Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/18/2010
Publication Date: 5/25/2010
Citation: Krutz, L.J., Shaner, D.L., Zablotowicz, R.M. 2010. Enhanced Degradation and Soil Depth Effects on the Fate of Atrazine and Major Metabolites in Colorado and Mississippi Soils. Journal of Environmental Quality, 39:1369-1377. Interpretive Summary: This study was conducted to compare degradation of the herbicide atrazine in soil collected from different depths and herbicide use histories. Pooled across depth, 50% of applied atrazine remained in soil 2 months after application when there was no prior exposure history; conversely, less than 50% of the herbicide remained after six days in soils with a prior exposure history. Results from this study will allow USEPA and USDA-ARS modelers to more accurately predict the herbicide’s off-site movement and subsequent environmental impact on surface and ground water quality.
Technical Abstract: This report’s aim is to inform modelers of the differences in atrazine fate between s-triazine-adapted and non-adapted soils as a function of depth in the profile, and to recommend input values for pesticide process sub-modules. The specific objectives of this study were to estimate the atrazine-mineralizing bacterial population (AMBP), cumulative atrazine mineralization, atrazine persistence and metabolite [desethylatrazine (DEA), deisopropylatrazine (DIA), and hydroxyatrazine (HA)] formation/dissipation in CO and MS s-triazine-adapted and non-adapted soils at three depths (0- to 5-cm, 5- to 15-cm, and 15- to 30-cm). Regardless of depth, the AMBP and cumulative atrazine mineralization was at least 4.9- fold higher in s-triazine-adapted than non-adapted soils. Atrazine half-life (T½) values pooled over non-adapted soils and depths approximated historic estimates, T1/2 = 61 d. Atrazine persistence in all depths of s-triazine-adapted soils, however, was at least 4-fold lower than that of the non-adapted soil. Atrazine metabolite concentrations were typically lower in s-triazine-adapted than non-adapted soil after 35 d of incubation, regardless of depth. Results indicate (i) accurate modeling of atrazine fate and transport will require modelers to discriminate between s-triazine-adapted and non-adapted soils; ii) an atrazine half-life of 6 d is advised for s-triazine-adapted soils, while a half-life of 60 d is recommended for non-adapted soils; iii) best estimates for DEA, DIA, and HA half-life values in non-adapted soils is 52 d, 36 d, and 60 d, respectively. Conversely, the recommended half-life for DEA, DIA, and HA in s-triazine-adapted soils is 10 d, 8 d, and 6 d, respectively; iv) the default maximum half-life factor, i.e., the multiple of the near-surface half-life that the half-life reaches at 100 cm, of 10 is accurate for non-adapted soils, but it is likely that the value must be set greater than 10 for s-triazine-adapted soils; and v) a reasonable estimate for amount of atrazine degraded to DEA, DIA, and HA in non-adapted soils is 10%, 72%, and 18%, respectively; conversely, the recommended estimate for s-triazine-adapted soils is 71% for HA, 23% for DEA, and 6% for DIA. Future field-scale modeling efforts, however, are required to verify these predictions.