I= DEGRADATION, TRANSFORMATION AND METABOLISM OF 14C-LABELLED CYFLUTHRIN (BAYTHROID) IN SOIL-PLANT SYSTEM UNDER LABORATORY AND FIELD CONDITIONS
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Title of Thesis
DEGRADATION, TRANSFORMATION AND METABOLISM OF 14C-LABELLED CYFLUTHRIN (BAYTHROID) IN SOIL-PLANT SYSTEM UNDER LABORATORY AND FIELD CONDITIONS

Author(s)
Institute/University/Department Details
University of the Punjab, Lahore
Session
1998
Subject
Philosophy
Number of Pages
242
Keywords (Extracted from title, table of contents and abstract of thesis)
baythroid, cyfluthrin,insecticide, pests, cotton, synthetic pyrethroid

Abstract
Baythroid is a commonly used insecticide to control insect pests of cotton in Pakistan. It contains cyfluthrin (a synthetic pyrethroid) as an active ingredient. Experiments were conducted in the laboratory, green-house and field lysimeter to study: a) the movement of cyfluthrin in soil and plant systems, b) its degradation and transformation into extractable and bound (humus) components, and c) influence of baythroid on soil microflora, soil microbial functions, plant growth, and nitrogen (N) nutrition of plants.

14C-labelled cyfluthrin was used in studies pertaining to the movement in soil and plant and transformations into different soil components, while in all other studies Baythroid, was used. In experiments on plant growth and N nutrition, 15N-labelled N chemicals (ammonium sulphate or potassium nitrate) were used to specifically study the effects of Baythroid on the plant availability of N from different sources i.e., native soil organic matter and applied fertilizer.

A spectrophotmetric method standardized to quantify cyfluthrin in methanol extracts of soil samples revealed an absorption maximum at 230 nm. By using this method, a rapid and substantial binding of cyfluthrin in soil was observed with the extent of binding (19-84% of the applied within 24 hrs. of contact) being dependent on clay and organic matter content of the soil; the two parameters showing a significant positive correlation with the amount of cyfluthrin bound. Movement of cyfluthrin in soil columns was also affected by organic matter content and the soil with high organic matter content (>3%) retained almost 100% of the applied cyfluthrin in the top 2.5 cm layer.

In laboratory incubation experiments, 44-58% of the applied cyfluthrin-14C was lost as CO2 from soil samples incubated for 18 weeks at different moisture regimes with or without organic amendment. Oxidation of cyfluthrin-14C was more rapid in unamended soils and at low moisture regime. In unamended soils, a higher proportion of cyfluthrin-14C was extractable with methanol. while in amended soils, more 14C was round as humic and fulvic acid. Lower moisture regime facilitated the transformation of cyfluthrin-14C into stable (humic and fulvic acid) humus forms. The route of degradation of cyfluthrin in soil appeared to be similar t~ that reported for other 3-phenoxybenzyl pyrethroids. two major metabolites of cyfluthrin determined. in methanol extracts of soil samples were i) CONH2-cyfluthrin (M I) and ii) 3-phenoxy-4-fluorobenzoic acid (M2). of the total 14C appearing in methanol extracts, 17-27% was attributable to M I and only 0.2-2.0 to M2 after 18 weeks of incubation. Rest of the 14C (66-79% of the total) was found as cyfluthrin. . Organic amendment led to a higher percentage of 14C in the two metabolites; no specific trends were observed for the effect of moisture regimes.

Under field situation, ca 50% of the cyfluthrin-14C applied to lysimeter soil was unaccounted after 9 weeks; losses during subsequent period of 29 weeks were only 10%. Wheat growth and organic amendment caused a decrease in the loss of 14C. A greater proportion (generally >80%) of the residual 14C in field lysimeter was determined in the top 0-10 cm of the soil profile suggesting a meager leaching into deeper soil layers. In general, 80-85% of the soil 14C was found in bound (non-extractable with methanol) forms. The uptake of cyfluthrin-14C by plants was also very low with a net uptake of 0.376% of the applied 14C by cotton and 0.011% by the succeeding wheat crop. In view of a relatively rapid dissipation from soil and efficient binding, movement of insecticide residues to sub-surface water and its entry into human-animal system may be limited.

In spite of being non-systemic, significant entry into and movement within the leaf tissues of cyfluthrin was observed, both through xylem and phloem. Autoradiography of leaves sprayed with 14C-cyfluthrin revealed a rapid distribution of 14C within the recipient leaf and its movement to the adjoining leaves and portions of shoot away from the site of application. Dissipation of 14C-cyfluthrin sprayed onto cotton leaves was fairly rapid with 64% loss of initially applied 14C after 2 days of application; the loss increased to 71 % after 35 days. of the residual 14C. a greater proportion (>60%) was determined in methanol extractable forms at different sampling intervals. Thin-layer chromatography and linear scanning of methanol extracts of leaves showed that up to 22% of the 14C was present as MI and 12% as M2 after 35 days of application. Nevertheless, a major proportion (61-71 %) of the extractable 14C was still determined as parent compound suggesting a fairly recalcitrant nature of cyfluthrin.

Several laboratory incubation. experiments were conducted to study the effect of Baythroid on soil microbiology (bacterial and fungal population and microbial biomass), and biochemistry (soil enzymes, immobilization-remineralization of inorganic N, mineralization of organic N, nitrification, and denitrification). Upto a certain level of addition (generally 3.2 μg g-1. soil), Baythroid caused a substantial increase in bacterial and fungal population, soil respiration and microbial biomass. .After 15 days of incubation, bacterial population was 14x106 in Baythroid-treated soil compared to 9x106 in untreated soil; respective values for fungal population were 26x104 and 14x 106. Soil respiration and microbial biomass showed an increase of 38.4% and 6.5%. Activity of enzymes like amylase, invertase, cellulase and urease also increased significantly (92, 111, 19 and 16 % increase, respectively) at Baythroid level of 1.6 μg g-1. soil. Microbial activities like immobilization-mineralization turnover of inorganic N and mineralization of organic N showed a significant positive response to Baythroid application; the latter increased by 190% at 64 μg g-1. Baythroid.

An important observation was that the process of nitrification was significantly inhibited by Baythroid, a finding with multifarious implications to N cycle processes and N nutrition of plants. Over a study period of over 3 weeks, extent of nitrification inhibition in incubated soil samples was found to be 0,49,80, 85 and 90% at 0.4, 0.8, 1.6, 3.2, and 6.4 μg g-1 Baythroid g-1. soil. respectively. Increase in other microbial processes described above was attributed mainly to nitrification inhibition and accumulation of NH4-N in soil treated with Baythroid. The inhibitory effect of Baythroid was fairly persistent and even 30 days after application to soil, it caused 69% inhibition of nitrification. The results of these experiments suggest that the fate and persistence of an agrochemical could be determined indirectly through its effect on certain soil microbial processes e.g., nitrification inhibition in the case of Baythroid.

Baythroid residues were found to have a positive effect on dry matter accumulation and N uptake of the three crop types i.e., maize, rice and wheat used in the present studies. Nitrogen was taken as a model nutrient with the view of considerable dependence of most plants on N uptake so far as the dry matter accumulation is concerned. The three plant types differed in their response to Baythroid application. Substantially positive effect was noted on maize where dry matter yield increased by 60-70% at 3.2 μg Baythroid g-1 soil. This increase was attributed mainly to an increased availability of N from soil organic matter as a result of added nitrogen interaction (ANI). Rice plants also showed a positive response to Baythroid application and the dry matter yield increased by 13% at 1.6 μg g-1 soil Baythroid. In case of wheat, however, Baythroid had a negative effect on dry matter production and N yield (27% and 19% decrease, respectively) at higher of the two rates tested i.e., 0.4 and 1.6 μg g-1 soil. This observation was attributable to a lack of epicuticular wax on wheat leaves due to Baythroid addition.

A major factor found responsible for increased dry matter accumulation by maize and rice plants following treatment of soil with Baythroid was inhibition of nitrification with consequent accumulation of NH4+-N. Inhibition of nitrification was considered to influence N dynamics and plant growth in various ways like: i) a greater mineralization of organic N in the presence of NH4Vs NO3 leading to substantial increase in mineralization and plant availability of soil nitrogen through the so-called €œpriming€™ effect or added nitrogen interaction (ANI), ii) preferential uptake of available NH4+. by microbes leading to increased availability to plants of any NO3 formed in soil or that already present, and iii) prolonged availability of NH4+ along with NO3 , a situation of N availability considered favourable for plant growth. Aside from these factors, however. results of incubation studies suggested a positive effect of Baythroid on soil microbial functions that may be beneficial to plant growth.

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S. No. Chapter Title of the Chapters Page Size (KB)
1 0 Contents
84.48 KB
2 1 Introduction and review of literature 1-15
121.99 KB
  1.1 Introduction 1
  1.2 Review of literature 5
  1.3 Concluding remarks 15
3 2 Materials and methods 16-33
143.14 KB
  2.1 Baythroid 16
  2.2 Cyfluthrin and its metabolites 16
  2.3 14 C-labelled cyfluthrin 18
  2.4 N-serve 19
  2.5 15 N-labelled chemicals 20
  2.6 Soil 20
  2.7 Indicator plants 30
  2.8 Harvesting of plants and processing of plant material for analyses 30
  2.9 Autoradiography of leaves 31
  2.10 Extraction and determination of 14 C residues from leaves 32
4 3 Results and discussion 34-136
1038.22 KB
  3.1 Fate of Baythroid/cyfluthrin in the soil-plant system 34
  3.2 Soil microflora and microbial functions 77
  3.3 Baythroid and plant growth 104
5 4 Literature cited 127-159
1082.99 KB
  4.1 Appendix