Sorption and desorption of atrazine by sludge-amended soil: dissolved organic matter effects

Abstract

Addition of insoluble and soluble organic C to soil through management practices, such as sewage sludge (SS) application, may greatly alter pesticide sorption-desorption in soil. Batch equilibrium techniques were used to determine the effects of four sewage sludges (liquid-SS, solid-SS, limed-SS, and composted-SS) and their water dissolved organic matter (DOM), on the sorption-desorption of atrazine (2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine) by a silt loam soil. Atrazine sorption on the sludges increased in the order: iimed-SS < liquid-SS < solid-SS < composted-SS. Sludge addition to soil increased atrazine sorption in the same order, although the effectiveness of the mixtures to sorb atrazine was lower than expected from the sorption capacity of the isolated soil and sludges. The effects of the DOM extracted from the different sludges on atrazine sorption varied with sewage sludge. For liquid-, solid-, and limed-SS, DOM reduced atrazine sorption on soil. A low association between these DOMs and atrazine was measured in solution by dialysis technique, and indicated that processes at the soil/solution interface may have contributed to reduce atrazine sorption. In contrast, enhanced atrazine sorption in the presence of DOM extracted from composted-SS indicated atrazine was bound by DOM associated with the soil. Atrazine desorption from soil increased in the presence of DOM from all four sludges; however, DOMs had little effect on atrazine desorption from sludge and from sludge-amended soil. Interactions of soil surfaces with organic amendments and their DOM are shown in this work as a major process determining atrazine sorption-desorption in amended soil.