Enhanced Transport of Atrazine Under Irrigation with Effluent

Enhanced transport of atrazine (2‐chloro‐4‐(ethylamino)‐6‐(isopropylamino)‐ s ‐triazine; C 8 H 14 CIN 5 ) applied to a corn ( Zea mays L.) field was observed after irrigation with secondary effluent. Cores to 4 m were obtained from 10 effluent‐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 n (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 CaCl 2 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.