A laboratory study on adsorption-desorption behavior of flupyradifurone in two Indian soils: effect of soil properties and organic amendment

Purpose In the soil-water system, adsorption-desorption characteristics of pesticides significantly influence their environmental fate (mobility, degradation, and transformation). However, bioavailability of pesticides can be modified by the addition of organic amendments in soils. Flupyradifurone is a neonicotinoid insecticide widely used to control sucking insect pests of vegetables in India. In this experiment, effect of organic amendment was investigated on the adsorption-desorption behavior of flupyradifurone in two Indian soils. Methods Soils used in this experiment were collected from the plough layer (0-15 cm) of two different agroclimatic zones of India; Terai soil of West Bengal (Entisol) and Alluvial soil of Delhi (Inceptisol). The batch equilibrium technique was used to evaluate the kinetics and sorption behavior of flupyradifurone in test soils. Residues of flupyradifurone were quantified by HPLC (High-Performance Liquid Chromatography). Results Sorption kinetics of flupyradifurone indicated that maximum adsorption was achieved at 24 h in both soils, and sorption kinetics was best explained by pseudo second-order model. High clay and organic carbon content of Entisol could be attributed to higher adsorption (37.92 +/- 0.19) of flupyradifurone in Entisol as compared to Inceptisol (22.37 +/- 0.19). Furthermore, addition of farmyard manure (FYM) markedly increased the adsorption capacity of both soils (49.98 +/- 0.19 for Entisol and 22.37 +/- 0.19 for Inceptisol). Adsorption data were best fitted with Freundlich adsorption isotherm, and slope of the Freundlich adsorption isotherm (1/n) in all soils were < 1 indicating that sorption was non-linear. Calculation of thermodynamic parameters pointed out that sorption was spontaneous and more favored at high temperatures. Flupyradifurone's desorption rate is slower than the adsorption rate for two test soils, indicating that positive hysteresis occurs. The primary mechanism involved in flupyradifurone sorption for both amended and unamended soils was physical adsorption (surface adsorption and partition). Conclusion This experiment has relevance in assessing the fate of flupyradifurone in amended field conditions. Additionally, dose optimization can also be done in an attempt to reduce soil/groundwater contamination.