Dipyridyl herbicides Flashcards
2 specific dipyridyl herbicides?
Paraquat and diquat
4 uses?
- Broad spectrum dessicant contact herbicides
- Paraquat is RUP, diquat GUP
- Concentrated forms (5-20%) for agriculture use and dilute forms for lawns/gardens
- Sprayed as 0.5 lb/acre for ag use
Sources of toxication?
- Ingestion of concentrates
- Malicious
Stability?
Unstable, rapidly inactivated by light and soil
Solubility?
Salts are soluble in water, poorly soluble in alcohol, and insoluble in hydrocarbon solvents
Stability of solutions?
Stable in neutral or acidic conditions but destroyed by alkali
What does paraquat bind strongly to?
Soil
what are dipyridyl herbicides caustic to?
Mucous membranes
Which animals are susceptible?
All animals, especially dogs
Oral LD50?
Ranges from 25-75 mg/kg in cats, dogs, pigs, sheep, and humans
What enhances paraquat’s toxicity?
- Selenium
- Vitamin E deficiency
- Depletion of tissue glutathione
- Oxygen therapy
What will cause chronic toxicity and death in dogs?
Daily oral exposure to 170ppm paraquat
Where is diquat absorbed from?
Poorly absorbed from GI tract
Where is paraquat absorbed from? Where is it distributed?
- Absorbed from GI tract (<20%) and skin (<10%)
- Distributed all over the body and achieves high conc. in lungs (10x)
How is paraquat excreted?
Excreted w/in 24hrs mainly unchanged in urine (minimal metabolism)
Mechanism of action?
- Reduced by nicotinamide-adenine dinucleotide phosphate (NADPH) to produce singlet oxygen
- Singlet oxygen reacts w/ lipids of cell membranes to form hydroperoxides
- Production of free radical and membrane damage and cellular degeneration and necrosis (esp lung tissue)
What are the early signs of acute toxicosis?
- May be vomiting, anorexia, or depression
- High doses may cause ataxia, dyspnea, and seizures
- Signs may not be observed until 3 days after exposure to paraquat
What are the delayed signs of acute toxicosis?
- (2-7 days)
- Respiratory signs: tachypnea, dyspnea, harsh resp sounds, cyanosis, and reduced pulmonary compliance
What are the signs of subacute or chronic toxicosis and when do they occur?
- 1-3 weeks
- Resp signs due to progressive pulmonary fibrosis
Where are the lesions mainly found?
Respiratory tract
Specific lesions? Other findings?
- Pulmonary congestion edema, congestion, hemorrhage, fibrosis, and failure of lungs to collapse
- Lingual ulcers may be seen
- Liver, kidney, and spleen may be congested and enlarged
- Microscopic lesions are consistent with gross findings
Chemical analysis?
- Specimens are suspected plant, stomach contents and urine (acute cases) or lungs (chronic cases)
- Urine samples may be negative after 48hrs from exposure
Radiography?
Mild changes in lungs
DDx?
- Pneumonias
- Inhalent toxicants such as toxic gases, vapors, and dusts
What is the specific antidote?
There is none
:(
Detoxification?
- Emetics
- Activated charcoal preferred
- Bentonite or Fuller’s earth orally (several times daily for 2 days)
- Saline cathartics following the adsorbent
Supportive treatment?
- Oxygen contraindicated b/c it may increase toxicity
- Fluid therapy may be used to cause diuresis and support kidney fx
- Hemodialysis or peritoneal dialysis
Biochemical antagonists (antioxidants)?
- Orgotein (superoxide dismutase)
- Acetylcysteine
- Ascorbic acid
- Niacin or riboflavin
Are the treatments helpful?
None of the treatments are likely to be of much help unless begun w/in 24hrs of exposure
Prognosis?
Guarded or grave
