MSc

The study entitled “Sorption and movement of flupyradifurone in sandy loam soils with and without organic amendment” was conducted in Department of Soil Science and Agricultural Chemistry and the laboratory attached to the All India Network Project (AINP) on Pesticide Residues, College of Agriculture, Vellayani, Thiruvananthapuram, Kerala during 2017-19. The main objectives of the experiment were to study the adsorption, desorption, persistence and leaching of flupyradifurone in sandy loam soils with and without addition of organic amendment at the rate of 0.5 per cent farmyard manure. The soil was collected from the sandy belts of Kazhakkoottam, Thiruvananthapuram. The physical and chemical analysis of the soil revealed that the soil was acidic with 0.84 per cent organic matter content. Among the major nutrients, phosphorus content was found to be high; potassium was medium while other nutrients were low. The method for estimation of flupyradifurone residues from the soil was validated at 0.1, 0.5 and 1 µg g-1 level of flupyradifurone. Modified QuEChERS method with acetonitrile as the extracting solvent and Primary Secondary Amine (PSA) sorbent for cleanup was found to be suitable for the estimation of flupyradifurone and its metabolites from the soil. The method validation for estimation of flupyradifurone residues from water was done by liquid- liquid partitioning using dichloromethane, concentrated and made up in HPLC grade methanol for LC- MS/ MS analysis.
The adsorption- desorption studies were carried out at 5 concentrations of 20, 40, 60, 80 and 100 μg levels each both in soil and 0.5 per cent FYM amended soil in completely randomized design (ten treatments and three replications) . The study was also conducted under direct spiking of flupyradifurone at 3 levels viz., 20, 40 and 60 μg in 10g soil. The adsorption and desorption data fitted well in isotherms. The distribution coefficient Kd (mean value) was found high in the soil amended with FYM (2.58) than soil without amendment (2.41) which indicated increased sorption in both systems at all levels. The kf values (adsorption coefficient) were 2.57 and 2.46 for amended and soil without amendment respectively, indicating a high sorption capacity for the amended soil. The desorption was carried out in three cycles, the percentage desorption decreasing in each consecutive cycle. The desorption percentages were found in the range of 15.68, 17.14 , 20.74 , 23.69 and 27.77 per cent for the initial concentrations of 20, 40, 60, 80 and 100 µg, respectively and was found reduced in FYM amended soil viz., 14.39, 15.99, 19.29 , 22.74 and 26 percent for each of the concentrations. In all levels of concentration, hysteresis effect (ndes/nads) was noticed indicating desorption was slower than adsorption. In the soil samples directly spiked with flupyradifurone done in completely randomized design with six treatments and three replications, the desorption percentages were found lower and a still higher hysteresis was observed.
Mobility of flupyradifurone was assessed in completely randomized design with eighteen treatments and three replications i.e by loading 3 levels viz., 25, 50 and 75 µg formulation of flupyradifurone, separately on top of 200g soil columns loaded in PVC pipes and followed by eluting with 40, 80 and 160 mL of water @ 0.4ml min-1. In the sandy loam soil without amendment, flupyradifurone moved down the soil column which resulted in residue levels ranging from 13.84-9.56, 26.38- 19.08 and 34.30- 23.17 µg at 25, 50 and 75 µg levels, respectively when eluted with different volumes of water. In the soil amended with 0.5 per cent FYM, the corresponding residues ranged from 15.48- 11.79, 34.96- 22.00 and 36.62- 29.78 µg at 25, 50 and 75 µg levels indicating a higher retention in soil. The residue present in the leachate was found below detectable level for both amended soil and soil without amendment.
The persistence of flupyradifurone in sandy loam soil and 0.5 per cent FYM amended soil under three soil moisture conditions was studied using the formulation of flupyradifurone added at the rate of 1, 2 and 4 mg kg-1 in completely randomized design with eighteen treatments and three replications. The half- life of flupyradifurone in air dry soil when applied 1, 2 and 4 mg kg-1 levels were 19.38, 20.87, 22.47 days respectively and they were 20.41, 21.79 and 22.94 days, respectively in amended soil. For the soil at the field capacity level, application at 1, 2 and 4 mg kg-1 levels resulted in half- life of 11.14, 13.08 and 13.21 days for normal soil and 9.51, 14.59 and 15.74 days for amended soil, respectively. Under saturated soil conditions, the half- life were 9.08, 9.12 and 9.85 days in soil without amendment and 10.02, 10.12 and 10.28 days for the amended soil at 1, 2 and 4 mg kg-1 levels of application respectively. In the persistence study, no metabolites of flupyradifurone were detected.
Soil under the study was acidic, low in organic matter with 10.80 per cent clay, 20.50 per cent silt and 68.70 per cent sand. Extraction using acetonitrile followed by dispersive solid phase clean up using MgSO4-PSA was ideal for extraction of flupyradifurone. The estimation was done using LC-MS/ MS with retention time for flupyradifurone, 6-chloronicotinic acid and difluro ethyl amino furanone as 4.65, 4.22 and 1.34 respectively.
The study concluded that the adsorption coefficient was higher in FYM amended soil indicating stronger adsorption than soil without amendment and the desorption percentages were reduced in the same. Hysteresis effect was noticed in all the treatments indicating slower desorption than adsorption. The mobility of flupyradifurone was found to be slightly higher in soil without amendment compared to the 0.5 per cent FYM amended soil. The dissipation was found to be the fastest under submerged condition followed by field capacity and dry moisture conditions.