Amitrole Residues and Rate of Dissipation in Irrigation Water

Abstract

The maximum concentrations of 3-amino-s-triazole (amitrole) found in two flowing-water canals (1.13 and 0.65 cu m/sec) following treatment of a single ditchbank of each canal with 4.5 and 3.4 kg/ha of amitrole-ammonium thiocyanate (amitrole-T) were 31 and 43 ppb. Conjunctive treatment of both banks of another canal, prior to entry of water, resulted in a maximum of 98 ppb of amitrole upon turning 1.42 cu m/sec of water into the canal. Two hours after passage of the main body of amitrole-bearing water at the last sampling station on each canal, amitrole levels were down to approximately 1 ppb or less. The dissipation of amitrole in canals, for distances up to about 14.5 km, was a linear function of amitrole concentration and downstream flow. The rate of dissipation was fastest on a canal in which the herbicide was placed directly into the water (slope of 3.8), modest for a single bank treatment (slope of 2.7), and slowest where opposite banks of a canal were treated (slope of 1.8).