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Title:   Author  item
                                            Schneider, Sharonitem
                                            Koskinen, Williamitem
                                            COX, LUCIA - CSIC-IRNAS SEVILLA SPAINitem
                                            Rice, Pamelaitem
                                            CLAY, SHARON - SOUTH DAKOTA STATE UNIVitem
                                            WERDIN-PFISTERER, NANCY - UNIVERSITY OF MINNESOTAitem
                                            NORBERG, KRISTEN - UNIVERSITY OF MINNESOTA
  Submitted to: Journal of Agricultural and Food Chemistry
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 8/31/2006
                                    Publication  Date: 10/11/2006
                                    Citation: Papiernik, S.K., Koskinen, W.C., Cox, L., Rice, P.J., Clay, S.A., Werdin-Pfisterer, N.R., Norberg, K. 2006. Sorption-desorption of imidacloprid and its metabolites in soil and vadose zone materials. Journal of Agricultural and Food Chemistry. 54:8163-8170.Interpretive Summary: Sorption-desorption is arguably the most important process affecting the transport of pesticides through soil since it controls the amount of pesticide available for transport. Sorption is usually characterized by determining coefficients, which measure the chemical's distribution between soil and water. Sorption coefficients are then used in transport models to predict movement from the soil surface through the subsoils. Variability in subsurface soil properties can significantly affect prediction in pesticide transport. This research characterized the sorption-desorption of the insecticide imidicloprid, and three of its metabolites, as a function of changing soil properties with depth in two soils. We found that the soil properties and sorption was significantly different in subsoils as compared to surface soils. The common approach of estimating subsurface sorption coefficients based on the surface soil sorption coefficient and the organic matter content of the subsurface soil resulted in both overprediction (by a factor of >7) and underprediction (up to a factor of  >20) of the measured sorption value of each compound. In all cases, sorption was not readily reversible (the chemicals did not release from the soils), further complicating the accurate prediction of pesticide mobility in the subsurface. These results emphasize the importance of sorption/mobility measurements for increasing the accuracy of models that attempt to predict the frequency of groundwater contamination by pesticides and expected pesticide concentrations in the subsurface. These results will benefit scientists in understanding the variability of soil properties and processes as a function of soil depth, so they will be able to more accurately predict potential transport of pesticides to ground water.
                                Technical Abstract: Sorption-desorption is arguably the most important process affecting the transport of pesticides through soil since it controls the amount of pesticide available for transport. Sorption is usually characterized by determining batch sorption coefficients. These coefficients are often used in transport models to predict pesticide movement in the subsurface. Variability in subsurface soil properties can significantly affect pesticide transport and the potential for groundwater contamination. This research characterized the sorption-desorption of imidicloprid (1-[(6-chloro-3-pyridinyl)-methyl]-N-nitro-2-imidazolidinimine), and three of its metabolites, 1-[(6-chloro-3-pyridinyl)methyl]-2-imidazolidinone (imidacloprid-urea), 1-[(6-chloro-3-pyridinyl)methyl]-4,5-dihydro-1H-imidazol-2-amine (imidacloprid-guanidine) and 1-[(6-chloro-3-pyridinyl)methyl]-1H-imidazol-2-amine (imidacloprid-guanidine-olefin), as a function of changing soil properties with depth in two soils. Sorption of each compound was highly variable, and sorption was hysteretic in all cases. Normalizing the sorption coefficients (Kf) to the organic carbon or the clay content of the soil did not reduce the variability in sorption coefficients for any compound. The common approach of estimating subsurface sorption coefficients based on the surface soil normalized sorption coefficient and the organic carbon content of the subsurface soil resulted both overprediction and underprediction of the sorption of each compound. These results illustrate the importance of evaluation of the sorption data used to predict potential mobility. Understanding the variability of soil properties and processes as a function of soil depth is necessary for accurate prediction of pesticide dissipation.


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