Af!Pf! VIJA VAN THESIS. Submitted in p.rt;al lulfl1mbnt of the requirement for the degree of. Faculty of Agriculture KerlllltJAgricultural University

Transcription

1 CARBOFURANRESIDUES IN BANANA By Af!Pf! VIJA VAN THESIS Submitted in p.rt;al lulfl1mbnt of the requirement for the degree of ~udi1r 11 'qiin5.oply~ Faculty of Agriculture KerlllltJAgricultural University iu J\gticulture DEPARTMENT Of SOIL SCIENCE AND AGRICULTURAL CHEMISTRY COLLEGE OF HORTICULTURE VELLANIKKAR~ THRJSSUR~ 6~O 654 Kerma.India 2000

2 Dr. N. P. Chinnamma Professor and Head Department of Soil Science & Agricultural Chemistry College of Horticulture Vellanikkara CERTIFICA TE Certified that the thesis entitled "Carbofuran residues in banana" is a record of research work done by Sri. A. P. Vijayan, under my guidance and supervision and that it has not previously formed basis for the award of any degree, fellowship or associateship to him. etl~ ~ Dr. N. P. Chinnamma Chairperson Advisory Committee

3 ABSTRACT An investigation was carried out during to study the fate of carbofuran in banana. An analytical method using HPLC was standardised for the estimation of carbofuran and its metabolite residues in banana. Carbofuran and its metabolites were estimated directly without any derivatisation and all the metabolites are detected simultaneously in a single chromatographic run. Due to high sensitivity, up to sub-nanogram quantities were detected. Since only few steps were involved, recoveries of the test compounds were very high (81.4 to 98.14%). Extraction and cleanup procedures were simple, fast and less expensive. Owing to the above advantages, the present method can be used in research and in environmental monitoring programms. A series of studies were conducted to investigate the absorption, translocation and metabolism of carbofuran applied to banana at different doses, at different periods of time and through different routes of administration, with special emphasis on the residues in fruit. The treatments comprised of two levels and three modes of carbofuran application viz. soil application of750 and 1500 mg ai planr1, leaf axil filling with 375 and 750 mg ai. planr1 and pseudo stem implantation with 375 and 750 mg a:iplanr1at 7thmonth in addition to the normal recommended practice. Absorption of carbofuran from soil application of 1125 mg planr1 (average of two levels) and leaf axil application of mg planr1 (average of two levels) was similar. Absorption of the insecticide increased up to 10 days, declined thereafter and ceased by about 21 days. When the granules were implanted at a rate of mg planr1 (average of two levels) by boring the pseudostem, the absorption was much higher which continued up to 33 days. When applied by foliar spray of a 100

4 ppm solution, one-third of carbofuran was absorbed by third day and further absorption was limited. Carbofuran applied in soil enters the plant root dissolved in water and hence soil moisture is a decisive factor in its availability. Since leaf axil is not a natural absorption site, carbofuran applied at the axil has to penetrate the cuticular barrier to enter the plant system. These absorption limiting factors do not exist in case of pseudostem implantation and hence the high rate of absorption from pseudostem. This new method of administration besides being more economic will help to reduce the pesticide load of soils cropped to banana. Persistence of carbofuran in leaf was determined by the method of application. In case of soil application, it persisted up to 33 days. In case of leaf axil application, it was detected in leaf up to 63 days. Similarly, when applied by pseudostem implantation, it was detected up to 63 days in leaf but the level was much higher. Degradation rate of carbofuran (TI/2)in banana in the three modes of application were 9.5d, 15.8d and 13.5 d respectively. Residue dynamics in leaf was characterised by a fast depletion of carbofuran with a concomitant build-up of 3-0H-carbofuran. At the end of the 63-day period post application, the residues consisted of 1.5% carbofuran and 98.5% 3-0H-carbofuran in addition to small amounts of 3-0H-carbofuran conjugate. Though small amounts of 3- ketocarbofuran were detected at the initial stages, its presence was transitory. The metabolism of carbofuran applied as a foliar spray was much slow with the result that the residues at 18 days comprised of 84.7% carbofuran and 15.3% 3-0Hcarbofuran. A pathway of metabolism of carbofuran in leaf comprising of carbofuran, 3- OH-carbofuran, 3-ketocarbofuran and 3-0H-carbofuran conjugate is proposed.

5 Evidence was gathered for the direction of movement of carbofuran in banana plant. Carbofuran applied to leaf was found to move only upwards and reverse movement was not observed. The terminal residues of carbofuran in banana grown in three soil types were studied. Carbofuran was applied at 750 and 1500 mg planrl at the 7th month. Carbofuran residues were not detected in fruit. In a field experiment, carbofuran was applied at 8 times the recommended dose to banana after bunching (8thmonth). The residue distribution at harvest showed that about 96.2% of the total residues of carbofuran were concentrated in the leaf. Pseudostem core, leaf sheath, peduncle, corm and fruit contained meagre amounts of the residue. Of the residues in the fruit, 91% was located in the fruit peel and the rest 8% in the fruit pulp. Banana in Trichur and Kunnamkulam town markets were periodically sampled during and anlysed for carbofuran residues. All the samples tested negative for carbofuran residues. Carbofuran is readily absorbed from granules applied in the soil, placed in the leaf axil or implanted in the pseudostem. The residues are concentrated in the leaf where it is metabolised fast to 3-0H-carbofuran that persists up to the senescence of the leaf. Mobilisation of the residues to the fruit seldom occurs even at double the recommended dose and late application up to the 7thmonth.