Experimental Variability in Characterization of Cyfluthrin Sorption to Soil

To assess the risk of a pesticide to leach to groundwater or to run off to surface water after application, it is necessary to characterize the sorption of the pesticide to soil. For pyrethroids, their hydrophobicity, strong sorption to various materials, and low solubility make it difficult to accurately characterize sorption processes. The objective of this research was to evaluate the variability in cyfluthrin ((RS)-α -cyano-4-fluoro-3-phenoxybenzyl (1RS,3RS;1RS,3SR)-3-(2,2-dichlorovinyl)-2,2-dimethylcyclopropanecarboxylate) sorption to soil as affected by experiment conditions. To minimize cyfluthrin sorption on the walls of glass, silanized-glass, stainless steel, and PTFE centrifuge tubes, cyfluthrin solution was added to aqueous soil slurries or directly to soil, after which it was equilibrated with aqueous solution. Depending on the soil, variation in sorption coefficients, K _oc, obtained using different experimental methodologies with one soil can be comparable to the variation in K _oc values obtained for soils with different physical and chemical properties using one method. K _oc values for cyfluthrin ranged from 56,000 to 300,000 L kg⁻¹. Sorption methodology needs to be evaluated before sorption coefficients are used in predictive transport models.

Key Words:

• Cyfluthrin
• Sorption
• Batch equilibration method

Notes

¹Sn:Sl = solution:soil (g:g).

²Cy = ¹⁴C-cyfluthrin concentration (% solvent): 4 μ g L⁻¹ (0.4%), 0.7 and 1 μ g L⁻¹ (0.1%).

³KS = Kansas clay loam sediment, CA = Fresno sandy loam, G = glass vessel, GD = dichloromethylsilane treated glass vessel, GS = Surfasil treated glass vessel, PFT = polytetrafluoroethylene bottle.

¹KS = Kansas clay loam sediment, CA = Fresno sandy loam, ND = Gardena clay loam, FL = Vero Beach sand.

²Cyfluthrin applied to either the 0.01 M CaCl₂ solution or directly to the soil prior to addition of the CaCl₂ solution. Solution:soil (g:g) = 200:1. Cyfluthrin concentration = 1 μ g L⁻¹ (0.1% solvent) or 0.2 μ g g⁻¹.