EVALUATION OF ATRAZINE BINDING TO SURFACE SOILS
1
Heather M. Lesan and 2Alok Bhandari
Department of Civil Engineering, Kansas State University, Manhattan, KS 66506-2905; Phone:
(785) 532-7717; 1E-mail: hmlesan@ksu.edu; 2E-mail: bhandari@ksu.edu.
Triazine herbicides and their derivatives are major contaminants of surface water in the
midwestern United States. Every spring 150 million pounds of triazine herbicides are applied to
corn and grain sorghum fields in this region. Atrazine, (2-chloro-4-ethylamino-6-isopropylamino1,3,5-triazine) is the most frequently applied chemical and is used extensively as a pre-emergent
broad-leaf herbicide. Although atrazine and its partial degradation products are relatively mobile in
soil, once applied they can associate with a variety of soil components including soil organic matter,
soil solution, or the surfaces of suspended particulate matter such as colloids and humic or fulvic
acids. Associations between organic matter and pesticides can result in either immobilization or
enhanced transport of the contaminant, depending on the nature of the interaction. Our study
focused on evaluating the nature of association of atrazine with two Kansas surface soils. The soils
chosen were characterized as silty loams and belonged to the Woodson series. One soil was
obtained from an agricultural field (3.4% organic matter) while the other was collected from an
adjacent forested area (6.2% organic matter). U-ring-14C-labeled atrazine was used to improve
detection limits and better track the distribution of the herbicide among various soil components.
Bottle-point adsorption experiments with constant soil dosage were conducted for a period of 7 days
followed by sequential extraction (desorption) with synthetic "surface water." The strongly
adsorbed atrazine fraction was removed by multiple extractions with ethyl acetate. Next, the soil
was extracted with alkali under a nitrogen atmosphere. The organic matter removed by this method
was fractionated into humic and fulvic acid components, and the atrazine associated with each
component was determined. Finally, the herbicide remaining on the alkali-extracted soil was
quantified by combusting the soil at 925°C and counting the 14CO2 on a liquid scintillation counter.
The effect of the presence of the soil enzyme, horseradish peroxidase, on the nature and extent of
binding was also evaluated.
Key words: soil, pesticide, binding, atrazine, isotherms