ENHANCED TRANSPORT OF ATRAZINE UNDER IRRIGATION WITH EFFLUENT

Enhanced transport of atrazine (2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine; C8H14ClN5) applied to a corn (Zea mays L.) held was observed after irrigation with secondary effluent. Cores to 4 m were obtained from 10 effuent-irrigated and 10 high-quality water-irrigated plots after two growing seasons and two winter rainy seasons. In most of the effluent-irrigated cores, atrazine was widely distributed with depth, with an average center of atrazine mass at 115 +/- 39 cm and a mean variance around the center of mass of 142 cm. In the high-quality water-irrigated cores, atrazine was concentrated in the upper soil horizons with an average center of mass at 63 +/- 64 cm and a mean variance around the center of mass of 58 cm. The mean centers of atrazine mass in the effluent-irrigated profiles and high-quality water-irrigated profiles are significantly different (Student's t-test, P = 0.06). The equilibrium sorption isotherm for atrazine in the presence of high-quality water was nonlinear, with a Freundlich n of 0.87 and a distribution coefficient (K-f) of 1.07. The atrazine isotherm in the presence of effluent had a similar a (0.86) but a significantly lower K-f of only 0.93. Atrazine at a rate of 4 mg/kg(-1) was added to soil columns filled with the < 1-mm size fraction of the 0 to 30-cm horizon of soil from an uncultivated site adjacent to the field site. Three replicate columns were leached with 0.85 pore volumes of either secondary effluent or 0.005 M CaCl2 solution at constant head. Atrazine in the effluent-treated columns was more strongly leached from the upper columns and peaked at higher concentrations lower in the columns.