Estimation of sorption coefficients for fungicides in soil and turfgrass thatch

Environmental fates of turf-applied fungicides are not well understood. The role of thatch as a sorptive surface for fungicides has not been evaluated. Thatch may decrease mobility of fungicides and decrease their potential to be transported off-site. Batch type sorption studies were conducted to determine sorption coefficients (K(f)) for the fungicides triadimefon, [1-(4-chlorophenoxy)-3,3-dimethyl 1-1-(1H-1,2,4-triazol-1-g- l)butanone], vinclozolin [3-(3,5-dichlorophenyl)-5-methyl-5-vinyl-1,3- oxazolidine-2,4-dione], and chloroneb (1,4-dichloro-2,5-dimethoxybenzone) in thatch and in the underlying soil. The K(f) values also were derived from octanol/water partitioning coefficients (K(ow)) for these and five other compounds. All K(ow) values were determined with reverse-phase high pressure liquid chromatography (HPLC) and calculated from physical properties of the fungicides. The K(f) values [μmol(l-n) L(n)kg^-1] determined from isotherm data for thatch and soil (respectively) were 90 and 10 for triadimefon, 163 and 21 for chloroneb, and 431 and 47 for vinclozolin. When K(f) values were adjusted for organic C content of the sample, the resulting K(oc) values were similar for thatch and soil. The K(oc) values estimated from HPLC-derived K(ow) values were consistently less than those obtained using batch isotherm methods. The K(ow) values calculated from physical properties of the fungicides were poorly correlated with measured values. The HPLC method appears to be useful for determining sorption coefficients. Results indicate that thatch substantially increases fungicide sorption, which, in turn, decreases the potential for these compounds to migrate off site.