Use
Photolytic. When methidathion in an aqueous buffer solution (25°C and pH 7.0) was
exposed to filtered UV light (l >290 nm) for 24 hours, 17% decomposed to 5-methoxy-
3H-1,3,4-thiadiazol-2-one. At 50°C, 56% was degraded after 24 hours. Degradation
occurred via hydrolysis of the thiol bond of the phosphorodithioic ester. Under acidic and
alkaline conditions, hydrolytic cleavage occurred at the C-S and P-S bonds, respectively
(Burkhard and Guth, 1979). Smith et al. (1978) demonstrated that methidathion degraded
to methidathion oxon at a faster rate in six air-dried soils than in moist soils. Half-lives
for methidathion in the air-dried soils ranged from 19 to 110 days. In addition, methidathion
degraded faster in an air-dried soil exposed to ozone (half-lives 2.5 to 7.0 days).Chemical/Physical. Emits toxic fumes of phosphorus, nitrogen and sulfur oxides when
heated to decomposition (Sax and Lewis, 1987). Methidathion oxon was also found in
fogwater collected near Parlier, CA (Glotfelty et al., 1990). It was suggested