Fate of Azinphosmethyl in a Sugarcane Field: Distributions in Canopy, Soil, and Runoff

Abstract

Azinphosmethyl (O,O-dimethyl S-[4-oxo-1,2,3-benzotriazin-3(4H)-yl)methyl] phosphorodithioate) dynamics in surface soils, on canopy leaves and in runoff waters was studied on six 0.2-ha sugarcane (Saccharum sp. Hyb.) plots of a Commerce silt loam (fine-silty, mixed, nonacid, thermic Aeric Fluvaquent) during three growing seasons (1993-1995). Three applications of azinphosmethyl was made yearly (at 0.82 kg/ha) as a mixed emulsifiable concentrate with a water carrier. We found only 1 to 2% of applied azinphosmethyl remained within the canopy and the soil surface 10 to 12 d following application. Azinphosmethyl on leaf surfaces diminished sharply following rainfalls with subsequent increases in amounts in surface soil. Azinphosmethyl losses in runoff water decreased with time and maximum concentration was 10 to 21.9 μg/L. Concentrations were <2 μg/L in runoff waters 30 d after application. Based on first-order decay estimates, azinphosmethyl half-lives on canopy leaves ranged from 2 to 8 d whereas in surface soil it ranged from 6 to 66 d. A compartmental model also was used to estimate azinphosmethyl disappearance and transfer from leaves to soil based on rain conditions. Such an approach provided poor description of peak concentrations and predicted a much faster rate of disappearance than that measured.