Glyphosate - Herbicides (Weedicides)

Glyphosate

Glyphosate, an aminophosphonate (non-cholinesterase inhib-itor-organophosphate compound), is used as a herbicide. It has a low order of toxicity in mammals, but the surfactant or other components contained in many preparations may contribute to toxic effects. It is an odourless, colourless to white crystalline powder and is weakly acidic.

Glyphosate herbicides are commonly applied in spray form and primarily formulated as either a water-soluble liquid or concentrate solution, or a solution made with a water-soluble powder and other ingredients. The following preparations are also available: pressurised liquids, aerosols, emulsions, pellets/ tablets, granules, powders, and microencapsulated products.

Glyphosate formulations and their toxicity differ depending on the type and concentration of the active ingredient and/or the added surfactants. The polyoxyethylene tallowamines (e.g. polyoxyethylene amine or POEA) is a class of surfactants most commonly used in glyphosate formulations. Other glyphosate herbicide additives include sulfuric and phosphoric acid and a variety of inert materials.

Brands

Glycel, Glyphos, Roundup, Sampoo.

Mode of Action

·              The surfactant present in commercial solution, polyoxyethylenea-mine, an anionic surfactant, may be responsible for many of the toxic effects of glyphosate. Surfactants alone may cause circula-tory failure, respiratory failure, seizures, generalised oedema and gastric erosion.

·              Glyphosate appears to undergo minimal metabolism. Results from animal studies indicate that essentially no toxic metabolites are produced and nearly 100% of the body burden is parent compound.

Usual Fatal Dose

Ingestion of > 200 ml is likely to produce severe toxicity.

Clinical Features

While instances of glyphosate poisoning have not been very common in India, cases are beginning to be reported.

·      Common features include pain in the mouth and throat, mucosal erosion/ulceration, vomiting, mild hepatotoxicity, and leukocytosis. Endoscopy in patients with ulceration showed gastritis, oesophagitis, and mucosal oedema, but no full thickness injury.

·      Less commonly, the patient may suffer from diarrhoea, abnormal mental status, oliguria/anuria, metabolic acidosis; hyperthermia, pulmonary oedema and shock.

·      Various cardiac arrhythmias, including ventricular arrhyth-mias, bradycardia, and cardiac arrest have been reported.

·      Poor prognosis is associated with the combination of pulmo-nary oedema, acidosis and hyperkalaemia.

·      Dermatitis resembling sunburn has been seen when the material has been in contact with skin for more than 30 minutes. No systemic symptoms have been seen due to absorption via intact or abraded skin.

Treatment

·            Serum levels of glyphosate are not clinically useful in assessing the severity of exposure or poisoning.

·            Monitor CBC, serum creatinine, BUN, liver function tests, serum electrolytes, arterial blood gases, urinalysis, and chest radiograph in symptomatic patients. Monitor cardiovascular function; including blood pressure frequently. Obtain baseline ECG; repeat as indicated.

·            Emesis is not recommended. Instead, rinse the mouth and dilute with milk or water.

·            Activated charcoal can be administered in the usual manner.

·            Obtain consultation concerning endoscopy as soon as possible, and perform endoscopy within the first 24 hours when indicated. If burns are found, follow 10 to 20 days later with barium swallow or oesophagram.

·            Scintigraphy: Scans utilising radioisotope labelled sucral-fate (technetium 99m) may represent an alternative to endoscopy, particularly in young children, as no sedation is required for this procedure.

·              The use of corticosteroids for the treatment of caustic ingestion is controversial.

·            The use of antibiotics is suggested if corticosteroids are used, or if perforation or infection is suspected. Agents that cover anaerobes and oral flora such as penicillin, ampicillin, or clindamycin are to be preferred.

·            For acute lung injury, maintain adequate ventilation and oxygenation with frequent monitoring of arterial blood gases and/or pulse oximetry. If a high FIO₂ is required to maintain adequate oxygenation, mechanical ventilation and positive-end-expiratory pressure (PEEP) may be required; ventilation with small tidal volumes (6 ml/kg) is preferred if ARDS develops.

·            For hypotension, infuse 10 to 20 ml/kg of isotonic fluid and place in Trendelenburg position. If hypotension persists, administer dopamine or noradrenaline.

·            Treat severe acidosis (less than pH 7.1) with IV sodium bicarbonate. Begin with 1 mEq/kg in adults and in children. Repeat doses of no more than half the original amount may be given, no more often than every 10 minutes if required.

·            Glyphosate is excreted rapidly in the urine. Maintaining an adequate urine output is important as the clearance of glyphosate by the kidney (52.9 ml/min) was as good as by haemodialysis (52.5 ml/min); both of which were superior to haemoperfusion (6.4 ml/min).