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Scientists find enzymes that degrade herbicide dicamba toxicity
In recent years, scientists have developed crop varieties that are resistant to the herbicide dicamba. This herbicide is considered relatively eco-friendly compared to other options. However, as resistant weed populations continue to grow, the effectiveness of traditional herbicides has declined. To address this issue, researchers have turned to genetic modification as a potential solution for more sustainable weed control in agriculture.
In a study focused on a soil bacterium capable of breaking down dicamba, Mark R. Behrens and his team discovered specific enzymes that can convert the herbicide into non-toxic compounds. These enzymes were then introduced into several crop species. When these genetically modified plants were exposed to dicamba, the enzyme effectively prevented the herbicide from reaching harmful levels within the plant.
The researchers emphasize that dicamba is widely used due to its low cost and environmental benefits. It does not persist in the soil for long periods and is nearly non-toxic to wildlife and humans, making it an attractive option for agricultural use.
**About Dicamba**
- **Chinese Name**: 麦è‰å¨ (Mà icÇŽo WÄ“i), Baicao enemy
- **English Name**: Dicamba, Banvel, Mediben, Velsicol 58-CS-11, Banvel 4S
- **CAS Number**: 1918-00-9
- **Molecular Formula**: C₇H₄Cl₂O₂
- **Molecular Weight**: 221.0 g/mol
- **Melting Point**: 114–116°C
- **Vapor Pressure**: 0.5 Pa at 100°C
- **Toxicity (LD50)**:
- Acute oral toxicity in rats: 2,900 mg/kg
- Chronic toxicity: No adverse effects observed in rats fed 500 mg/kg for two years, or dogs fed 50 mg/kg for two years
- Fish toxicity (LC50, 96h): Rainbow trout 28 mg/L, Bluegill sunfish 23 mg/L
**Properties**
Dicamba appears as a pale yellow crystalline solid initially, but the pure form is colorless. It is stable under normal conditions and shows resistance to hydrolysis and oxidation.
**Solubility (at 25°C)**
- Water: 6.5 g/L
- Acetone: 810 g/L
- Dichloromethane: 261 g/L
- Ethanol: 922 g/L
- Toluene: 130 g/L
- Xylene: 78 g/L
**Use**
Dicamba is commonly used as a foliar or soil-applied herbicide, absorbed through leaves and roots. It is effective against both annual and perennial broadleaf weeds in crops like corn, sorghum, wheat, sugarcane, and asparagus. It is also used to manage woody shrubs in farmland. It is typically applied alone or in combination with other herbicides such as phenoxy carboxylic acids.
**Preparation**
It is synthesized by hydrolyzing 1,2,4-trichlorobenzene with sodium hydroxide in methanol, followed by reaction with carbon dioxide to produce 2-hydroxy-3,6-dichlorobenzoic acid. The final step involves dimethyl methylation using sulfuric acid.
**Consumption Quota (per ton of product)**
- 1,2,4-Trichlorobenzene (100%): 5.57 kg
- Xylene: 34.5 L
- Methanol: 25.3 L
- Dimethyl sulfate (100%): 2.864 kg
- Sodium hydroxide (100%): 17.38 kg
**Other Information**
Dicamba begins to decompose around 200°C. It remains stable under normal storage conditions and is known for its resistance to degradation. Its low toxicity and environmental profile make it a popular choice in modern agriculture.