title: Enhanced degradation and soil depth effects on the fate of atrazine and major metabolites in Colorado and Mississippi soils.
abstract: The aim of this report is to inform modelers of the differences in atrazine fate between s-triazine-adapted and nonadapted soils as a function of depth in the profile and to recommend atrazine and metabolite input values for pesticide process submodules. The objectives of this study were to estimate the atrazine-mineralizing bacterial population, cumulative atrazine mineralization, atrazine persistence, and metabolite (desethylatrazine [DEA], deisopropylatrazine [DIA], and hydroxyatrazine [HA]) formation and degradation in Colorado and Mississippi s-triazine-adapted and nonadapted soils at three depths (0-5, 5-15, and 15-30 cm). Regardless of depth, the AMBP and cumulative atrazine mineralization was at least 3.8-fold higher in s-triazine-adapted than nonadapted soils. Atrazine half-life (T1/2) values pooled over nonadapted soils and depths approximated historic estimates (T1/2 = 60 d). Atrazine persistence in all depths of s-triazine-adapted soils was at least fourfold lower than that of the nonadapted soil. Atrazine metabolite concentrations were lower in s-triazine-adapted than in nonadapted soil by 35 d after incubation regardless of depth. Results indicate that (i) reasonable fate and transport modeling of atrazine will require identifying if soils are adapted to s-triazine herbicides. For example, our data confirm the 60-d T1/2 for atrazine in nonadapted soils, but a default input value of 6 d for atrazine is required for s-triazine adapted soils. (ii) Literature estimates for DEA, DIA, and HA T1/2 values in nonadapted soils are 52, 36, and 60 d, respectively, whereas our analysis indicates that reasonable T1/2 values for s-triazine-adapted soils are 10 d for DEA, 8 d for DIA, and 6 d for HA. (iii) An estimate for the relative distribution of DIA, DEA, and HA produced in nonadapted soils is 18, 72, and 10% of parent, respectively. In s-triazine-adapted soils, the values were 6, 23, and 71% for DIA, DEA, and HA, respectively. The effects of soil adaptation on metabolite distribution need to be confirmed in field experiments.
authors.affiliation: USDA-ARS, Crop Production Systems Research Unit, P.O. Box 350, Stoneville, MS 38776, USA. jason.krutz@ars.usda.gov
authors.forename: L Jason
authors.initials: LJ
authors.lastname: Krutz
authors.forename: Dale L
authors.initials: DL
authors.lastname: Shaner
authors.forename: Robert M
authors.initials: RM
authors.lastname: Zablotowicz
mesh_terms: D000383:Agriculture; D001280:Atrazine / Q000737:chemistry* / Q000378:metabolism; D003120:Colorado; D006540:Herbicides / Q000737:chemistry* / Q000378:metabolism; D008922:Mississippi; D012987:Soil / Q000032:analysis*; D012989:Soil Pollutants / Q000737:chemistry* / Q000378:metabolism; D013997:Time Factors
chemical_list: D006540:Herbicides; D012987:Soil; D012989:Soil Pollutants; D001280:Atrazine