Demeton-O-methyl sulfone is an organophosphate insecticide. Very little data are available on its environmental fate or ecotoxicology. Demeton-O-methyl sulfone is an acetylcholinesterase inhibitor and neurotoxin.
The following alerts are based on the data in the table below. No alert does not mean the substance has no effects on human health, biodiversity or the environment, just that we don\’t have the data to make a judgment.
Demeton-O-methyl is an organic compound with the molecular formula C6H15O3PS2. The substance is a colorless to slightly yellow oily liquid, practically insoluble in water. The O in the name refers to the linkage of the ethylthioethane chain to the dimethylphosphorothioate group through an oxygen atom.
Demeton-O-methyl is used as an insecticide and acaricide. It usually occurs in combination with endo-S-methyl, and this mixture is simply called endo-S-methyl. The trade name for this substance is Methylsystox.
The substance decomposes on heating and on burning producing toxic fumes including phosphorus and sulfur oxides.
The substance may have effects on the nervous system and inhibit cholinesterase.
Demeton-S-methyl, first described by Schrader in 1950, is widely used as an insecticide because it is less toxic to humans than previously used demeton.  In the first days it was used mostly with Demeton-O-methyl in an O:S ratio of 70:30. Since 1957, only pure Demeton-S-methyl has been used.  Due to its high toxicity and serious poisoning effect on the human body, demeton-S-methyl has been listed as a highly toxic substance by the World Health Organization, and its agricultural use is prohibited worldwide.
Demeton-S-Methyl is a compound structurally closely related to VX. The structure is C6H15O3PS2. Demeton-S-Methyl has a molecular weight of 230.28 g/mol It appears as a colorless to pale yellow oily liquid with a garlic-like odor.  It has a density of 1.2 g/cm3, slightly heavier than water. Melting and boiling points are <25 °C (<77 °F) and 118 °C (244 °F), respectively, although the compound decomposes before reaching the boiling point. The relatively low 0.0004 mmHg (at 20 °C (68 °F; 293 K))  means that Demeton-S-Methyl evaporates very slowly and remains mostly liquid. Demeton-S-Methyl is less stable than its predecessor, Demeton, but is used due to its lower toxicity to humans. Demeton-S-methyl hydrolyzes rapidly in alkaline media.  Demeton-S-methyl is easily soluble in water and most organic compounds.