EVALUATION OF METHODS FOR CHARACTERIZING CARBOFURAN HYDROLYSIS IN SOIL

The objective of this study was to develop a method that could be applied to investigations of soil/environmental factors influencing the spatial and temporal variability of carbofuran hydrolysis in field soils. Two factors were considered: (i) soil handling and pesticide application, and (ii) the method of data summarization. Three soil handling/pesticide treatments were evaluated: (i) sieved soil/sprayed pesticide application, (ii) injected pesticide application/sieved soil, and (iii) injected pesticide application/intact core incubation. This last method was developed to mimic field conditions where high localized concentrations of carbofuran (2,3-dihydro-2,2-dimethyl-7-benzofuranyl methylcarbamate) occur as a result of banded application of granular carbofuran at planting time. For all three treatments sigmoidal (CO2)-C-14 production kinetics were observed. Several mathematical models for describing sigmoidal product appearance data were evaluated and a general saturation model was found to yield the best fit. Using parameter estimates obtained from this model in statistical tests, we found that the intact core soil treatment yielded significantly longer half lives for carbofuran degradation. Additional experimental evidence suggests that soil structure of the intact cores retarded diffusion of the (CO2)-C-14 produced from carbofuran degradation and influenced the kinetic pattern observed.