COMPARATIVE FATES OF ATRAZINE AND DEETHYLATRAZINE IN STERILE AND NONSTERILE SOILS

Assessment of biotic and abiotic mechanisms of atrazine (ATR) and deet hylatrazine (DEA) breakdown is necessary to identify major degradation pathways and understand soil conditions necessary for these mechanism s to occur. Our purpose was to compare fates of ATR and DEA in laborat ory radiotracer studies to elucidate the effects of soil moisture stat us and soil depth on degradation and persistence. Atrazine and DEA wer e more persistent in subsurface soil than in surface soil. After 120-d incubation, bound residues were significantly greater in surface soil s than in subsurface soils. In C-14-DEA-treated soil, biological activ ity contributed to decreased persistence of DEA in saturated surface s oil in contrast with unsaturated surface soil after 60 d. Biological a ctivity 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 greate r amounts of DEA, deisopropylatrazine (DIA), and polar degradation pro ducts compared with other treatments. The percentage of applied C-14-A TR that degraded to DEA and DIA increased approximately threefold duri ng the 60- to 120-d incubation in nonsterile saturated subsurface soil . Greater quantities of polar degradation products were formed in C-14 -DEA-treated nonsterile compared with sterile soils. Half-lives (from first-order degradation rate constants) of ATR and DEA were significan tly longer in subsurface soil compared with surface soils. Biotic mech anisms 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 mois ture conditions.