several workers. Emphasis was placed by several workers on the need for much additional information on various aspects of the problem regarding the use of DDT, 2,4-D, and other pesticides. There is direct importance in studies on the metabolism of DDT. 

Toxic organic compounds commonly found in groundwater are presented in Table 18.4. Other toxic organic compounds (representing 1% of cases) include PCBs (polychlorinated biphenyls), 2,4-D, 2,4,5-TP (silvex), toxaphene, methoxychlor, lindane, and endrin, of which 2,4-D and silvex are commonly used for killing aquatic and land weeds. Inorganic toxic substances commonly found in... 

A waste is toxic under 40 CFR Part 261 if the extract from a sample of the waste exceeds specified limits for any one of eight elements and five pesticides (arsenic, barium, cadmium, chromium, lead, mercury, selenium, silver, endrin, methoxychlor, toxaphene, 2,4-D and 2,4,5-TP Silvex using extraction procedure (EP) toxicity test methods. Note that this narrow definition of toxicity relates to whether a waste is defined as hazardous for regulatory purposes in the context of this chapter, toxicity has a broader meaning because most deep-well-injected wastes have properties that can be toxic to living organisms. 

Conversion of a toxic organic compound to a nontoxic organic compound. The pesticide 2,4-D can be detoxified microbially to 2,4-dichlorophenol. 

Conversion of a nontoxic molecule to one that is toxic, or a molecule with low potency to one that is more potent. Examples include the formation of the phenoxy herbicide 2,4-D from the corresponding butyrate, formation of nitrosamines, and methylation of arsenicals to trimethylarsine. 

Herbicide 2,4,5-T was not alone. We do not know the fate of the toxic dioxins that spread throughout the USSR in the formulations of different pesticides 2,4,5-trichlorophenol, 2,4,5-trichlorophenol copper salts, 2,4-D, pentachlorphenol, propanile, and many other formulations made up of various components. 

Many dioxins were, and still are, introduced into the environment together with phenoxyherbicides - derivatives of 2,4,5-T and 2,4-D. Therefore, the general toxic background created by these herbicides may be much higher than expected, since they can contain many other dioxins as additives along with 2,3,7,8-TCDD. Moreover, these compounds can evolve dioxins when transformed in natural conditions. Thus, the danger of all such pesticides must be measured in two ways by the content of highly toxic dioxins, and by the dioxin precursors [38]. 

The phenolic functional group consists of a hydroxyl attached directly to a carbon atom of an aromatic ring. The OH group can also be the consequence of further oxidation or combination with other pollutants such as pesticides, aldehydes, and alcohols (i. e., 2,4-D, cyclic alcohols, cresols, naphthols, quinones, nitrophenols, and pentachlorophenol compounds) forming new more toxic compounds [17,42,160]. 

The hydroxylation of the ring moiety of 2,4-D similarly converts the parent herbicide to a non-toxic product. Microorganisms may bring about such a detoxification when they hydroxylate the ring in the 4-position, a process that leads to a migration of the chlorine to give 2,5-dichloro-4-hydroxyphenoxy-acetic acid. 

When used commercially, 2,4-D has produced serious eye and skin irritation among agricultural workers. The direct risks of the chemical to humans makes it an ERA toxicity class Ill-slightly toxic when ingested orally, but toxicity class I-highly toxic, for eye exposure. Immediate, direct, acute, and high-level exposure can injure liver, kidney, muscle, and brain tissues. ... 

Toxicity of 2,4-D to animals and nontarget plant species is far less clear-cut. It is slightly toxic to wildfowl (e.g., quail and mallard ducks) and moderately toxic to some other bird species. The toxicity of the chemical to aquatic life varies both by chemical formulation and by animal species, though it is clearly toxic to many species, including stream trout, earthworms, and beneficial insects. 2,4-D has been shown to cause genetic damage in crops including barley, wheat, rice, and onions and can also increase the severity of some plant diseases. ... 

In contrast to the broad-spectrum herbicides, others are more selective. The phenoxy herbicides, which include chemicals such as 2,4-D, 2,4,5-T, and MCPA, are toxic to broad-leaf plants but do not affect narrow-leaf plants such as grasses. 

Activated carbon studies on widely used herbicides and pesticides have shown that it is successful in reducing the concentration of these toxic compounds to very low levels in wastewater [16]. Some examples of these include BHG, DDT, 2,4-D, toxaphene, dieldrin, aldrin, chlordane, malathion, and parathion. Adsorption is affected by many factors, including... 

The phenoxy herbicides inexpensiveness, selectivity, nonpersistency and low toxicity to animals are difficult to beat. Application is usually accomplished by spraying on the leaves. The herbicides cannot themselves be applied to the soil because they are washed away or decomposed by microorganisms in a few weeks. They can be applied by this method using a sulfonic acid derivative that, after hydrolysis in the soil and oxidation by bacteria, can form 2,4-D in the plant. 2,4-D is still the main herbicide used on wheat. 

Herbicides are designed to kill plants, not animals, and in general have lower mammalian toxicity than insecticides. Most herbicides interfere with plant hormones or enzymes that do not have any direct counterpart in animals. The most serious human health concerns have been related to contaminants of the primary chemical herbicide. There is an enormous amount of animal and some human toxicity data on 2,4-D and 2,4,5-T, but it now appears that much of this toxicity is caused by the contaminant TCDD. Military personnel exposed to Agent Orange, often contaminated with TCDD, reported birth defects, cancers, liver disease, and other illness. These concerns led to improvement in the manufacturing process to reduce TCDD contamination and ultimately to a reduction in use of 2,4-D herbicides. There is also concern that some herbicides may affect wildlife. For example, atrazine, a persistent herbicide, may adversely affect frogs. Persistence of herbicides may also... 

Recent research has proved 2,4-D to be effective in brush control, and oil seems to be essential in the formulations. For spra)dng, a fairly heavy, low toxicity oil has proved best. There are indications that a coarse spray which only spots the leaves will foster translocation of the 2,4-D after it has been absorbed. 

In the utilization of petroleum oils in the field of chemical weed control, oils function as toxicants, as solvents, as filming agents, and as carriers. In view of the very effective synthetic compounds now used as toxicants (substituted phenols), the toxicity of the oils themselves is somewhat less important than it once was. Oils may serve as adjuvants in formulations involving 2,4-D, 2,4,5-T, dinitro compounds, trichloroacetates, and others. They have the unique property of aiding in the contact, spreading, and penetration of herbicides. In addition, synthesis of wetting agents, emulsifiers, and special herbicides may be dependent on petroleum products. 

Dichlorophenoxyacetic acid (2,4-D), 2,4,5-trichlorophenoxyacetic acid (2,4,5-T), and their salts and esters are compounds of interest as herbicides used for the destruction of weeds (Figure 56-1). They have been assigned toxicity ratings of 4 or 3, respectively, which place the probable human lethal dosages at 50-500 or 500-5000 mg/kg, respectively. 

J. C. Lamb, J. A. Moore, and T. A. Marks, Evaluation of 2,4-dichlo-rophenoxyacetic Acid (2,4-D) and 2,4,5-trichlorophenoxyacetic Acid (2,4,5-T) and 2,5,7,8-tetrachlorodibenzo-p-dioxin (TCDD) Toxicity in C57BL-6 Mice, Publication NTP-80-44 (Research Triangle Park, N.C. National Toxicology Program, 1980). 

Example of Differential Toxicity Analysis 35 Table 2.3 Physical/chemical properties related to differential toxicity for diuron and 2,4-D. 

The lowest dose effects of diuron are seen at 0.27 mg kg-1 per day. Almost all of the low-dose expression changes are related to genes involved with xenobiotic metabolism and transport, including cytochrome P450 enzymes and several transferases. These data indicate that the cells are responding appropriately to a potentially toxic xenobiotic. These effects are widespread across the set of chemicals tested in ToxCast, so it is of interest that 2,4-D does not trigger a similar xenobiotic metabolism response. 

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