Submitted to: Journal of Environmental Science and Health
Publication Type: Peer reviewed journal
Publication Acceptance Date: 11/1/2005
Publication Date: 5/2/2006
Citation: Koskinen, W.C., Rice, P.J., Seebinger, J.D. 2006. Experimental variability in characterization of cyfluthrin sorption to soil. Journal of Environmental Science and Health. 41(4):323-331. Interpretive Summary: To assess the risk of a pesticide to leach to ground water or to runoff to surface water after application, it is necessary to understand the pesticide's tendency to bind to soil (sorption) or be dissolved in water. For pyrethroids, their low water solubility and strong sorption to various materials, including soil and glassware, make it difficult to accurately determine their sorption to soil using standard laboratory procedures. The overall goal of such experiments is to calculate a value (sorption coefficient, Koc) that is the distribution of the compound between soil and water. Sorption coefficients can be utilized with computer models to predict chemical transport, chemical availability, and assess risk. The objective of this research was to evaluate the variability in cyfluthrin sorption to soil as influenced by experiment conditions; material of the test vessel, different soils, and method of pesticide application to the test vessel. We found there was a greater variation in measured Koc for cyfluthrin when one soil was evaluated using different methods than when one methodology was utilized to measure Koc for several soils with different characteristics. These results show scientists or modelers that before sorption coefficients are used in predictive transport models, the values must be evaluated with regard to the sorption methodology used to obtain the value.
Technical Abstract: To assess the risk of a pesticide to leach to ground water or to runoff 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 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. Variation in sorption coefficients, Koc, obtained using different experimental methodologies with one soil was greater than variation in Koc values obtained for soils with different physical and chemical properties using one method. Koc for cyfluthrin ranged from 56,000 to 300,000 ml g-1. Sorption methodology needs to be evaluated before sorption coefficients are used in predictive transport models.