MERPHOS

Chemical properties

Nearly colorless liquid. Insoluble in water; soluble in a variety of organic solvents.

The Uses of MERPHOS

Merphos is an organothiophosphorus compound used as a defoliant but the active ingredient is no longer contained in any registered pesticide product in the US and in EU. Therefore, Environmental Protection Agency (EPA) is characterizing it as canceled.
The status of merphos in the EU pesticide database is ‘Not Approved’ under the Regulation EC 1107/2009 and not authorized at national level in EU countries. However a maximum level of residues (MRL) is regulated in foods as the default MRL of 0.01 mg kg-1 according to Art 18(1)(b) Reg 396/2005.
Merphos was used to defoliate cotton at application rates of 1.1–2.2 kg active ingredient per acre and can induce leaf abscission in some other plants, such as roses and hydrangeas. It was particularly suited for total defoliation of cotton preparatory to machine harvesting because the natural action of the substance causes the leaves to drop in a relatively green state with fresh weight adequate to cause them to fall to the ground.
The technical product used to have 95% purity. Formulation used to contain 720 g active ingredient per liter or being an emulsifiable concentrate containing 6 lb per gallon.

The Uses of MERPHOS

Organophosphate pesticide used in the agriculture industry

General Description

Emulsifiable oil.

Reactivity Profile

Organothiophosphates, such as MERPHOS, are susceptible to formation of highly toxic and flammable phosphine gas in the presence of strong reducing agents such as hydrides. Partial oxidation by oxidizing agents may result in the release of toxic phosphorus oxides.

Hazard

Cholinesterase inhibitor.

Safety Profile

Poison by intraperitoneal route. Moderately toxic by ingestion and skin contact. A cholinesterase inhibitor. Combustible when exposed to heat or flame. Can react vigorously with oxidzing materials. When heated to decomposition it emits highly toxic fumes of POx and SOx. Used as a defoliant. See also PARATHION.

Environmental Fate

Merphos is adsorbed strongly to soil and oxidized to S,S,S-tributyl phosphorotrithioate (DEF). The Koc estimated for merphos is theoretically 62 000; accordingly, merphos would be immobile in soil.
In water, merphos will be oxidized to DEF. The fact that merphos is expected to adsorb strongly to particulate matter in the water column, apparently did not impede its oxidation.
In the atmosphere, merphos will exist as an aerosol and be removed by gravitational settling and readily oxidized to DEF. Vapor-phase merphos will react with photochemically produced hydroxyl radicals, with an estimated half-life of 4.9 h.