Dicamba
| Structural formula | |||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|
|||||||||||||||||||
| General | |||||||||||||||||||
| Surname | Dicamba | ||||||||||||||||||
| other names |
|
||||||||||||||||||
| Molecular formula | C 8 H 6 Cl 2 O 3 | ||||||||||||||||||
| Brief description |
white solid with a cresol- like odor |
||||||||||||||||||
| External identifiers / databases | |||||||||||||||||||
|
|||||||||||||||||||
| characteristics | |||||||||||||||||||
| Molar mass | 221.04 g mol −1 | ||||||||||||||||||
| Physical state |
firmly |
||||||||||||||||||
| density |
1.49 g cm −3 (25 ° C) |
||||||||||||||||||
| Melting point |
115 ° C |
||||||||||||||||||
| boiling point |
> 200 ° C |
||||||||||||||||||
| Vapor pressure |
4.5 mPa (25 ° C) |
||||||||||||||||||
| solubility |
heavy in water (6.1 g l −1 at 20 ° C) |
||||||||||||||||||
| safety instructions | |||||||||||||||||||
|
|||||||||||||||||||
| As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions . | |||||||||||||||||||
Dicamba, or 3,6-dichloro-2-methoxybenzoic acid, is a chemical compound that acts as a synthetic auxin and is used as a herbicide . Dicamba was first marketed by Velsicol Chemical Corporation in 1965 .
Extraction and presentation
Dicamba can be prepared starting from 1,2,4-trichlorobenzene . This reacts with sodium hydroxide to form 2,5-dichlorophenol , which reacts with carbon dioxide , potassium hydroxide , dimethyl sulfate and water to form the end product.
use
Plant protection
Dicamba is used as a herbicide against dicotyledons in cereals , in fruit growing , on grassland and lawns . Many of today's dicamba preparations are approved for use against weeds on ornamental lawns, turf and grass verges on roads. In addition to other herbicidal active ingredients, they often contain 2,4-dichlorophenoxyacetic acid . Plant protection products with the active ingredient dicamba are approved in many EU countries, including Germany and Austria, as well as Switzerland.
Around 2500 tons of dicamba were applied in the USA in 2014.
The herbicide is and was sold under the names Banvel, Banex, Dianat, Fallowmaster, Mediben, Metambane, Tracker, Trooper and Velsicol.
With a decision by a court in San Francisco on June 3, 2020, the weed killer had initially lost its approval in the USA. In October 2020, however, the US Environmental Protection Agency approved Dicamba products again.
effect
Dicamba is absorbed through leaves and roots, it can be transported within the plant. Dicamba is a growth substance herbicide that accelerates the growth of dicotyledonous plants so much that they die due to the resulting nutrient deficiency. This process is further accelerated by heat or other growth-promoting weather. Plants need several days of active growth before the herbicidal effect occurs.
toxicity
characteristics
The colorless crystals decompose when heated and form corrosive , toxic vapors ( hydrogen chloride ). Dicamba is soluble in acetone , dichloromethane , 1,4-dioxane , ethanol , toluene and xylene .
acute toxicity
The lethal dose LD 50 (oral) for the male rat is 1581 mg, for the female rat 1879 mg dicamba / kg body weight. It is 1180 mg / kg in male mice and 2392 mg / kg in females.
When absorbed through the skin, the LD 50 for the male rat is> 6000, for the female rat> 8000 and for the rabbit> 2000 mg / kg body weight. In rabbits, dicamba does not irritate the skin , but is very irritating to the eyes. Skin sensitization has been observed in guinea pigs .
The following symptoms characterize dicamba poisoning: anorexia , vomiting, muscle weakness, bradycardia , shortness of breath, CNS symptoms, benzoic acid in the urine, urinary or fecal incontinence , cyanosis .
In addition, Dicamba irritates the mucous membranes and eyes, a temporary clouding of the cornea is the result of direct eye contact. Most people with massive dicamba poisoning recovered within 2-3 days without permanent damage.
Chronic toxicity
Doses of 25 mg / kg / day over a period of 2 years produced no measurable effects in rats with regard to death rate, body weight, food consumption, organ weight, blood chemistry or tissue structure. High dicamba doses caused changes in liver tissue and a decrease in body weight in rats and mice.
other
There is almost no absorption through the skin. In a study of three generations of rats, dicamba had no measurable effects on the reproductive rate at use concentrations. Teratogenic , carcinogenic and mutagenic effects were not observed.
ecology
Degradability
ground
Dicamba is moderately persistent in the soil. The half-life is 1 to 4 weeks. Under optimal conditions (soil moisture <50%, pH slightly acidic), metabolism by microorganisms takes place within 2 weeks, photolysis only plays a subordinate role. Due to its water solubility and its very low tendency to adsorb on soil particles, contamination of the groundwater through leaching is possible.
water
Since dicamba is stable in water, 95% of its degradation is through microorganisms and 5% through photolysis.
vegetation
The differences in the rate of degradation of dicamba to 3,6-dichloro-1-hydroxy-benzoic acid in different plant species are the cause of its selective effect. In addition, a hydroxylation at the 5-position of the ring is important, via which polar conjugates can be formed.
volatility
Dicamba is believed to be volatile and therefore to be able to easily reach neighboring fields. A new variant called XtendiMax, which was only approved in the USA in 2017, appears to be similarly volatile, but even more poisonous for plants. There were complaints of crop failures in the US this year, and several states are considering banning the herbicide. Independent scientists said they couldn't fully test the new product before it hit the market. Monsanto stated that the new product has been extensively tested.
In mid-2020, the distribution of Dicamba in the United States was initially prohibited by a court. The EPA's extension of approval at the end of 2018 violated federal law. In the opinion of the court, the risks were not adequately examined.
Ecotoxicity
Dicamba is not dangerous to bees .
The acute lethal dose (LD 50 ) for the mallard is 2000 mg / kg body weight. In the 8-day feeding test with mallard and Japanese quail , the lethal concentration was> 10,000 mg / kg feed.
The LC 50 of Dicamba is 135 mg / L for rainbow trout (96 h) and 465 mg / L for carp (48 h). It is therefore not considered toxic to fish.
The EC 50 (48 h) for Daphnia magna and the LC 50 (96 h) for flea cancer are more than 100 mg / L.
Dicamba is poisonous to algae and higher aquatic plants.
Dicamba-resistant plants
The University of Nebraska and Monsanto used genetic engineering to develop soybeans that are resistant to dicamba. In January 2009, Monsanto and BASF - the most important manufacturer of dicamba and products containing dicamba - agreed on a cooperation for the development of new, herbicide-resistant plants. Against the backdrop of the proliferation of weeds resistant to glyphosate (Roundup), the companies are working together to develop seeds that are resistant to both glyphosate and dicamba. Corresponding soy seeds have been sold since 2016.
Individual evidence
- ↑ a b c d e f g h Entry on Dicamba in the GESTIS substance database of the IFA , accessed on February 7, 2017(JavaScript required) .
- ↑ Entry on Dicamba in the Classification and Labeling Inventory of the European Chemicals Agency (ECHA), accessed on February 1, 2016. Manufacturers or distributors can expand the harmonized classification and labeling .
- ↑ Thomas A. Unger: Pesticide Synthesis Handbook . William Andrew, 1996, ISBN 0-8155-1853-6 , pp. 789 ( preview ).
- ↑ General Directorate Health and Food Safety of the European Commission: Entry on Dicamba in the EU pesticide database; Entry in the national registers of plant protection products in Switzerland , Austria and Germany ; accessed on March 13, 2016.
- ↑ ccme: Canadian Water Quality Guidelines for the Protection of Aquatic Life - DICAMBA (English).
- ↑ Dicamba weed killer loses US approval for the time being - PROCESS-Online, accessed on June 4, 2020 .
- ↑ EPA Announces 2020 Dicamba Registration Decision. In: epa.gov . United States Environmental Protection Agency, October 27, 2020, accessed October 28, 2020 .
- ↑ a b c d e f g Werner Perkow: “Active substances in plant protection and pest control agents”, 2nd edition, 3rd supplementary delivery March 1992, Paul Parey publishing house.
- ↑ tagesspiegel.de: Is Monsanto to blame for the US plant crisis? August 10, 2017. Retrieved October 4, 2017.
- ↑ washingtonpost.com: This miracle weed killer was supposed to save farms. Instead, it's devastating them . August 29, 2017, accessed October 4, 2017. Furthermore, US farmers sue Monsanto. Weedkiller Dicamba creates new problems. , Deutschlandfunk , October 6, 2017.
- ↑ Reuters: US court bans sale of herbicide dicamba June 4, 2020, accessed June 4, 2020.
- ↑ MR Behrens, N. Mutlu u. a .: Dicamba Resistance: Enlarging and Preserving Biotechnology-Based Weed Management Strategies. In: Science. 316, 2007, pp. 1185–1188, doi : 10.1126 / science.1141596 (English).
- ↑ BASF and Monsanto agree to jointly develop formulation technologies with dicamba herbicide , press release January 20, 2009.
- ^ Purchasingnetz.org: Social and ecological problems caused by gene plants ( Memento from September 7, 2008 in the Internet Archive ).
- ↑ Agriculture in Illinois - Glyphosate dependent . In: Deutschlandfunk . ( deutschlandfunk.de [accessed on October 23, 2017]).