Study on the fate of controlled-release formulation of carbon-14 thiobencarb in a model paddy ecosystem

The fate of a calcium alginate controlled-release formulation of carbon-14 labelled thiobencarb was studied in a model paddy ecosystem. The concentration of the released thiobencarb first increased with time and then declined. The herbicide was transformed into 12 radiolabelled degradation products in water. The major metabolite remained unidentified. In the soil most of the herbicide was found in the upper layer and there were at least 6 metabolites, some of which were conjugated in the form of soil-bound residues. At the time of harvest 45.6% of the total thiobencarb-related radioactivity present in the soil was extractable will the solvents, and the rest remained bound. The herbicide translocated into all parts of the rice plants grown in the treated soil, and residues were found in straw, roots, grain and husk. More than 92% of these residues were in the form of tissue-bound residues. In the plant the herbicide was degraded into 9 metabolites. The relatives proportion of the metabolites changed with time. The residues which were extracted from the plant contained 55.9, 6.1 and 11.2% thiobencarb in the straw, grain and the husk, respectively. The predominant metabolite in the grain remained unidentified. (author). Abstract only