FATE OF ~(14)C-PIRIMICARB IN CHINESE CABBAGE AND SOIL

摘要

A pot trial was conducted to investigate the persistence and metabolism of ~(14)C-pirimicarb in Chinese cabbage and meadow soil, a common loam soil type of North China. Radioassay and thin layer chromatography techniques were used. During incubation, the temperature was maintained at 25 ± 1℃, and sufficient light and moisture were provided to grow the cabbage. The results showed that ~(14)C-pirimicarb was slightly persistent on the surface of the leaves, the majority of which penetrated the shoots rapidly; its half-life on the surface of the leaves was approximately 6 days. Carbon 14-pirimicarb was persistent in meadow soil, with a half-life of about 9 days. For the whole soil-cabbage system, the half-life was approximately 11 days, and about 82% of the applied ~(14)C-pirimicarb disappeared within 15 days, mainly by degradation. Two metabolites of ~(14)C-pirimicarb were determined, both in cabbage and in meadow soil, one being chloroform soluble and the other methanol soluble. The ~(14)C-pirimicarb that penetrated the cabbage converted to metabolites relatively slowly, within a few days after being sprayed, but penetration was slightly faster after this period; in turn, the metabolites degraded to CO_2 very rapidly. It was also found that a very small amount of the ~(14)C-pirimicarb that penetrated the shoots could be assimilated to become bound ~(14)C residues. In soil, the ~(14)C radioactivity in the chloroform extractable residues decreased steadily during the course of incubation, while the methanol extractable residues increased steadily up to the end of incubation. It was also found that ~(14)C-pirimicarb was weakly sorbed by soil.