|Cheng, H -|
Submitted to: Meeting Proceedings
Publication Type: Proceedings
Publication Acceptance Date: October 10, 2009
Publication Date: October 10, 2009
Citation: Cheng, H.H., Koskinen, W.C. 2009. Effects of “Aging” on Bioreactive Chemical Retention, Transformation, and Transport in Soil. In: Proceedings Molecular Environmental Soil Science at the Interfaces in the Earth's Critical Zone. October 10-14, 2009, Hangzhou, China. 2010 CDROM. Technical Abstract: The purpose of this paper is to illustrate how aging can affect the behavior of bioreactive chemicals in the soil. This paper will focus on the sorption process, which can directly or indirectly control transformation and transport processes. Most commonly, aging effects have been characterized by batch equilibration and batch sequential extraction methods, in which changes in sorption coefficients (i.e. Kd) are determined for the chemical remaining after a given equilibration or incubation period. Alternative innovative methods to determine aging effects include isotopic exchange and supercritical fluid extraction methods. Kd values have generally been shown to increase with aging time. The mechanisms that result in aging effects on sorption in soils can be artifacts of the methodology used to characterize sorption, or changes in chemical or physical processes, or a combination of these processes, all of which may affect the retention or sorption/desorption of the chemical in soil, which in turn affects pesticide transport and transformation. Regardless of the mechanisms involved in aging, observed increases in sorption during pesticide aging should be taken into account during characterization of the sorption process for mathematical models of pesticide transport; potential transport of the pesticide would be over predicted if freshly treated soil Kd values were used to predict transport. The question of whether increases in sorption with aging affect degradation is still unanswered.