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TECHNICAL REPORT
Organic Compounds in the Environment

Coupled Effects of Treated Effluent Irrigation and Wetting–Drying Cycles on Transport of Triazines through Unsaturated Soil Columns

Department of Agronomy, Purdue Univ., West Lafayette, IN 47907

* Corresponding author (lslee{at}purdue.edu)

Received for publication August 31, 2000. The physical and chemical parameters controlling the movement of atrazine (6-chloro-N²-ethyl-N⁴-isopropyl-1,3,5-triazine-2,4-diamine; 98.8%) and prometryn [N,N'-bis(1-methylethyl)-6-(methylthio)-1,3,5-triazine-2,4-diamine; 99.5%] were investigated in columns infiltrated with treated effluent under unsaturated transient conditions and subjected to drying events at 22 or 60°C followed by rewetting. Three soils varying in soil pH and texture and three solutions were used. The infiltrating solutions consisted of either a CaCl₂ matrix (CC), a swine waste–derived lagoon effluent (SW), or a simulated buffer solution (SB) representative of the element composition and pH of the SW but with no dissolved organic matter. Several parameters were monitored including leachate triazine concentrations, pH, dissolved organic carbon (DOC), inorganic carbon, and flow rates. Compared with CC, application of SW and SB increased column leachate pH, enhanced dissolution of organic carbon and particle dispersion, and decreased average flow rates, which allowed for increased desorption time. The coupled effect of these processes enhanced movement of triazines in some cases, with SW generally having the greatest effect. The individual effect of increased pH was more pronounced for prometryn (pK_a = 4.05) versus atrazine (pK_a = 1.66), and most dramatic for the soil with the lowest initial pH. High-temperature drying, which simulated intensive evaporation, further enhanced the dissolution of soil organic matter and the reduction in leachate flow rates with SW and SB applications; however, the net effect under the experimental conditions employed varied with soil type. Relative to low-temperature drying, high-temperature drying in the silty clay loam–packed columns reduced pesticide migration.

Abbreviations: CC, solution consisting of a CaCl₂ matrix • DOC, dissolved organic carbon • DOM, dissolved organic matter • IC, inorganic carbon • M_I, initial pesticide mass applied • M_L, pesticide mass measured in leachate fractions • M_C, pesticide mass remaining in the soil column • SB, simulated buffer solution • SOM, soil organic matter • SW, swine waste–derived lagoon effluent

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