Techniques Used in the Application of a 14C-Labelled Herbicide

The butylic ester of 2.4-D-214C was used to apply the herbicide in the chemical form adopted for field spraying. Esterification of the acid was carried out in the Labelled Molecules Division of the National Atomic Energy Commission's Department of Scientific Research. For purposes of the experiment the ester was prepared in the form of two emulsions of different concentrations ('concentrated' and 'dilute'), the first being based on the average amount used in field application in Argentina. The remaining components of the emulsions, i.e. the emulsifier and the solvent, were these normally used in Argentina, since in this country the import of herbicides based on 2,4-D is not permitted. The tests were carried out on specimens of quinoa (Chenopodium spp.), Datura ferox and Cyperus (Cyperus rotundus), kept in greenhouses. The duration of the treatment was three days in all cases except in that of Cyperus, where it was twelve days. The distribution of the radioisotope in the plants following application of the labelled substance was always limited, as was shown by the autoradiographs. All the doses used proved to be suitable for obtaining autoradiographs, including the lowest dose, containing 0.118 μCi of activity in the least of the volumes used (10 A). Quantitative determination of the percentage of the dose (amount of radioactivity) localized in a quinoa plant gave a figure of 16.3%. (author)