Fate of 14C-carbofuran in model rice/fish and rice/fish/Azolla ecosystems

Model rice/fish (RF) and rice/fish/Azolla filiculoides (RFA) ecosystems were used to study the distribution and transformation of 14C-carbofuran in components of the two ecosystems. Carbofuran applied to paddy soil transferred to components in the ecosystems, whereas the distribution of 14C-carbofuran residues in components was very different. The 14C-carbofuran residues in water were much higher after surface application in the RF ecosystem in study I (1986) than after mixing into the soil in the RF and RFA ecosystems in study II (1987). The residues decreased slowly in study I, but rapidly in study II. Most of the 14C residues was found in the surface soil. Rice plants accumulated 14C-carbofuran slowly; less 14C was recovered in study II than in study I. In comparing the two ecosystems, there were no significant differences in the behaviour of residues in the soil, plants and fish, but residues in water of the RF ecosystem were always higher than those of the RFA ecosystem; those in fish were a little higher in the RFA than in the RF ecosystem. Most of the 14C residues in the soil, plants and fish were unextractable. The extractable residues in fish remained lower than 0.1 ppm in study II (identification of residues is still in progress). In study I, 14C-carbofuran phenol was the main degraded product in the water and soil, and 3-hydroxy-carbofuran was the predominant metabolite in plants and fish after the first 2 weeks. (author). 7 refs, 4 figs, 4 tabs