Fate and kinetics of carfentrazone-ethyl herbicide in California, USA, flooded rice fields

Little is known of the environmental fate of the aryltriazolinone herbicide carfentrazone-ethyl (compound I). Rice field applications of Shark(R) 400 commercial formulation to duplicate 5.7 m(2) rings (119 g a.i./ha) and 464 m(2) commercial basins (224 g a.i./ha) produced pseudo-first-order half-liv es (t(1/2)) of 6.5 to 11.1 h in water and 37.9 to 174 h in sediment. The ra pid dissipation from water was due to its hydrolysis to the chloropropionic acid (compound II), which further degraded to its propionic, cinnamic, and benzoic acids. Compound I degraded similarly in soil, but propionic and ci nnamic acid levels were higher. Compound I was only weakly adsorbed, but la teral movement of compound II through soil occurred. Laboratory hydrolysis produced quantitative yields of compound II, t(1/2) values of 131 h at pH 7 and 3.36 h at pH 9, and slow dissipation at pH 5 (43% at 830 h). Ultraviol et (UV) irradiation of compound I in pH 7 buffer gave dissipation rates sim ilar to those in dark controls (t(1/2) 113 h vs 128 h), while compound II w as comparatively stable to photolysis (t(1/2), 765 h) and also did not vola tilize from water. Ester hydrolysis followed by off-site movement of the ac id (compound II) account for the dissipation of compound I.