Methylarsonate is used as a contact herbicide in either the monosodium or disodium salt form. It goes by the trade names Weed-E-Rad, Ansar 170 H.C., Ansar 529 H.C., DiTac and others. Methylarsonate is considered only slightly toxic, having an oral LD50 of 2200 mg/Kg for rats. The inhalation risk is greater with LD50 Rats >20 mg. Long term studies with people exposed to organoarsenicals has shown an increased risk of skin cancer (Spiewak, 2001), lung cancer and some liver cancers, although some recent studies have shown some arsenic containing compounds (specifically Arsine trioxide) may have anticarcinogenic properties (Wang, 2001). In mammals, Methylarsonate is also an intermediate in the detoxification of inorganic arsenic.
Arsenic is found in the environment primarily as arsenate and arsenite species. Arsenate is reduced to arsenite by arsenate reductase and can be subsequently methylated to Methylarsonate. This is then reduced and methylated to Dimethylarsinate (Zakharyan, 1999), which can excreted and is considerably less toxic to the organism than any of the previous intermediate compounds. In some bacteria, yeasts and fungi, this process is carried further to yield Trimethylarsine gas (Cullen et al., 1979; Pickett et al., 1981).
The following is a text-format methylarsonate pathway map. An organism which can initiate the pathway is given, but other organisms may also carry out later steps. Follow the links for more information on compounds or reactions. This map is also available in graphic (12k) format.
Methylarsonate
Cryptococcus humicolus MMA-1
|
| methylarsonate
| reductase
|
v
Methylarsonous acid
|
| methylarsonite
| methyltransferase
|
v
Dimethylarsinate
|
| dimethylarsinate
| reductase
|
v
Dimethylarsinous acid
|
| dimethylarsinite
| methyltransferase
|
v
Trimethylarsine oxide
|
| trimethylarsine
| oxidase
|
v
Trimethylarsine
Page Author(s): Kevin Watts
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