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Title: EFFECTS OF SAMPLE HANDLING (AIR-DRYING) ON SORPTION OF ATRAZINE BY SOILS AND CLAYS

Author
item CHAPPELL, MARK - AGRONOMY, IOWA STATE UNIV
item Laird, David
item THOMPSON, MICHAEL - AGRONOMY, IOWA STATE UNIV

Submitted to: Clay Minerals Society Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 6/12/2003
Publication Date: 6/12/2003
Citation: CHAPPELL, M.A., LAIRD, D.A., THOMPSON, M.L. EFFECTS OF SAMPLE HANDLING (AIR-DRYING) ON SORPTION OF ATRAZINE BY SOILS AND CLAYS. CLAY MINERALS SOCIETY MEETING. 2003. Abstract p. 41.

Interpretive Summary:

Technical Abstract: The influence of sample handling (air-drying) on atrazine sorption by a reference smectite and three smectite-dominated soils was investigated. Surface horizon samples of three soils (Sparta, Sperry, and Zook) with clay fractions dominated by smectite were collected and stored in sealed containers at 4 deg C without drying. Portions of these soil samples were air-dried. A batch equilibration technique was used to determine atrazine sorption affinity. Both the moist and air-dry samples were suspended in 10 mM CaCl2 for 24 hrs. Afterwards, atrazine was added and the suspensions were allowed to equilibrate for another 24 hrs. Freundlich sorption constants, K'F were less for the air-dry Sparta and Zook samples than for the moist Sparta and Zook samples. The air-drying treatment had no effect on KF values for the Sperry samples. The effects of air-drying on K- and Ca-saturated Panther Creek (PC) smectite were also studied. Sample handling effects were tested either by keeping the homoionic PC in the 10 meq L-1 suspension (moist) or by air-drying and then resuspending the homoionic PC samples in 10 meq L-1 KCl or CaCl2 solutions (dry) for seven days. Air-drying the clays increased the atrazine distribution coefficient, KD, by approximately one order of magnitude for the K-PC but had little effect on the Ca-PC. X-ray diffraction analysis of the clay suspensions showed that the air-dry treatment decreased d-spacings for the K-PC clay. Our results suggest that hysteresis induced by air-drying regulates the physical organization (hydrated phase) of smectites, which in turn influences atrazine sorption affinity. A similar sample-handling effect also appeared to alter the affinity of the soil samples for atrazine.