In-situ atrazine biodegradation dynamics in wheat (Triticum) crops under variable hydrologic regime

A comprehensive biodegradation reaction network of atrazine (ATZ) and its 18 byproducts was coupled to the nitrogen cycle and integrated in a computational solver to assess the in-situ biodegradation effectiveness and leaching along a 5 m deep soil cultivated with wheat in West Wyalong, New South Wales, Australia. Biodegradation removed 97.7% of 2 kg/ha ATZ yearly applications in the root zone, but removal substantially decreased at increasing depths; dechlorination removed 79% of ATZ in aerobic conditions and 18% in anaerobic conditions, whereas deethylation and oxidation removed only 0.11% and 0.15% of ATZ, respectively. The residual Cl mass fraction in ATZ and 4 byproducts was 2.4% of the applied mass. ATZ half-life ranged from 150 to 247 days in the soil surface. ATZ reached 5 m soil depth within 200 years and its concentration increased from 1 x 10(-6) to 4 x 10(-6) mg/kg(dry-soil) over time. The correlation between ATZ specific biomass degradation affinity Phi(o) and half-life t(1/)2, although relatively uncertain for both hydrolyzing and oxidizing bacteria, suggested that microorganisms with high Phi(o) led to low ATZ t(1/2). Greater ATZ applications were balanced by small nonlinear increments of ATZ biodegraded fraction within the root zone and therefore less ATZ leached into the shallow aquifer.