Distribution and metabolism of carbofuran in paddy rice from controlled release formulations

This study was conducted to evaluate slow release formulations of carbofuran in aquatic systems. Laboratory, greenhouse and field experiments in a rice paddy were carried out to determine the behaviour and fate of the important systemic insecticide carbofuran after application of new formulations. The release rates into water and the residues in the plant and soil were determined. Metabolites were identified by gas chromatography-mass spectrometry. Carbon-14 labelled carbofuran was used for the experiments. The results showed that the cellulose based (hydroxyethyl-cellulose) formulations released the active ingredient carbofuran at a significantly slower rate than commercial formulations, but that the concentration of carbofuran in water and plants was high enough to protect the plants against insects. Recovery of the insecticide in the rice paddy was only about 30%. Most was lost by changing the water in the paddy field, according to the usual cultivation practice, and by possible evaporation. The radioactivity found in grain and straw was 0.03% and 0.2%, respectively. The distribution of carbofuran in soil at different layers was: 0-5 cm: 17%; 5-15 cm: 7%; 15-25 cm: 4%; 25-40 cm: 2%. Less than 10% of the total radioactivity could be extracted from plants (Soxhlet extraction); thus, most of the carbofuran was metabolized and bound to the plant-grain constituents. (author). 4 refs, 5 figs, 4 tabs