Fate of 14C-maneb in soyabean plants

Seeds of soyabean were cultivated under normal field conditions in June 1988. 14C-maneb, diluted with ETU-free cold maneb to a final specific activity of 2 mCi/g, was applied three times at weekly intervals with a total dose of 6.45 mg maneb/plant. Different parts of plant samples, collected at different intervals, were extracted with ethanol-chloroform, ethylene diamine tetracetate and water. The overall data indicated that no more than 5% of the applied dose was detected on/in the plant. Residues in leaves and stem showed a gradual increase of both chloroform and water extracts. Analysis of residues in these extracts showed that ETU and ETM were significant transformation products in addition to two major unknown compounds. The concentration of ETU in both extracts from the leaf increased from 0.0105 ppm after 26 days to 0.163 ppm after 76 days. In stem, ETU increased from 0.007 ppm to 0.110 ppm for the same period. Total residues in seeds declined from 0.074 ppm after 40 days to 0.037 ppm after 76 days. Almost half of these residues was methanol-unextractable. The major part of extractable residues in seeds was hydrophobic in nature and characterized in the extracted soyabean oil as ETU, ETM and two unknowns. ETU in oil increased from 2 ppb after 40 days to 7 ppb after 76 days following the first treatment. (author). 7 refs, 7 tabs, 1 scheme