Malaoxon

Malaoxon is a highly toxic organophosphate compound that is the oxidative metabolite, or oxon, of the insecticide malathion. It is formed when the thiono sulfur in malathion is oxidized to an oxygen atom. It is more potent as an acetylcholinesterase (AChE) inhibitor than malathion itself.

In mammals, hepatic cytochrome P450 enzymes can convert malathion to malaoxon, contributing to malathion's overall toxicity. In the environment, malaoxon can be formed from malathion through photochemical or microbial oxidation, and it may accumulate in soils and water.

Malaoxon rapidly inhibits acetylcholinesterase at cholinergic synapses, causing accumulation of acetylcholine. This leads to muscarinic effects (salivation, lacrimation, bronchial secretions, gastrointestinal symptoms) and nicotinic effects (muscle fasciculations, weakness), potentially progressing to respiratory failure and seizures in severe cases.

Because of its higher potency, malaoxon is a significant contributor to malathion toxicity in exposed organisms. It is not typically used as a standalone pesticide but is considered a transformation product; regulatory frameworks often address malathion and its oxon derivatives separately in toxicity assessments and environmental monitoring.

Malaoxon exemplifies how metabolic oxidation can convert a relatively moderate pesticide into a more toxic metabolite, highlighting considerations for exposure, monitoring, and safety measures.