NONEQUILIBRIUM SORPTION AND DEGRADATION OF 3 2-CHLORO-S-TRIAZINE HERBICIDES IN SOIL-WATER SYSTEMS

Miscible displacement techniques were used for the simultaneous study of nonequilibrium sorption and degradation of atrazine (2-chloro-4-ethylamino-6-isopropylamine-s-triazine), simazine (2-chloro-4,6-bis(ethylamino)-s-triazine), and cyanazine (2-(4-chloro-6-ethylamino)-s-triazine-2-ylamino-2-proprionitrile) on two central New York soils. A bicontinuum model, which considers sorption in two domains and includes a description of first-order degradation, was applied to describe experimentally determined breakthrough curves. Values of the equilibrium sorption constant, K, and first-order degradation rate constant, mu, were independently measured using batch and mass-balance techniques. Values of the sorption rate coefficient (fitted with a bicontinuum model) were inversely correlated with K, and were dependent on concentration and velocity. Estimates of the rate of atrazine degradation were on the same order, but slower when measured with miscible displacement vs. batch incubation techniques. The techniques presented in this study provide an opportunity to better quantify sorption and degradation parameters that are required in environmental fate models.