Dicamba

Dicamba can be synthesized from 1,2,4-trichloro-benzene . It reacts with sodium hydroxide turning into 2,5-dichloro-phenol, which after reaction with carbon dioxide in the presence of potassium hydroxide , and dimethyl sulfate and water forms the final product ^[3] .

Herbicide

The influence of dicamba on plant growth was discovered by Zimmerman and Hitchcock in 1942. Shortly thereafter, field trials of the drug were conducted at an experimental station in the English village of Jellots Hill .

Dicamba is used as a herbicide against dicotyledonous weeds in crops of crops , in fruit growing, in meadows and lawns . Many of today's dicamba-containing herbicides are approved for weed control on lawns and turf strips along roads. Quite often, such preparations contain, along with other herbicides, 2,4-dichlorophenoxyacetic acid . Similar herbicidal mixtures with dicamba as an active substance are allowed in many EU states, including Germany, Austria and Switzerland ^[4] .

The substance is absorbed by the plant through the leaves and roots and moves along it ^[5] . Dicamba is a growth regulating herbicide, it significantly accelerates the growth of dicotyledonous plants, after which they die in the resulting nutrient deficiency. Warm and favorable for growth weather accelerates the process of dying. To achieve herbicidal activity requires several days of active plant growth.

Features

Colorless crystals decompose upon heating, thereby forming corrosive, toxic fumes ( hydrogen chloride ). Dicamba is soluble in acetone , dichloromethane , 1,4-dioxane, ethanol , toluene and xylene .

Acute Toxicity

The LD ₅₀ (oral) for male rats is 1581 mg, for female rats - 1879 mg / kg body weight. In male mice, it is 1180, in women ^{[ what? ]} 2392 mg / kg.

When entering through the skin, LD ₅₀ for male rats -> 6000, for female rats> 8000 and for rabbits> 2000 mg / kg body weight. In a rabbit, dicamba does not irritate the skin, does not irritate, but strongly irritates the mucous membrane of the eye. In guinea pigs, skin sensitization was observed ^[5] .

Dicamba poisoning is characterized by the following symptoms: anorexia , vomiting, muscle weakness, bradycardia , shortness of breath, CNS symptoms, benzoic acid in urine, urinary incontinence or fecal incontinence, cyanosis .

Additionally, dicamba irritates the mucous membranes and eyes, temporary clouding of the cornea is the result of direct contact with the eyes. Most people after poisoning with hard dicamba recover within 2-3 days without any particular complications.

Chronic Toxicity

Doses of 25 mg / kg per day for a two-year period in rats did not cause measurable effects with respect to mortality, body weight, food intake, body weight, biochemical analysis of blood or tissue structure. High doses of dicamba cause changes in liver tissue and weight loss in rats and mice.

Miscellaneous

The drug is almost not absorbed through the skin. In a study of three generations of dicamba rats, there was no noticeable effect on reproduction rate. Teratogenic, carcinogenic and mutagenic effects were not observed.

Degradation

Soil

Dicamba is moderately stable in soil. The half-life is from 1 to 4 weeks. Under optimal conditions (soil moisture <50%, pH slightly acidic) is metabolized by microorganisms for 2 weeks, photolysis plays only a secondary role in the breakdown of this substance. Due to its solubility in water and a very low tendency to adsorption on soil particles, groundwater contamination is possible due to leaching.

Water

Since dicamba is stable in water, the contribution of microorganisms to the destruction of the substance is reduced to 95%, and the remaining 5% is due to photolysis.

Vegetation

Differences in the rate of degradation of dicamba to 3,6-dichloro-1-hydroxybenzoic acid in different plant species are the cause of its selective action. In addition, hydroxylation at the 5th position of the ring leads to the formation of polar conjugates ^[5] .

Toxicity to other organisms

Dicamba is not dangerous for bees ^[5] .

LD ₅₀ for ducks is 2000 mg / kg body weight. In an 8-day mallard and dumb quail feeding trial, the lethal dose was> 10,000 mg / kg feed ^[5] .

LC ₅₀ for rainbow trout (96 h) 135 mg / l, for carp (48 h) 465 mg / l, that is, the substance is considered non-toxic to fish ^[5] . The EC ₅₀ (48 h) for Daphnia magna , as well as the LC ₅₀ (96 h) for amphipods, is more than 100 mg / l ^[5] .

Dicamba is toxic to algae and higher aquatic plants.

Some weed species have become resistant to this substance. Dicamba Resistant Bassia scoparia was discovered in 1994; the mechanism of resistance could not be explained in the framework of the standard model of resistance based on absorption, translocation or metabolism ^[6]

The soil bacterium Pseudomonas maltophilia (strain DI-6) converts dicamba to 3,6-dichlorosalicylic acid, which is more adsorbed by the soil and does not possess herbicidal activity. Little is known about the toxicity of this decay product. The enzyme responsible for the first step in the degradation of this substance is a three-component system called dicamba-O-demethylase. Recently, Monsanto inserted one component of a three-component enzyme system into the genome of soy and other broad-leaved cereals, making them resistant to dicamba ^[7]. Monsanto distributes its genetically modified plants under the brand name Xtend ^[8] .

1. ↑ Record of CAS RN 1918-00-9 in the GESTIS Substance Database of the IFA .
2. ↑ ccme: Canadian Water Quality Guidelines for the Protection of Aquatic Life - DICAMBA
3. ↑ Thomas A. Unger. Vorschau Pesticide Synthesis Handbook . - William Andrew, 1996. - P. 789. - ISBN 0-81551853-6 .
4. ↑ Generaldirektion Gesundheit und Lebensmittelsicherheit der Europäischen Kommission: Eintrag zu Dicamba in der EU-Pestiziddatenbank ; Eintrag in den nationalen Pflanzenschutzmittelverzeichnissen der Schweiz Archived copy of August 20, 2016 to Wayback Machine , Österreichs Archived copy of March 5, 2016 to Wayback Machine und Deutschlands (link not available) (link not available) (link not available) ; abgerufen am 13.
5. ↑ ^{1 2 3 4 5 6 7} Werner Perkow: “Wirksubstanzen der Pflanzenschutz- und Schädlingsbekämpfungsmittel”, 2. Auflage, 3. Ergänzungslieferung März 1992, Verlag Paul Parey.
6. ↑ Cranston, Harwood J .; Kern, Anthony J .; Hackett, Josette L .; Miller, Erica K .; Maxwell, Bruce D .; Dyer, William E. Dicamba resistance in kochia (neopr.) // Weed Science. - 2001. - T. 49 , No. 2 . - S. 164 . - DOI : 10.1614 / 0043-1745 (2001) 049 [0164: DRIK] 2.0.CO; 2 .
7. ↑ Behrens, MR; Mutlu, N .; Chakraborty, S .; Dumitru, R .; Jiang, WZ; Lavallee, BJ; Herman, PL; Clemente, TE; Weeks, DP Dicamba Resistance: Enlarging and Preserving Biotechnology-Based Weed Management Strategies (Eng.) // Science: journal. - 2007. - Vol. 316 , no. 5828 . - P. 1185-1188 . - DOI : 10.1126 / science.1141596 . - PMID 17525337 .
8. ↑ Charles, Dan . Crime In The Fields: How Monsanto And Scofflaw Farmers Hurt Soybeans In Arkansas (August 1, 2016).