Comparative fates of atrazine and deethylatrazine in sterile and nonsterile soils

Assessment of biotic and abiotic mechanisms of atrazine (ATR) and deethylatrazine (DEA) breakdown is necessary to identify major degradation pathways and understand soil conditions necessary for these mechanisms to occur. Our purpose was to compare fates of ATR and DEA in laboratory radiotracer studies to elucidate the effects of soil moisture status and soil depth on degradation and persistence. Atrazine and DEA were more persistent in subsurface soil than in surface soil. After 120-d incubation, bound residues were significantly greater in surface soils than in subsurface soils. In ¹⁴C-DEA-treated soil, biological activity contributed to decreased persistence of DEA in saturated surface soil in contrast with unsaturated surface soil after 60 d. Biological activity also contributed to decreased persistence of ATR in saturated subsurface soil in contrast with unsaturated subsurface soil after 120 d, and the decreased persistence corresponded to significantly greater amounts of DEA, deisopropylatrazine (DIA), and polar degradation products compared with other treatments. The percentage of applied ¹⁴C-ATR that degraded to DEA and DIA increased approximately threefold during the 60- to 120-d incubation in nonsterile saturated subsurface soil. Greater quantities of polar degradation products were formed in ¹⁴C-DEA-treated nonsterile compared with sterile soils. Half-lives (from first-order degradation rate constants) of ATR and DEA were significantly longer in subsurface soil compared with surface soils. Biotic mechanisms contributed to the half-lives of ATR (in surface and subsurface soil) and DEA (in subsurface soil) being significantly shorter under saturated soil moisture conditions compared with unsaturated soil moisture conditions.