Sorption and mobility of dithiopyr in golf course greens rooting medium

Sorption and mobility of dithiopyr in golf course greens rooting medium (RM) were studied. The sorption increased from 20 to 27 degrees C at 24 h after treatment (HAT) and reached equilibrium in 48 HAT at 20 degrees C. The sorption isotherms had Freundlich values (KF) of 1122, 27.44 to 35.16, and 0.053 to 0.168 for peat moss, the RM, and quartz sand, respectively, and solid to aqueous phase partition coefficients (Kd) of 470 to 1706 L/kg, 14.61 to 84.4 L/kg, and 0.07 to 0.29 L/kg for peat moss, RM, and quartz sand, respectively. Generally, higher dithiopyr concentration in the aqueous solution and the reduced pH of the solution corresponded to the higher Kd values. The average values for dispersion (D, cm2/min), retardation coefficient (R), beta, and omega parameters for solute transport in the RM lysimeter; obtained from CXTFIT curve fitting of Br- breakthrough curves; were 0.95, 1.01, 1, and 93.89, respectively. After elutriation by 18 L of aqueous KNO3 (10 mM), greater than 90% of the added dithiopyr remained in the top 10 cm of the RM lysimeter and no detectable dithiopyr was present at depths beyond 35 cm. The lysimeter effluent contained dithiopyr at concentrations less than 3.5 microg/L. The R value obtained from CXFIT curve fitting is 38.5. Results from both sorption and mobility experiments indicated that dithiopyr is quite immobile in golf course greens RM and has minimal potential for movement into surface water drainage or ground water.