Effect of Dissolved Organic Matter in Treated Effluents on Sorption of Atrazine and Prometryn by Soils

Abstract

The apparent enhanced transport of soil‐applied atrazine following irrigation of treated effluents has been hypothesized to be from complexation of atrazine with effluent‐borne dissolved organic matter (DOM). Under long‐term effluent irrigation, even small DOM‐induced decreases in pesticide sorption can result in significant enhanced pesticide movement due to cumulative effects. The effect of atrazine and prometryn association with DOM extracted from municipal wastewater (MW), swine‐derived lagoon wastewater (SW), and dissolved Aldrich humic acid (HA) on sorption by two soils was measured in batch equilibration studies. Individual association of pesticides to DOM, sorption of DOM to soil, and pesticide sorption by soil were also quantified. Pesticide association to DOM normalized to organic carbon (OC) ranged from 30 to 1000 L/kg OC. DOM sorption by soil ranged from 1.5 to 10 L/kg with a silt loam having a higher affinity for the DOM than the sandy loam. DOM up to 150 mg OC/L did not significantly suppress sorption by soils of either atrazine or prometryne in agreement with predictions using the independently measured binary distribution coefficients in a model that assumed linear equilibrium behavior among pesticide, soil, and DOM. A sensitivity analysis was performed using the same model to identify what combination of soil, pesticide, and DOC variables may suppress sorption, resulting in facilitated transport. Results from the sensitivity analysis are presented and the potential for effluent properties other than DOM to facilitate pesticide transport is discussed.