Metaldehyde - Molluscicides

MOLLUSCICIDES

Compounds which kill molluscs such as snails and slugs. For example, metaldehyde.

Metaldehyde

It is a tetramer compound with an 8 member ring containing aldehyde molecules, and is a cyclic polymer of acetaldehyde. Metaldehyde is a popular molluscicide being effective against snails and slugs. It is a tasteless substance with a mild charac-teristic odour. It is available in some countries in tablet form for the purpose of producing coloured flames used in entertaining.

Instances of poisoning are however rare. It is a local irri-tant on skin and mucous membrane and a systemic convulsant. Metaldehyde overdosage results in lethargy, severe abdominal pain, nausea, vomiting, diarrhoea, hyperthermia, seizures, coma, and death. Profound hyperthermia may occur in asso-ciation with seizures. Metabolic acidosis and respiratory alkalosis have been reported. Other effects have included renal tubular injury and liver necrosis. Increased tracheobronchial secretions are prominent. Respiratory failure may occur 24 to 40 hours after ingestion. Mydriasis has been reported. Inhalation of metaldehyde fumes may cause CNS depression.

The probable lethal dose is in the range of 100 mg/kg for adults.

Bait that contains metaldehyde can be detected by placing the substance in a test tube and gently warming. Metaldehyde sublimes to form copious “artificial snow”.

Treatment is mainly directed at decontamination and management of convulsions. Activated charcoal may be benefi-cial. Dialysis is ineffective. Unproved antidotes which have been tested in animals or suggested include: calcium gluconate for seizures; D-penicillamine; N-acetylcysteine; thiamine; and ascorbic acid. None of these have been tested in humans.