Premasis Sukul

Influence and persistence of phorate and carbofuran insecticides on microorganisms in rice field.

An experiment was conducted in microplots (4 m x 4 m) with two insecticides, phorate and carbofuran at rates of 1.5 and 1.0 kga.i.ha(-1) respectively, to investigate its effect on the population and distribution of bacteria, actinomycetes and fungi as well as the persistence of the insecticidal residues in rhizosphere soils of rice (Oryza sativa L., variety IR-50). Application of the insecticides stimulated the population of bacteria, actinomycetes and fungi in the rhizosphere soils, and the stimulation was more pronounced with phorate as compared to carbofuran. Both the insecticides did not have marked effect on the numbers of Streptomyces and Nocardia in the rhizosphere soils. However, the growth of Bacillus, Escherichia, Flavobacterium, Micromonospora, Penicillium, Aspergillus and Trichoderma with phorate and that of Bacillus, Corynebacterium, Flavobacterium, Aspergillus and Phytophthora with carbofuran were increased. On the other hand, the numbers of Staphylococcus, Micrococcus, Fusarium, Humicola and Rhizopus under phorate and Pseudomonas, Staphylococcus, Micrococcus, Klebsiella, Fusarium, Humicola and Rhizopus under carbofuran were inhibited. Both the insecticides persisted in the rhizosphere soil for a short period of time and the rate of dissipation of carbofuran was higher than that of phorate in the soil depicting the half-life (T1/2) 9.1 and 10.4 days, respectively.

Insecticides: their effect on microorganisms and persistence in rice soil.

A field experiment was conducted to investigate the effect of four insecticides, HCH, phorate, carbofuran and fenvalerate, at recommended doses on the preponderance of bacteria, actinomycetes and fungi. We also measured the persistence of the insecticides in the rhizosphere soil of rice. HCH and fenvalerate stimulated the proliferation of all of the microorganisms significantly. Phorate increased the population of bacteria and actinomycetes. Carbofuran accentuated the preponderance of actinomycetes in soil. Insecticides, in general, did not have marked influence on the proliferation of Bacillus, Streptomyces, Aspergillus and Fusarium in soil. However, we observed a stimulation of growth of Staphylococcus, Proteus and Sarcina with HCH, Pseudomonas, Corynebacterium, Erysipelothrix and Rhizopus with phorate, Serratia, Corynebacterium, Klebsiella, Escherichia, Rhizopus and Humicola with carbofuran, and Staphylococcus, Sarcina, Klebsiella and Nocardia with fenvalerate. On the other hand, there was an inhibition in growth of Pseudomonas, Micrococcus, Nocardia and Penicillium with HCH, of Pseudomonas, Micrococcus and Penicillium with carbofuran, and of Pseudomonas, Micrococcus and Micromonospora with fenvalerate. Different types of insecticides exhibited differential patterns of dissipation in soil. HCH had the highest persistence followed by phorate, carbofuran and fenvalerate, respectively.

Extraction and clean up procedures for the analysis of permethrin, cypermethrin, deltamethrin and fenvalerate in crops by GLC ‐ ECD

The extraction and clean up of four synthetic pyrethroids, (permethrin, cypermethrin, deltamethrin and fenvalerate) from soil and chickpea and green gram foliage, pod and grain is described. The interferences from the co‐extractives are removed by thin layer and column chromatography using different adsorbent and solvent system. Finally analysis is carried out by electron capture gas‐liquid chromatography. Pesticides from foliage and pod samples were well extracted with acetone in a waring blender while extraction was carried out in soxhlet with hexane in case of soil and grain. TLC with silica gel a adsorbent and hexane — acetone (9:1) as solvent system was the best clean up method because it gives good recovery value and has better capacity of removing co‐extractives.

Photodecomposition of isoproturon in the presence and absence of photocatalysts like H2O2 and TiO2

Isoproturon was photolysed in presence and absence of H2O2 and TiO2 at different wave lengths (254 nm, 290 nm and 300–800 nm). The impact of H2O2 and TiO2 to enhance the photodegradation of isoproturon was established. Eight photoproducts were identified by GC‐MS. N‐demethylation, hydroxylation, dimerisation, deisopropylation, methylation of aryl amine, removal of dimethylamine followed by methoxylation were found to be the main processes during photoreaction.

METALAXYL : ITS PERSISTENCE AND METABOLISM IN SOIL

Different biotic and abiotic factors were found to play a vital role in attenuating metalaxyl residues in soil. In addition to metalaxyl many other products were found by HPLC and GC‐MS analysis while studying its soil metabolism in presence of natural sunlight. Three compounds were identified and characterized: 2,6‐dimethylaniline, 2,6‐dimethyl‐N‐ethylacetanilide and N‐(2,6‐dimethyl phenyl) alanine methyl ester.

Dissipation of phosphamidon and its effect on the change of some biomolecules of Indian mustard (Brassica juncea L. Czern and Coss)

The dissipation pattern of phosphamidon residues in Indian mustard (Brassica juncea L. Czern and Coss) has been studied along with its effect on the changes of chlorophyll, sugar, starch, oil and some fatty acids and minerals. The safe waiting period was calculated to be 12.56 days for 0.03% and 15.19 days for 0.05% in green foliage; the corresponding values in green pods were 12.50 and 15.30 days. For both the doses, the T1/2 were 3.34 days in green foliage and 3.58 and 3.86 days in green pods. The chlorophyll content was lowered after the application of phosphamidon but increased with dissipation of the pesticide. The carbohydrate was lowered whereas the oil contents were greatly increased in the treated seeds. The individual fatty acids did not differ much albeit the erucic acids in treated seeds were found to be higher than the control.